TW202340134A - Process for preparing alkyl methacrylates with improved yield and reduced emissions of volatile organic compounds - Google Patents

Abstract

The present invention relates to an environmentally friendly process for preparing alkyl methacrylate, especially methyl methacrylate (MMA), comprising the preparing of an alkyl methacrylate precursor; esterifying; working up the crude product and storing the pure product, wherein alkyl methacrylate is recovered from the gaseous output streams from the process by at least one absorption step and is recycled into the process in a suitable manner. In particular, the alkyl methacrylate precursor is an MMA precursor, for example methacrylamide (MAA) or the hydrogensulfate thereof (MAA•H2SO4).

Description

Preparation method of alkyl methacrylates that improves yield and reduces volatile organic compound emissions

The present invention relates to an environmentally friendly method for preparing alkyl methacrylate (especially methyl methacrylate (MMA)), which includes preparing an alkyl methacrylate precursor; esterification; and post-processing crude The product and the pure product are stored, wherein the alkyl methacrylate is recovered from the gaseous output stream from the process by at least one absorption step and recycled in a suitable manner to the process. In particular, the alkyl methacrylate precursor is an MMA precursor, such as methacrylamide (MAA) or its hydrosulfate salt (MAA·H ₂ SO ₄ ). With the help of the process according to the invention, it is possible to obtain high yields of alkyl methacrylates (especially MMA) and at the same time reduce the release (emission) of volatile organic compounds into the environment. In particular, the present invention encompasses a method and an apparatus for separately or jointly carrying out at least one absorption step, in which a gaseous output stream (such as waste air and waste gas) loaded with gaseous by-products and co-products and auxiliaries is used to establish the ideal process engineering. Under the parameters, use the appropriate receiving phase (absorbent) to process. As a result, in particular, precursors and intermediates that can be converted into MMA target products, or MMA itself, are consumed in the gaseous output stream and recycled to the process.

