WO2023169810A1 - Process for producing alpha-hydroxyisobutyric acid methyl ester, and its use in the electronics industry - Google Patents

Abstract

The present invention relates to a process for producing alkyl methacrylates (AMA), in particular methyl methacrylate (MMA), and alpha-hydroxyisobutyric acid alkyl esters (2-HIBSA), in particular alpha-hydroxyisobutyric acid methyl esters (2-HIBSM) and/or methacrylic acid (MAS) with improved yields, comprising the process steps of amidation, conversion, hydrolysis/esterfication and reprocessing. According to the invention, in particular 2-HIBSM can be isolated and extracted with a level of purity suitable for use in the electronics industry.

Description

Process for the production of alpha-hydroxyisobutyric acid methyl ester and its application in the electronics industry

Field of invention

The present invention relates to a process for producing alkyl methacrylates (AMA), in particular methyl methacrylate (MMA), and alpha-hydroxyisobutyric acid alkyl esters (2-HIBSA), in particular alpha-hydroxyisobutyric acid methyl ester (2-HIBSM) and/or methacrylic acid (MAS) with improved yield, comprising the process steps amidation, conversion, hydrolysis/esterification and workup. In particular, 2-HIBSM can be isolated and discharged in a purity suitable for use in the electronics industry.

Starting from hydrogen cyanide and acetone, the acetone cyanohydrin (ACH) obtained from them is first subjected to amidation using sulfuric acid. The subsequent conversion includes the conversion of the sulfuric acid reaction mixture obtained in the amidation, which contains a high proportion of alpha-sulfoxyisobutyric acid amide (2-SIBA), into a sulfuric acid reaction mixture containing methacrylic acid amide (MASA). In the final hydrolysis-esterification step, this is converted with water and alcohol to form a sulfuric acid stream containing MMA and MAS, which contains controllable amounts of alpha-hydroxyisobutyric acid (2-HIBS) and alpha-hydroxyisobutyric acid methyl ester (2-HIBSM). By carrying out the hydrolysis as well as the esterification and the subsequent processing according to the invention, on the one hand the amount of the valuable product 2-HIBSM supplied via waste streams for thermal recycling can be reduced and, moreover, its isolation and material recycling can be made possible. The invention therefore contributes significantly to a production process for MMA, 2-HIBSM and/or MAS with high atom economy.

State of the art

Methyl methacrylate (MMA) is used in large quantities to produce polymers and copolymers with other polymerizable compounds. Furthermore, methyl methacrylate is an important building block for various special esters, based on the chemical base substance methacrylic acid (MAS), which can be produced by transesterification of MMA with the corresponding alcohol or are accessible by condensation of methyl acrylic acid and an alcohol. This results in great interest in the simplest, most economical and environmentally friendly manufacturing processes possible for this raw material.

Alpha-hydroxyisobutyric acid alkyl esters have long been increasingly used as special solvents. KR 20200085010 describes cleaning solutions that are used to remove photoresist residues in the production of electronic components. Such cleaning solutions can typically also contain 20% to 80% 2-HIBSM in addition to other alkoxy-substituted esters and / or substituted pyrrolidones and are characterized due to a high level of purity, especially due to the absence of foreign metals, which interfere with electronic applications. Further applications of 2-HIBSM as a solvent for paints and resins in the electronics sector are described, for example, in JP 2020077642. Other alkyl esters of alpha-hydroxyisobutyric acid are also used in the commercial production of electronic components. CN 106952745 describes the production of ruthenium oxide-based high-performance capacitors, in which alpha-hydroxyisobutyric acid ethyl ester is used as a solvent.

Due to the sensitivity of electronic (semiconductor) components to impurities, especially doping metals, the high purity of electronic chemicals is particularly important. Numerous processes have been published in the patent literature that describe the removal of trace contaminants from solvents.

The production of complementary metal oxide semiconductors (CMOS) involves a variety of different steps in which contact patterns made of the thinnest metal layers are defined photolithographically. After lithography, the unexposed parts of the so-called photoresist used are typically removed either by plasma etching or by wet chemical processing using specially developed organic solvents. During the removal of the resist, many component layers are susceptible to contamination by trace metals such as sodium (Na) or iron (Fe), the main source of which is, in addition to the machines and apparatus used for component production, such as the walls of the high-temperature plasma etching chambers Solvents themselves are. In particular, wet processing using so-called stripper solvents has been identified as the main Na contamination route in the production of CMOS components.

Metal contamination, especially sodium, is critical for device technology because sodium ions' mobility leads to a deterioration in the electronic stability of components. For example, the positive sodium ions at the Si-SiC>2 interface induce a negative charge in the silicon substrate, which reduces the positive gate bias voltage required to generate channel current at a given drain voltage. Sodium ion densities as low as 10 ¹⁰ / cm ² can cause threshold voltage shifts of a few tenths of a volt in metal-oxide-semiconductor field effect transistors (MOSFETs) with a gate thickness of about 1000 Å. N-channel devices are generally more sensitive to contamination, particularly sodium, than p-channel transistors. Other contaminants, such as iron, in dissolved or particulate form, result in degradation or failure of the integrity of the gate oxide.

In the steps of forming metal channels and connection structures, especially during the metallization steps or the so-called back-end process, various solvents, which are typically organic in nature, are used to clean the component. During back-end cleaning processes, dielectric and metallic layers such as TiN are particularly susceptible to contamination by trace amounts of alkali and alkaline earth ions, e.g. Na ⁺ , K ⁺ and Ca ²⁺ . The risk of contamination is exacerbated by the fact that the solvents in the Back-end cleaning processes typically contain about 10 to 15 ppb, i.e. 0.6 to 6.0 x 10 ¹⁵ alkali metal ions per milliliter of solvent. Due to the high absorption rates, most of the metal ions in the solvent generally remain on the wafers.

To prevent or minimize Na contamination, two-stage cleaning can be used. This method according to EP 04 650 69 includes post-cleaning etching of oxide layers with selective etching agents, for example glycol-based. However, this cleaning process is expensive and time-consuming in terms of chemical consumption and time. Another strategy to minimize Na contamination involves complexing the Na contaminations with ligands such as crown ethers, polyalcohols, and other clathrates. However, these organic ligands can be carcinogenic and pose a health risk, so extreme care should be taken in product formulation and application.

Alternatively, methods have been published to remove (earth) alkali contamination from the solvents used for cleaning before application. US 6,133,158, for example, teaches the removal of sodium ions by treating solvents with absorbents containing titanium oxide, so-called sacrificial bodies. To avoid such an additional cleaning step, it is desirable to be able to provide the corresponding solvents with the required purity in simplified manufacturing processes. Likewise, US 2018/273465 A1 describes a process for the purification of carboxylic acid esters, for example methyl hydroxyisobutyrate, whereby anionic impurities and metal ion impurities such as Ag, Al, Au, Ca, Cr, Cu, Fe, K, Mg, Na, Sn, and Zn, can be removed by treatment with anion and cation exchangers. It is described that a highly pure carboxylic acid ester with a proportion of metallic impurities of less than 1 ppb and a proportion of anionic impurities of less than 1 ppm can be obtained.

Today, MMA is produced using various processes that start with C2, C3 or C4 building blocks. The general state of the art is essentially described in current reviews and overview articles:

“Trends and Future of Monomer-MMA Technologies”, K. Nagai & T. Ui, Sumitomo Chemical Co., Ltd.; Basic Chemicals Research Laboratory, http://www.sumitomo-chem.co.jp/english/rd/report/files/docs/20040200_30a.pdf (accessed March 10, 2022), 2005, and

“Many paths lead to methyl methacrylate,” S. Krill, A. Ruehling, H. Offermans, Chem. Unserer Zeit, 2019, 53; © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

The use of propene as a basic raw material was also intensively investigated, with the steps of hydrocarbonylation, for example to produce isobutyric acid, and dehydrogenative oxidation to produce methacrylic acid in moderate yields.

A commercial process used worldwide is based on acetone as a raw material and is usually referred to as the C3 process or ACH-sulfo process. Acetone is mixed with hydrocyanic acid (HCN) is converted into the central intermediate acetone cyanohydrin (ACH). This intermediate product is isolated and used for the following process steps to produce MAS and/or MMA.

A typical process for producing MMA starting from ACH using the classic sulfuric acid-based process is described, for example, in US 4,529,816. A number of other documents describe how the various aspects of the partial reaction steps can be improved and optimized, with the ultimate aim of increasing the overall yield of the desired monomers MAS and MMA.

In the ACH-sulfo process, ACH is hydrolyzed using sulfuric acid to form alpha-hydroxyisobutyric acid amide (2-HIBA) and its sulfate ester (SIBA). This substep is referred to in the relevant literature as amidation or hydrolysis, since the nitrile group of ACH is formally converted into an amide function.

2-HIBA, SIBA and MASA already formed in the amidation are then thermally converted into MASA and smaller amounts of MAS in the sulfuric acid reaction mixture. This sub-step is referred to in the relevant literature as conversion, whereby the sulfoxy group of SIBA is formally converted into an olefinic double bond function in the sense of a ß-elimination, with MASA emerging from SIBA and formally free sulfuric acid being released again.

Depending on the water content in the sulfuric acid used, there is also a proportion of HIBA in addition to SIBA in the amidation mixture. For example, if you use 97% by weight sulfuric acid (1.5 equivalents of H2SO4 relative to ACH), around 25% by weight of 2-HIBA is already formed, which can no longer be selectively and completely converted into MASA. The relatively high proportion of water in the amidation at temperatures of 90 ° C to 110 C results in a relatively high proportion of 2-HIBA, which can only be converted relatively unselectively to the target intermediate MASA x H2SO4 by conventional conversion. With more or less complete SIBA x H2SO4 conversion, the conversion step proceeds with a MASA x H2SO4 yield of approximately 94% to 95%. In addition to the losses in the amidation due to the side reactions described above, only between 90% to 92% MASA (relative to ACH) is available for the subsequent esterification to the desired product, methyl methacrylate (MMA). In principle, there are two important connections, namely that the proportion of 2-HIBA in the amidation and conversion is influenced by the water content of the sulfuric acid used, and that 2-HIBA has different, fundamentally slower conversion kinetics to MASA compared to 2-SIBA Comparison with 2-SIBA has. It should be noted that other water sources, namely the water content of the hydrocyanic acid used (up to 0.1% by weight) and the acetone used (up to 0.4% by weight), also influence the 2-HIBA formation.

Due to the drastic reaction conditions, significant amounts of condensation and addition products of the intermediates are formed as by-products in this process step. The sulfuric acid MASA solution obtained after conversion can then be mixed with methanol and water to produce MMA through an esterification reaction. Alternatively, the sulfuric acid MASA solution obtained after the conversion can be reacted with water to form methacrylic acid (MAS) in a hydrolysis. 2-HIBA present in addition to MASA is typically partially converted to alpha-hydroxyisobutyric acid methyl ester (2-HIBSM), but also partially hydrolyzed to alpha-hydroxyisobutyric acid (2-HIBS). With more or less complete MASA x H2SC>4 conversion, the esterification occurs in the optimal case with an MMA yield of approx. 98% to 99% based on the MASA used (summary selectivity of MAS + MMA). In addition to the losses in amidation and conversion due to the side reactions described above, MMA yields of a maximum of 90 to 93% relative to ACH can be achieved in the overall process across all stages with optimal reaction control.

In principle, it is known according to the prior art that MMA is obtained in monomer quality at the top of a pure distillation column. Accordingly, methacrylic acid and HIBSM are enriched in the bottom of this column. This bottom mixture is usually returned to the esterification reactor in order to convert and isolate part of the methacrylic acid into the valuable material MMA. In the conventional process, HIBSM undergoes hydrolysis to form high-boiling acids such as methoxyisobutyric acid (MIBS) and hydroxyisobutyric acid (HIBS). As a result, it is not possible to completely retain HIBSM in the insulation circuit of the MMA system. In this process, the hydrolysis products HIBS and MIBS ultimately end up in waste acid and are ultimately burned.

The basic process for producing MAS has essentially similar characteristics to that for producing MMA. In MAS production and MMA production, amidation and conversion are often fundamentally similar or identical, with the highest possible MASA yield from ACH being desired in both cases. If the MASA-containing reaction mixture is reacted only with water without alcohol, the reaction in the form of hydrolysis of MASA typically leads to crude MAS mixtures. In contrast, the reaction, more precisely esterification, of the MASA-containing reaction mixture in the presence of water and alcohol, in particular methanol, leads to alkyl methacrylates, in particular in the case of methanol to MMA. In this context, the person skilled in the art is aware that for the selective production of MAS, higher molar proportions of water must be made available than is the case for the production of MMA.

