JP2006306731A - Method for continuously producing unsaturated carboxylic ester using alkane as raw material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of stably obtaining an unsaturated carboxylic ester in a high yield in continuously producing the unsaturated carboxylic ester using an alkane as a raw material. <P>SOLUTION: In carrying out the gas phase catalytic oxidation reaction of an alkane as a raw material with an oxygen-containing gas, the yield of the target unsaturated carboxylic ester can be increased by relatively increasing the selectivity of the unsaturated aldehyde formed compared to the selectivity of the unsaturated carboxylic acid. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a method for producing an unsaturated carboxylic acid ester.

  The present invention relates to a method for producing an unsaturated carboxylic acid ester. In particular, the present invention relates to a production method in which an alkane raw material is mainly converted to an unsaturated aldehyde and an unsaturated carboxylic acid ester is obtained directly from the obtained unsaturated aldehyde and alcohol. The most common method for producing an unsaturated carboxylic acid ester is a method of obtaining an ester reaction from an unsaturated carboxylic acid and an alcohol using an acid as a catalyst, which is widely used as a known technique. The unsaturated carboxylic acid used as the raw material is generally a known technique for producing an unsaturated aldehyde by oxidizing an olefin or further oxidizing the unsaturated aldehyde to produce an unsaturated carboxylic acid. Currently, research on yield improvement by vigorous catalyst improvement is ongoing. That is, it is a reaction method using an unsaturated carbon bond rich in reactivity of olefins. As a specific example, acrylic acid is obtained via acrolein by a gas phase two-stage oxidation reaction using propene as a raw material. Further, methacrylic acid is obtained through methacrolein from isobutene as a raw material.

  The esterification of acrylic acid and methacrylic acid obtained in this way with the usual acid-catalyzed reaction with alcohol, for example carboxylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, etc. Has been widely performed as a known technique. The present invention uses alkane, which has been mainly used for fuels as an inert material, as a raw material, and mainly converts oxygen to an unsaturated aldehyde, and then collects the recovered unsaturated aldehyde and alcohol in the presence of oxygen. The present invention relates to a method for directly producing an unsaturated carboxylic acid ester by reacting with a catalyst in a liquid phase state.

  In addition, the produced unsaturated carboxylic acid ester is separated and recovered to obtain a high-purity product, and the loss of the raw material alkane is reduced to efficiently obtain the unsaturated carboxylic acid ester. I let you. That is, the present invention provides a process realizing high raw material utilization efficiency by devising and optimizing a plurality of recycling processes other than the main reaction process. Unsaturated carboxylic esters are commercially important chemical reagents. Of particular importance are (meth) acrylic acid esters. Polymerized alone or with other monomers, it is widely used as a commercially effective polymer as a plastic material such as paints, adhesives, sealants and caulks. Various methods for producing unsaturated carboxylic acid esters have been proposed and commercialized since ancient times.

  Olefin is a chemical raw material obtained from naphtha crackers and the like, and shortage of raw material accompanying an increase in demand in recent years and rising prices as raw materials are serious problems. On the other hand, alkanes such as propane and isobutane are very stable and poor in reactivity, as expected from the chemical structure, compared to olefins such as propylene and isobutene, and are therefore less used as chemical raw materials. However, since alkanes are abundant in natural gas and the supply amount is stable, in recent years, research and development of useful chemical products using alkane as a raw material has been aimed at, for example, directly synthesizing acrylic acid from propane. Catalyst development has been actively conducted.

JP-A-2000-24501, JP-A-2001-137709 and the like disclose a catalyst for directly producing an unsaturated carboxylic acid from an alkane, and a method for producing the catalyst. That is, it is the development of a catalytic reaction technique that can oxidize a corresponding unsaturated carboxylic acid by a one-step oxidation reaction without using an alkane as a raw material and obtaining an intermediate aldehyde. If an unsaturated carboxylic acid is obtained, an unsaturated carboxylic acid ester can be obtained almost quantitatively and easily by an esterification reaction of an acid and an alcohol, which is known in the prior art. In other words, in the prior art, research and development have been progressed aiming at a route for obtaining unsaturated carboxylic acid from alkane as a raw material.
Japanese Patent Publication No.41-8954 JP-A-51-34257 Japanese Patent Laid-Open No. 52-42549

  In a continuous process for producing an unsaturated carboxylic acid ester using an alkane as a raw material, a method for stably obtaining an unsaturated carboxylic acid ester in a high yield is provided.