Methyl methacrylate (MMA) is used in large quantities to prepare polymers and copolymers with other polymerizable compounds. Furthermore, methyl methacrylate is an important monomer for different specialized esters based on the chemical synthesis component methacrylic acid (MA), which can be prepared by transesterification of MMA with a suitable alcohol or can be Obtained by condensation of methacrylic acid and alcohol. The methacrylic acid required for this purpose can be obtained from MMA by hydrolysis with water. Therefore, there is great interest in extremely simple, economical and environmentally friendly methods of producing such raw materials. There are several known commercial processes for the production of alkyl methacrylates, especially methyl methacrylate (MMA), on an industrial scale starting from C2, C3 or C4 units. The general prior art is basically described in existing reviews, such as K. Nagai, T. Ui ("Trends and Future of Monomer MMA Technology", Sumitomo Chemical Co., Ltd.; Basic Chemistry Research Laboratory ("Trends and Future of Monomer MMA Technology") -MMA Technologies", Sumitomo Chemical Co. Ltd.; Basic Chemicals Research Laboratory)), S. Krill ("Viele Wege führen zum Methacrylsäuremethylester" [Many ways to obtain methyl methacrylate], Chem. Unserer Zeit, 2019, 53 ; 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim). Generally, methods of preparing MMA involve converting C2, C3 or C4 units into a reactive MMA precursor compound, which is subsequently reacted with methanol and optionally water to produce a crude product comprising MMA (see Figure 1). Examples of general reactive MMA precursor compounds are methacrolein (MAL) in the case of the C2-based method, and derivatives or 2-methacrylamide (MAA) in the case of the C3-based method. Derivatives of hydroxyisobutyric acid (2-HIBA), and in the case of the C4-based method, methacrylic acid (MA). Work-up of the crude MMA-containing product by a suitable sequence of thermal separation steps generally provides a pure MMA product, which is often stored and/or transported prior to further use. To prevent the formation of polymeric deposits and other by-products, suitable stabilizers are generally added to MMA for storage. The C2 unit as the basis for the preparation of MMA Even ethylene has good availability as the C2 unit, on which basis MMA is produced only to a small extent. All commercially relevant C2-based processes commonly use methanol both for the formation of methyl ester functionality and for the preparation of formaldehyde (FA) intermediates. Therefore, methanol along with ethylene is the most important raw material for the preparation method of the C2 series. In the preparation of MMA from ethylene by the BASF process, propionaldehyde (PA) is obtained by hydroformylation (e.g. according to C. He, F. You, Ind. Eng. Chem. Res. 2014, 53, 11442-11459) ) first reacts with formaldehyde (FA) in a first reaction step to produce methacrolein (MAL) (eg DE 3220858 A1). In the second reaction step, the MAL is selectively converted into methacrylic acid (MA) in the gas phase in the presence of atmospheric oxygen using a thermally stable heteropoly acid, which serves as a reactive MMA precursor compound. . MA is then reacted with methanol via catalytic esterification to produce MMA. In the so-called ALPHA process, ethylene is converted by methoxycarbonylation into methyl propionate (MP), which serves as a reactive MMA precursor compound (eg WO 9619434 A1 or EP3272733 A1). In the subsequent reaction step, the formaldehyde liquid obtained by the oxidation of methanol is dehydrated to produce anhydrous formaldehyde (FA), and then in the gas phase, a doped catalyst based on mixed zirconium-silicon oxide is used, Reacts with preformed MP to produce MMA. This method often has >94% selectivity. This method, known as the LiMA method, is similar to the BASF method in that in the first stage ethylene is reacted with a synthesis gas to produce propionaldehyde (PA), advantageously using a rhodium-based phosphine or phosphite ligand. As a catalyst. Reaction with formaldehyde solution provides MAL as a reactive MMA precursor compound in almost quantitative yield (eg WO 2016/042000 A1). Subsequently, in the presence of methanol, the MAL is directly converted into MMA in a direct oxidative esterification using a noble metal heterogeneous catalyst (such as WO 2014/170223), in which high conversion rate and selectivity can be achieved. C3 Unit The commercial method used worldwide as the basis for the preparation of MMA is based on acetone (C3 unit) as starting material and is often referred to as the C3 method or the ACH-sulfo method. Acetone here first reacts with hydrogen cyanide (HCN) to produce the central acetone cyanohydrin (ACH) intermediate. The intermediate is isolated and used in subsequent process steps for the preparation of methacrylic acid (MA) and MMA. A general method for the preparation of MMA starting from ACH by the ACH-sulfo process of the sulfuric acid system is described, for example, in US 4529816. For example, DE 10 2006 058250 describes a process for the preparation of alkyl methacrylates, which consists of preparing ACH from HCN and acetone, purifying the ACH, using sulfuric acid to prepare methacrylamide from ACH, in a mixture of water and sulfuric acid. The methacrylamide is esterified with an alkanol in the presence of a mixture to produce methacrylic acid, and the ester is finally purified. In this ACH-sulfo method, ACH is hydrolyzed with the help of sulfuric acid to form α-hydroxyisobutylamine (2-HIBAm) and its sulfate ester (2-SIBA). This compositional step is referred to in the literature as amide or hydrolysis because the nitrile group of the ACH is formally converted into a amide function. 2-HIBAm, 2-SIBA, and methacrylamide sulfate (MAA) that has been formed by elimination in the amidation are thermally converted to MAA in the sulfuric acid-based reaction mixture to a small extent. Geothermal energy is converted into MA, and SIBA into MAA is basically easier than HIBAm into MAA. This compositional step is often called transformation. The reaction conditions such as heat supply and residence time must generally be optimized to specifically promote the desired main reaction in the conversion (ie SIBA à MAA) and the equally desired conversion of the HIBAm by-product to MAA. Gaseous by-products such as carbon monoxide and carbon dioxide formed in this conversion are generally discharged from the process. The sulfuric acid-based MAA solution (reactive MMA precursor compound) obtained after conversion can subsequently be esterified with methanol and water to produce MMA (esterification). Alternatively, after this conversion, a sulfuric acid-based solution of MAA can be reacted with water to produce methacrylic acid (MA) (hydrolysis). The residual 2-HIBAm is generally partially converted to 2-hydroxyisobutyric acid methyl ester (2-MHIB) but is also partially hydrolyzed to 2-hydroxyisobutyric acid (2-HIBAc). Yield-relevant thermal cleavage of the intermediates can occur especially during the conversion, but also during the esterification step. Therefore, gaseous secondary components and other components also need to be removed in this esterification step. In addition to the ACH-sulfo process, this prior art also describes other C3-based process variations that do not require the use of sulfuric acid. Thus, problems associated with the use of sulfuric acid, the plant components for its recovery (sulfuric acid recovery, SAR), and the formation of ammonium sulfate as a by-product are avoided. For example, the multistage Mitsubishi-Gas-Chemical process (MGC) was developed from the mid-1980s and implemented in the 1990s. In the first stage of the MGC process, hydrogen cyanide is added to acetone to produce ACH. This ACH is then hydrated using a manganese dioxide catalyst to produce hydroxyisobutylamide (2-HIBAm) as a reactive MMA precursor compound (eg EP 0487853). In this subsequent step, methanol first reacts homogeneously with CO under pressure and in the presence of a strong catalytic base (eg sodium methoxide) to produce methyl formate (eg according to DE 3436608). Methyl formate as the activated ester is then reacted with hydroxyisobutylamine in a transamidation reaction to produce formamide and methyl hydroxyisobutyrate MHIB. Generally, at a selectivity of 98%, the conversion rate is about 85% (for example, US 5312966A). The two products are often further processed separately. Formamide can be cleaved, for example, at low pressure and 450-580°C and using a heterogeneous catalyst based on iron or aluminum phosphate with various dopants to produce hydrogen cyanide and water. The yield of HCN is typically about 94%. Both HCN and water are typically returned to the cycle of the MMA process, significantly reducing hydrogen cyanide requirements. Separate dehydration of 2-MHIB in the gas phase to produce MMA in the presence of methanol using heterophasic zeolite catalysts as described in US 5075493, US 5371273 or US 5739379 typically achieves >90% yields . A by-product formed during this step is methacrylic acid. The use of sulfuric acid is also avoided in the Aveneer process of the C3 series of Evonik Röhm GmbH. The hydrogen cyanide already obtained by the Andrussow, BMA or BF process is first converted into ACH. The ACH and water are hydrated in this first step, often using a modified manganese dioxide catalyst (eg DE 102008044218) in substantial quantitative yield, to produce 2-HIBAm as the reactive MMA precursor compound. 2-HIBAm is then reacted with methanol to produce methyl 2-hydroxyisobutyrate (2-MHIB) (eg EP 2043994). The ammonia released is often recovered here and recycled as feedstock to the HCN process. For example in DE 102005023975 or DE 102005023976, another central step is the catalytic cross-transesterification of methacrylic acid and 2-MHIB to produce MMA and 2-hydroxyisobutyric acid (2-HIBA). Methacrylic acid itself is produced by catalytic dehydration of the resulting hydroxyisobutyric acid. C4 Units as Base for Preparation of MMA A process for the preparation of MMA based on these C4 units (isobutylene, methyl tert-butyl ether or tert-butanol) involves converting them into the reactive MMA precursor compound (methyl tert-butyl ether). acrolein and methacrylic acid). In particular, the following three C4-based processes are known: The so-called tandem C4 direct oxidation process (Sumitomo process) is generally carried out without intermediate isolation of methacrolein. Here, MAL is prepared from isobutylene in a first step and oxidized to MA in a second method step before MA is esterified with methanol to produce MMA in a third method step. This method is also referred to as the "cascade method" in the literature because the process gas from the first stage is directly oxidized to MA without isolating the MAL intermediate. In the so-called different C4 direct oxidation (Mitsubishi process), MAL is prepared from isobutylene in a first process step, analogously to the series process. MAL is then typically isolated and purified in liquid form in a different second process step before being evaporated and oxidized to MA in a third process step. Esterification with methanol to produce MMA is then carried out in a fourth process step. Asahi's direct metha method is also often described as a direct oxidative esterification method. In a first process step, MAL is also produced from isobutylene in the gas phase using a first catalyst and is isolated and intermediately purified in a second process step. In the third method step, MAL is directly oxidized and esterified to MMA, and this step is generally performed in the liquid phase using a suspended catalyst. The main difference between this method and the other two C4 methods is the combination of process steps in the gas phase and oxidation steps in the liquid phase. The mentioned C4-based method is described in the prior art, for example, Vapor Phase Catalytic Oxidation of Isobutene to Methacrylic Acid by S. Nakamura, H. Ichihashi, Stud. Surf. Sci. Catal. 1981, 7, 755-767. Storage and Stabilization of MMA When storing alkyl methacrylates such as MMA, it is usually necessary to add suitable stabilizers to prevent the formation of oligomeric and polymeric conversion products. In addition to product loss and contamination, the release of reaction enthalpy and the risk of loss of control of exothermic reactions also constitute safety-related aspects (such as the 2008 Methacrylate Safe Handling Manual, Methacrylate Manufacturers Association Methacrylate Esters Safe Handling Manual, Methacrylate Producers Association and Methacrylates Sector Group of the European Chemical Industry Council, 2008). Phenol compounds, phenylenediamine compounds, quinones or catechols or amine N-oxides are often used as stabilizers. Frequently used stabilizers are often those that perform their function only in the presence of small amounts of free oxygen. In order for these stabilizers to function effectively, dissolved oxygen is essentially required as it acts as an initially effective free radical scavenger. Alkyl methacrylates such as MMA should therefore essentially never be disposed of in an oxygen-free environment. An oxygenated environment is generally provided above the liquid level in the storage tank to ensure the effectiveness of the stabilizer. Oxygen is normally and gradually consumed here as part of the free radical scavenger mechanism. Therefore, it is often necessary to pass continuously or periodically through the storage tank a small amount of an oxygen-containing gas mixture, such as air (so-called stabilizer air) or a nitrogen/oxygen gas mixture with 5 to 21 volume % oxygen. Because some alkyl methacrylate vapors such as MMA vapor form flammable mixtures with air at room temperature, a gas mixture having less than 21 volume % of oxygen, such as a nitrogen/oxygen gas mixture, may be suitably used to reduce flammability. However, the gas mixture (gas environment) above the alkyl methacrylate should contain at least 5% oxygen to ensure the effectiveness of the stabilizer. The waste air obtained from the storage of alkyl methacrylates often loads alkyl methacrylates up to saturation limits and therefore emits a significant proportion of valuable products from the process. For example, based on the vapor pressure of MMA at a storage temperature of 25°C, a typical airflow of 150 m³/h may cause MMA to lose 18.5 tons per year. Their emissions and avoidance The production of alkyl methacrylates such as MMA and the transformation products derived therefrom such as MA and other alkyl methacrylates is carried out in complex plants, which typically produce up to several hundred thousand tons of products per year . In this aspect, even slight improvements in yield can result in significant savings. In particular, waste gases and waste air streams containing alkyl methacrylates such as MMA, and methanol are yield-related losses, which should be converted back to the target product by suitable measures. Also for environmental reasons, there is a high need to reduce gas emissions of volatile organic compounds (VOCs). The minimization of MMA emissions via gaseous output streams is regulated extremely strictly by law. Some methacrylates are classified as volatile organic compounds (VOCs) under the US Clean Air Act. MMA is classified as a hazardous air pollutant under the Clean Air Act Amendment of 1990 by the US Environmental Protection Agency (EPA). Within the EU, MMA is handled and stored in accordance with Directive 96-61-EC for the control and prevention of emissions and in accordance with the REACH regulation (EC No. 1907/2006), in accordance with which , direct discharge to the atmosphere must be monitored and approved. This prior art describes various precautions for preventing or minimizing VOC emissions when producing and storing MMA. These include not only purely physical methods such as absorption, adsorption and condensation, but also combined physicochemical methods, in which MMA is converted (often irreversibly) into substances that can be obtained from MMA more easily than MMA due to their higher boiling points The gas stream separates and/or may be released to the atmosphere without further processing due to its lower reactivity and/or toxicity. It is clear to those skilled in the art that vapors of organic compounds can be condensed from gas mixtures by increasing the pressure, or by controlled cooling depending on the temperature dependence of their vapor pressures. For example, as the temperature decreases by 40K, the vapor pressure of MMA and methanol will generally decrease by one-tenth. This prior art describes, for example, different condensation methods. Cooling of the organic vapor can be accomplished indirectly, for example using a heat exchanger or by direct contact, for example by trickle flow of the gas stream in a plate column or packed column, or by in the gas stream (using a downstream mist eliminator) Or the injection of the coolant in a Venturi nozzle (injection) operated with the coolant. If the partial pressure of the organic matter to be condensed is significantly reduced due to the high inert gas content, only a small portion can be condensed out at a specific coolant temperature. This has been found to be disadvantageous for gaseous output streams loaded with MMA and/or methanol at room temperature, since high inert gas contents (especially nitrogen contents) often require extremely low coolant temperatures and therefore a high use of cooling energy. Alternatively, the proportion of organic matter condensed out can be increased by increasing the pressure in the condensation system, again requiring compression energy. CN 104815514 A describes the recycling of polymethyl methacrylate (PMMA) by depolymerization, wherein the resulting MMA-containing vapor is first subjected to a multi-stage preliminary cooling and then a similar multi-stage combination of compression and cooling. The disadvantage here is that multiple stages of cooling and compression are required and therefore a lot of energy expenditure. If the evaporation enthalpy released during the condensation of organic vapors is to be utilized in this process (energy accumulation), this necessarily requires a high complexity of equipment. Standard methods for adsorbing organic compounds depleted in gaseous output streams are described, for example, in F. Woodard's Industrial Waste Treatment Handbook Butterworth-Heinemann 2001. Removal of organic compounds by adsorption onto solid particles (such as activated carbon) is often used for the removal of volatile organic compounds (VOCs). Activated carbon treatment systems (adsorption towers) for treating gas streams are configured, for example, as cylindrical tanks with a bed of activated carbon particles. This usually requires parallel and/or continuous connection of several adsorption towers so that the spent beds can be adsorbed in continuous operation. Exchange (eg CN 109045940 A). A disadvantage of adsorption removal using activated carbon is often that the loaded adsorbent must be discarded as waste or can only be regenerated with a high degree of complexity. In the case of adsorbed MMA, furthermore, adequate stabilization must be ensured to prevent runaway polymerization (e.g. Manual on the Safe Handling of Methacrylates 2008, Methacrylates Manufacturers Association of the European Industry Conference and Methacrylates Sector Group (Methacrylate Esters Safe Handling Manual, Methacrylate Producers Association and Methacrylates Sector Group of the European Chemical Industry Council, 2008). Activated carbon beds should therefore only be used for MMA-depleted exhaust gases. To prevent any kickback into the storage tank in question, the activated carbon bed must always be additionally isolated from the storage tank by a flame suppression system (eg flame arresters, scrubbers, etc.). Other adsorbents such as resins, activated alumina, silica gel and molecular sieves are also known. Standard methods for absorbing depleted (absorbed) organic compounds in gaseous output streams are described, for example, in NP Cheremisinoff's 2002 Handbook of Air Pollution Prevention and Control, Chapter 7 - Prevention and Control Hardware), Butterworth-Heinemann, pages 389-497. Absorption methods are widely used in the treatment, separation and cleaning of gas streams containing high concentrations of organic matter, such as in the cleaning of natural gas. Typically, absorption involves dissolving the organic material in the liquid solvent (receiver phase or absorbent) of the gas stream. The contact between the absorption liquid and the waste gas takes place, for example, in a countercurrent spray tower, a scrubber, a tower with random packing or a plate tower. The availability of suitable absorbents often limits the use of depleted absorbents. In addition, suitable absorbents should have high solubility for vapors or gases, low vapor pressure, low viscosity and low cost. Typical absorbents include water, mineral oil or other non-volatile oils. Water is used to absorb VOCs that have relatively high water solubility. Amphiphilic block copolymers added to the water can increase the solubility of hydrophobic VOCs in the water, but remain in the loaded absorbent and complicate their reuse. A further consideration when using absorption methods is the treatment or disposal of the waste stream carrying the absorbent. WO 9627634 A1 describes the recovery of unconverted monomers during the polymerization of olefins with the aid of an inert solvent as absorbent. This involves passing the off-gas from the polymerization process through a scrubber and absorbing the unconverted monomers present in the off-gas as well as the gaseous by-products of the polymerization in the inert solvent. The loaded absorbent is subsequently processed in multiple distillation steps and partially recycled. A disadvantage of the described method is the complex and energy-intensive absorbent recovery. DE 2023205 A1 describes a process for the recovery of volatile unconverted monomers produced in the polymerization of a monomer mixture containing acrylonitrile and unsaturated monomers such as MMA, and in which It does not require any further purification before recycling to the downstream polymerization reaction. This involves cooling the monomer-loaded vapor mixture to about 15°C and drying them, and then contacting them with a liquid consisting essentially of acrylonitrile. The residual vapor mixture is then contacted with the aqueous phase, with the acrylonitrile being absorbed by the aqueous phase. Disadvantages of this method are that the monomer-laden vapor mixture must be cooled and dried, and that high equipment complexity and high operating costs are required for freezing. EP 2083020 A1 describes a method for the absorption recovery of unconverted monomers without prior cooling. It is possible here to recover 15-80% of the ethylene that is not converted in the polyolefin preparation by utilizing the cooled absorption of liquid long-chain hydrocarbons, such as hexane. This involves recycling the hydrocarbons used for absorption for re-absorption after subsequent desorption of the absorbed ethylene. The disadvantage of this method is the use of additional substances as absorbents, with the inherent risk of further contamination. Established procedures based on physicochemical methods for minimizing emissions of MMA in waste air and waste gas streams associated with processes and storage are described, for example, in the Manual on the Safe Handling of Methacrylates 2008, the European Industry Conference Described in Methacrylate Esters Safe Handling Manual, Methacrylate Producers Association and Methacrylates Sector Group of the European Chemical Industry Council, 2008. Therefore, the first step recommended for treating waste air from MMA storage tanks is a reactive scrubbing operation. If the exhaust gas has been protected from high organic contamination, an activated carbon cartridge may be used for final exhaust gas cleaning. A corresponding industrial method is disclosed in CN 212733497 U, for example. This depletes the MMA in the waste air from the oil storage site from 1000-2500 mg/m³ to 50 mg/m³ by using a fan to pass the waste air through an alkaline-operated scrubber in which the MMA is first Physically dissolves, and the action of the base immediately hydrolyzes it into methanol and water-soluble alkali metal methacrylates. The spent exhaust gas is passed through an activated carbon bed. The disadvantage of this method is that the removed MMA cannot be recycled economically, if at all. It is also possible to oxidize organic matter in the gas stream into harmless substances such as CO ₂ . For example, CN 211216181 U describes passing exhaust gas containing butyl acetate, cyclohexanone and MMA through a mixture containing ultra-fine bubbles and hydrogen peroxide. Achieve consumption of >90% of the organic component. Disadvantages here are that the MMA is not available for further processing and the provision of ultra-fine foam incurs high energy costs. CN 111359600 A describes a type of ambient pressure variation that utilizes a fixed bed catalyst containing nanostructured titanium dioxide, a photosensitizer and an active redox system to oxidatively degrade organic vapor in an output stream. By this method, MMA can also be removed from the waste air and exhaust gases of the corresponding load, but it is not recovered for further use. Document CN 112 691 513 A describes a method for cleaning exhaust gases containing VOCs, which involves two-stage absorption. For example, here any VOC-containing exhaust gas is cooled and treated in a first stage with a water-soluble organic solvent (eg methanol) and in a second stage with water. In addition, this prior art describes various methods that incorporate some of the above-mentioned basic operations to achieve the goal of recovering MMA and obtaining a gaseous output stream that is free of MMA. CN 109621676 A describes a method for recovering MMA, in which the MMA vapor from the depolymerization of PMMA is first partially condensed out in a heat exchanger operated with brine at -15 to 18°C. The remaining exhausted gas stream is then heated, treated in a scrubber containing a water-alkali operation and finally sent to total oxidation. The method described here requires high energy costs for the recovery of MMA in the cooling step as well as additional costs for equipment and auxiliary agents such as bases or carrier gases for waste gas incineration. In summary, none of the methods described makes it possible to substantially completely recycle MMA and methanol (both valuable materials) from the corresponding loaded gaseous output stream of the MMA production process and to convert them without losses into the target products. In principle, in the purely physical process described, only an insufficient proportion of the valuable material can be recovered from this gaseous output stream at an acceptable level of cost and complexity. In the described physicochemical methods, it is often the case that the removed MMA is irreversibly bound to or converted into other compounds by chemical reactions and therefore cannot be recycled into the production process and is lost as a valuable product . There is therefore still a high need for commercial processes for producing alkyl methacrylates such as MMA and for substantially complete recycling of alkyl methacrylates such as MMA present in gaseous output streams such as waste air and waste gas streams. In particular, it is desirable to recover alkyl methacrylates such as MMA from the output stream from the preparation of the reactive MMA precursor compound, the esterification with methanol and the storage of the pure alkyl methacrylate. Problem The problem solved by the present invention is to provide a process for the preparation of alkyl methacrylates (preferably MMA), which overcomes the listed problems at a low level of capital costs and a stable high operational reliability. Disadvantages of Prior Technology. In particular, it is desirable to continuously increase the yield of low-emission processes for the preparation of alkyl methacrylates, preferably MMA. In particular, the problem solved by the present invention is to reduce the release of the MMA target product when prepared by the C3 method (especially the ACH sulfo method). In principle, it is possible by the method according to the invention to process the gaseous output stream and recover the alkyl methacrylate (preferably MMA) in all standard and above-mentioned preparation methods of alkyl methacrylate (preferably MMA). ). Solution It has been found that the above objects are surprisingly achieved because in the process according to the invention the recovery of alkyl methacrylate (preferably MMA) is optimized by the gaseous output stream (e.g. waste gas, waste air) The absorption process and the advantageous recycling of the resulting loaded absorbent are significantly improved. This increases the overall process yield of the preparation method and minimizes emissions of volatile organic compounds (VOC). More particularly, it has been found that by utilizing a single stage or multi-stage absorption (scrubbing) with a combination of an alcohol-containing (preferably methanol-containing) absorbent and an aqueous absorbent, it is possible to provide an MMA-loaded absorbent stream which can is recycled into the manufacturing process, with an increase in the overall yield. These loaded absorbent streams advantageously supplement or displace the supply of fresh alcohol, especially fresh methanol, and fresh water to the esterification step. With the help of the method according to the invention, it is possible to avoid the combustion of the gaseous output stream contaminated with organic matter, with the accompanying formation of CO ₂ . Furthermore, the supply of foreign substances to the process is avoided, and the absorbent used can be used directly in the process as a reactant stream. This method is additionally simple, robust and cheap, and combines the advantages of reduced VOC emissions and increased yield of the MMA. The invention and its characteristic features are described in detail below.