In addition to the classic ACH-Sulfo process, other process variants are described that do not require the use of sulfuric acid, such as the multi-stage Mitsubishi Gas Chemical Process (MGC), which was developed in the mid-1980s and implemented in the 1990s. Although this process is based on acetone and HCN, it avoids the use of sulfuric acid and thus the SAR sub-system (SAR = Sulfuric Acid Recovery) for its recovery. The formation of ammonium sulfate as a by-product is therefore obsolete. In the first stage of the MGC process, hydrogen cyanide is added to acetone to form ACH. Then, for example according to EP 04 878 53, the ACH is hydrated to alpha-hydroxyisobutyric acid amide (2-HIBA) using a manganese dioxide catalyst.

In the following step, for example according to DE 34 366 08, methanol is first reacted homogeneously with CO under pressure in the presence of a strong catalyst base, such as sodium methoxide, to form methyl formate. As an activated ester, methyl formate now exchanges the amide function in a transamidation reaction with alpha-hydroxyisobutyric acid amide. The thermodynamically favored formamide is formed, which in turn can serve as a starting material for the production of HCN, and alpha-hydroxyisobutyric acid methyl ester 2-HIBSM. As described, for example, in US 5,312,966, the conversion here is 85% with selectivities of 98%.

The two products are separated and processed separately. Formamide is split at low pressure and a temperature between 450 and 580 °C at a heterogeneous contact consisting of iron or aluminum phosphate with various dopants to produce hydrogen cyanide and water. The yield of HCN is 94%. Both HCN and water are returned to the MMA process cycle.

The circulation reduces the need for hydrogen cyanide drastically. As described in US 5,075,493, US 5,371,273 or US 5,739,379, 2-HIBSM is dehydrated separately in the gas phase on a heterogeneous zeolite contact in the presence of methanol to give MMA, with high yields of over 90% being achieved. Methacrylic acid is formed as a byproduct in this step.

Overall, the MGC process achieves high yields and selectivities. The raw material costs are particularly advantageous due to the regeneration of ammonia. However, the process complexity is reflected in comparatively high energy costs, especially in the steam and coolant consumption.

The use of large amounts of sulfuric acid, which is characteristic of the conventional ACH-sulfo process, is also avoided in other C3-based processes. In the so-called Aveneer process, hydrogen cyanide is first converted into ACH. The hydrogen cyanide can be obtained beforehand, for example using the Andrussow, BMA or BF process (BMA = hydrogen cyanide from methane and ammonia, BF = biaustic acid from formamide). In the first step, the ACH is hydrated with water on a modified brownstone contact according to DE 102008044218 in almost quantitative yields to form 2-HIBA. According to EP 20 439 94, this is then reacted with methanol to give methyl alpha-hydroxyisobutyrate (2-HIBSM). The ammonia released is also recovered quantitatively and can be recycled as a starting material in an HCN process. This step is also very efficient with a selectivity greater than 98%. Further central steps are the catalytic cross-transesterification of methacrylic acid with 2-HIBSM to MMA and alpha-hydroxyisobutyric acid (2-HIBS), as described, for example, in EP 18 885 03 or DE 102005023976. The methacrylic acid itself is produced by catalytic dehydration of the resulting alpha-hydroxyisobutyric acid. US 4,529,816 describes the concentration of 2-HIBSM as a by-product of the reaction of ACH with sulfuric acid, with a 2-HIBSM-containing stream from the isolation being dehydrated in the presence of large amounts of highly concentrated sulfuric acid. The process causes an increase in MMA yield by converting 2-HIBSM. After the conversion and esterification reaction steps, 2-HIBSM is separated from MMA in at least one distillation and dehydrated together with the amidation mixture, which contains over 30% by weight of methacrylamide.

In this context, a process very similar to US 4,529,816 is described in US 5,393,918. 2-HIBSM is obtained as a byproduct of MMA formation according to the steps of the ACH-Sulfo process in a concentrated form and is dehydrated in the presence of water and a C1 to 012 alcohol, preferably methanol, to increase the MMA yield. According to this teaching, dehydration takes place at a heterogeneous contact in the gas phase. This is the main distinguishing feature of US 5,393,918 compared to US 4,529,816.

Both MAS production and MMA production are carried out in plant complexes that often produce up to several 100,000 tons of product per year. In this respect, even minor improvements in yield can lead to significant savings. A side effect for the ecological footprint of the processes that should not be underestimated is the consideration of the waste materials from these processes. As a rule, considerable amounts of waste acid are generated, which often have to be regenerated again with great energy expenditure in order to recover the sulfuric acid as a starting material. The portions of 2-HIBS, 2-HIBSM and their derivatives contained in the waste acid are converted into CO2 and lost as valuable materials. In addition, tar-like impurities in the waste acid usually have to be removed manually from time to time and disposed of at great expense, which places high demands on technology and occupational safety.

Some approaches for the utilization and conversion of 2-HIBSM by dehydration to methyl methacrylate are described:

For example, EP 04,298.00 describes the reaction of 2-HIBSM or a mixture of 2-HIBSM and a corresponding alpha- or beta-alkoxy ester in the gas phase in the presence of methanol as a co-feed on a heterogeneous catalyst consisting of a crystalline aluminosilicate and a mixed doping of an alkali metal element on the one hand and a noble metal on the other. Despite initially high values for conversion and selectivity of the catalyst, as the reaction time increases, the catalyst is deactivated quite drastically, which is accompanied by falling yields.

A similar approach is followed in EP 09 419 84, according to which the gas phase dehydration of HIBSM is described as a substep of an MMA synthesis in the presence of a heterogeneous catalyst consisting of an alkali metal salt of phosphoric acid on SiO2. Overall, however, this multi-stage process is complicated, requires increased pressures in partial steps and therefore expensive equipment, and only delivers unsatisfactory yields. In addition to the work presented above on the dehydration of 2-HIBSM and related esters to the corresponding alpha, beta-unsaturated methacrylic acid compounds in the gas phase, there are also suggestions for carrying out the reaction in the liquid phase, as set out, for example, in US 3,487,101.

The production of MAS starting from 2-HIBS is described, for example, in US 3,487,101, where the production of various methacrylic acid derivatives, in particular methacrylic acid and methacrylic acid esters, starting from alpha-hydroxyisobutyric acid in the liquid phase, is characterized in that the conversion of 2-HIBS to methacrylic acid in the presence of a dissolved basic catalyst at high temperatures between 180 and 320 ° C in the presence of high-boiling esters such as dimethyl phthalate and internal anhydrides such as phthalic anhydride. Here, with HIBS sales greater than 90%, MAS selectivities of around 98% are achieved. No information is given about the long-term stability of the liquid catalyst solution, particularly the exhaustion of the anhydride used.

DE 1191367 relates to the production of methacrylic acid starting from 2-HIBS in the liquid phase, characterized in that the conversion of 2-HIBS to MAS in the presence of polymerization inhibitors (such as copper powder) in the presence of a catalyst mixture consisting of metal halides and alkali halides at high temperatures between 180 and 220 °C is carried out. Here, with 2-HIBS conversions greater than 90%, MAS selectivities of over 99% are achieved. The best results are achieved with catalyst mixtures of zinc bromide and lithium bromide. It is generally known that the use of halide-containing catalysts at high temperatures places drastic demands on the materials to be used and that these problems with regard to the halogenated carryover by-products in the distillate also occur in subsequent parts of the system.

EP 04 878 53 describes the production of MAS starting from ACH, characterized in that in the first step ACH is reacted with water at moderate temperatures in the presence of a heterogeneous hydrolysis catalyst and in the second step 2-HIBA is reacted with methyl formate or methanol/carbon monoxide to form formamide and alpha-hydroxyisobutyric acid methyl ester, and in the third step 2-HIBSM is saponified with water in the presence of a heterogeneous ion exchanger to form 2-HIBS, and finally in the fourth step 2-HIBS is dehydrated by being in the liquid phase at high temperatures in the presence of a soluble alkali salt can react. The MAS production ex 2-HIBS is described at high conversions of around 99% with more or less quantitative selectivities. The large number of necessary reaction steps and the need for intermediate isolation of individual intermediates, in particular the implementation of individual process steps at increased pressure, make the process complicated and ultimately uneconomical.

DE 1768253 describes a process for producing MAS by dehydrating 2-HIBS, which is characterized in that 2-HIBS is produced in the liquid phase at a temperature of at least 160 ° C in the presence of a dehydration catalyst consisting of a metal salt of 2 -HIBS exists, implements. The alkaline ones are particularly suitable in this case. and alkaline earth metal salts of 2-HIBS, which are prepared in situ in a 2-HIBS melt by reacting suitable metal salts. MAS yields of up to 95% based on 2-HIBS are described here, with the feed of the continuous process consisting of 2-HIBS and approx. 1.5% by weight of HIBS alkali metal salt.

An economical process for isolating 2-HIBS and converting it into MAS is described in EP 17 160 93. However, it does not contain any information on the isolation and excretion of 2-HIBSA.

Commercial processes for the targeted production of 2-HIBSA are presented in a large number of publications. For example, US 3,536,750 describes a procedure for obtaining 2-HIBSM by oxidizing methyl isobutyrate.

EP 04 636 76 teaches a process for producing 2-HIBSM, according to which a 2-hydroxyiminomethyl ester hydrochloride is first formed from 2-hydroxyisobutyronitrile, methanol and anhydrous hydrogen chloride and is reacted with water to form the target product in a subsequent step.

Both processes are based on starting materials, some of which only occur in very small traces in the process streams of the ACH-sulfo process (e.g. HIBS) and each require at least one further synthesis and purification step to get to the desired target product.

It is also known that 2-HIBS or 2-HIBSA can be produced starting from acetone cyanohydrin (ACH) by saponifying the nitrile function in the presence of mineral acids. The prior art describes processes in which ACH is amidated and hydrolyzed in the presence of water, with the hydroxy function in the molecule being retained at least in the first steps of the reaction. See, for example, WO 2005/077878, JP H04 193845 or JP S57 131736.

For example, JP S6361932 describes that ACH is saponified to alpha-hydroxyisobutyric acid in a two-stage process, whereby 1 mol of ACH is first reacted in the presence of 0.2 to 1.0 mol of water and 0.5 to 2 equivalents of sulfuric acid and the corresponding Amide salts are formed. Already in this step, when using low concentrations of water and sulfuric acid, which are necessary to obtain high yields, short reaction times and small amounts of waste process acid, massive problems arise with the stirrability of the amidation mixture due to the high viscosity of the reaction mixtures, especially towards the end of the reaction time. If the molar amount of water is increased to ensure a low viscosity, the reaction slows down drastically and side reactions occur, in particular the fragmentation of ACH into the starting materials acetone and hydrogen cyanide, which further react under the reaction conditions to form secondary products. Even when the temperature is increased, the viscosity of the reaction mixture can be controlled according to the specifications of the patent publication mentioned and the corresponding reaction mixtures can be stirred due to the decreasing viscosity, but here too the side reactions increase drastically even at moderate temperatures, which ultimately results in only moderate yields (see comparative examples). If you work at low temperatures, for example below 50 ° C, which would ensure a selective reaction, towards the end of the reaction time the increase in the concentration of the amide salts, which are poorly soluble under the reaction conditions, initially leads to the formation of a suspension that is difficult to stir and finally to complete solidification of the reaction approach. In the second step of the same patent publication, water is added to the amidation solution and hydrolyzed at temperatures higher than the amidation temperature, whereby alpha-hydroxyisobutyric acid is formed from the amide salts formed after the amidation with the release of ammonium hydrogen sulfate.

In addition to the selective production of the target product 2-HIBS in the reaction, the isolation from the reaction matrix or the separation of 2-HIBS from the remaining process acid is essential for the economic viability of a technical process. In JPS 57131736, this problem is dealt with by treating the reaction solution containing 2-HIBS and acid ammonium hydrogen sulfate obtained by hydrolytic cleavage after the reaction between ACH, sulfuric acid and water with an extractant, whereby the 2-HIBS passes into the extractant and the acid ammonium sulfate remains in the aqueous phase. According to this process, before the extraction, the still free sulfuric acid in the reaction medium is neutralized by treatment with an alkaline medium in order to increase the degree of extraction of HIBS into the organic extraction phase. The necessary neutralization is associated with a considerable additional expenditure of amine or mineral base and thus with considerable waste quantities of corresponding salts that cannot be disposed of ecologically and economically.