  When performing a gas phase catalytic oxidation reaction using an alkane as a raw material with an oxygen-containing gas, the selectivity of the unsaturated aldehyde to be produced is relatively higher than that of the unsaturated carboxylic acid. The rate can be increased.

  According to the present invention, in the method of obtaining an unsaturated carboxylic acid ester by catalytically oxidizing an alkane raw material with molecular oxygen, a catalyst and conditions for producing a large amount of unsaturated carboxylic acid as an intermediate product are selected as in the conventional method. It is possible to increase the yield of the target unsaturated carboxylic acid ester by selecting a catalyst or conditions that produce a large amount of unsaturated aldehyde, rather than.

In the present invention, a reaction process is devised and constructed based on a completely different concept and reaction from the conventional process for producing an unsaturated carboxylic acid ester. That is, the present inventors have found a method for obtaining an unsaturated carboxylic acid ester with a high yield using alkane as a raw material, and have reached the present invention. That is, instead of synthesizing from alkane to carboxylic acid in one step, an unsaturated aldehyde is obtained as an intermediate, and the obtained unsaturated aldehyde is directly reacted with an alcohol to obtain an ester (direct meta method). It is a revolutionary method that has been established. The characteristics of this method will be described in detail for each process.
The method according to the present invention comprises a gas phase oxidation reaction step, a rapid cooling step, a dehydration step, an unsaturated aldehyde absorption step, an alkane recovery and recycling step, an oxidative esterification reaction step, an unreacted unsaturated aldehyde recovery step, an oil-water separation step, an unsaturated state. It consists of a carboxylic acid ester purification step and an unsaturated carboxylic acid esterification step.

  First, the gas phase oxidation reaction process will be described. As an alkane, for example, propane and / or isobutane are used as raw materials, and gas phase catalytic oxidation is performed in a gas phase oxidation reactor together with a gas containing molecular oxygen to obtain a reaction gas rich in acrolein and / or methacrolein. In the case of the present invention, this reaction is extremely important. In contrast to conventional alkane oxidation techniques, which focus mainly on obtaining unsaturated carboxylic acids, the present invention rather suppresses the formation of carboxylic acids and identifies the ratio of aldehyde formation to carboxylic acid formation. It was found that it is extremely important to carry out the control within the range. From the viewpoint of the prior art, since carboxylic acid is the target product, a reaction with an increased carboxylic acid yield is carried out in this step.

  On the other hand, the feature of the present invention is that the yield of unsaturated carboxylic acid ester from alkane can be increased as a whole process, and since it has a reaction step of converting aldehyde directly to ester, aldehyde has a high concentration region. It is operated by. The condition of the high concentration region of aldehyde here is extremely important. For example, when isobutane is described as an example, methacrolein and methacrylic acid are mainly produced as main products. In the method of the present invention, if methacrolein is obtained, methyl methacrylate is obtained in the next reaction step by, for example, reaction with methanol. However, the conversion rate of alkane is low under the conditions where methacrolein is obtained without producing methacrylic acid, and a polymer is easily produced under the catalyst and conditions where only methacrolein is produced. It was found that obstruction due to was likely to occur.

  That is, it has been found that obtaining methacrolein at a high concentration has a problem in maintaining the process stably. That is, it has been found that a catalyst and conditions for partially producing methacrylic acid are extremely important in the process. On the other hand, if a catalyst or condition that produces too much methacrylic acid is selected, COx increases and the alkane yield decreases, and if the production of methacrylic acid increases, the polymer that is estimated to be due to another phenomenon increases. It was found that a clogging phenomenon occurred in the process of the quenching tower from the reactor outlet. Not only the stability of the process but also an increase in methacrylic acid is not preferable because the load of a normal esterification reaction step by an acid catalyst is increased, which reduces the features and effects of the present invention.

That is, in the gas phase oxidation process of alkane, it is important to carry out by controlling the unsaturated carboxylic acid and unsaturated aldehyde within a specific range, and as an example of a specific operation index, the unsaturated carboxylic acid is a product. The ratio of unsaturated aldehyde / unsaturated carboxylic acid is 0.5 to 30% and the ratio of unsaturated aldehyde / carboxylic acid is 2 or more and 19 or less, preferably the selectivity of carboxylic acid is 1 to 20%. Is selected from the range of 3 to 19 and more preferably the carboxylic acid selectivity is 1 to 12% and the ratio of unsaturated aldehyde / unsaturated carboxylic acid is 4 to 18 and the catalyst. As a catalyst capable of activating alkane, a heteropolyacid compound catalyst can be used. Among them, for example, PW system, PMo system, SiW system, SiMo system, PMoW system, PMoV system, heteropoly acids are preferred, more preferably, for example, heteropolyacids acids having the Keggin structure represented by the element ratio _{PMo 12} Is preferred.