The present invention relates to a method for preparing alkyl methacrylate (preferably methyl methacrylate (MMA)), which comprises the following steps: a. Preparing at least one alkyl methacrylate precursor compound, which Comprised of reacting acetone cyanohydrin with sulfuric acid in a first reaction stage (amidation) to produce a first reaction mixture, and converting in a second reaction stage comprising heating the first reaction mixture, preferably to 130 to a temperature in the range of 200° C. to obtain a second reaction mixture comprising the alkyl methacrylate precursor compound and sulfuric acid; and b. mixing the second reaction mixture with water in a third reaction stage (esterification) react with an alcohol (preferably methanol) to obtain a third reaction mixture comprising an alkyl methacrylate (preferably methyl methacrylate) as a crude alkyl methacrylate product; and c. In the work-up zone of the distillation step, alkyl methacrylate (preferably MMA) is separated from the third reaction mixture, wherein low boilers are separated from the crude alkyl methacrylate product in a distillation step. , and the high boilers are separated from the crude alkyl methacrylate product in another distillation step to obtain a pure alkyl methacrylate product (preferably a pure MMA product) as the pure alkyl methacrylate product from the last distillation step. overhead fraction; and d. storing the pure alkyl methacrylate product obtained in method step c in at least one storage device and optionally the third reaction mixture (crude methacrylate) obtained in method step b (alkyl acrylate product) is temporarily stored in at least one intermediate storage device; and e. absorbing the gaseous state by treating at least one gaseous output stream obtained in process steps b, c and/or d with at least two liquid absorbents Output stream GS to obtain at least one alkyl methacrylate-loaded absorbent (preferably at least one MMA-loaded absorbent), wherein the liquid absorbent contains at least one absorbent containing an alcohol (preferably containing methanol) and at least one aqueous absorbent. More particularly, the present invention relates to a method for preparing an alkyl methacrylate (preferably methyl methacrylate (MMA)), which comprises the above steps (a) to (e), wherein in the method step ( The at least one alkyl methacrylate-loaded absorbent obtained after processing the gaseous output stream GS in e) is fed at least partially in liquid form to process step b. In the context of this invention, the expression "ppm" means ppm by weight (eg mg/kg) without further qualification. The expression "a stream, phase or portion comprising reactants, products and/or by-products" is understood, within the context of the present invention, to mean that the compounds mentioned are present in that individual stream; e.g. the reactants , a major portion of the products and/or by-products are to be found in the corresponding stream. In principle, further components can be present in addition to the compounds mentioned. The naming of these ingredients is often used to clarify individual process steps. In the context of this invention, the expression "vapor" or "vapor stream" refers to a gaseous process stream, such as a gaseous overhead stream from a distillation column. In the context of the present invention, the expression "low boilers" refers to chemical compounds with a lower boiling point than the corresponding alkyl methacrylate (such as MMA). In the context of the present invention, the expression "high boilers" refers to chemical compounds with a higher boiling point than the corresponding alkyl methacrylate (such as MMA). In the context of the present invention, the expression "isolated in a distillation step" means that the compound mentioned is consumed in the corresponding mixture or corresponding material stream in the distillation step. More particularly, the present invention relates to a process for the preparation of alkyl methacrylates, in particular MMA, by the ACH sulfo process. In principle, it is possible to utilize an absorption post-treatment of the gaseous output stream (absorption step (e)), which is also described according to the invention in the various processes for the preparation of alkyl methacrylates, in particular MMA. For example, the absorption according to the present invention can be utilized in the above-mentioned C3 system method, in which sulfuric acid is not used as a reactant. For example, the absorption according to the invention can be applied to the preparation of MMA by Mitsubishi Gas Chemical Process (MGC), for example according to EP 0487853 or by the Aveneer method, for example according to DE 102008044218, EP 2043994, DE 102005023975, DE 102005023976, where 2-HIBAm was obtained as a reactive MMA precursor compound and reacted with methanol. In addition, the absorption according to the present invention can be applied by the above-mentioned C2 system method, for example by the BASF method (for example, according to C. He, F. You, Ind. Eng. Chem. Res. 2014, 53, 11442 -11459) to prepare alkyl methacrylates (especially MMA), wherein in particular, methacrylic acid (MA) as a reactive MMA precursor compound is reacted with methanol through catalytic esterification to produce MMA. It is also possible to apply the absorption according to the invention to the process for the preparation of alkyl methacrylates, in particular MMA, by the LiMA process described above (for example according to WO 2016/042000 A1 and WO 2014/170223), in particular MAL as The reactive MMA precursor compound is converted in direct oxidative esterification in the presence of methanol using a heterogeneous catalyst. In addition, the absorption according to the present invention can be applied to the preparation of alkyl methacrylates (especially MMA) by the above-mentioned C4 system method, wherein especially methacrylic acid (MA) as a reactive MMA precursor compound is prepared by Conversion to MMA by esterification of methanol, for example, the series C4 direct oxidation method by the Sumitomo method, the different C4 direct oxidation by the Mitsubishi method and the direct metha method by Asahi. Preferably, it is possible to process a gaseous output stream containing alkyl methacrylate (especially containing MMA) in the absorption according to the invention, which is the process of storing the alkyl methacrylate product (especially MMA product) Those who win. More preferably, it is possible to process the gaseous output stream in the absorption according to the invention, which is obtained during the storage of the pure alkyl methacrylate product (especially the pure MMA product), for example during distribution and /or obtained before delivery of finished product. Typically, during storage, this gaseous output stream is formed by providing a gaseous environment containing oxygen, which is often required to activate the stabilizer. Preferably, the gaseous output stream GS treated in the absorption in process step (e) contains at least two gaseous output streams GS1 selected from the group consisting of gaseous output stream GS1 obtained in process step (a), which contains carbon monoxide and sulfur dioxide; GS2 The gaseous output stream GS2 obtained in method step (b), which contains an alkyl methacrylate (preferably MMA), particularly preferably 1.0% to 5.0% by volume of an alkyl methacrylate (more preferably MMA). Preferably MMA) and not more than 10% by volume, preferably 0.1% to 10% by volume oxygen, based on the total volume of the output stream GS2; GS3 The gaseous state obtained in method step (c) Output stream GS3, which contains alkyl methacrylate (preferably MMA), preferably 1.0% to 5.0% by volume of alkyl methacrylate (preferably MMA) and no more than 10% by volume, preferably is 0.1% by volume to 10% by volume oxygen, in each case based on the total volume of the output stream GS3; and GS4 The gaseous output stream GS4 obtained in method step (d), which contains alkyl methacrylate (relative to Preferably MMA), particularly preferably 1.0% to 5.0% by volume of alkyl methacrylate (preferably MMA) and at least 10% by volume, preferably 10% to 20% by volume oxygen. The above conditions are Based on the total volume of the output logistics GS4. In a further preferred embodiment, the gaseous output stream GS processed in the absorption of method step (e) comprises at least two gaseous output streams selected from the group consisting of the gaseous output streams GS2, GS3 and GS4, and the gaseous output stream GS Better includes all output logistics GS2, GS3 and GS4. The gaseous output streams GS2, GS3 and GS4 can be introduced in particular as gaseous output streams GS (for example via (5)) partially or completely, individually or in combination, into the absorption in method step (e). . Advantageously, in method steps (b), (c) and/or (d) one or more stabilizers are added to different material streams in order to prevent or reduce the alkyl methacrylate, preferably methyl Polymerization of methyl acrylate). For example, it is possible to add a stabilizer to the third reaction mixture obtained after this esterification. For example, one or more stabilizers can be added during the storage in method step (d) and/or during optional intermediate storage. In particular, stabilizers which usually exert their effect only in the presence of gaseous oxygen are used. After the reaction of the oxygen, what remains is oxygen-depleted air, which is typically the waste gas obtained in process steps (b), (c) and/or (d), and which is preferably available as a gaseous output stream GS2, GS3 and/or GS4 are directed to method step (e) (eg via (5)) for the purpose of recovering the alkyl methacrylate. Preferably, a gas mixture containing oxygen, preferably air, is passed through at least part of the apparatus for post-treatment in process step (c) and/or the storage apparatus in process step (d) to provide the oxygen. Preferably, the amount of oxygen-containing gas mixture is small compared to other material streams in the process. The volume of the oxygen-containing gas mixture is usually 50 to 1500 m ³ (STP)/h, preferably 100 to 500 m ³ (STP)/h. In the esterification of method step (b) and/or in the treatment after method step (c) and/or in the storage of method step (d), it is preferred to use phenol compounds, phenylenediamine compounds, quinones and/or catechols. It is further possible to use amine N-oxides (eg TEMPOL), or combinations of the mentioned stabilizers. General stabilizers include but are not limited to hydroquinone monomethyl ester (MEHQ, CAS 150-76-5), hydroquinone (HQ, CAS 123-31-9), 2,4-dimethyl-6-tertiary butyl phenol (BDMP, DMTBP or Topanol-A® / AO30® / IONOL K78®, CAS 1879-09-0), 2,6-di-tert-butyl-4-methylphenol (BHT/Topanol-O® , CAS 128-37-0), containing phenylenediamine compounds (such as N-(1,4-dimethylpentyl)-N'-phenyl-p-phenylenediamine (CAS 3081-01-4), N,N'-diisopropyl-p-phenylenediamine (CAS 4251-01-8), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (CAS 4251-01-8) CAS 793-24-8), such as Naugard® I-4701 or Santoflex ^TM 434PD) compounds or mixtures. In particular during or after the first reaction stage (amidation) and/or the second reaction stage (conversion), it is additionally possible to add one or more stabilizers to the first and second reaction stages obtained in step (a). /or second reaction mixture. It is preferably possible to add a stabilizer to the cooled second reaction mixture. During the amidation and/or conversion in process step (a), it is preferred to use phenothiazines and other stabilizers with similar effects. In a preferred embodiment, the pure alkyl methacrylate product obtained in process step (c) and/or is obtained as a third reaction crude alkyl methacrylate product in process step (b) The mixture contains at least one stabilizer, which is generally activated by molecular oxygen; and in method step (d), the gas mixture containing oxygen is passed through the storage device and optionally the intermediate storage device, and in method step (d) Producing at least one gaseous output stream GS4, which contains an alkyl methacrylate (preferably methyl methacrylate), and at least 10% by volume, preferably 10% to 20% by volume, and more preferably 10% by volume to 15% by volume of oxygen, based on the total output stream GS4, wherein this gaseous output stream GS4 is conducted into the absorption in process step (e). Amination and conversion in step (a) Process step (a) of the process according to the invention comprises anamidation in the first reaction stage and conversion in the second reaction stage. Generally, process step (a) provides a gaseous output stream GS1, which in particular contains the off-gases from the first and/or second reaction stage of process step (a). Preferably, the gaseous output stream GS1 mainly contains carbon monoxide and sulfur dioxide; particularly preferably, the gaseous output stream GS1 contains 70% to 99% by volume of carbon monoxide and 1% to 20% by volume of sulfur dioxide, in each case. Based on the total volume of the output logistics GS1. This gaseous output stream GS1 can be at least partially processed in the absorption of process step (e). In particular, the gaseous output stream GS1 can be treated in the absorption of process step (e) together with at least one further gaseous output stream selected from GS2, GS3 and GS4. In a specific example, all gaseous output streams GS1, GS2, GS3 and GS4 are at least partially (preferably completely) processed in the absorption of method step (e). Preferably, the gaseous output stream GS1 is discharged partially or completely from the process (eg via (1b) and (12)). In particular, a gaseous output stream GS1 is obtained in process step (a), which contains carbon monoxide and sulfur dioxide, wherein this gaseous output stream GS1 is identical to the gaseous output stream GS1 obtained in process steps (b), (c) and/or (d). The output stream is discharged separately from the process. Typically, the discharged gaseous output stream GS1 can be sent for incineration, for example in a plant for regenerating the sulfuric acid connections. Depending on the circumstances, the discharged gaseous output stream GS1 may be subjected to exhaust gas scrubbing and/or partial condensation. In a preferred embodiment, the gaseous output stream GS1 from process step (a) is directed partially or completely to process step (b) (eg via (1b)). The first reaction stage in step (a) (amidation). The method according to the invention comprises the reaction of acetone cyanohydrin (ACH) and sulfuric acid in step (a) of the method. This reaction is generally in the first reaction stage. (amidation) in one or more reactors, preferably in the temperature range of 70 to 130°C, more preferably 70 to 120°C, to obtain generally containing sulfoxyisobutylamine (SIBA) and The first reaction mixture of methacrylamide (MAA). Preferably, the concentration of sulfuric acid used in the first reaction stage ranges from 98.0 to 100.5% by weight, preferably from 98.0 to 100.0% by weight, preferably from 99.0 to 99.9% by weight. More preferably, the usage concentration of the sulfuric acid is based on the total mass of the sulfuric acid feed stream fed to the first reaction stage. The ACH used can be prepared by known industrial methods (see, for example, Ullmanns Enzyklopädie der technischen Chemie (Ullmann's Encyclopedia of Industrial Chemistry), Volume 7, 4th Edition). Typically, hydrogen cyanide and acetone are converted to ACH in an exothermic reaction in the presence of an alkaline catalyst (eg, an amine). This method phase is described, for example, in DE 10 2006 058 250 and DE 10 2006 059 511. Generally, the acylation of ACH and sulfuric acid forms α-hydroxyisobutylamine (HIBAm) or its hydrogen sulfate (HIBAm·H ₂ SO ₄ ), the sulfate ester of HIBAm (α-sulfoxyisobutylamine) as the main product. amide, SIBA) or its hydrogen sulfate (SIBA·H ₂ SO ₄ ) and methacrylamide hydrogen sulfate (MAA·H ₂ SO ₄ ), which are in the form of solutions of excess sulfuric acid. It is known to those skilled in the art that the proportions of the mentioned components in the reaction mixture can vary and depend on the reaction conditions. This first reaction stage is preferably carried out using excess sulfuric acid. The excess sulfuric acid is particularly useful in maintaining a low viscosity of the reaction mixture, which ensures faster removal of the heat of reaction and a lower temperature of the reaction mixture. Typically, the supplied ACH stream contains 98.0 to 99.8 wt%, preferably 98.3 to 99.3 wt% acetone cyanohydrin, 0.1 to 1.5 wt%, preferably 0.2 wt%, based on the ACH stream. to 1% by weight of acetone, and 0.1% to 1.5% by weight, preferably 0.3% to 1% by weight of water. Preferably, sulfuric acid and ACH are used in the first reaction stage of process step (a), wherein the molar ratio of sulfuric acid to ACH ranges from 1.2 to 2; preferably from 1.25 to 1.6; more preferably from 1.4 to 1.45. To carry out the amidation (hydrolysis) in the first reaction stage, it is in principle possible to use any reactor known to those skilled in the art for carrying out hydrolysis reactions, such as stirred tank reactors and loop reactors or the The combination of other reactors. Alternatively, multiple reactors may be used, optionally connected in parallel, but preferably in series. In a possible specific example, 1 to 5 reactors are connected in series; preferably, a continuous configuration of 2-3 reactors is used. In the first reaction stage, the reaction of acetone cyanohydrin with sulfuric acid is exothermic. It is therefore advantageous to remove substantially or at least partially the resulting heat of reaction, for example with the help of suitable heat exchangers, in order to obtain improved yields. However, excessive cooling should generally be avoided so as not to increase the viscosity of the reaction mixture too significantly and to prevent crystallization of the components and thus damaging deposits on, for example, heat exchangers. Generally, the temperature range of the refrigerant (especially cooling water) is 20 to 90°C, preferably 50 to 90°C and more preferably 60 to 70°C. Typically, the temperature difference at the inlet/outlet of the device on the product side is about 1 to 20°C, especially 2 to 7°C. The conversion of ACH and sulfuric acid in one or more reactors in the first reaction stage (amidation) is in the range of 70 to 130°C, preferably 70 to 120°C, more preferably 85 to 110°C carried out at the temperature. Generally, this first reaction stage (amidation) can be carried out batchwise and/or continuously. This first reaction stage is preferably carried out continuously, for example in one or more loop reactors. Suitable reactors and methods are described, for example, in WO 2013/143812. Advantageously, the first reaction stage is carried out in a cascade of two or more reactors, preferably two loop reactors. Alternatively, it may be carried out using stirred or circulating pumped continuously stirred tank reactors (CSTRs), or a combination of reactors. The residence time in this amidation step is designed to be sufficient to maximize the yield of HIBAm, SIBA, MA and MAA. Generally, the static residence time in the reactors, especially in the loop reactor, ranges from 5 to 35 minutes, preferably from 8 to 20 minutes. The reactors (eg the loop reactors) used for the first reaction stage (amidation) preferably each comprise at least one gas separator (gas outlet). Typically, gaseous by-products are separated off here and discharged. Generally, the gaseous by-product formed in the amidation is mainly carbon monoxide, which is preferably discharged from the process in the form of or as part of the off-gas stream GS1. It is also possible to combine the gaseous output stream obtained in the first reaction stage with the gaseous output stream obtained in the second reaction stage (conversion). In a preferred embodiment, the gaseous output stream obtained in the first reaction stage and/or the second reaction stage is directly obtained from the absorption in process step (e) without being fed to it. This method discharges. Second reaction stage (conversion) in step (a) The process according to the invention also comprises in process step (a) the conversion of the first reaction mixture, the conversion comprising heating the first reaction mixture to preferably The temperature is in the following range: 130 to 200°C, preferably 130 to 170°C, more preferably 140 to 170°C, further preferably 140 to 165°C. Typically, the conversion is carried out in one or more reactors (eg heat transfer equipment or conversion reactors) to obtain a second reaction mixture mainly containing methacrylamide (MMA) and sulfuric acid. Typically, during the conversion, the amount _of MAA or MAA· _H2SO4 is determined by dehydrating the HIBAm during heating of the first reaction mixture to a temperature in the range of 130 to 200°C or by It is enhanced by eliminating sulfuric acid from SIBA, wherein the first reaction mixture is a sulfuric acid solution containing SIBA, HIBAm and MAA, each primarily in the hydrosulfate form. This conversion can in principle be carried out in a reactor which is known to achieve the stated temperatures within the stated duration. Energy can be supplied in a known manner, for example with steam, hot water, suitable heat carriers, electrical energy or electromagnetic radiation such as microwave radiation. Preferably, the conversion in the second reaction stage is carried out in one or more thermal conversion units. The heat medium used may be any heat medium known to those skilled in the art, such as thermally durable oil, salt bath, electromagnetic radiation, superheated water or steam. It is better to use saturated steam as the heating medium. The residence time of the reaction mixture in the second reaction stage (conversion) is usually in the range of 2 to 15 minutes, preferably 2 to 10 minutes. Preferably, the second reaction stage consists of heating the first reaction mixture in a preheater section called the conversion reactor and subsequent retention of the reaction mixture in a so-called delay section, which are in particular Operate adiabatically. In the process step of the conversion, it is advantageous to heat the reaction mixture to the required temperature very quickly and within a first defined duration (preheating, preheater section) and then to bring it to this temperature The following is the duration of the