The proposals for an alternative amidation in the presence of water lead, depending on whether carried out in the presence of methanol or without methanol, either to the formation of alpha-hydroxyisobutyric acid methyl ester (2-HIBSM) or to the formation of alpha-hydroxyisobutyric acid (2-HIBS). For example, according to JP S57 131736, the reaction of 1 mol of ACH with 0.8 to 1.25 equivalents of sulfuric acid in the presence of less than 0.8 equivalents of water takes place below 60 ° C and then the reaction with more than 1.2 equivalents of methanol for the 2nd -HIBSM at temperatures greater than 55°C.

Another alternative for the production of esters of 2-HIBS, in particular 2-HIBSM, starting from ACH is described in JPH 04193845. Accordingly, 1 mol of ACH is first amidated with 0.8 to 1.25 equivalents of sulfuric acid in the presence of less than 0.8 equivalents of water below 60 ° C and then at temperatures above 55 ° C with more than 1.2 equivalents of alcohol, in particular methanol , converted to 2-HIBSM or corresponding esters. The presence of viscosity-reducing media that are stable to the reaction matrix is not discussed here. The disadvantages and problems of this process are again the technical implementation due to the formation of extraordinary viscosity at the end of the reaction. Other methods describe the targeted production of 2-HIBSM with HCl from ACH. Due to the high level of contamination with chlorine or metal compounds resulting from the process, 2-HIBSM produced in this way is not suitable for use as a cleaning agent in the electronics industry. The procedure described, for example, in JP 2926375 for the production of largely chlorine- and metal-free esters of 2-HIBS, first completely hydrolyzing ACH in the presence of phosphoric acid and then reacting it with alcohols to the corresponding esters within 8 hours at 70 ° C, is uneconomical due to the long process times described and the subsequent necessary distillation in the thin-film evaporator. An analogous process is described, for example, in JP 3336077.

The above-mentioned procedures enable the provision of 2-HIBS or 2-HIBSA. However, under the conditions mentioned, methacrylic acid or its esters cannot be obtained at the same time in the same process, so a separate production facility is required for this. The processes also do not open up the possibility of profitably using the 2-HIBS or 2-HIBSA-containing fractions that arise in the MMA or MAS production process. Furthermore, 2-HIBSA produced according to the processes mentioned does not meet the purity requirements required for use in the electronics industry.

Although the production of 2-HIBSM, which is suitable as a solvent for the electronics industry, as a by-product of MMA production is known, the processes described so far have the disadvantage of forming a high salt load. According to JPH 0899934, 2-HIBSM is obtained after the reaction of ACH with sulfuric acid and subsequent esterification with methanol by first neutralizing the entire reaction mixture with bases and removing both the MMA formed as the main product and the 2-HIBSM formed as a by-product by distillation and be separated from each other. Significant amounts of sulfates are formed.

There is therefore still a need for a commercial process that allows the flexible production of high-purity alpha-hydroxyisobutyric acid alkyl esters while simultaneously increasing the atom economy in the production of alkyl methacrylates and / or methacrylic acid.

Task

In view of the prior art described, the present invention was primarily based on the object of overcoming the disadvantages mentioned above and of providing an economical and simple process for the production of methyl methacrylate and / or methacrylic acid, which is achieved through the simultaneous production of high-purity, metal-free alpha-hydroxyisobutyric acid alkyl esters, especially alpha-hydroxyisobutyric acid methyl esters (2-HIBSM).

It was a particular object of the present invention that this alpha-hydroxyisobutyric acid alkyl ester is obtained in such a quality and purity that it is suitable for use in electronic applications. This particularly applies to product quality that is characterized by a low trace content of critical metals.

Furthermore, it was an object of the present invention to improve the method according to the invention in such a way that it also allows flexible adjustment of the production quantity of 2-HIBSM. For example, the maximum should be the provision of up to 5 kt of 2-HIBSM per 95 kt of MMA.

Another task of the process was to increase the efficiency of the manufacturing process for MMA through the targeted removal of the valuable product 2-HIBSM.

In addition, it was the object of the invention to ensure a simple and efficient removal of formic acid or methyl formate from the manufacturing process for MMA or 2-HIBSM. This is intended to extend the usability of cost-intensive absorber beds for the separation of formic acid or methyl formate or, ideally, to make them unnecessary.

Further tasks not explicitly mentioned may arise from the description, the claims, the examples or the overall context of the invention.

Solution

The tasks were solved in that in the process according to the invention, the alpha-hydroxyisobutyric acid alkyl ester (2-HIBSA), which is obtained as a by-product of the production of methacrylic acid alkyl ester, is removed from the esterification process by at least one distillation step. The 2-HIBSA obtained in this way is characterized by its high purity. The other components contained in the distillation, 2-HIBS, methacrylic acid (MAS) and mainly alkyl methacrylate (AMA - in the case of using methanol, methyl methacrylate / MMA), are returned to the esterification process. There, after conversion to 2-HIBSA, they are fed back into the distillative discharge of 2-HIBSA or converted into AMA and purified.

In particular, the process according to the invention for producing alkyl methacrylate and alpha-hydroxyisobutyric acid alkyl esters is characterized by the presence of the following process steps:

In a process step a. As is generally known from the prior art, acetone cyanohydrin and sulfuric acid are first reacted and a first reaction mixture containing alpha-sulfoxyisobutyric acid amide and methacrylic acid amide is obtained.

In a fundamentally well-described process step b. The first reaction mixture is then converted. This conversion includes in particular heating to a temperature in the range from 130 to 200 ° C, whereby a second reaction mixture containing predominantly methacrylic acid amide, alpha-hydroxyisobutyric acid amide and sulfuric acid is obtained. In a subsequent process step c. the second reaction mixture is reacted with water and alcohol in a third reaction stage, i.e. esterified. A third reaction mixture is obtained which contains methacrylic acid, alkyl methacrylate, alpha-hydroxyisobutyric acid alkyl ester and formic acid.

In a subsequent process step d. The products alkyl methacrylate and alpha-hydroxyisobutyric acid alkyl ester are isolated from the third reaction mixture. In addition to optional further steps, this isolation includes at least two distillation steps and optionally in particular at least one phase separation. The end product alkyl methacrylate is condensed as the top product of a final rectification I and is preferably obtained directly in a commercially usable purity, i.e. corresponding to a general monomer specification. The alpha-hydroxyisobutyric acid alkyl ester is in turn isolated in a further stream and optionally further processed.

In a process step e. Finally, a bottom product from rectification I, which in particular contains further alkyl methacrylate, methacrylic acid and alkyl hydroxyisobutyrate as well as one or more polymerization inhibitors, is fed to at least one further rectification II or IV.

According to the invention, the alcohol is in process step c. preferably methanol, correspondingly in the case of the alkyl methacrylate preferably around MMA and in the case of the alpha-hydroxyisobutyric acid alkyl ester around alpha-hydroxyisobutyric acid methyl ester.

For the purposes of the present invention, information in “%” or “ppm” describes information in% by weight or in ppm by weight, unless stated otherwise or as otherwise apparent from the context.

For the purposes of the invention, the formulations stream, phase or fraction containing a starting material, product and/or by-product are to be understood as meaning that the compound(s) mentioned is (are) contained in the respective stream, for example the majority of the educt, product and/or by-product in the corresponding stream. In principle, in addition to the compounds mentioned, other components can be included. The naming of the components often serves to clarify the respective process step.

For the purposes of the invention, the term “vapors” or “vapor stream” refers to a gaseous process stream, for example a gaseous top stream of a distillation column.

In the sense of the invention, the term “adiabatic” or “adiabatic” means that no or only negligible heat exchange with the environment takes place.

The term rectification describes a specific distillation column, which is characterized by the fact that the column has at least two or more theoretical separation stages and optionally includes a stripping section and a rectification section. The column can optionally be equipped with internals and/or fills to improve the mass and heat transfer between the gas and liquid phases. In a first embodiment of the present invention, additional alkyl methacrylate is preferably obtained at the top of rectification II and at the same time a fraction enriched in methacrylic acid and alpha-hydroxyisobutyric acid alkyl ester is obtained in a lower section and/or in the bottom of rectification II. Furthermore, a methacrylic acid-enriched fraction is obtained in rectification II, which is fed to a further rectification III, in which alpha-hydroxyisobutyric acid alkyl ester is removed as a liquid condensate in highly pure form.

Further preferably, in this first embodiment of rectification III, a bottom stream containing methacrylic acid and inhibitor is removed, which is at least partially fed to or returned to reaction step c).

Particularly preferably, a bottom stream containing methacrylic acid and inhibitor is taken from rectification I and passed into rectification II, after which a further bottom stream is taken from rectification II, which in turn is fed to rectification III, the hydroxyisobutyric acid alkyl ester, preferably hydroxyisobutyric acid methyl ester 2-HIBSA , is obtained in highly pure form as the top distillate of this rectification III and at the same time a bottom stream containing methacrylic acid and inhibitor is removed from the bottom of the rectification III, which can be at least partially fed to reaction step c).

In an alternative second embodiment of the present invention, a bottom stream containing methacrylic acid and hydroxyisobutyric acid alkyl esters, which may also contain inhibitors, is removed from rectification I and passed into rectification IV. In such an embodiment, rectification IV replaces rectifications II and III of the first embodiment in just one column. From this rectification IV, the 2-HIBSA is then produced in highly pure form as a liquid condensate in the side stream. At the top of rectification IV, further alkyl methacrylate is obtained, which can at least partially also be fed to rectification I.

In a preferred embodiment, a bottom stream containing methacrylic acid and inhibitor is removed from rectification I and passed into a rectification IV, with hydroxyisobutyric acid alkyl ester, preferably hydroxyisobutyric acid methyl ester (2-HIBSA), being taken in highly pure form as a side stream of this rectification IV and at the same time at the bottom of rectification IV a bottom stream containing methacrylic acid and inhibitor is removed, which is at least partially fed to reaction step c).

At the same time, a bottom stream containing methacrylic acid and inhibitor will be removed. This bottom stream can then preferably be at least partially fed to process step c).

Regarding process step a.

In process step a. it is an amidation, in particular the reaction of acetone cyanohydrin (ACH) and sulfuric acid in one or more reactors I at a temperature in the range from 70 to 130 ° C, preferably 70 to 120 ° C, the first Reaction mixture containing alpha-sulfoxyisobutyric acid amide and methacrylic acid amide is obtained.

The sulfuric acid used in the first reaction stage preferably has a concentration in the range from 98.0 to 100.5% by weight, preferably from 98.0 to 100.0% by weight and particularly preferably from 99.0 to 99.9% by weight. In particular, the specified concentration of the sulfuric acid used relates to the total mass of the sulfuric acid feed stream to the first reaction stage.

Methods for determining the water content of material streams, for example sulfuric acid feed streams, are generally known to those skilled in the art. For example, the water content of material streams can be determined by mass balances, by measuring the density or speed of sound, by gas chromatography, by Karl Fischer titration or by using HPLC.

The ACH used can be produced using known technical processes. See, for example, Ullmann's Encyclopedia of Technical Chemistry, 4th edition, volume 7. Typically, hydrogen cyanide and acetone are converted into ACH in an exothermic reaction in the presence of a basic catalyst, for example an amine. Such a process step is described, for example, in DE 102006058250 and DE 102006059511.

Typically, the main products formed during the amidation of ACH and sulfuric acid are alpha-hydroxyisobutyric acid amide (2-HIBA) or its hydrogen sulfate (2-HIBA H2SO4), sulfuric acid esters of 2-HIBA (alpha-sulfoxyisobutyric acid amide, 2-SIBA) or its hydrogen sulfate (2 -SIBA H2SO4) and methacrylamide hydrogen sulfate (MASA H2SO4) as a solution in excess sulfuric acid. It is known to those skilled in the art that the proportions of the components mentioned in the reaction mixture are variable and depend on the reaction conditions.