  More preferably, catalyst systems containing Mo such as PMoVCuSb, AsMoVCuSb, SiMoVCuBi, PMoWCuSb, and SiWMoVCu are examples of effective catalyst systems. Also, in the catalyst having the formula AaMomNnXxOo, A is at least one of Bi, V, W, N is at least one of Nb, Ta, Zr, Cu, Mn, Fe, Ni, Co, and X Is at least one of Sb, Bi, Te, a is 1 to 1.5, m is 12, n is 1 to 8, x is 1 to 5, and so on. , Fe, Co, Mn, Cr, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sm, Gd. It can also be included.

Preferred are catalysts containing molybdenum and niobium, and more preferred are bronze-like VMoNb (Sb / Te) -based and VMoNb (Sb / Te) Bi-based catalysts containing molybdenum, vanadium, niobium and antimony. In order to adjust the activity and selectivity of these catalysts, Ni, Fe, Co, Mn, Cr, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, A single component or a plurality of components selected from Sm and Gd may be included, but this is not a limitation.
In addition, as an effective method for obtaining an aldehyde from an alkane, performing an alkane in combination with a dehydrogenation catalyst and an oxidation catalyst is one effective method. An aldehyde can be obtained by charging the pre-reactor with a dehydrogenation catalyst, feeding only the alkane, partially dehydrogenating and converting, and then combining an oxidation catalyst system widely known to obtain aldehydes from olefins. Although this method requires a pre-reactor, it does not require an intermediate olefin separation and production step, and is one of the methods that are excellent in terms of reaction characteristics. As the dehydrogenation catalyst, an optimum catalyst can be selected from alumina, Cr oxide / alumina, Pt / alumina, Pt / Zn-alumina, activated carbon and the like together with the selection of the oxidation catalyst. As the oxidation catalyst, composite oxides containing molybdenum and iron such as MoBiFeNiMgCe and MoSbFeCoCeCs having a celite structure are preferably used.

  There is an important relationship between the selection of the oxidation reactor and the catalyst structure. In general, when the reactor used for the gas phase oxidation reaction is a heat exchanger type fixed bed reactor, the pressure loss at the reaction condition gas linear velocity is low. Uses a catalyst designed and molded into a shape that is 70% or less of a cylindrical catalyst. When a fluidized bed reactor or a riser type reactor is used as the reactor, the catalyst particles contain silica selected from the range of 30 to 70% by weight, and the average particle size is 20 to 150 μm, preferably 30 to A spherical catalyst having a particle size distribution of 100 μm is used. When using a riser reactor, the target product is obtained by oxidizing alkane with lattice oxygen held by the catalyst, and the catalyst is transferred to the regeneration tower, and then reoxidized with oxygen-containing gas to regenerate the catalyst. The method is also effective and can be selected.

The reaction system is selected from two conditions outside the explosion range composed of alkane, oxygen, inert gas, and the like. One is a composition with a low concentration below the lower limit of the alkane explosion range, in which alkane is reacted at a high conversion rate, and the loss of unreacted alkane is negligible. Second, a concentration higher than the upper limit of the explosion range can be selected. In this case, in order to avoid the explosion range, it is insufficient from the stoichiometric amount to react all the isobutane supplied. Therefore, the reaction method is characterized in that a large amount of unreacted isobutane remains and the reaction is carried out while collecting and recycling. Each has advantages and disadvantages, and it is preferable to carry out by selecting a catalyst and reaction system suitable for the situation.
Next, details of the reactor-to-cooling tower process will be described. Since the product gas containing an unsaturated aldehyde and an unsaturated carboxylic acid produced by the oxidation reaction of alkane is highly reactive, it tends to cause thermal decomposition (afterburning) and polymerization reaction of the product. Therefore, it is preferable to shorten the residence time of the reaction gas coming out of the catalyst layer as much as possible. The specific time is 3 seconds or less, preferably 2 seconds or less, and more preferably 1 second or less. It is also effective to rapidly cool the reaction gas by heat exchange. The cooling method can be selected from optimum methods such as steam, water spray, heat removal by a heat exchanger. Cooling is performed at a temperature of 350 ° C. or lower where unsaturated aldehydes are not easily denatured. It is preferable to cool to 330 ° C. or lower, more preferably 300 ° C. or lower.