second definition (dwell, delay section). A delay section similar to the preheater section may consist of one or more tubes, except in contrast these are usually not preheated. A preferred configuration of this second reaction stage (conversion) and suitable equipment (including a preheater section and a delay section) is described in the international patent application PCT/EP2021/077640. Thermal conversion equipment for this conversion may further preferably be combined with one or more gas separators. For example, the reaction mixture may be directed through a gas separator after it leaves the preheater section and/or after it leaves the delay section of the thermal conversion device. In particular, it is possible here to separate gaseous by-products in the form of the gaseous output stream GS1 from the reaction mixture. In a preferred embodiment, in method step (a), a gaseous output stream GS1 is obtained, which contains carbon monoxide and sulfur dioxide. This gaseous output stream GS1 is formed in particular by one or more gaseous output streams from the first and/or second reaction stage and/or downstream process steps (eg cooling and/or intermediate storage). In a preferred embodiment, the second reaction mixture mainly containing methacrylamide and sulfuric acid obtained in the second reaction stage is obtained after the conversion, for example, by using a refrigerant with a temperature range of 60 to 100°C. In the cooler, it is cooled to a temperature lower than 120°C, preferably to a temperature range of 90 to 120°C. Preferably, during cooling of the second reaction mixture, gaseous by-products are at least partially separated from the second reaction mixture comprising carbon monoxide and sulfur dioxide in the form of gas stream GS1. In a specific example, the second reaction mixture, in particular the cooled second reaction mixture, is stored in a storage device before conversion as a stream fed to process step (b) (esterification), e.g. in the storage tank (buffer tank). It is therefore advantageously possible to ensure a homogeneous feed to downstream process step (b) (esterification). Secondly, the intermediate storage allows, inter alia, further degassing of the cooled second reaction mixture and thus acts as a gas separator. For cooling the second reaction mixture, it is in principle possible to use known and suitable refrigerants. It is advantageous to use cooling water. Generally, the refrigerant has a temperature in the range of 30 to 120°C. Preferably, the gaseous output stream GS1 obtained in the cooling step (in the gas separator after the conversion) and/or in the intermediate storage after the conversion is discharged completely or partially from the process (e.g. as stream 1c). Furthermore, this gaseous output stream GS1 can be conducted completely or partially to process step (b) (esterification) (for example as stream 1b). Typically, the degassed second reaction mixture is conducted entirely to process step (b) (esterification). The third reaction stage in step (b) (esterification) The process according to the invention comprises in process step (b) the second reaction mixture (generally mainly containing MMA) with water and alcohol in the third reaction stage (esterification). ) to obtain a third reaction mixture containing an alkyl methacrylate (preferably methyl methacrylate) as a crude alkyl methacrylate product. In a preferred embodiment, the reaction (esterification) of the second reaction mixture mainly containing MMA with water and methanol is performed to obtain a third reaction mixture containing methyl methacrylate. The conditions for this esterification on an industrial scale are known to those skilled in the art and are described, for example, in US 5,393,918. Preferably, a gaseous output stream GS2 is obtained in method step (b), wherein the output stream GS2 preferably contains 1.0 to 5.0% by volume, preferably 3.0% to 5.0% by volume of alkyl methacrylate ( Preferably methyl methacrylate), and no more than 10% by volume, preferably 0.1% to 10% by volume oxygen, each based on the total volume of the output stream GS2. In a preferred embodiment, the gaseous output stream GS2 from process step (b) is at least partially processed in the absorption of process step (e). Particularly advantageously, the gaseous output stream GS2 is processed in the absorption of process step (e) together with at least one further gaseous output stream selected from GS3 and GS4. The gaseous output stream GS2 may be partially discharged from the process (eg via (2b) and (12)). The conversion in this third reaction stage of method step (b) (esterification) is preferably carried out in one or more suitable reactors, for example in a heated tank. In particular, it is possible to use steam-heated tanks. In a preferred embodiment, the esterification is carried out in two or more, for example three or four, continuous tanks (tank cascade). Typically, the esterification is carried out at a temperature in the range of 100 to 180°C, preferably 100 to 150°C, and a pressure up to 7 bar, preferably up to 2 bar, using sulfuric acid as a catalyst. . The second reaction mixture is preferably reacted with an excess of alcohol, preferably methanol, and water. The addition of the second reaction mixture mainly containing methacrylamide and the addition of alcohol are preferably performed in such a way that the molar ratio of methacrylamide to alcohol is in the range of 1:1.0 to 1:1.6. Preferably, the alcohol supplied to the third reaction stage (esterification) is from a new supply of alcohol to the process (fresh alcohol) and/or from a recycled stream in the process according to the invention (recycled Composed of the alcohol present in the stream). Preferably, at least a part of the alcohol used in this third reaction stage, more preferably all of the alcohol used in this third reaction stage is based on the supported methane obtained in process step (e) (e.g. 11). Alkyl acrylates are provided in the form of absorbents. Typically, the alkyl methacrylate-loaded absorbent is obtained in liquid phase from an exhaust gas scrubber. Typically, water is added in this third reaction stage in such a way that its concentration ranges from 10% to 30% by weight, preferably from 15% to 25% by weight, in each case based on the total reaction mixture. . In principle, the water supplied to the third reaction stage (esterification) can come from any source and can contain different organic compounds, as long as there are no compounds that have a negative effect on the esterification or on the downstream process stages. The water supplied to the third reaction stage preferably comes from a recycled stream (recycle stream) in the process according to the invention, for example from the purification of the alkyl methacrylate. If necessary, it is additionally possible to supply fresh water, in particular demineralized water or well water, to this third reaction stage (esterification). Preferably, at least a part of the water used in the third reaction stage, more preferably a major part of the water used in the third reaction stage, is in the form of the load obtained in method step (e) (e.g. 11) Alkyl methacrylates are provided in absorbent form. Typically, the alkyl methacrylate loaded absorbent is obtained as the aqueous liquid phase from an exhaust gas scrubber. Esterification with methanol generally provides a third reaction mixture containing an alkyl methacrylate (preferably MMA), an alkyl hydroxyisobutyrate (especially methyl hydroxyisobutyrate (MHIB)), and further by-products. , as well as significant amounts of water and unconverted alcohol (such as methanol). Preferably, in the esterification of process step (b), the vaporizable part of the third reaction mixture is removed from the reactors in gaseous form (vapor) and sent to further work-up, such as a distillation step. If it is preferred to use a cascade consisting of multiple reactors (eg multiple tanks), it is possible to remove the evaporable part of the resulting reaction mixture as a vapor stream in each tank and direct it to further work-up. Preferably, only the evaporable part of the reaction mixture formed in the last two tanks is removed as a vapor stream and directed to further work-up. In a preferred embodiment, the vaporizable fraction from process step (b) is at least partially processed in the absorption of process step (e) as a composition containing an alkyl methacrylate, preferably methyl methacrylate. Gaseous output stream GS2 of ester) and not more than 10% by volume oxygen. Processing after step (c) The process according to the invention comprises, in process step (c), removing an alkyl methacrylate, preferably MMA, from the third processing zone after comprising at least two distillation steps. The reaction mixture (obtained after esterification) is separated, the low boilers being separated from the crude alkyl methacrylate product in one distillation step and the high boilers being separated from the crude alkyl methacrylate product in another distillation step. The alkyl methacrylate product is separated to obtain a pure alkyl methacrylate product (preferably a pure MMA product) as the overhead fraction from the final distillation step. Generally, in method step (c), a gaseous output stream GS3 is obtained, wherein the output stream GS3 preferably contains 1.0% to 5.0% by volume, preferably 3.0% to 5.0% by volume of alkyl methacrylate (rel. Preferably MMA), and no more than 10% by volume, preferably 0.1% to 10% by volume oxygen, based on the total volume of the output stream GS3. In a preferred embodiment, the gaseous output stream GS3 from process step (c) is at least partially processed in the absorption of process step (e). Particularly advantageously, the gaseous output stream GS3 is at least partially processed in the absorption of process step (e) together with at least one further gaseous output stream selected from GS2 and GS4. The gaseous output stream GS3 can be partially discharged from the process (eg via (3b) and (12)). In the treatment zone after method step (c), it is particularly possible to use separation steps known to those skilled in the art, in particular distillation, extraction, stripping and/or phase separation steps. Preferably, the separation of methyl methacrylate from the third reaction mixture includes at least two distillation steps, at least two phase separation steps and at least one extraction step. A better implementation of the post-processing zone is described, for example, in the international application PCT/EP2021/077488. The work-up preferably involves good purification of the third reaction mixture obtained in the esterification. More preferably, the pre-purification includes at least one distillation step, at least one phase separation step and at least one extraction step. The pre-purification preferably includes at least one (preferably at least two) distillation steps. More particularly, this pre-purification provides an alkyl methacrylate product, preferably an MMA product, with a purity in the range of at least 85% by weight. Preferably, the work-up includes a good purification of the alkyl methacrylate product with a purity in the range of at least 85% by weight, wherein the good purification includes at least one (preferably at least two) distillation steps. More particularly, this good purification provides an alkyl methacrylate product, preferably an MMA product, with a purity in the range of at least 99% by weight. In particular, it is possible to obtain pure alkyl methacrylates in the required specifications, obtained as overhead fraction from the last distillation step in process step (c), and generally after storage in process step (d), is directed out of the process as a product stream (eg (14)). In a preferred embodiment, the pure alkyl methacrylate product obtained in method steps (c) and/or (d) contains at least 99.9% by weight, based on the total pure alkyl methacrylate product, Preferably at least 99.95% by weight of alkyl methacrylates, especially MMA. The by-products present may generally be from 10 to 300 ppm of methacrylonitrile (MAN) and/or not more than 10 ppm of acetone, based in each case on the total pure alkyl methacrylate product. Advantageously, one or more stabilizers are added in different streams of process step (c) in order to prevent or reduce the polymerization of the methyl methacrylate. Preferably at least one stabilizer activated by molecular oxygen is used. A small amount of an oxygen-containing gas mixture, preferably air, is preferably passed through at least several parts of the apparatus for subsequent processing in method step (c) to provide oxygen for activating the stabilizer. The reaction of the oxygen leaves an oxygen-depleted gas mixture, which leaves process step (c) as waste gas and generally contains an alkyl methacrylate product, in particular MMA. In a preferred embodiment, the waste gas from process step (c) is at least partially treated in the absorption of process step (e) to contain alkyl methacrylate (preferably methyl methacrylate) and gaseous output stream GS3 containing not more than 10% by volume oxygen. Particularly advantageously, the gaseous output stream GS3 is processed in the absorption of method step (e) together with at least one further gaseous output stream selected from GS2 and GS4 to form a gaseous output stream GS. Typically, process step (b) (esterification) produces a liquid waste stream consisting essentially of dilute sulfuric acid. This waste stream is typically discharged from the process. This waste stream (especially together with one or more aqueous waste streams from the process according to the invention) is preferably sent to a process for regenerating sulfuric acid or to a process for obtaining ammonium sulfate. Storage in step (d) and optional intermediate storage The process according to the invention comprises, in process step (d), storing the pure alkyl methacrylate product obtained in process step (c) in In at least one storage device, and optionally the crude alkyl methacrylate (third reaction mixture) obtained in process step b (third reaction mixture) is temporarily stored in at least one intermediate storage device. Preferably, the storage or storage facility and optionally the intermediate storage or the intermediate storage facility comprise means for containing the product, such as the pure alkyl methacrylate product and/or the crude alkyl methacrylate product. ) tank (for example storage tank d), at least one product inlet, at least one product outlet and at least one feed port for a gas mixture containing oxygen and at least one outlet for a gas mixture depleted of oxygen, wherein the stored product Contains at least one stabilizer activated by molecular oxygen. Typically, the amount of oxygen-containing gas mixture used in the storage and optionally the intermediate storage is in the range of 50 to 1500 m ³ (STP)/h, preferably 100 to 500 m ³ (STP)/h middle. Typically, the oxygen-depleted gas mixture contains alkyl methacrylates (especially MMA) and is processed in the absorption of process step (e) as gaseous output stream GS4. Preferably, the pure alkyl methacrylate product stored in method step (d) is conducted out via the at least one outlet into the conveying device. For example, the pure alkyl methacrylate product may be distributed to a conveyor tank and/or fed to downstream processing operations via one or more conduits. Generally, the storage of the pure alkyl methacrylate product (preferably the pure MMA product) in process step (d) provides an off-gas comprising alkyl methacrylate, preferably an off-gas comprising MMA. In a preferred embodiment, the waste gas from process step (d) is at least partially processed in the absorption of process step (e) as gaseous output stream GS4. Particularly advantageously, the gaseous output stream GS4 is processed in the absorption of process step (e) together with at least one other gaseous output stream selected from GS2 and GS3 as gaseous output stream GS (for example (5)). The gaseous output stream GS4 may be partially discharged from the process (eg via (4b) and (12)). Preferably, the gaseous output stream GS4 contains an alkyl methacrylate, preferably methyl methacrylate, and at least 10% by volume of oxygen, based on the total volume of the output stream GS4. Particularly preferably, in method step (d), a gaseous output stream GS4 is obtained, which contains 0.1% to 5.0% by volume, preferably 0.2% to 2.0% by volume, of an alkyl methacrylate (preferably MMA) , and at least 10% by volume, preferably 10% to 20% by volume, more preferably 10% to 15% by volume oxygen, in each case based on the total volume of the output stream GS4. In particular, the volumetric proportions of oxygen, alkyl methacrylate (preferably methyl methacrylate) and optionally methanol in the gaseous output stream GS4 are below the lower explosion limit (LEL), which is determined by Ignition test determination in autoclave as described in DIN EN 1839:2017-04. Typically, the pure alkyl methacrylate product stored in process step (d) contains at least one stabilizer, in particular at least one stabilizer activated by molecular oxygen. If necessary, this stabilizer can be added again in method step (d). Preferably, in method step (d), the storage device and optionally the intermediate storage device are configured with a dry oxygen-containing gas environment covering the surface of the stored alkyl methacrylate to provide for activating the Stabilizer oxygen. For example, a gas mixture containing oxygen (eg air) can be passed through the storage device and optionally an intermediate storage device. The reaction of the oxygen leaves an oxygen-depleted gas mixture which leaves process step (d) as waste gas and generally contains alkyl methacrylates, in particular MMA. Within the context of the present invention, the storage and optionally the intermediate storage in method step (d) may be carried out in any storage device known to a person skilled in the art, such as a storage tank. The capacity of the storage device and the optional intermediate storage device can generally be freely selected. It has been found useful to adjust the capacity according to the desired volume and frequency of filling and emptying operations. To ensure uninterrupted operation, it is preferred that the minimum capacity be 1.5 times the desired filling volume. The storage device and the optional intermediate storage device may be constructed, for example, as an above-ground trough with a vertical casing, a flat bottom and a tapered top. The design selected should specifically allow for uniform mixing of the contents during the filling operation. To avoid the risk of damage and associated product escape, the storage facility and the optional intermediate storage facility may be established on a concrete base with a concrete embankment of sufficient capacity. For safety reasons, the storage equipment and/or intermediate storage equipment and any conveying devices connected to them should preferably always be located in a bunded and/or walled area. For emptying the storage facility and/or the intermediate storage facility, a tank shaft is preferably provided with a grounded outflow pipe through the base of the tank. The storage device and/or the intermediate storage device is preferably mainly composed of steel or stainless steel. Polyethylene, polypropylene or fluoropolymers are equally suitable and can be used in particular for seals and fittings. The storage equipment and/or intermediate storage equipment preferably have appropriate safety devices such as heat-repellent coatings and/or thermal insulators to minimize the absorption of heat energy from the environment; to avoid energy input through sparks electrical earth; a device for detecting temperature (such as a thermocouple) to identify possible aggregation; a measuring device for determining the fill level to avoid overfilling the storage device; a device for closing the tank for further processing High level switch of material port. An example of a suitable fill level measuring device is a pressure difference transducer made of steel or stainless steel and flushed with dry oxygen-containing gas. The storage or optional intermediate storage in method step (d) should always be carried out at a pressure higher than the vapor pressure of the corresponding alkyl methacrylate (eg MMA) at the storage temperature. The storage equipment and/or intermediate storage equipment may generally have equipment for pressure relief, in particular to prevent damage caused by uncontrolled conditions of the polymerization reaction. Typically, such devices for pressure relief may include desired breaches in the form of seams and/or roof construction. Alternatively or additionally, the storage facility and/or intermediate storage facility may be equipped with pressurized manhole covers or bursting discs with low reaction pressure. Typically, the storage device and/or intermediate storage device may include a pressure compensation valve and/or an overflow device, such as a heavily pressurized pallet valve or a vent valve with a flexible membrane, a seal containing ethylene glycol Can. Preferably, the storage and optional intermediate storage in method step (d) are at temperatures suitable to minimize evaporation of the alkyl methacrylate (eg MMA), but preferably separate cooling is not necessary. Preference is given to storage at ambient temperature and optional intermediate storage in method step (d). In particular, the storage or optional intermediate storage in method step (d) contains at least one exhaust device, in particular to prevent corrosion and polymerization. To ensure a low water vapor concentration in the gas space of the storage facility and/or the intermediate storage facility, desiccants can be used. Suitable desiccants include, for example, alumina, molecular sieves and calcium chloride. The desiccant can be installed, for example, in the exhaust pipe, in the filling gas pipe for introducing the oxygen-containing gas mixture or in the inlet pipe for the stabilizer. The desiccant is preferably regenerated at appropriate intervals, typically every 3 to 6 months, to ensure efficiency and prevent clogging by polymer. Absorption of the gaseous output stream GS in step (e) The process according to the invention comprises the absorption of the gaseous output stream GS in process step (e) by treating it in process step b with at least two liquid absorbents. , c