The first reaction stage is preferably operated with an excess of sulfuric acid. Sulfuric acid serves, among other things, as a solvent. At the same time, the sulfuric acid serves as a reactant, in particular for the formation of the intermediate product 2-SIBA, and as a catalyst for the reaction. The excess sulfuric acid can serve in particular to keep the viscosity of the reaction mixture low, which can ensure a faster removal of reaction heat and a lower temperature of the reaction mixture. This can bring about significant yield advantages in particular. Although viscosity and dissolving power are improved with more sulfuric acid, which ultimately also brings with it a general increase in selectivity, the amount of sulfuric acid used is ultimately limited for economic reasons, since the resulting amount of waste acid has to be recycled or further processed.

In a preferred embodiment, the reaction mixture of acetone cyanohydrin (ACH) and sulfuric acid in the first reaction mixture has a total amount of water in the range from 0.1 to 20 mol%, in particular from 0.4 to 10 mol%. This information is based on that total ACH supplied to the first reaction stage. As a rule, acetone cyanohydrin (ACH) is used in the first reaction stage, with the ACH or the supplied ACH material streams having an acetone content of less than or equal to 10,000 ppm, based on the total amount of ACH supplied to the first reaction stage of less than or equal to 1000 ppm. The ACH used or the ACH material streams supplied preferably has an ACH content of greater than or equal to 98% by weight, particularly preferably greater than or equal to 98.5% by weight, particularly preferably greater than or equal to 99% by weight. Typically, the supplied ACH material stream additionally contains 0.1 to 1.0% by weight, usually 0.2 to 1.0% by weight, of acetone and 0.1 to 1.5% by weight, usually 0.3 up to 1% by weight, or from 0.1 to 10 mol%, in particular 0.4 to 5 mol%, of water.

In principle, any reactor known to those skilled in the art for carrying out hydrolysis reactions can be used to carry out the amidation in the first reaction stage. Examples of this are stirred tank reactors and loop reactors or combinations of said reactors. Alternatively, several reactors, possibly connected in parallel, but preferably in series, can be used. In one possible embodiment, one reactor or 2 to 5 reactors connected in series are used; a sequential arrangement of 2 to 3 reactors is preferably used.

Molar ratios of sulfuric acid to ACH in a range from 1.2 to 2.0, preferably from 1.25 to 1.6, particularly preferably from 1.4 to 1.45 are preferably used. Two or more reactors I are preferably used in the first reaction stage, with in such an embodiment sulfuric acid and ACH in the first reactor I in a molar ratio of sulfuric acid to ACH in the range from 1.6 to 3, preferably from 1.7 to 2. 6 and particularly preferably from 1.8 to 2.3 can be used. Furthermore, in such an embodiment, sulfuric acid and ACH in the last reactor I, for example in the second of two reactors I, in a molar ratio of sulfuric acid to ACH in the range 1.2 to 2.0, preferably from 1.2 to 1.8 and particularly preferably used from 1.3 to 1.7. A molar ratio of 1.25 to 1.6 proves to be the optimal compromise between the achievable yield and sulfuric acid consumption, which can ultimately be evaluated from an economic optimization perspective. More sulfuric acid increases the costs for this feedstock and the effort involved in disposing of the resulting waste acid mixture, but the yield based on ACH can also be slightly increased again.

The reaction of acetone cyanohydrin with sulfuric acid in the first reaction stage is exothermic. It is therefore advantageous to largely or at least partially remove the resulting heat of reaction, for example with the help of suitable heat exchangers, in order to obtain an improved yield. Since the viscosity of the reaction mixture increases sharply as the temperature drops, making circulation, flow and heat exchange in the reactors I more difficult, excessive cooling is generally to be avoided. In addition, at low temperatures in the first reaction mixture, partial or complete crystallization of ingredients on the heat exchangers can occur, resulting in abrasion, for example in the pump housings, pipelines and the heat exchanger pipes of the reactors I and in extreme cases can lead to the system being switched off.

In principle, known and suitable cooling media can be used to cool the reactor circuits. The use of cooling water is advantageous. Typically, the cooling medium, in particular the cooling water, has a temperature below the selected process conditions. The cooling medium, in particular the cooling water, advantageously has a temperature in the range from 20 to 90 °C, preferably from 50 to 90 °C and particularly preferably from 60 to 70 °C.

To avoid falling below the crystallization point of methacrylamide, the heat exchanger is typically operated with a hot water secondary circuit. Temperature differences in the product-side inlet/outlet of the apparatus of approximately 1 to 20° C., in particular 2 to 7° C., are preferred.

The reaction of ACH and sulfuric acid in one or more reactors I takes place at a temperature in the range from 70 to 130 ° C, preferably from 75 to 120 ° C, particularly preferably from 85 to 110 ° C. If several reactors are used for the amidation, the temperatures of the various reactors can be the same or different. With regard to different stoichiometry in the reactors, it is preferred to operate the first reactor with a higher excess of sulfuric acid colder than the subsequent reactor or reactors. The amidation is often carried out in the first reaction stage in reactor I or in several reactors I at normal pressure.

Typically, process step a. be carried out batchwise and/or continuously. The first reaction stage is preferably carried out continuously, for example in one or more loop reactors. Suitable reactors and processes are described, for example, in WO 2013/143812. The first reaction stage can advantageously be carried out in a cascade of two or more loop reactors. Particularly preferably, the implementation of the first reaction stage takes place in one or more, preferably exactly two, loop reactors, the respective reaction mixture being reacted at a circulation ratio, i.e. the ratio of circulation volume flow to feed volume flow, in the range from 5 to 90, preferably 10 to 70 Alternatively, stirred or pumped continuous stirred tank reactors, in particular CSTR reactors, or a combination of CSTR apparatus and loop reactors can be used.

The residence time in the respective reactor is designed so that the time is sufficient to maximize the yield of 2-HIBA, 2-SIBA, MAS and MASA. Typically, the static residence time in the reactors I, in particular in the loop reactors I, is in the range from 5 to 35 minutes, preferably from 8 to 20 minutes.

A suitable loop reactor preferably has the following elements:

- one or more addition points for ACH

- one or more addition points for sulfuric acid - one or more gas separators

- one or more heat exchangers

- one or more mixers

- at least one pump.

The mixers are often designed as static mixers.

In principle, the ACH can be added at any point in one or different reactors I. However, it has proven to be advantageous if the ACH is added at a well-mixed point. The ACH is preferably added to a mixing element, for example a mixer with moving parts or a static mixer.

The sulfuric acid can in principle be added at any point in one or more reactors I. The sulfuric acid is preferably added before the ACH is added. The sulfuric acid is particularly preferably added on the suction side of the respective reactor pump. This can often improve the pumpability of the gas-containing reaction mixture.

The reactors I each preferably comprise at least one gas separator. Typically, on the one hand, the product stream, in particular the first reaction mixture, can be continuously removed via the gas separator, and on the other hand, gaseous by-products can be separated and discharged here. Typically, the gaseous byproduct that forms is mainly carbon monoxide. The exhaust gas stream from the reactors I is preferably combined with the exhaust gas from the buffer container/separator I.

In a preferred embodiment, the first reaction stage comprises the reaction of acetone cyanohydrin (ACH) and sulfuric acid in at least two separate reaction zones, preferably in at least two separate reactors, particularly preferably in at least two loop reactors.

The reaction of acetone cyanohydrin (ACH) and sulfuric acid preferably takes place in such a way that the reaction volume is distributed over at least two reaction zones and the total amount of ACH is metered separately into the different reaction zones. Preferably, the amount of ACH fed to the first reactor or reaction zone is greater than or equal to the amounts of ACH fed to the subsequent reactors or reaction zones.

Preferably 50 to 90% by weight, preferably 60 to 75% by weight, of the total volume flow of ACH supplied is introduced into the first reactor. The remaining amount of ACH supplied is passed into the second reactor and, if necessary, into further reactors.

Typically, the total amount of ACH is divided between the first reactor I and a second reactor I in the mass ratio of the first reactor I to the second reactor I in the range from 70 to 30 to 80 to 20, preferably from about 75 to 25. The molar ratio of added sulfuric acid to ACH in the first reactor or in the first reaction zone is preferably greater than the corresponding molar ratio in optionally subsequent reactors or in the subsequent reaction zones.

In a particularly preferred embodiment, the reaction in the first reaction stage takes place in two or more loop reactors, the total amount of ACH being metered into the first and at least one further loop reactor. Particularly preferably, each loop reactor comprises at least one pump, a heat exchanger cooled with water as a medium, a gas separation device, at least one exhaust gas line connected to the gas separation device, and at least one feed line for ACH in liquid form. The at least two loop reactors are preferably interconnected in such a way that the entire resulting reaction mixture from the first reactor is fed into the subsequent reactors and the reaction mixture in the subsequent reactors is mixed with further liquid ACH and optionally further amounts of sulfuric acid.

The first loop reactor is typically operated at a circulation ratio, i.e. a ratio of circulation volume flow to feed volume flow, in a range from 5 to 110, preferably from 10 to 90, particularly preferably from 10 to 70. In a subsequent loop reactor, the circulation ratio is preferably in a range from 5 to 100, preferably from 10 to 90, particularly preferably from 10 to 70.

Typically, after process step a. a first reaction mixture is obtained which contains 5 to 35% by weight of alpha-sulfoxyisobutyric acid amide (2-SIBA), 5 to 25% by weight of methacrylamide (MASA) and less than 5% by weight of alpha-hydroxyisobutyric acid amide (2-H IBA), each based on the entire reaction mixture , dissolved in sulfuric acid reaction matrix. This first reaction mixture is preferably conveyed into the second reaction stage with the aid of a discharge pump with a constantly regulated mass flow. The constantly regulated mass flow enables, in particular, precise control of the static residence time of the reaction mixture in process step (b), the conversion. The first reaction mixture resulting from process step a is preferred. conveyed in a constantly regulated mass flow by means of a discharge pump, starting from at least one reactor I through at least one reactor II.

Regarding process step b.

In process step b. This is a so-called conversion, i.e. converting the first reaction mixture. This process step includes b. first heating to a temperature in the range from 130 to 200 ° C, preferably from 130 to 170 ° C, particularly preferably from 140 to 165 ° C in one or more reactors II. This reactor II or these reactors II can also be used as a heat conversion apparatus or conversion reactors. From this process step b. A second reaction mixture containing predominantly methacrylic acid amide (MASA) and sulfuric acid is obtained. The second reaction mixture obtained in reaction step b) preferably has an alpha-hydroxyisobutyramide content of 0.1 to 2.0% by weight.

According to the invention, during the conversion, the residence time of the reaction mixture in reactor II is generally in a range from 2 to 15 minutes, preferably from 2 to 10 minutes. Typically, the specified residence time refers to the entire conversion reactor (reactor II). Typically, the residence times in all conversion reactors are within the specified ranges. The residence time in a preferably implemented preheater segment of the conversion reactor is preferably 0.1 to 5 minutes, particularly preferably 0.2 to 2 minutes.

During the conversion, heating takes place in process step b. in one or more reactors II, preferably at least one reactor II comprising a preheater segment which can be heated by means of a heating medium that is spatially separated from the reaction mixture. The reaction mixture is additionally heated by 10 to 100 °C, preferably by 15 to 80 °C. Typically, the temperature increase of 10 to 100 ° C is to be understood as meaning that a corresponding temperature increase takes place starting from the original temperature of the first reaction mixture supplied when it enters the respective preheater segment.

Typically, during the conversion when heating the first reaction mixture to a temperature in the range of 130 to 200 ° C, the amount of MASA or MASA H2SO4 is increased by dehydration of the 2-HIBA or by sulfuric acid elimination from 2-SIBA, the first Reaction mixture is a sulfuric acid solution containing 2-SIBA, 2-HIBA and MASA, predominantly in the form of the hydrogen sulfates.

The heating in process step b., the conversion, preferably takes place over the shortest possible period of time. In particular, the heating takes place in the form of remaining in the preheater segment of the reactor II over a period of 0.1 to 14 minutes, preferably 0.1 to 5 minutes, particularly preferably 0.2 to 2 minutes. The heating of the first reaction mixture from the reactors I is usually carried out for a shorter time than the conversion in the almost adiabatic elements themselves.

Particularly preferably, the conversion takes place at a temperature in a range between 130 and 200 °C, preferably between 130 and 170 °C and particularly preferably between 140 and 170 °C. The total residence time in reactor II or several reactors II, usually connected in series, is preferably in a range from 2 to 15 minutes, preferably from 2 to 10 minutes.