and/or d at least one gaseous output stream obtained in order to obtain at least one absorbent loaded with alkyl methacrylate, wherein the liquid absorbent includes at least one absorbent containing alcohol (preferably containing methanol) and At least one aqueous absorbent. In a preferred embodiment, in method step (e), the gaseous output stream depleted of alkyl methacrylate is obtained after treatment with the at least two liquid absorbents. Typically, this gaseous output stream depleted of alkyl methacrylate is discharged from the process, optionally after thermal treatment (eg stream (9)). Preferably, the exhaust gas stream contains less than 5 grams of alkyl methacrylate, especially MMA, per cubic meter of exhaust gas. According to the invention, the at least one alkyl methacrylate-loaded absorbent obtained after processing the gaseous output stream GS in process step (e) is fed at least partially, preferably completely, in liquid form to process step ((e) b) (esterification) and optionally partially fed to process step c. Particularly preferably, the alkyl methacrylate-loaded absorbent constitutes a mixture of the alcohol-containing absorbent and the aqueous absorbent, each in the form of a loaded alkyl methacrylate. The gaseous output stream containing alkyl methacrylate (for example containing MMA) released in the above process step is contacted in process step (e) with a liquid phase as absorbent, which liquid phase is preferably for methacrylic acid. Alkyl ester vapors such as MMA vapor (receiving phase) have high absorption capacities. Typically, the alkyl methacrylate (eg MMA) is dissolved in the liquid phase by mass transfer and is simultaneously consumed in the gas phase. If the gas phase contains only alkyl methacrylate (eg MMA), the gas phase disappears completely due to the absorption operation. If the gas phase, as in the present method, contains not only alkyl methacrylate (MMA) but also further gaseous components having a lower solubility in the absorbent than the alkyl methacrylate (for example MMA), These will remain in the gas phase and leave the absorption step (e) as a gaseous output stream depleted of alkyl methacrylate (eg MMA). In principle, absorption can be carried out or promoted by physical interaction between the absorbent and the substance to be absorbed, and also by chemical reactions (chemical absorption). In method step (e), for the removal of alkyl methacrylates (eg MMA) with the help of alcohols and water (eg methanol and water), said intermolecular interactions are exploited to facilitate the absorption operation. In principle, absorbents that have high solubility for individual alkyl methacrylates (eg MMA) and do not have any miscibility gap therewith are preferred. It is particularly advantageous to use an absorbent which can be carried over unchanged to the previous step and where it helps to form the alkyl methacrylate target product (eg MMA). According to the invention, at least one absorbent containing an alcohol, preferably containing methanol, is used in method step (e). Particularly preferably, the alcohol-containing absorbent contains at least 50% by weight, preferably at least 80% by weight, more preferably at least 95% by weight of alcohol (preferably methanol), based on the total alcohol-containing absorbent. In a preferred embodiment, the alcohol-containing absorbent contains at least 99% by weight methanol. For the preparation of other alkyl methacrylates, it is preferred to use the corresponding alcohols as absorbents. Advantageously, the loaded alkyl methacrylate and alcohol-containing absorbent can be directed to process step (b) of esterification, wherein it is reacted with the reactive MMA precursor compound, preferably MAA, to Alkyl methacrylates (eg MMA) are produced. According to the invention, method step (e) additionally comprises treating the gaseous output stream GS with at least one aqueous absorbent. Generally, the aqueous absorbent contains at least 50% by weight, preferably at least 80% by weight, and more preferably at least 95% by weight of water based on the total aqueous absorbent. In particular, it is possible to use demineralized water or tap water as aqueous absorbent. In a preferred embodiment, the absorption in process step (e) comprises: at least one absorption step (e1), wherein the gaseous output stream GS is prepared in a first liquid stream containing at least 50% by weight of alcohol, preferably methanol. Treatment of a liquid with an alcohol-containing absorbent to obtain an absorbent loaded with alkyl methacrylate and an alcohol-rich gas stream; and at least one second absorption step (e2), wherein the alcohol-rich gas stream (from (e1)) is It is treated with a second aqueous absorbent containing at least 50% by weight of water to obtain an alcohol-loaded aqueous absorbent. Typically, the second absorption step (e2) with the second aqueous absorbent is intended to transfer the alcohol, especially methanol, from the alcohol-rich gas stream obtained in the first absorption step (e1) to the aqueous phase (receiving phase) in. The alcohol-loaded absorbent can preferably be directed to the esterification in process step (b). Preferably, the alcohol-loaded aqueous absorbent obtained in the second absorption step (e2) and the alkyl methacrylate-loaded absorbent obtained in the first absorption step (e2) are at least partially Feed into process step (b) (esterification) and optionally partially into process step (c). Here, the two loads of absorbent from (e1) and (e2) may be recycled separately or combined. In a preferred embodiment, the two loaded absorbents are completely recycled into the esterification in process step (b). In particular, it is thus possible to reduce the amount of fresh alcohol and fresh water required in the esterification. The first absorption step (e1) and the second absorption step (e2) can be carried out in at least two different separate absorption devices (washing devices) or in one absorption device. In a preferred embodiment, the absorption in method step (e) comprises the following steps: (e1) In the first absorption device, an alcohol-containing solution containing at least 50% by weight of alcohol (preferably methanol) is used. treating the gaseous output stream GS (preferably one or more of the gaseous output streams obtained in process steps b, c and/or d) with a liquid absorbent to obtain an alcohol-rich gas stream, and (e2) in the second absorption device wherein the alcohol-rich gas stream obtained in method step (e1) is treated with an aqueous absorbent containing at least 50% by weight of water. In another preferred embodiment, the absorption in method step (e) is carried out in a single absorption device in the following manner: one or more of the methods obtained in method steps b, c and/or d The gaseous output stream is fed in the lower part of the absorption device and the at least two liquid absorbents are added in the upper part of the device, preferably at different points. In this context, the gaseous output stream and the at least two absorbents are preferably conducted counter-currently. In a further preferred embodiment, the absorption in method step (e) is carried out in a single absorption device, wherein one or more gaseous output streams obtained in method steps b, c and/or d are fed In the lower part of the absorption device; in the first absorption step (e1), an alcohol-containing liquid absorbent containing at least 50% by weight of alcohol (preferably methanol) is fed to the feed port of the gaseous output stream Above; In the second absorption step (e2), at least one aqueous absorbent containing at least 50% by weight of water is fed above the feed port of the alcohol-containing absorbent; and wherein the gaseous output stream and the at least The two absorbents are directed countercurrently. In particular, the single absorption device here is a separation device containing at least two different structured packings (especially a structured packing for absorbing MMA with methanol and a structured packing for absorbing methanol with water). It is also possible that the at least one absorbent containing alcohol, preferably containing methanol, and the at least one aqueous absorbent are fed together in the form of a mixture to the absorption in process step (e), for example to the single absorption device middle. Preferably, in the absorption of method step (e), the gaseous output stream GS is 0.1 to 5.0 kg of liquid absorbent per m³ of the gaseous output stream GS (based on the total amount of the absorbent) and is between 5 and 5. Processed at a temperature of 40°C. Preferably, the at least two absorbents used for absorption in method step (e) have temperatures in the range of 5 to 30°C, and 5 to 40°C are established when performing the absorption operation in method step (e). ℃ temperature. In this absorption of method step (e), customary absorption equipment known to those skilled in the art may be used. In particular, gas-liquid contact devices (scrubbers) used, for example, in air quality management may be known to those skilled in the art. These can generally come in multiple types and sizes to remove one or more gaseous components from the gas stream by mass transport (diffusion) and transferring them to the liquid phase. The gaseous phase and the liquid phase can be contacted with each other in different ways in the scrubber used according to the invention. In a first possible embodiment of the construction, for example in a tower absorber with transfer disks, a bubble column, a tank type absorber or a dispersion mixer, the gas is dispersed into the associated receiving liquid phase (absorbent) . In a further possible embodiment, the receiving liquid phase (absorbent) can be sprayed into the associated gas, for example in an empty space scrubber without internal devices, such as in a venturi, syringe, sprayer, annular gap or radiant flow Scrubbers, or scrubbers with rotating internal devices such as rotary, cross-spray or plate type scrubbers. The absorption equipment used in the absorption of method step (e) is preferably a customary gas-liquid contacting equipment known to the person skilled in the art, in which a membrane of the associated gas phase and the associated receiving phase (absorbent) is Develop lower contacts on, for example, fixed or moving substrates. Examples of these are column absorbers with random or structured packing, fluidized bed absorbers, or trickling film or surface absorbers. These absorption plants are generally characterized by a low pressure drop of about 2 to 5 mbar/m, the possibility of variable gas velocities and, similar to plate columns, a high number of theoretical plates that can be achieved. In a preferred embodiment, the absorption equipment used in method step (e) is a packed tower commonly used in gas absorption. These systems consist, for example, of cylindrical towers providing gas inlets and distribution spaces at the bottom, liquid inlets and distribution spaces at the top, and liquid and gas outlets at the bottom and top. Typically, the column contains plates, screens, trays, random packing, or structured packing, which are generally made of chemically inert solid materials. For example, the absorption in process step (e) can be carried out in a packed column with trickle flow, in which the liquid absorbent (receiving phase) flows from the top through the packing and wets it downstream. The gaseous output stream typically enters the column from the bottom, is spread over the panels, and flows upward through the interstices in the packing, countercurrent to the liquid absorbent. The tower can be provided with external cooling to further increase absorption levels. The packing of the column can be any material preferably with a low packing density that is chemically inert to the liquid used. Suitable materials are GFRP materials such as steel, stainless steel, porcelain, glass, ceramic or PTFE, and PTFE/PFA/PVDF substrates. Advantageously, it is possible to use beds with regularly shaped cells such as rings, grids, spirals and comminuted solids. In principle, the absorption in method step (e) can be carried out in a counter-current device, a co-current device or a combination of counter-current and co-current devices. Generally, co-current absorption can be implemented by using a jet pump or nozzle. In this case, the exhaust gas to be treated is contacted with finely divided liquid absorbent to provide maximum surface area for mass transfer. [Description of the Figure] Figure 1 depicts a highly extensive reaction network for the formation of methyl methacrylate from a reactive MMA precursor compound that is selectively made from C2 unit ethylene, C3 unit acetone, or C4 unit isobutylene. In the BASF process, starting from ethylene, it is first hydroformylated and the resulting propionaldehyde is condensed with formaldehyde formed by the oxidation of methanol to produce methacrolein. Vapor phase oxidation yields methacrylic acid as a reactive MMA precursor compound, which can be directly esterified with methanol to produce MMA. In the alpha method, the reactive MMA precursor compound methyl propionate is formed directly from ethylene by methoxy carbonylation and condensed with formaldehyde formed by the oxidation of methanol to produce MMA. In the LiMA process, methacrolein (reactive MMA precursor compound) formed analogously to the BASF process by hydroformylation and subsequent condensation with formaldehyde from ethylene is directly oxidized with methanol to ester to produce MMA. In the C3-based method, starting from acetone and cyanide, acetone cyanohydrin (ACH) is first prepared with the addition of an alkaline catalyst (such as diethylamine Et ₂ NH or an alkali metal hydroxide). In the ACH sulfo method, the acetone cyanohydrin is reacted with sulfuric acid in several reaction steps to produce the reactive MMA precursor compound methacrylamide hydrosulfate (MAA·H ₂ SO ₄ ), which Subsequent conversion to methacrylic acid (MA) by hydrolysis or esterification with methanol (MeOH) to methyl methacrylate (MMA). Alternatively, the Aveneer process and the Mitsubishi Gas Chemical process are performed via the reactive MMA precursor compound 2-HIBAm obtained from ACH by hydrolysis. Starting from the C4 unit isobutylene, it can first be converted into methacrolein in a gas phase oxidation, and the methacrolein is then oxidized in a further gas phase reaction similarly to the third stage of the BASF process. , to produce the reactive MMA precursor compound methacrylic acid. Subsequent esterification with methanol sequentially produces MMA. MMA can also be transesterified with other alcohols to produce alkyl methacrylates, with the release of methanol. Depending on the chosen process variant, it is additionally economically feasible to prepare methacrylic acid from MMA by hydrolysis. Figure 2 (scheme for comparative examples V1 and V2) shows a flow diagram for the preparation of MMA, which includes the following process steps: a prepares a reactive MMA precursor compound, b reacts the reactive MMA precursor compound with methanol, to A crude MMA product is produced, c the crude MMA product is thermally purified to produce a pure MMA product and d the pure MMA product is stored, and f the gaseous output stream obtained from the mentioned process step is treated in a condensation f . Method step a includes the preparation of methacrylamide (MAA), methacrylic acid (MA) and as MMA precursor by the reaction of acylation and conversion of acetone cyanohydrin 16 (ACH) and sulfuric acid 17 in reactor a A mixture of hydroxyisobutyrylamine (HIBA) compounds. A gas stream GS1 containing carbon monoxide and containing sulfur dioxide is obtained from method step a . Gas stream GS1 can be fed to the esterification in process step b via 1b and/or can be discharged from the process via 1c and 12 and/or can be fed to the condensation step f via 1a and 5 . Subsequently, in reactor b (process step b), the second reaction mixture obtained is reacted with methanol 6 and water 8 by esterification to obtain a crude MMA product (third reaction mixture). A gas stream GS2 containing MMA, preferably containing no more than 10% by volume of oxygen, is conducted from method step b . Gas stream GS2 can be discharged from the process via 2b and 12 and/or can be fed to the condensation step f via 2a and 5 . In the apparatus c (process step c), the crude MMA product is subjected to a thermal workup with concomitant separation of MMA from the crude MMA product, wherein low boilers are present in a first distillation step, from which the crude MMA product Separation, and high boilers are separated from the crude MMA product in a second distillation step to obtain pure MMA product 13 as overhead fraction. An MMA-containing gas stream GS3 , preferably containing no more than 10% by volume oxygen, is derived from method step c . Gas stream GS3 can be discharged from the process via 3b and 12 and/or can be fed to the condensation step f via 3a and 5 . Subsequently, the pure MMA product 13 is conducted into a storage tank d (process step d), and the oxygen-containing gas mixture 15 flows through the storage tank d . An MMA-containing gas stream GS4 , preferably containing at least 10% by volume of oxygen, is directed from the storage tank and preferably has a combustible content below the Lower Explosive Limit (LEL). Gas stream GS4 can be discharged from the process via 4b and 12 and/or can be fed to the condensation step f via 4a and 5 . A product stream 14 of the pure alkyl methacrylate product is removed from the storage tank d. Gaseous output stream 5 obtained from process steps a, b, c and/or d, in particular formed by one or more of streams GS1/1a , GS2/2a , GS3/3a and/or GS4/4a to the condensation plant f , wherein the condensate obtained in process step f is recycled via 11a to process steps b and optionally c and optionally partially discharged via 11b . Figure 3 (scheme used in Example B1 of the present invention) shows a flow chart of a preferred specific example of the method according to the present invention. The method steps a, b, c and d associated with the material flow correspond to what was described above with respect to FIG. 2 . The gaseous output stream obtained from process steps a, b, c and/or d is conducted to the absorption step e as gaseous output stream 5 , in particular via GS1/1a , GS2/2a , GS3/3a and/or Formed by one or more of GS4/4a . In the specific example according to Figure 3, the gaseous output stream 5 is fed to the first absorption step e1 (methanol washing), where it is treated with fresh methanol 6 . This produces a methanol-rich and MMA-depleted gas stream 7 , which is directed to this second absorption step e2 (water washing), and an MMA-loaded absorbent 11 which is recycled via 11a to process step b and optionally is partially recycled to process step c and optionally partially discharged from the process via 11b ). In the second absorption step e2 , the MMA-depleted gas stream 7 is treated with fresh water 8 to obtain an MMA- and methanol-depleted off-gas 9 , which is discharged from the process and sent, for example, to incineration. Also obtained is a methanol-loaded aqueous absorbent 10 , which is recycled to this first absorption step e1 , optionally partially recycled via 10a and 11 to method step b , and optionally via 10b from this Method partially discharged. Figure 4 (scheme for example B2 of the present invention) shows a flow diagram of a further preferred embodiment of the method for preparing MMA according to the present invention, especially the treatment of the gaseous output stream 5 , especially by absorption from GS2 , formed by GS3 and GS4 , in which the absorption of MMA with methanol and the absorption of methanol with water are carried out in equipment e . In the absorption tower e , fresh methanol 6 is added above the addition point of the gaseous output stream 5 and fresh water 8 is added above the addition point of fresh methanol 6 . The air flow 5 and the liquid absorbents 6 and 8 are preferably conducted counter-currently. The MMA and methanol depleted off-gas 9 is discharged from the process. The MMA and methanol loaded absorbent 11 is recycled to process step b . The abbreviations of the reference symbols listed in Figure 1 and the description of Figure 1 have the following meanings: ACH Acetone cyanohydrin; FA formaldehyde 2-HIBAm α-Hydroxyisobutylamide; HIBA H ₂ SO ₄ α-Hydroxyisobutyrylamine hydrosulfate; HIBAc α-Hydroxyisobutyric acid; MHIB Alpha-hydroxyisobutyric acid methyl ester MAL methacrolein MAN Methacrylonitrile; MA Methacrylate; MAA Methacrylamide; MAA·H ₂ SO ₄ Methacrylamide hydrosulfate; MMA Methyl methacrylate; MP Methyl propionate PA Propionaldehyde 2-SIBA α-Sulfoxyisobutylamide; SIBA·H ₂ SO ₄ α-Sulfoxyisobutylamide hydrosulfate; SIBN α-Sulfoxyisobutyronitrile; In Figures 2 to 4, the reference symbols have the following meaning: Equipment: (a) Amidation and conversion (b) Esterification (c) Thermal post-treatment area (d) Storage/storage tank (e1) First absorption step ( Methanol wash) (e2) Second absorption step (water wash) (e) Absorption/combined methanol-water wash (f) Partially condensed material stream: (GS1) Gas stream containing carbon monoxide and sulfur dioxide from method step a (GS2) Gas stream containing MMA from method step b (preferably having an oxygen concentration of <10 vol%) (GS3) Gas stream containing MMA from method step c (preferably having an oxygen concentration of <10 vol%) (GS4) From storage d Gas stream containing MMA (preferably below the lower explosion limit LEL) (1a,b,c) Off-gas from amination/conversion (preferably <10 vol% O ₂ ) (2a,b) From esterification Waste gas (including MMA; preferably <10 volume% O ₂ ) (3a, b) Waste gas from thermal post-treatment (including MMA; preferably <10 volume% O ₂ ) (4a, b) Oil storage Waste gas from the site (including MMA; preferably >10 volume % O ₂ ) (5) Gaseous output stream GS for post-processing (6) Fresh methanol (reactant and optional washing liquid) (7) Methanol-rich gas stream from e1 (depleted of MMA) (8) Fresh water (reactants and optional scrubbing liquid) (9) Waste gas (depleted of MMA and methanol) (10,10a,b) Methanol-loaded Aqueous absorbent (11,11a,b) MMA loaded absorbent (including water, MMA and methanol) (12) Waste gas for thermal post-treatment (13) Pure MMA product (14) Pure MMA from storage Product stream of products (15) Gas mixture feed containing oxygen (16) ACH feed (17) Sulfuric acid feed

EXAMPLES Comparative Example V1: Condensation of the Combined Gaseous Output Streams GS1, GS2, GS3 and GS4 for Recovery of MMA Comparative Example V1 relates to a process based on the flow diagram according to Figure 2 for use with the ACH-sulfo group Methods Methods for preparing methyl methacrylate (MMA). The results obtained are detailed in Table 1. (a) Amination/conversion In method step a , 13 847 kg/h acetone cyanohydrin (ACH) 16 (which has the composition of 99.0% acetone cyanohydrin, 0.3% acetone, 0.5% water) and Separated sulfuric acid 17 was fed to the amide/conversion at a mass ratio of 1.63/1 [kg H ₂ SO ₄ /kg ACH] with 99.7% sulfuric acid. The amidation was carried out at 98°C and the conversion was carried out at 158°C and a pressure of 980 mbar(a). Furthermore, during the amidation/conversion, the waste gas GS1 formed by the side reaction is separated from the liquid reaction mixture and fed to the condensation f in the form of mass stream 1a . The composition of the exhaust gas GS1 or 1a is shown in Table 1. (b) Esterify the second reaction mixture obtained during the amidation/conversion of a (which is composed of methacrylamide (MAA), methacrylic acid (MA) and hydroxyisobutylamide (HIBAm) ), dissolved in sulfuric acid) is sent to the esterification b . Without the use of recycle stream 11 , the second liquid reaction mixture is supplied with 4850 kg/h methanol as stream 6 ; 2000 kg/h water as stream 8 and 3220 kg/h at about 100-140°C and Esterification is carried out under direct steam at a slightly elevated pressure of 50-150 mbar (g). The crude MMA product formed in the esterification b is then distilled and fed with recycle stream 11a from condensation f to remove MMA from the thermal workup c . The diluted spent acid remaining in process step b is discharged from process (b). To inhibit polymer formation, solutions of stabilizers of the phenylenediamine series are used at various points in method step b . For optimal functionality, oxygen is required. In method step b , for this purpose, air with an oxygen content of 21% by volume is fed at several points as oxygen-containing gas mixture 15 . In the esterification b , in particular in the distillation of the crude MMA product in b , a gaseous output stream GS2 is obtained. (c) The separation of thermally post-treated MMA from the crude MMA product includes a plurality of thermal separation steps c and at least two distillation stages, and the low-boiling fraction is separated in the first stage and the high-boiling fraction is separated in the first stage. The second stage separation yields the pure MMA product 13 as the overhead fraction from the final distillation step. In the thermal post-treatment c , as in method step b , air with an _O content of 21% by volume is added as auxiliary to the stabilizer in the form of the oxygen-containing gas mixture 15 . Obtain gaseous output stream GS3 . The amounts and compositions of GS2 and GS3 are summarized in Table 1. The resulting exhaust gas volumes are shown in Table 1. The purified pure MMA product 13 obtained in thermal process step c is subsequently cooled to 8° C. and fed to storage tank d . (d) Storage of the pure MMA product In order to optimize the function of the stabilizer in the oil storage field d , air with an O ₂ content of 21% by volume is also fed into the oil storage field d . As a gas mixture containing oxygen 15 . A gaseous output stream GS4 is obtained with an MMA content according to Table 1. In addition, additional MMA-saturated off-gas from successive filling and emptying operations is added to this outlet stream GS4 . The output stream GS4 is likewise fed to the partial condensate f for recovery of MMA. The amounts and composition of GS4 are summarized in Table 1. (f) Condensation of the gaseous output streams combines the gaseous output streams GS1 , GS2 , GS3 and GS4 to produce a combined process off-gas 5 and is sent to equipment for condensation f . This condensation f takes place at a surface temperature level of approximately 12°C. The refrigerant used is cold water at a feed temperature of about 1°C. The cooling and partial condensation of the gas from the MMA 5 was carried out countercurrently in the condensation f in a vertically arranged shell-and-tube type apparatus at a slightly reduced pressure of 990 mbar (a). The condensed MMA 11a is continuously sent to thermal aftertreatment c , while the spent exhaust gas 9 is sent to post-combustion. Comparative Example V2: Condensation of the Combined Gaseous Output Streams GS2, GS3 and GS4 for Recovery of MMA Comparative Example V2 relates to the preparation of methyl methacrylate ( MMA) method. The results obtained are detailed in Table 1. Comparative Example V2 is implemented based on the above-mentioned Comparative Example V1. In contrast to comparative example V1, only the gaseous output streams GS2 , GS3 and GS4 are combined to produce a gas stream 5 and directed to the condensation f for recovery of MMA. The waste gas GS1 formed by the side reactions in the amidation/conversion is separated from the liquid reaction mixture and is discharged from the process in the form of mass stream 1c and sent for incineration. The composition of the waste gas GS1 or 1c is shown in Table 1. Table 1 : Comparison between comparison examples V1 and V2 flow describe unit V1 V2 (a) ACH (99.0%) kg/h 13 847 13 847 (a) Total H ₂ SO ₄ (99.7%) kg/h 22 570 22 570 (a) Amide yield (ACH) % 93.4 93.4 (6) Fresh methanol for esterification kg/h 4850 4850 (8) Demineralized water for esterification kg/h 2000 2000 GS1 Amide exhaust gas m³ (STP)/h 280 280 GS1 CO/ _SO2 content Volume % ＞90/3 ＞90/3 GS1 oxygen content Volume % 2 2 GS1 Monomer* content Volume % - - GS2+3 Esterification waste gas + thermal post-treatment m³ (STP)/h 212 212 GS2+3 Inerts/non-condensables % ＞80% ＞80% GS2+3 oxygen content Volume % 8 8 GS2+3 Monomer*/MeOH content Volume % 4.8/4 4.8/4 GS4 Oil storage yard exhaust gas m³ (STP)/h 522 522 GS4 Inerts/non-condensables % ＞97% ＞97% GS4 oxygen content Volume % ＞20% ＞20% GS4 Monomer* content Volume % 0.5 0.5 (5) Gaseous output stream to condensation - GS1+GS2+ GS3+GS4 GS2+GS3+GS4 (5) Gaseous output stream to condensation m³ (STP)/h 1014 734 (5) Monomer* content g/m³ 48 65 (f) condensation temperature ℃ 12 12 (11) Recycled monomer* kg/h 9 26 (9) MMA content g/m ³ 38 30 (9) MMA losses kg/h 39 twenty three (11) Recycled monomer* t/a 69 198 MMA yield, in ACH % 91.0 91.1 * The monomers contain MMA and MA (present in small amounts as by-products) Inventive Example B1: Absorption of the combined gaseous output streams GS1, GS2, GS3 and GS4 in scrubbers e1 and e2 for the recovery of MMA Inventive Example B1 Regarding a method for preparing methyl methacrylate (MMA) by the ACH sulfo method based on the flow chart according to Figure 3. The procedures for method steps a (amidation/conversion), b (esterification), c (thermal post-treatment) and d (storage of the pure MMA product) are described in comparative example V1. The results obtained are detailed in Table 2. In contrast to comparative example V1, only the gaseous output streams GS2 , GS3 and GS4 are combined to produce gas stream 5 and directed to the absorption e for the recovery of MMA. The off-gases (gaseous output stream GS1 ) formed by the side reactions in the amidation/conversion a are separated from the liquid reaction mixture and discharged from the process in the form of material streams 1c and 12 and sent for incineration . The amide mixture (second reaction mixture) fed to process step b (which uses the recycle stream 11a constituting the MMA-loaded absorbent from the absorption e or from the absorptions e1 and e2 ) is supplied with 3220 kg/h It is esterified under direct steam at a slightly elevated pressure of about 100-140°C and 50-150 mbar (g). (e) The absorption of the gaseous output stream in e1 and e2 combines the gaseous output streams GS2, GS3 and GS4 to produce a combined gaseous output stream 5 and is sent to the scrubber (absorption) into the gaseous output stream at 20°C and 10 mbar ( g) In the first countercurrent packed column e1 operated under. The first absorption tower e1 is operated with a supply of discharge stream 10 from the second absorption tower e2 and with a supply of 4850 kg/h of methanol as feed stream 6 . In this first absorption step e1 , the MMA present in the combined output stream 5 is at least partially converted into the liquid phase comprising methanol, which is removed from the column e1 as MMA-loaded absorbent 11 and Complete recirculation into method step b . The methanol-rich gas stream 7 leaving the absorption column e1 (which is essentially methanol saturated and depleted of MMA) is then fed to the second absorption step e2 in a second packed countercurrent column e2 , which is at 20°C and 10 mbar(g), with 2000 kg/h of water supplied as feed stream 8 . In this second absorption step e2 , the methanol present in the gas stream 7 is at least partially converted into the aqueous liquid phase, producing a methanol-loaded aqueous absorbent 10 , which is discharged from the column e2 and completely recycled to the process In step e1 . Furthermore, in this second absorption step e2 , at the top of column e2 , a methanol-depleted and essentially water-saturated gas stream is obtained, which is discharged from the process as waste gas 9 . The methanol washing liquid (absorbent) used as fresh methanol 6 and the water used as fresh water 8 in the absorption towers e1 and e2 are the MMA-loaded absorbent 11 (containing MMA-loaded alcohol and Water (wash solution) was fed to process step b as co-reactants in the esterification, wherein they partially replaced the supply of fresh methanol and water (cf. Table 2). Inventive Example B2: Absorption of the combined gaseous output streams GS1, GS2, GS3 and GS4 in a scrubber e for the recovery of MMA Inventive Example B2 relates to a flow diagram based on Figures 3 and 4 for the ACH sulfo method for the preparation of methyl methacrylate (MMA). The effect of Example B2 is based on the above Example B1. In contrast to Example B1, the combined gas streams GS2, GS3 and GS4 were treated in a single absorption device e (scrubber) according to Figure 4, as explained below. (e) The absorption of the gaseous output stream in e combines the gaseous output streams GS2 , GS3 and GS4 to produce a combined gaseous output stream 5 and is fed from the bottom or near the bottom into the countercurrent packed column e (according to Figure 4) to Washing (absorption), which is operated at 20°C and 10 mbar (g). The absorption tower e has two structured packing units arranged one above another. The lower structured packing unit e was operated with 4850 kg/h of methanol supplied as feed stream 6 and the first absorbent 6 added in the upper part of the lower structured packing unit. The upper structured packing unit was operated with a supply of 2000 kg/h of demineralized water and the addition of the second absorbent 8 in the upper portion of the upper structured packing unit. In the absorption step e , the MMA present in the combined output stream 5 is at least partially converted into the liquid phase (absorbent), which contains methanol and water, and which is removed from the column e as load MMA of absorbent 11 and is completely recycled to method step b . Furthermore, in this absorption step e , at the top of column e, a gas stream depleted of methanol and MMA and substantially saturated with water is obtained, which is discharged from the process as waste gas 9 . The methanol washing liquid (absorbent) 6 and water 8 used in the absorption towers e1 and e2 are in the form of the MMA-loaded absorbent 11 and are fed to the method step as co-reactants in the esterification b , where they replace the supply of fresh methanol and water (see Table 2). Table 2 : Comparison of Examples B1 and B2 with Comparative Example V2 flow describe unit B1 B2 V2 (16) in (a) ACH (99.0%) kg/h 13 847 13 847 13 847 (6) of (b) Fresh methanol for esterification kg/h 4850 4850 4857 (6) in (e1) Proportion of fresh alcohol used for absorption (e1+e2) kg/h 600 600 - In (b) of (8) Demineralized water for esterification kg/h 2000 2000 2000 (8) in (e2) Proportion of demineralized water used for absorption (e1+e2) kg/h 700 700 - (11) Liquid for recycling in esterification kg/h 1345 1345 30 GS1 Amide waste gas GS1 treated in (e1+e2) or (f) whether no no no GS2 Esterification waste gas GS2 treated in (e1+e2) or (f) whether yes yes yes GS3 Distillation waste gas GS3 treated in (e1+e2) or (f) whether yes yes yes GS4 Oil storage yard waste gas GS4 treated in (e1+e2) or (f) whether yes yes yes (5) Gaseous output stream to absorption m³ (STP)/ h 734 734 734 (5) MeOH content g/m³ 20.2 20.2 20.2 (5) Monomer* content g/m³ 65 65 65 (5) oxygen content Volume % >20 >20 >20 (e1+e2) / (e) / (f) Absorption/condensation temperature ℃ 20 20 12 (11) Recycled monomer* (MMA+MA) kg/h 46 45 26 (11) Recycled monomer* (MMA+MA) t/a 353 349 198 (9) MMA content g/m ³ 2.8 2.8 30 (9) MMA losses kg/h 2 <3 twenty two (9) MeOH loss kg/h 4 4 11 MMA yield, in ACH % 91.3 91.3 91.1 Methanol yield, in ACH % 94.0 94.0 93.9 * The monomers contain MMA and MA (present in small amounts as by-products). Comparison of the description of Examples V1 , V2 , B1 and B2 shows with Examples V1 and V2 that significant amounts of MMA are present in the output stream GS4 from the described process. This output The flow is caused by the air being introduced to stabilize it. This output stream GS4 does have a relatively small MMA concentration, but is greater than the other gaseous output streams GS2 and GS3. The high inert gas content of the feed air reduces the partial pressure of MMA in the output stream and makes it difficult to recover MMA by cooling and partially condensing the output stream. In the comparative example V1, the interconnection of all gaseous output streams from process steps a, b, c and d and the downstream condensation at low temperatures is used, which corresponds to the process as standard in the prior art. If, as in comparative example V2, only the MMA-rich gaseous output streams GS2, GS3 and GS4 from process steps b, c and d are used for recovery, the recovery volume of MMA can be increased from 69 t/h to 198 t/h. h, which corresponds to a 0.1% increase in yield. However, this increase is much smaller than the increase in the recovery amount of MMA in Inventive Examples B1 and B2. It is clear from inventive examples B1 and B2 that the use of absorption operated with methanol and water allows to recover significantly greater amounts of MMA from the gaseous output stream from the C3 process than by partial condensation according to the prior art. In the process according to the present invention, it is possible to achieve a higher MMA yield of 0.2%, together with a higher methanol yield, without using additional reactants or generating additional waste streams. As shown in Table 2, the branch streams of the methanol and demineralized water reactants used in the esterification were in individual cases used as absorbents in the absorption unit e or in two different absorption units e1 and e2 and recycled as a reactant into the esterification of supported MMA. Inventive Example B2 additionally shows that when the packed column used here has introduction devices for corresponding absorbents at multiple locations, two-stage absorption using methanol and water can be carried out in the separation device. In this way, absorption recovery of MMA is significantly simplified and does not constitute any greater equipment complexity than partial condensation, with the concomitant increase in the recirculation volume of MMA.