The conversion can in principle be carried out in known reactors, which enable the temperatures mentioned to be achieved in the periods mentioned. The energy can be supplied in a known manner, for example using steam, hot water, suitable heat transfer media, electrical energy or electromagnetic radiation, such as microwave radiation. The conversion is preferably carried out in the second reaction stage in one or more heat conversion apparatus. The still hot second reaction mixture emerging from the conversion is cooled before entering the subsequent reaction step c, the esterification, in order to ensure a defined residence time of the reaction mixture leaving the last conversion reactor at high temperatures and yield-reducing subsequent reactions of the valuable products MAS and MAS formed in the conversion to stop MASA. Gaseous by-products are preferably at least partially separated off from the second reaction mixture. Typically, the cooled and degassed second reaction mixture is completely passed into reaction stage c, the esterification or hydrolysis. Preferably, the exhaust gas obtained after the conversion is completely or partially discharged from the process. Furthermore, it is preferred that the exhaust gas obtained after the conversion, together with the exhaust gases from the reactor(s) I for the amidation reaction, be completely or partially fed into a column (in the figures (E)) for the separation of high boilers in process step c ., i.e. esterification or hydrolysis.

In principle, known and suitable cooling media can be used to cool the second reaction mixture. The use of cooling water is advantageous. The cooling medium, in particular the cooling water, advantageously has a temperature in a range from 30 to 120 °C, preferably from 50 to 110 °C and particularly preferably from 60 to 100 °C. The exit temperature of the cooled reaction mixture leaving the cooler and thus the entry temperature into the subsequent reaction step of process step c. is preferably below the maximum temperature occurring in the conversion reactor, typically in a range from 70 to 110 ° C.

Regarding process step c.

The process step involves esterification or hydrolysis. The method according to the invention comprises in method step c. the reaction of the second reaction mixture, containing predominantly MASA, with water and optionally an alcohol, in particular methanol, in one or more reactors III. A third reaction mixture containing methacrylic acid and/or methyl methacrylate is obtained.

In a preferred embodiment, which involves an esterification, the second reaction mixture, containing predominantly MASA, is reacted with water and an alcohol, in particular with methanol, with a third reaction mixture containing an alkyl methacrylate, in the case of methanol, methyl methacrylate ( MMA). The conditions of esterification on an industrial scale are known to those skilled in the art and are described, for example, in US 5,393,918.

In an alternative embodiment of the hydrolysis, the second reaction mixture, containing predominantly MASA, is reacted with water, giving a third reaction mixture containing methacrylic acid. The conditions for the hydrolysis of methylacrylamide to methacrylic acid and the process for large-scale processing Scales are known to those skilled in the art and are described, for example, in DE 102008000787 and EP 2292580.

The reaction in the process step in the form of esterification or hydrolysis is preferably carried out in one or more suitable reactors, for example in heated kettles. In particular, boilers heated with steam can be used. In a preferred embodiment, the esterification takes place in two or more, for example three or four, successive kettles. This approach is also known as a boiler cascade.

Typically, the esterification is carried out at temperatures in a range from 100 to 180 ° C, preferably from 100 to 150 ° C and at pressures of up to 7 bara, preferably at pressures up to 2 bara. The reaction is preferably carried out using sulfuric acid as a catalyst.

The reaction of the second reaction mixture preferably takes place with an excess of water and optionally alcohol. The addition of the second reaction mixture, containing predominantly methacrylamide, and the addition of alcohol are preferably carried out in such a way that a molar ratio of methacrylamide to alcohol results in a range from 1 to 1.0 to 1 to 1.6.

In a preferred embodiment, the reaction in the third reaction stage takes place in two or more reactors III, with a molar ratio of methacrylamide to alcohol in the first reactor III in the range from 1 to 0.7 to 1 to 1.4, preferably from 1 to 1.0 to 1 to 1.4, and in the second and the possible subsequent reactors III there is a molar ratio of methacrylamide to alcohol in the range from 1 to 1.05 to 1 to 1.3.

The alcohol fed into the third reaction stage is preferably composed of alcohol freshly fed into the process (fresh alcohol) and alcohol which is contained in recycled streams, i.e. recycling streams, of the process according to the invention. It is also possible to use methanol in the process according to the invention, which is contained in recycling streams from downstream downstream processes.

Typically, water is added to the reactor III or to the reactors III of the third reaction stage in such a way that the concentration of water is in the range from 10 to 30% by weight, preferably from 15 to 25% by weight, based on the total reaction mixture in the reactor III, lies.

In principle, the water supplied to the third reaction stage, regardless of whether it is an esterification or a hydrolysis, can come from any source and contain various organic compounds, provided that no compounds are present which would disadvantage the esterification or the subsequent process stages influence. The water fed into the third reaction stage preferably comes from recycled streams (recycling streams) of the process according to the invention, for example from the purification of the methyl methacrylate or methacrylic acid. It is also possible Fresh water, in particular fully desalinated water or well water, in process step c. to supply.

The preferred esterification with methanol typically produces a third reaction mixture containing methyl methacrylate (MMA), methyl alpha-hydroxyisobutyrate (2-HIBSM) and other by-products described above, as well as significant amounts of water and unreacted methanol.

In a preferred embodiment, the esterification takes place in two or more, in particular three or four, successive boilers in the form of a so-called boiler cascade, with the liquid overflow and the gaseous products being fed from the first boiler into the second boiler. Typically, possible subsequent boilers are handled in a similar manner. In particular, such a driving style can reduce the formation of foam in the boilers. Alcohol can also be added to the second kettle and any subsequent kettles. The amount of alcohol added is preferably at least 10% by weight smaller compared to the previous boiler. The concentrations of water in the different boilers can typically differ from one another. Typically, the temperature of the second reaction mixture fed into the first vessel is in the range from 100 to 180 ° C. Typically, the temperature in the first boiler is in the range of 90 to 180 °C and the temperature in the second and possible subsequent boilers is in the range of 100 to 150 °C.

In a particular embodiment of the present process according to the invention, in reaction step c. MMA as an ester arising from MASA and 2-HIBSM as an ester arising from 2-HIBA are condensed at the top of a distillation column (E) upstream of rectification I. This condensate breaks down into two liquid phases, whereby the upper organic phase containing MMA and 2-HIBSM can be fed to rectification I after the low boilers have been separated off.

In a preferred embodiment, in reaction step c), MMA is condensed as alkyl methacrylate at the top of a distillation column upstream of rectification I, the condensate breaking down into two liquid phases, the upper organic phase containing MMA as alkyl methacrylate and 2-HIBSM as hydroxyisobutyric acid alkyl ester after removal of low boilers is fed to rectification I.

Regarding process step d.

In process step d. it involves the isolation of the products alkyl methacrylate and alpha-hydroxyisobutyric acid alkyl ester from the third reaction mixture. This process step includes in particular at least two distillative steps and optionally at least one phase separation, the end product alkyl methacrylate being condensed as the top product of a rectification I and the alpha-hydroxyisobutyric acid alkyl ester being isolated in a further stream and optionally further processed. In addition, others known to those skilled in the art can Separation steps are used. Examples of this are, in particular, rectification, extraction, stripping and/or phase separation steps.

The workup preferably includes the prepurification of the third reaction mixture, which is obtained in the esterification. In particular, the prepurification includes at least one distillation step, at least one phase separation step and at least one extraction step. Furthermore, the pre-cleaning preferably comprises at least one, preferably at least two, distillation steps. In particular, an MMA raw product is obtained in the pre-cleaning, which has a purity in the range of at least 85% by weight.

The workup preferably includes the fine cleaning of the raw product, the fine cleaning comprising at least one, preferably at least two, distillation steps. Particular preference is given to obtaining an MMA raw product in the fine cleaning which has a purity of at least 99.0% by weight.

In a further embodiment, the workup includes the separation of methacrylic acid (MAS) from the third reaction mixture. Methacrylic acid is also formed when in process step c. is an esterification. Details of the processing to obtain MAS are well known and described, for example, in DE 102008000787.

The workup of the third reaction mixtures includes, for example, a suitable sequence of separation operations, preferably selected from rectification, extraction, stripping and/or phase separation steps. Process streams can preferably be recycled into the upstream process steps which still contain intermediate products such as 2-HIBSM or 2-HIBS that can be converted into the target product. Particularly preferably, the process streams containing 2-HIBSM are processed in a sequence of separation operations in such a way that a 2-HIBSM pure stream is obtained. In addition, the appropriate choice of operating parameters for the separation operations should preferably ensure that methyl methacrylate that has already been formed does not decompose into by-products in a value-reducing manner.

In a preferred embodiment, the vaporizable part of the third reaction mixture, in particular after esterification with methanol, is removed in gaseous form as vapors from the reactors III (marked as D in the figures, for example) and is subjected to further workup, for example a distillation step (in the Fig. marked as E, for example). If a cascade of several reactors III, for example several boilers, is preferably used, the vaporizable part of the resulting reaction mixture can be removed in each boiler as a vapor stream and passed on to further workup. Preferably, only the vaporizable part of the reaction mixture formed in the last two boilers is removed as a third reaction mixture in the form of a vapor stream and fed into further workup. The bottom stream obtained during the distillation is returned to the reactor or reactors III. The MMA-rich condensate from the column (E) described is fed to a liquid/liquid phase separation (marked as F in the figures, for example) with the addition of fresh water to remove high boilers. The methanol-containing aqueous phase from the phase separation (F) is preferably fed again to the reactor or reactors III (D). The organic phase from the phase separation (F) is then advantageously fed to a further column (in particular a low boiler column, marked for example as G in the figures) for the separation of low boilers, whereby an exhaust gas can be removed at the same time. The low boilers are washed with further fresh water, for example in an extraction/phase separation (marked as H in the figures, for example). When the process is carried out in this way, an organic phase is obtained, which is returned to the low boiler column (G). The bottom product, which is depleted in low boilers, is purified in rectification I (marked as I in the figures, for example). In this case, this takes place while obtaining a pure MMA product at the top of the column. According to the prior art, the stream remaining as the bottom product of rectification I (I) can be recycled into the reactor or reactors III (D), the alpha-hydroxyisobutyric acid methyl ester contained in the stream being converted in the esterification to MMA or to high-boiling by-products (Die The execution of the method described here is not shown in the diagrams below).

One or more stabilizers can advantageously be added to various streams of the process according to the invention in order to prevent or reduce polymerization of the methyl methacrylate and/or the methacrylic acid. For example, a stabilizer may be added to the third reaction mixture obtained after esterification. Phenothiazine and other adequately acting stabilizers are preferably used in the amidation and conversion part; Phenolic compounds, quinones and catechols are used in the esterification or processing part. In addition, amine-N-oxides, such as TEMPOL or combinations of the stabilizer systems mentioned, are used.

A waste stream consisting essentially of dilute sulfuric acid is preferably removed from the reactor or reactors III, i.e. the esterification or hydrolysis. This waste stream is typically removed from the process. This waste stream is preferably fed, in particular together with one or more aqueous waste streams from the process according to the invention, to a process for regenerating sulfuric acid or a process for obtaining ammonium sulfate.

Regarding process step e.

In process step e, which particularly characterizes the present invention. it is an isolation of the process product alpha-hydroxyisobutyric acid alkyl ester, a bottom product of rectification I from process step d., which in particular further alkyl methacrylate, methacrylic acid and alpha-hydroxyisobutyric acid alkyl ester as well as one or has several polymerization inhibitors, is fed to at least one further rectification, either a rectification II or a rectification IV.

As already stated, there are in particular two embodiments of this method step e., which are to be viewed as equally preferred.

Regarding the first embodiment of method step e.

In the first embodiment, additional alkyl methacrylate is obtained at the top of rectification II. At the same time, in a lower section and/or in the bottom of rectification II, a fraction enriched in methacrylic acid and alpha-hydroxyisobutyric acid alkyl ester is obtained, which is fed to a further rectification III. In this rectification III, the alpha-hydroxyisobutyric acid alkyl ester is finally removed as a liquid condensate in highly pure form.

Furthermore, in this first embodiment of rectification III, a bottom stream containing methacrylic acid and inhibitor is preferably removed, which can be at least partially fed to or returned to reaction step c).

Rectification II is preferably carried out at a pressure of 1 to 200 mbar and a maximum bottom temperature of 105 ° C.