a: Amination and conversion b: Esterification c: Thermal post-treatment area d: Storage/storage tank e1: First absorption step (methanol washing) e2: Second absorption step (water washing) e: Absorbed/combined methanol - water scrubbing f: partial condensation GS1: gas stream from process step a containing carbon monoxide and sulfur dioxide GS2: gas stream from process step b containing MMA (preferably with an oxygen concentration of <10% by volume) GS3: gas stream from process step c Gas stream containing MMA (preferably with an oxygen concentration of <10% by volume) GS4: Gas stream containing MMA from storage d (preferably below the lower explosion limit LEL) 1a, b, c: Waste gas from amination/conversion ( Preferably <10% by volume O ₂ ) 2a, b: Waste gas from esterification (including MMA; preferably <10% by volume O ₂ ) 3a, b: Waste gas from thermal post-treatment (including MMA; preferably less than 10% by volume) Preferably <10 volume % O ₂ ) 4a, b: Waste gas from oil storage tank (including MMA; preferably > 10 volume % O ₂ ) 5: Gaseous output stream GS for post-processing 6: Fresh methanol ( Reactants and optional scrubbing liquid) 7: Methanol-rich gas stream from e1 (depleted of MMA) 8: Fresh water (reactants and optional scrubbing liquid) 9: Waste gas (depleted of MMA and methanol) 10,10a,b: Methanol-loaded aqueous absorbent 11,11a,b: MMA-loaded absorbent (including water, MMA and methanol) 12: Waste gas for thermal post-treatment 13: Pure MMA product 14: From storage Product stream of the pure MMA product 15: Gas mixture containing oxygen feed 16: ACH feed 17: Sulfuric acid feed