Furthermore, the bottom stream from rectification I is preferably used as the feed stream from rectification II. This stream generally has 20 to 90% by weight of alkyl methacrylate, preferably methyl methacrylate, 1 to 20% by weight of methacrylic acid and 1 to 20% by weight of hydroxyisobutyric acid alkyl ester, preferably alpha-hydroxyisobutyric acid methyl ester.

The top product of rectification II preferably has a methyl methacrylate content of at least 95% by weight, preferably at least 99% by weight, particularly preferably 99.5% by weight. This is either added as a pure monomer according to the Rectification I specification or removed directly from the process as a product.

The bottom stream from rectification III in turn preferably has an alpha-hydroxyisobutyric acid content of 0.01 to 5.0% by weight. This bottom stream is preferred in order to increase the overall yield of the process, then at least partially to reaction step c. supplied. Further alpha-hydroxyisobutyric acid methyl ester is produced here by reaction with methanol.

As a rule, in this embodiment, rectification III is operated at a pressure of 1 to 200 mbar, a maximum bottom temperature of 105 ° C and optionally at a lower pressure and an identical or lower bottom temperature than rectification II.

Rectifications II, III and IV are particularly preferably carried out at a pressure of 1 to 200 mbar and a maximum bottom temperature of 105 ° C.

The top stream of rectification III in turn preferably has, in addition to the main component 2-HIBSM, a formic acid content of between 100 ppm and 5.0% by weight. Furthermore, the product condensed at the top of rectification III with a purity of at least 90% is preferably treated in an additional distillation column. This further distillation column is characterized by the fact that internals, packing and container materials are at least partially made of non-metallic materials such as polymers or mineral materials such as glass or are coated with these over the entire surface.

Regarding the second embodiment of method step e.

In the second embodiment of the present invention, the bottom product of rectification I is fed to a rectification IV, which is a sidestream column. In this embodiment, the 2-HIBSA, in particular 2-HIBSM, pure product is obtained as a sidestream product, and a further column, as in the other embodiment, rectification III, is not necessary. In such an embodiment, rectification IV replaces rectifications II and III of the first embodiment in just one column.

Furthermore, a bottom stream containing methacrylic acid and inhibitor is simultaneously removed from this rectification IV, which is preferably at least partially fed to or returned to reaction step c).

The bottom stream from rectification I is preferably used as the feed stream from rectification IV. This stream has 20 to 90% by weight of methyl methacrylate, 1 to 20% by weight of methacrylic acid and 1 to 20% by weight of alpha-hydroxyisobutyric acid methyl ester.

Rectification IV is preferably operated at a pressure of 1 to 200 mbar, a maximum bottom temperature of 105 ° C and optionally at a lower pressure and an identical or lower bottom temperature than column II in the alternative first embodiment.

The bottom stream from rectification IV in turn preferably has an alpha-hydroxyisobutyric acid content of 0.01 to 5.0% by weight. This bottom stream is preferred in order to increase the overall yield of the process, then at least partially to reaction step c. supplied. Here, further 2-hydroxyisobutyric acid methyl ester is produced by reaction with methanol.

In addition to the main component 2-HIBSM, the side stream of rectification IV preferably has a formic acid content of between 100 ppm and 5.0% by weight.

Overall, the process according to the invention is preferably carried out in such a way that hydroxyisobutyric acid alkyl ester, preferably hydroxyisobutyric acid methyl ester 2-HIBSM, by rectification and separation, preferably independently of the selected embodiment of process step e., of alkyl methacrylate, preferably methyl methacrylate, and methacrylic acid as well as phenolic and N-oxide-containing Process inhibitors are isolated and purified in such a way that the hydroxyisobutyric acid alkyl ester, preferably hydroxyisobutyric acid methyl ester 2-HIBSM, is one Content (or a purity) of at least 60% by weight, preferably greater than 90% by weight and particularly preferably greater than 98% by weight.

Overall, however, it can be stated about the method according to the invention that the separation and recycling of intermediate products described in various places involves energy expenditure and it would therefore be advantageous if these steps could be minimized. This can be done in such a way that the smallest possible proportions of these intermediate products are produced in the upstream process steps. As a rule, the most complete conversion possible, in particular from 2-HIBA to MASA, in the conversion, i.e. in process step b., has an advantageous effect on the entire production process. Overall, the method according to the invention aims at the highest possible overall selectivity of the target products MMA and HIBSM, which are also based on the intermediate product HIBA.

The following can also be added to this: In a preferred embodiment, the process according to the invention comprises in the third reaction stage and thus in process step c. the esterification of MASA to MMA. Therefore, the most complete conversion of 2-HIBA and 2-SIBA to MASA is crucial for a high yield of the entire process. The efficiency of the process according to the invention can thus be determined as the difference between the yield after the amidation process step and the yield after the conversion process step. The yield after the amidation process step results from the measured amounts of 2-HIBA, 2-SIBA, MAS and MASA. The yield after thermal conversion results from the measured amounts of MAS and MASA.

Furthermore, the alpha-hydroxyisobutyric acid alkyl ester obtained or recoverable by means of the process according to the invention, in particular alpha-hydroxyisobutyric acid methyl ester, is part of the present invention. This is characterized in particular by the fact that the content of ions of semimetals and metals in the end products purified according to the invention does not exceed a value of 1 ppm by weight and is less than 5 ppm by weight in total. Examples of such ions that can be present in the product are, in particular, those of the elements Si, Na, Fe, Co, Mn or Cr.

Furthermore, the use of alpha-hydroxyisobutyric acid alkyl ester, in particular alpha-hydroxyisobutyric acid methyl ester, is part of the present invention. This alpha-hydroxyisobutyric acid alkyl ester used according to the invention is characterized in that it has a content of at least 90% by weight, preferably greater than 95% by weight and particularly preferably greater than 98% by weight of alpha-hydroxyisobutyric acid alkyl ester, preferably alpha-hydroxyisobutyric acid methyl ester and a cumulative content of metal and semi-metal ions less than 5 ppm by weight. The alpha-hydroxyisobutyric acid alkyl ester can be produced using the method according to the invention described and is used in the production of electronic components or assemblies. Description of the characters

Figure 1: Reaction network

Figure 1 describes the reaction network for the formation of methacrylic acid and/or methyl methacrylate starting from methane and ammonia as well as acetone. Starting from methane (CH4) and ammonia (NH3), hydrogen cyanide can be produced using the BMA process (hydrocyanic acid from methane and ammonia) using catalytic dehydrogenation (CH4 + NH3 —> HCN + 3 H2) (variant 1).

Alternatively, hydrogen cyanide can be produced using the Andrussow process starting from methane and ammonia with the addition of oxygen (CH4 + NH3 + 1.5 O2 —> HCN + 3 H2O) (variant 2).

Other sources of hydrogen cyanide known to those skilled in the art for the production of acetone cyanohydrin are acrylonitrile processes, in which propylene ammoxidation also produces 5-15% hydrogen cyanide, relative to the main product acrylonitrile, and the so-called formamide process, in which formamide is converted into HCN in the gas phase with dehydration becomes.

In the next step, starting from acetone and hydrogen cyanide, acetone cyanohydrin (ACH) is produced with the addition of a basic catalyst, such as diethylamine Et2NH or alkali metal hydroxides. The hydroxy group of acetone cyanohydrin is subsequently esterified with sulfuric acid, initially obtaining alpha-sulfoxyisobutyronitrile (2-SIBN). The nitrile group of alpha-sulfoxyisobutyronitrile (2-SIBN) can be saponified in the next step under the action of sulfuric acid and water, giving alpha-sulfoxyisobutyronitrile hydrogen sulfate (2-SIBA H2SO4). As a side reaction, the formation of methacrylonitrile (MAN) can occur with the elimination of sulfuric acid from SIBN; alpha-sulfoxyisobutyramide hydrogen sulfate (2-SIBA H2SO4) can also partially form alpha-hydroxyisobutyramide hydrogen sulfate (alpha-hydroxyisobutyramide hydrogen sulfate, 2-HIBA H2SO4). be hydrolyzed. The reverse reaction to the sulfuric acid ester 2-SIBA H2SO4 is also possible. As a byproduct, alpha-hydroxyisobutyric acid (2-HIBS) can be formed by further hydrolysis of 2-HIBA H2SO4.

Starting from 2-SIBA H2SO4, methacrylamide hydrogen sulfate (MASA H2SO4) is formed with the elimination of sulfuric acid (conversion). The slow conversion of 2-HIBA or 2-HIBS to MAS or MASA can also take place as an elimination reaction with the elimination of NH4HSO4 or water. Subsequently, methacrylamide hydrogen sulfate (MASA H2SO4) can be converted to methacrylic acid (MAS) by hydrolysis or to methyl methacrylate (MMA) by esterification with methanol (MeOH). If alpha-hydroxyisobutyric acid (2-HIBS) is carried into the esterification, it can be converted to alpha-hydroxyisobutyric acid methyl ester (2-HIBSM); The reaction of 2-HIBA with methanol leads to the same reaction product. Figure 2: C3 process with 2-column system for isolation of 2-HIBSM

Figure 2 thus shows a flow diagram of a preferred embodiment of the process according to the invention for producing MMA and simultaneous isolation of 2-HIBSM.

Figure 3: C3 process with sidestream column for the isolation of 2-HIBSM Figure 3 shows another variant of the process with optimized isolation of 2-HIBSM.

Figure 4: State of the art C3 process without 2-HIBSM insulation

Figure 4 thus shows the state of the art process for producing MMA using the C3 process, without isolating 2-HIBSM.

Figure 5: C3 method with different feedback of isolated return streams according to the prior art process

5 thus shows the C3 process with different returns of isolated return streams according to the prior art process.

List of reference symbols The reference symbols in the figures and descriptions have the following meanings:

Abbreviations

2-HIBA alpha-hydroxyisobutyric acid amide; alpha-hydroxyisobutyramide

2-HIBA H2SO4 alpha-hydroxyisobutyramide hydrogen sulfate, alpha-hydroxyisobutyramide hydrogen sulfate

2-HIBS alpha-hydroxyisobutyric acid

2-HIBSA alpha-hydroxyisobutyric acid alkyl ester

2-HIBSM alpha-hydroxyisobutyric acid methyl ester

2-SIBA alpha-sulfoxyisobutyramide, also known as sulfoxyisobutyramide or sulfoxyisobutyramide

2-SIBA H2SO4 alpha-sulfoxyisobutyric acid amide hydrogen sulfate, also called sulfoxyisobutyric acid amide hydrogen sulfate

2-SIBN alpha-sulfoxyisobutyronitrile, also known as sulfoxyisobutyronitrile

ACH acetone cyanohydrin;

AMA alkyl methacrylates

MAL methacrolein

MAN methacrylonitrile

MAS methacrylic acid

MASA methacrylic acid amide / methacrylamide

MASA H2SO4 methacrylic acid amide hydrogen sulfate MMA methyl methacrylate

MP methyl propionate

PA propionaldehyde

Apparatus

(A) Amidation reactor 1 Reactor I

(B) Amidation reactor 2 reactor I

(C) Conversion reactor reactor II

(D) Esterification reactor cascade with post-evaporation downstream from reactor III

(E) Washing column for removing high boilers

(F) Liquid/liquid phase separation

(G) Low boiler column with vacuum unit

(H) Phase separation

(I) Rectification I

(J) Rectification II

(K) Rectification III

(L) Rectification IV

material flows

(la) Acetone cyanohydrin feed to reactor 1

(l b) Acetone cyanohydrin feed to reactor 2

(2) Sulfuric acid feed to reactor 1

(3) Output from amidation reactor 1, before intermediate conversion (liquid)

(4a) Exhaust gas amidation reactor 1

(4b) Exhaust gas amidation reactor 2

(4c)Exhaust gas converter

(4) Amide exhaust

(6) Reaction mixture after conversion

(7) Methanol

(8) Azeotrope (mixture of MMA and methanol)

(9) Direct steam (4 barg)

(10) MAS/2-HIBS containing material stream (external feed)

(11) Vapors from the esterification cascade

(12) Bottom outlet of the column (E)

(13) Esterification exhaust gas after condensation

(14) Distillate of distillation (E)

(15a/b) DI water

(16) Aqueous phase (extract) of the extraction (17) Organic phase of extraction (raffinate)

(18) Low boiler distillate

(18a) Organic phase from the low boiler distillate extraction

(18b) Aqueous phase from the low boiler distillate extraction

(18c) recycled aqueous phase from the low boiler distillate extraction

(18d) discharged aqueous phase from the low boiler distillate extraction

(19) Bottom product free of low boilers

(20) Exhaust gas from the process stages (G, H, I)

(21) Low boiler-free raw MMA

(22) Bottom product of the MMA pure column phase I

(2-HIBSM enriched)

(23) MMA pure product

(24) 2-HIBSM depleted overhead product phase II

(25) 2-HIBSM/MAS/2-HIBS containing feed phase III

(26) 2-HIBSM product phase V

(27) Exhaust gas 2-HIBSM distillation (J, K, or L)

(28) MAS-containing bottom product (recycle stream) phase VI

(29) Fission acid

(30) Mixed stream containing 2-HIBSM

Examples

Example 1: Inventive process for isolating 2-HIBSM from the C3 MMA process using a 2-column system

The general implementation of the process for the production of MMA and the isolation of 2-HIBSM was carried out using the embodiment according to FIG. 1 and is described below, with the results being shown in Tables 1, 2 and 3.

13,500 kg/h of acetone cyanohydrin (1), with a composition of 98.8% acetone cyanohydrin, 0.3% acetone, 0.6% water and free sulfuric acid, was divided in a mass ratio of 75/25, resulting in a stream (1a) with 10,125 kg/h and a stream (1 b) at 3375 kg/h was obtained. Feed stream (1a) was then fed into the first amidation reactor (A).

The loop reactor (A) was operated with a circulation volume flow of 400 m ³ /h, which was operated constantly at around 98 ° C and 990 mbar (a) under a slight negative pressure.

Feed stream (1 a) was fed continuously and mixed in to the reactor circuit (A) described at a temperature of approximately 20 ° C.

The amount of sulfuric acid (2) necessary for the reaction of the reaction mixture in the reactors (A) and (B), which had a concentration according to Table 4, was in a mass ratio of 1.63/1 [kg/kg] to the total amount of ACH (1). Reactor (A) fed. Through this There was an excess of sulfuric acid in reactor (A) (sulfuric acid/ACH ratio of 2-2.5 kg/kg). The sulfuric acid mass flow supplied was approximately 22,080 kg/h.

The mixing mixture (3) obtained in the reactor, containing alpha-sulfoxyisobutyric acid amide, methacrylamide and sulfuric acid, was then transferred to the second amidation reactor (B) via intermediate heating operated at 125 ° C, with a residence time of approx. 3 minutes, while in the reactor (A) separated exhaust gas (4a) was directed in the direction of the subsequent process (E).

Reactor (B) was constructed analogously to reactor (A) and was operated under the same process conditions. The ACH stream (1 b) was then introduced into the reaction mixture of the second reactor (B). The H2SO4/ACH mass ratio in the reaction mixture was 1.63 kg/kg.

The exhaust gas (4b) formed by the side reaction was also separated from the reaction mixture using a gas separator.

A 98 ° C hot reaction mixture (5), consisting of alpha-sulfoxyisobutyric acid amide (2-SIBA), methacrylamide (MASA) and alpha-hydroxyisobutyric acid amide (2-HIBA), dissolved in sulfuric acid reaction matrix, was then added to the flow of the amidation reactors (A, B). receive. This mixture was then subjected to a conversion step (C). In this, the reaction mixture was heated to 155 ° C in a short time, then thermally converted in a residence time section and further waste gas (4c) was then separated off.

The exhaust gases from the amidation (4a), (4b), and (4c) were then combined and fed to the washing column (E) in the form of exhaust gas stream (4), which was approximately 240 m ³ /h.

The reaction mixture (6) enriched with methacrylamide leaving the conversion (C) was then fed to the esterification reaction (D). The mass flow obtained was 35,340 kg/h, the composition of which is given in Table 1.

The amount of convertible starting materials (MASA+MAS) obtained, which was then fed to an esterification (D), was: 12,420 kg/h, which corresponds to an amidation yield (MASA+MAS), based on the acetone cyanohydrin quality used, of 93 .1% corresponded.

In addition to the main components mentioned, the methacrylamide-containing stream (6) contained alpha-hydroxyisobutyric acid amide (2-HIBA) as an important byproduct. Its concentration is shown in Table 1.

The liquid reaction mixture (6), which was hot at over 150 ° C, was then fed to an esterification (D), the feed being carried out in a free flow into a reactor cascade consisting of 3 jacket-heated and approximately ideally mixed reactor vessels.

Material stream (6) was in process step (D) with a total of 3890 kg/h methanol (7), 1200 kg/h MMA/MeOH mixture (8), 3561 kg/h direct steam (9), 145 kg/h MAS and 2-HIBS -containing external feed as well as 4350 kg/h of demineralised water (15a, 15b) at approx. 100-140°C and a slight overpressure of 50-150 mbar(g). Substance mixture (8) consisted on average of 25% by weight Methyl methacrylate and 74% by weight of methanol and water and was fed to the esterification to utilize methanol and methyl methacrylate.

By appropriately interconnecting the educt streams (6), (7), (8); (9), (10), (15a), (15b) and the circulation streams (12), (16), (18c), (27), (28a) in the esterification (D) it was achieved that in each of the Esterification boiler there was a local, stoichiometric excess of methanol and water based on the substances methacrylamide and methacrylic acid that can be converted into methyl methacrylate.

In a side reaction of the esterification, the supplied amount of alpha-hydroxyisobutyric acid amide (2-HIBA) was converted almost quantitatively to alpha-hydroxyisobutyric acid (2-HIBS) and subsequently converted into alpha-hydroxyisobutyric acid methyl ester (2-HIBSM) by reaction with methanol. In this way, the amounts of alpha-hydroxyisobutyric acid methyl ester (2-HIBSM) given in Table 1 were formed in (D).

At the outlet of the reactor unit (D), post-evaporation operated with direct steam was also carried out, which reduced the proportion of monomers in the acid mixture (29) to a content of <0.1% MMA, <0.1% MAS, <0.1% MASA reduced, while the water content of the draining acid mixture (29) was kept constant.

The crude product formed in the esterification reaction and the methyl methacrylate (MMA) introduced via (8) were continuously removed from the esterification cascade (D) in the form of a vapor stream (11). According to the vapor/liquid equilibrium of the reaction mixtures, the vapor stream (12) represented a heteroazeotropic composition containing MMA, water, MeOH, MAS, acetone, 2-HIBSM and 2-HIBS.

In addition to the vapor stream (11), the exhaust gas stream from the amidation (4) was also fed to the bottom of the washing column (E). Vapor stream (11) was then subjected to countercurrent distillation by introducing the vaporous stream (11) and the gaseous stream (4) into the bottom region of a column (E). At the top of the column (E), complete condensation took place in condensers which were operated with cooling water and cold water. The two-phase distillates were combined and a partial stream was returned to the washing column (E).

The exhaust gas (13) obtained after the condensation, which was generated, among other things, by supplying material stream (4), was removed and sent for combustion.

Depending on the reflux ratio, a liquid distillate stream (14) and a liquid bottom stream (12) were obtained at the top of the column (E). The bottom stream (12) was continuously recycled into the esterification reaction (D). The two-phase distillate stream (14) was then fed to phase separation step (F). By treating with water (15a) in a liquid/liquid countercurrent extraction, an organic, light phase (17) containing MMA, water, methanol, acetone, MAS, 2-HIBSM, 2-HIBS as well as other heavy and Low boilers and a heavy, aqueous phase (16) containing water, methanol, MMA, acetone are obtained. Stream (16) was continuously recycled into the esterification reaction (D). Amounts and composition of material streams (16 and (17) are summarized in Table 2.

Stream (17) was then subjected to distillative processing (G). To remove high and low boilers, material stream (17) was fed to the top region of a low boiler column (G) operated in a vacuum (300 mbar), which was indirectly heated with heating steam. A condensed vapor stream (18) enriched in low boilers was separated from a bottom stream (19) enriched with methyl methacrylate, MAS, 2-HIBSM and 2-HIBS. The vapor stream (18) contained MMA, water, acetone and other low boilers. The amounts and compositions are summarized in Table 1.

The process exhaust gas (20) obtained on the gas side after the post-condensation was continuously discharged from the process.

The heteroazeotropic distillate (18) obtained after the main condensation was subjected to liquid/liquid phase separation (H) for further processing.

To improve phase separation, deionized water (15b) was added to the distillate stream (18) in the phase separator (H), so that an organic phase (18a) and an aqueous phase (18b) were obtained. The light, organic phase (18a) was continuously circulated as reflux to the top of the column (H), while the aqueous phase (18b) with a by-product portion of acetone was fed to the next process step. Amounts and compositions are described in Table 3.

Stream (18b) was then divided into stream (18c) and stream (18d) at a fixed mass ratio of 55/45. 55% of stream (18b) was recycled directly into the esterification reaction (D) as (18c). 45% of material stream (18b) was removed from the process (18d) and typically sent for incineration.

For further purification, the bottom product (19) obtained in the low boiler column (G) was mixed with a condensed, MMA-rich fraction (24) from rectification II (J) and then fed to rectification I (I). Stream (21) had a composition of MMA, MAS, 2-HIBS and 2-HIBSM according to Table 1.

Rectification I (I) was operated at 180 mbar(a) and had an amplification and stripping section. Stream (21) was fed into the middle of rectification I (I), whereby, depending on the equilibrium that was established, it was separated into a pure distillate phase (23) and a bottom stream (22) enriched in high boilers. The composition of the high-purity top product (23) is given in Table 1.

The bottom stream (22), which contained MMA, MAS, HIBS and HIBSM, was fed to the rectification distillation step II (J) to isolate HIBSM.

Rectification II (J) was operated at 50 mbar(a) and had an amplification and stripping section. Material stream (22) was fed into the middle of rectification II (J), whereby it condensed into an MMA-rich mixture in accordance with the equilibrium that was established Distillate phase (24) and a bottom stream (25) enriched with MAS, HIBSM and HIBS were separated.

Distillate (24) was continuously mixed with stream (19) and further processed in rectification I (I).

To isolate 2-HIBSM, bottom stream (25) was then fed to rectification III (K). Rectification III (K) was operated at 30 mbar(a) and had an amplification and stripping section. Material stream (25) was fed into the middle of the rectification III (K), which, depending on the equilibrium that was established, was converted into a 2-HIBSM-rich top product (26), the composition and quantity of which is shown in Table 1, as well as a MAS and 2-HIBS-enriched bottom stream (28) was separated.

Stream (26) was isolated as a product stream, while bottom stream (28) was continuously fed to the esterification reaction (D). The exhaust gas (27) from the distillation was removed from the process.

Example 2: Inventive process for isolating 2-HIBSM from the C3 MMA process using a 2-column system and optimized process parameters in the amidation for increased formation of 2-HIBSM

The production of methyl methacrylate, comprising the reaction of acetone cyanohydrin with sulfuric acid in the amidation/conversion (A, B, C), the subsequent esterification (D) with methanol as well as the distillative and extractive workup (E, F, G, H, I ) of the methyl methacrylate product, as well as the distillative isolation of 2-HIBSM (J, K) were carried out using the embodiment according to Figure 1 as described above (Example 1).

Different process settings are described below, with selected process parameters shown in Table 4.

The amount of sulfuric acid (2) necessary for the reaction of the reaction mixture in the reactors (A) and (B), which had a concentration of according to Table 4, was in a mass ratio of 1.63/1 [kg/kg] to the total amount of ACH (1). fed to the reactor (A). This resulted in an excess of sulfuric acid in reactor (A) (sulfuric acid/ACH ratio of 2-2.5 kg/kg). The sulfuric acid mass flow supplied was approximately 22,080 kg/h.

In the course of the amidation reactor (B), a 98 ° C hot reaction mixture (5), consisting of alpha-sulfoxyisobutyric acid amide (2-SIBA), methacrylamide (MASA) and alpha-hydroxyisobutyric acid amide (2-HIBA), dissolved in sulfuric acid reaction matrix, was obtained. This mixture was then subjected to a conversion step (C). In this, the reaction mixture was heated in a short time to a temperature according to Table 1, then thermally converted in a residence time section and the waste gas (4c) formed was separated. The reaction mixture (6) enriched with methacrylamide leaving the conversion (C) was then fed to the esterification reaction (D). The mass flow obtained and its composition are given in Table 1.