[Fig. 1] Describes a highly extensive reaction network for the formation of methyl methacrylate from a reactive MMA precursor compound that is selectively manufactured from C2 unit ethylene, C3 unit acetone, or C4 unit isobutylene. [Fig. 2] (Protocol for comparison of Examples V1 and V2) shows a flow chart for preparing MMA. [Fig. 3] (Scheme used in Inventive Example B1) shows a flow chart of a preferred specific example of the method according to the present invention. [Fig. 4] (Scheme for Inventive Example B2) shows a flow chart of a further preferred specific example of the method for preparing MMA according to the present invention.

a: Amidation and transformation

b:Esterification

c:Heat post-treatment area

d:storage/storage tank

e1: First absorption step (methanol washing)

e2: Second absorption step (water washing)

1a, 1b, 1c: Waste gas from amination/conversion (preferably <10 vol% O ₂ )

2a, 2b: Waste gas from esterification (including MMA; preferably <10 volume % O ₂ )

3a, 3b: Waste gas from thermal post-treatment (including MMA; preferably <10 volume % O ₂ )

4a, 4b: Waste gas from oil storage tank (including MMA; preferably >10 volume% O ₂ )

GS1: Gas stream containing carbon monoxide and sulfur dioxide from method step a

GS2: Gas stream containing MMA from method step b (preferably with an oxygen concentration of <10 vol%)

GS3: Gas stream containing MMA from method step c (preferably with an oxygen concentration of <10 vol%)

GS4: Gas flow containing MMA from storage d (preferably below the lower explosion limit LEL)

5: Gaseous output logistics GS for post-processing

6: Fresh methanol (reactants and washing liquid as appropriate)

7: Methanol-rich gas flow from e1 (depleted MMA)

8: Fresh water (reactants and washing liquid as appropriate)

9: Exhaust gas (exhaust MMA and methanol)

10,10a,10b: Aqueous absorbent loaded with methanol

11,11a,11b: MMA loaded absorbent (including water, MMA and methanol)

12: Waste gas used for thermal post-treatment

13: Pure MMA product

14: Product stream from storage of the pure MMA product

15: Feed of gas mixture containing oxygen

16:ACH feed

17: Sulfuric acid feed

Claims (14)

A method for preparing alkyl methacrylate (preferably methyl methacrylate), which comprises the following steps: a. Preparation of at least one alkyl methacrylate precursor compound comprising the reaction of acetone cyanohydrin with sulfuric acid in a first reaction stage (amidation) to produce a first reaction mixture, and conversion in a second reaction stage , which includes heating the first reaction mixture to obtain a second reaction mixture including the alkyl methacrylate precursor compound and sulfuric acid; and b. react the second reaction mixture with water and alcohol (preferably methanol) in the third reaction stage (esterification) to obtain a crude product containing an alkyl methacrylate (preferably methyl methacrylate) a third reaction mixture of an alkyl methacrylate product; and c. Separating the alkyl methacrylate (preferably MMA) from the third reaction mixture in a post-treatment zone comprising at least two distillation steps, wherein the low boilers are separated in one distillation step from the crude The alkyl methacrylate product is separated, and the high boilers are separated from the crude alkyl methacrylate product in another distillation step to obtain a pure alkyl methacrylate product (preferably a pure MMA product) As the overhead fraction from the final distillation step; and d. Store the pure alkyl methacrylate product obtained in method step c in at least one storage device and optionally the third reaction mixture (crude alkyl methacrylate) obtained in method step b products) are intermediately stored in at least one intermediate storage facility; and e. Absorbing the gaseous output stream GS by treating at least one gaseous output stream obtained in method steps b, c and/or d with at least two liquid absorbents to obtain at least one absorbent loaded with alkyl methacrylate , wherein the liquid absorbent comprises at least one absorbent containing alcohol (preferably methanol) and at least one aqueous absorbent, The at least one alkyl methacrylate-loaded absorbent obtained after processing the gaseous output stream GS in process step e is at least partially fed in liquid form to process step b. Such as the method of request item 1, where The pure alkyl methacrylate product obtained in process step c and/or the third reaction mixture obtained as crude alkyl methacrylate product in process step b comprises at least one stabilizer; and In process step d, the oxygen-containing gas mixture is passed through the storage device and optionally through the intermediate storage device to obtain in process step d at least one gaseous output stream GS4, which contains an alkyl methacrylate (preferably methane methyl acrylate), and at least 10% by volume of oxygen, based on the total volume of the output stream GS4, wherein in process step e the gaseous output stream GS4 is directed to the absorption. The method of claim 1 or 2, wherein the gaseous output stream GS processed during the absorption in step e of the method includes at least two gaseous output streams selected from the following: GS1 The gaseous output stream GS1 obtained in method step a, which contains carbon monoxide and sulfur dioxide; GS2 The gaseous output stream GS2 obtained in method step b, which contains an alkyl methacrylate (preferably methyl methacrylate), and not more than 10% by volume of oxygen based on the total volume of the output stream GS2 ; GS3 The gaseous output stream GS3 obtained in method step c, which contains an alkyl methacrylate (preferably methyl methacrylate), and not more than 10% by volume of oxygen based on the total volume of the output stream GS3 ;and GS4 The gaseous output stream GS4 obtained in process step d, which contains an alkyl methacrylate (preferably methyl methacrylate) and at least 10% by volume of oxygen, based on the total volume of the output stream GS4. The method of claim 3, wherein the gaseous output stream GS processed during the absorption in step e of the method includes at least two gaseous output streams selected from the gaseous output streams GS2, GS3 and GS4, and the gaseous output stream GS Better inclusion of all outbound logistics GS2, GS3 and GS4. A method as claimed in any one of claims 1 to 4, wherein the absorption in method step e includes At least one first absorption step e1, wherein the gaseous output stream GS is treated with a first alcoholic liquid absorbent containing at least 50% by weight of alcohol, preferably methanol, to obtain an absorbent loaded with alkyl methacrylate and alcohol-rich gas flow; and At least one second absorption step e2, wherein the alcohol-rich gas stream is treated with a second aqueous absorbent containing at least 50% by weight of water to obtain an alcohol-loaded aqueous absorbent. The method of any one of claims 1 to 5, wherein the gaseous output stream depleted of alkyl methacrylate obtained after treatment with the at least two liquid absorbents in method step e, optionally after heat treatment, is from This method discharges. The process of any one of claims 1 to 6, wherein the gaseous output stream GS1 is obtained in process step a and contains carbon monoxide and sulfur dioxide, and wherein the gaseous output stream GS1 is obtained in process steps b, c and/or The gaseous output stream obtained in d is discharged separately from the process. The method of any one of claims 1 to 7, wherein the gaseous output stream GS1 is obtained in method step a, which contains 70 to 99 volume % of carbon dioxide and 1 to 20 volume % of sulfur dioxide. A process as claimed in any one of claims 1 to 8, wherein in process step b a gaseous output stream GS2 is obtained and in process step c a gaseous output stream GS3 is obtained, wherein streams GS2 and GS3 comprise 1.0% by volume to 5.0% by volume ( Preferably, it is 3.0% to 5.0% by volume) alkyl methacrylate (preferably methyl methacrylate), and no more than 10% by volume (preferably 0.1% to 10% by volume) oxygen, In each case it is based on the total volume of this output stream GS2 or GS3. The method of any one of claims 1 to 9, wherein in method step d a gaseous output stream GS4 is obtained, which contains 0.1 to 5.0 volume % (preferably 0.2 to 2.0 volume %) of methacrylic acid alkyl ester (preferably methyl methacrylate), and at least 10% by volume (preferably 10% to 20% by volume, more preferably 10% to 15% by volume) oxygen. The method of any one of claims 1 to 10, wherein during the absorption in method step (e), the gaseous output stream GS is a gaseous output stream GS of 0.1 to 5.0 kg liquid absorbent/ ^m3 (in The total amount of the absorbent) and treated at a temperature of 5 to 40°C. The method of claim 1 to 11, wherein the absorption of method step (e) includes the following steps: e1. Treat the gaseous output stream GS with an alcohol-containing liquid absorbent containing at least 50% by weight of alcohol (preferably methanol) in a first absorption device to obtain an alcohol-rich gas stream, and e2. The alcohol-rich gas stream obtained in method step e1 is treated in a second absorption device with an aqueous absorbent containing at least 50% by weight of water. The method of any one of claims 1 to 12, wherein one or more gaseous output streams obtained in method steps b, c and/or d are fed into the lower part of the absorption device and at least two Two liquid absorbents are added to the upper part of the apparatus (preferably at different points), and the absorption in method step e takes place in a single absorption apparatus. The method of any one of claims 1 to 13, wherein the absorption in method step e is carried out in a single absorption device, wherein Feeding one or more gaseous output streams obtained in process steps b, c and/or d into the lower part of the absorption device; In the first absorption step (e1), at least one alcohol-containing liquid absorbent comprising at least 50% by weight of alcohol (preferably methanol) is fed above the feed of the gaseous output stream; In the second absorption step (e2), at least one aqueous absorbent comprising at least 50% by weight of water is fed above the feed of the alcohol-containing absorbent; And wherein the gaseous output stream and the at least two absorbents are directed in countercurrent flow.

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