In addition to the main components mentioned, the methacrylamide-containing stream (6) contained alpha-hydroxyisobutyric acid amide (2-HIBA) in increased concentration as an important by-product. The concentration level obtained is shown in Table 1.

The liquid reaction mixture (6), which was hot at over 150° C., was then fed to an esterification (D). The esters MMA and 2-HIBSM that formed were isolated using thermal separation processes, analogous to Example 1 according to the invention.

Example 3: Inventive process for isolating 2-HIBSM from the C3 MMA process using a 1-column system with liquid side draw

The production of methyl methacrylate, comprising the reaction of acetone cyanohydrin with sulfuric acid in the amidation/conversion (A, B, C), the subsequent esterification (D) with methanol as well as the distillative and extractive workup (E, F, G, H, I ) of the methyl methacrylate product, as well as the distillative isolation of 2-HIBSM (J, K) were carried out using the embodiment according to Figure 3.

Deviating from the process described in Example 1, the stream (22) obtained in rectification I (I) and enriched with 2-HIBSM was fed to the middle section of a side stream column rectification IV (L).

Rectification IV (L) was operated at 35 mbar(a) and had two amplification parts and one stripping part. Material stream (22) was fed into rectification IV (L) above the stripping section, whereby, depending on the equilibrium that was established, it was divided into an MMA-rich, condensed distillate phase (24), a MAS-rich bottom fraction (28) and a >90 % 2-HIBSM containing liquid side stream (26) was separated.

The 2-HIBSM product stream (26) was withdrawn from the column as a liquid stream below the upper rectification section.

Distillate (24) was continuously mixed with stream (19) and recycled in rectification I (I).

Relevant compositions and material flows are shown in Table 1.

Table 1: Comparison of examples B1, B2, B3 according to the invention

*) Average concentration determined from 8 representative HPLC analyzes (see tables 1, 2 and 3)

Explanations for Table 1: Based on Table 2 it becomes clear that it is possible to remove 2-HIBSM from the C3 process in an economical manner by implementing an additional separation step in the processing step of the process.

With slightly reduced quality of the isolated 2-HIBSM stream, it can also be shown (cf. Examples B1 and B3) that the desired additional separation operation can be carried out without a significant loss of MMA yield even with just one separation column.

In addition, through targeted parameterization of the amidation/conversion, the 2-HIBA content of the amide product stream (6) can be adjusted so that more 2-HIBA can be formed and thus more 2-HIBSM can be discharged without any loss of MMA yield.

The 2-HIBA content can be increased on the one hand by specifically adjusting the water content in the sulfuric acid used and on the other hand by adjusting the conversion temperature in process step (C).

Table 2: Comparison of comparative example V1 with example B1 according to the invention The following comparative example V1 was scaled with regard to the feed flows in accordance with the information in the prior art patent US 4,529,816 in order to achieve comparability. Material flow (30) refers to Figure 5 according to the prior art (US4529816).

*) Insulating current of a column, not specified

**) Value not specified

Explanations to Table 2:

It is clear from Table 2 that the claimed process, described in US 4,529,816, in a different place than the process according to the invention, contains a 2-HIBSM

Isolates the current and returns it to another point, namely between amidation and esterification, in order to subject the 2-HIBSM contained therein to dehydration. In the process according to the invention, however, pure 2-HIBSM is isolated and discharged and a recycle stream containing MAS is converted into MMA in the esterification. The different isolation of the 2-HIBSM-containing stream in the processing according to the prior art process (US 4,529,816) can be seen from the fact that the material stream obtained has a high water content (approx. 3%): This suggests that this one Phase separation is removed, which is not the case in the process according to the invention. In the process according to the invention, the 2-HIBSM stream is obtained anhydrous and sent for further processing. The specifically significantly higher 2-HIBSM-containing recycle stream in the prior art process also shows the completely different type of circulation flow. Because 2-HIBSM is discharged in the process according to the invention, circulation stream 29, for example, is significantly smaller than is the case in the prior art process.

Comparative example V1: State of the art process (according to US 4,529,816) for the partial recycling of 2-HIBSM from the workup of the C3 MMA process and subsequent dehydration to MMA in the amidation

According to the patent mentioned above, an amide mixture obtained in the amidation was subjected to conversion at 133 ° C and temporarily stored in a storage container at 90-100 ° C (see Fig. 5).

The amide mixture obtained was then mixed in a static mixer (with a 2-HIBSM-containing material stream from the thermal processing (E, F, G, H). The composition of the material streams can be found in Table 3.

The amide mixture (30) was mixed with stream 6 in a mass ratio of 4.4:1 kg/kg and reacted in a static mixer at approximately 137-140° C. and in a plug-shaped flow with a residence time of approximately 5.8 seconds brought.

The conversion of 2-HIBSM to MMA was approximately 54.1%. The resulting mixture of substances was then fed to the esterification reaction.

Comparative example V2: State of the art process C3 MMA process

The production of methyl methacrylate, comprising the reaction of acetone cyanohydrin with sulfuric acid in the amidation/conversion (A, B, C), the subsequent esterification (D) with methanol as well as the distillative and extractive workup (E, F, G, H, I ) of the methyl methacrylate product was carried out using the embodiment according to Figure 4.

Process settings that deviate from Example 1 according to the invention are described below, with selected process parameters being shown in Table 2. The amidation and esterification were carried out analogously to Example 1 with the feed streams shown in Table 2. However, no isolation of 2-HIBSM was carried out during thermal processing.

Table 3: Comparison of comparative example V2 with example B1 according to the invention

The comparative example V2 was scaled with regard to the feed streams in accordance with the information in the prior art patent in order to achieve comparability.

*) Unavailable

Explanations to Table 3:

It is clear from Table 3 that by carrying out the process of example B1 according to the invention, in addition to obtaining 2-HIBSM as a product stream, the degree of enrichment of formic acid in the MMA product stream can also be significantly reduced compared to comparative example C2.

Formic acid (HCOOH) is a disruptive secondary component in the MMA product stream and must be partially removed from the MMA product stream using a molecular sieve filter in the state-of-the-art C3 process in order to moderate the HCOOH content.

As can be seen from Table 3, the removal of HCOOH in the 2-HIBSM insulation product according to the invention makes it possible to significantly reduce the HCOOH content in the MMA product stream and thus significantly reduce the costs for changing the molecular sieve filter.

Claims

Expectations

1 . Process for the production of alkyl methacrylate and alpha-hydroxyisobutyric acid alkyl esters, comprising the process steps: a. Reaction of acetone cyanhydrin and sulfuric acid to a first reaction mixture containing alpha-sulfoxyisobutyric acid amide and methacrylic acid amide, b. Converting the first reaction mixture, comprising heating to a temperature in the range of 130 to 200 ° C, obtaining a second reaction mixture containing predominantly methacrylic acid amide, alpha-hydroxyisobutyric acid amide and sulfuric acid, c. Reaction of the second reaction mixture with water and alcohol in a third reaction stage, whereby a third reaction mixture containing methacrylic acid, alkyl methacrylate, alpha-hydroxyisobutyric acid alkyl ester and formic acid is obtained, i.e. Isolation of the products alkyl methacrylate and alpha-hydroxyisobutyric acid alkyl ester from the third reaction mixture, comprising at least two distillative steps and optionally at least one phase separation, the end product alkyl methacrylate being condensed as the top product of a rectification I and the alpha-hydroxyisobutyric acid alkyl ester being isolated in a further stream and optionally further processed , whereby in a process step e. a bottom product of rectification I containing alkyl methacrylate, methacrylic acid and alkyl hydroxyisobutyrate and one or more polymerization inhibitors are fed to at least one further rectification II or IV.

2. The method according to claim 1, characterized in that further alkyl methacrylate is obtained at the top of rectification II and in a lower section and / or in the bottom of rectification II a fraction enriched in methacrylic acid and hydroxyisobutyric acid alkyl ester is obtained, which is fed to further rectification III , in which hydroxyisobutyric acid alkyl ester is removed as a liquid condensate in highly pure form.

3. The method according to claim 1, characterized in that alkyl methacrylate is obtained at the top of rectification I and in a lower section and / or in the bottom of rectification I a fraction enriched in methacrylic acid and hydroxyisobutyric acid alkyl ester is obtained, which is fed to a further rectification IV, in the hydroxyisobutyric acid alkyl ester is removed as a liquid condensate in the side stream in highly pure form and further alkyl methacrylate is obtained at the top of rectification IV, which is at least partially also fed to rectification I.

4. The method according to claim 2, characterized in that a bottom stream containing methacrylic acid and inhibitor is removed from the rectification III and is at least partially fed to reaction step c).

5. The method according to claim 3, characterized in that a bottom stream containing methacrylic acid and inhibitor is removed from the rectification IV and is at least partially fed to reaction step c).

6. The method according to claim 2, characterized in that a bottom stream containing methacrylic acid and inhibitor is taken from rectification I and passed into a rectification II, and that a further bottom stream is taken from rectification II, which is fed to a rectification III, whereby hydroxyisobutyric acid methyl ester (2-HIBSA) is taken as hydroxyisobutyric acid alkyl ester in highly pure form as the top distillate of this rectification III and at the same time a bottom stream containing methacrylic acid and inhibitor is taken from the bottom of rectification III and is at least partially fed to reaction step c).

7. The method according to claim 3, characterized in that a bottom stream containing methacrylic acid and inhibitor is removed from rectification I and passed into a rectification IV, and that methyl hydroxyisobutyrate (2-HIBSA) as hydroxyisobutyric acid alkyl ester in highly pure form as a side stream of this rectification IV is removed and at the same time a bottom stream containing methacrylic acid and inhibitor is removed from the bottom of rectification IV, which is at least partially fed to reaction step c).

8. The method according to at least one of claims 1 to 7, characterized in that the rectifications II, III and IV are carried out at a pressure of 1 to 200 mbar and a maximum bottom temperature of 105 ° C.

9. The method according to at least one of claims 1 to 8, characterized in that the bottom stream of rectification I is used as a feed stream of rectification II or IV and contains 20 to 90% by weight of methyl methacrylate as alkyl methacrylate, 1 to 20% by weight of methacrylic acid and 1 to 20% by weight of alpha-hydroxyisobutyric acid methyl ester as hydroxyisobutyric acid alkyl ester.

10. The method according to at least one of claims 1 to 9, characterized in that the bottom stream of the rectification III has an alpha-hydroxyisobutyric acid content of 0.01 to 5.0% by weight and this bottom stream is at least partially fed to the third reaction stage c, further alpha-hydroxyisobutyric acid methyl ester is produced by reaction with methanol.

11. The method according to at least one of claims 1 to 10, characterized in that hydroxyisobutyric acid methyl ester (2-HIBSM) as hydroxyisobutyric acid alkyl ester by rectification and separation of methyl methacrylate as alkyl methacrylate and methacrylic acid as well as phenolic and N-oxide-containing process inhibitors is isolated and purified in such a way that the 2-HIBSM has a content of at least 60% by weight. Method according to claim 11, characterized in that the top stream of rectification III or the side stream of rectification IV has, in addition to the main component 2-HIBSM, a formic acid content of between 100 ppm and 5.0% by weight. Method according to claim 6, characterized in that the rectification III is operated at a pressure of 1 to 200 mbar, a maximum bottom temperature of 105 ° C and optionally at a lower pressure and an identical or lower bottom temperature than the rectification II. Process according to claim 7, characterized in that the rectification IV is operated at a pressure of 1 to 200 mbar, a maximum bottom temperature of 105 ° C and optionally at a lower pressure and an identical or lower bottom temperature than column II. Process according to at least one of claims 1 to 14, characterized in that the second reaction mixture obtained in reaction step b) has an alpha-hydroxyisobutyramide content of 0.1 to 2.0% by weight. Process according to at least one of claims 1 to 15, characterized in that in reaction step c) MMA is condensed as alkyl methacrylate at the top of a distillation column upstream of rectification I, the condensate breaking down into two liquid phases, the upper organic phase containing MMA as alkyl methacrylate and 2-HIBSM is fed to rectification I as hydroxyisobutyric acid alkyl ester after removal of low boilers. Method according to claim 6, characterized in that the product condensed at the top of rectification III with a purity of at least 90% is treated in an additional distillation column, with internals, packing and container materials being at least partially made of non-metallic materials such as polymers or mineral materials or with these are coated over the entire surface.