  However, when the temperature to the entrance such as quenching is lowered to 200 ° C. or lower, high-boiling by-products are likely to adhere, and therefore a temperature range of 220 ° C. or higher, preferably 250 ° C. or higher is preferable. The reaction gas introduced in the quenching or the like is cooled to 100 ° C. or lower, preferably 90 ° C. or lower, more preferably 80 ° C. or lower. Low boiling components such as unsaturated aldehydes and unreacted alkanes produced by this operation are separated from unsaturated carboxylic acid having a relatively high boiling point, water, and high boiling point by-products. Various cooling methods are possible, but as an example, a method of spraying a solution containing water condensed by the reaction by spraying and bringing it into contact with the reaction gas and cooling is preferable as an effective and simple method. In this case, the temperature at the bottom of the tower can be controlled at a constant temperature by adding water and controlling the liquidity and spraying, and circulating water to be sprayed by interposing a heat exchanger.

Further, when the spray method is used, it is preferable to install a strainer or the like in the piping line because the nozzles can be prevented from being blocked and a stable spray state can be maintained. From the bottom of the quenching tower, the bottom liquid is extracted so that the liquid level at the bottom of the tower is constant. The liquid extracted from the column bottom containing the unsaturated carboxylic acid is supplied to the next unsaturated carboxylic acid esterification step. In addition, the condensate at the bottom of the quenching tower also contains highly reactive by-products, so that clogging with a polymer is likely to occur. In order to suppress adhesion of a polymer or the like, it is effective to shorten the residence time, and the average residence time is within 10 hours, preferably within 5 hours, and more preferably within 3 hours.
Further, in the condensate at the bottom of the tower, tar-like substances are also generated by the cooling operation, so that they adhere to the tower walls and piping and are likely to be clogged. As a method of suppressing these, it is preferable to add a polymerization inhibitor. Further, it is preferable that a dispersing agent that suppresses aggregation is also present in order to facilitate the liquid extraction operation. The polymerization inhibitor used here is preferably one that dissolves in both water solubility and oil solubility. A polymerization inhibitor having its function alone is preferable from the operation, but it can also be carried out by combining a plurality. The amount to be added is selected from the range of about 1 to 1000 ppm, preferably in the range of 1 to 500 ppm, depending on the condensate composition and cost and effect. The polymerization inhibitor can be widely selected from hydroquinones and those having an N-oxyl structure.

Next, the details of the dehydration step will be described.
A gas containing an unsaturated aldehyde, an unsaturated aldehyde, an unreacted alkane, carbon dioxide gas, water and the like separated from the unsaturated carboxylic acid is led from the upper part of the quenching tower to the dehydrating tower. If the gas contains a large amount of moisture, water is brought into the subsequent oxidative esterification step, and the reactivity of the oxidative esterification is lowered. Therefore, it is very important for the oxidative esterification process to remove water in the previous stage of the oxidative esterification process. Although many methods for separating and removing water contained in gas are generally known, the method of the present invention is based on the following method. If necessary, an extremely efficient method of removing water by bringing the gas component from which the unsaturated carboxylic acid has been separated into contact with the alcohol used in the oxidative esterification step and a liquid containing the same kind of alcohol and by latent heat exchange between water and the alcohol It is. In a specific example, the liquid organic solvent liquid containing alcohol supplied from the upper part of the tower is contacted in countercurrent with a composition gas containing water such as unsaturated aldehyde, unreacted alkane, carbon dioxide gas, etc. rising from the lower part of the tower. However, due to an effect that seems to be a latent heat exchange action from the viewpoint of the heat change, the gaseous water is condensed and liquefied to become a liquid and descends to the bottom of the tower. On the other hand, the liquid organic solvent liquid containing alcohol takes heat from water and gasifies. The alcohol-containing organic component in the gaseous state is led from the top to the next unsaturated aldehyde absorption step in the same manner as the unsaturated aldehyde, unreacted alkane, carbon dioxide gas and the like. That is, it is a method of simply dehydrating using a latent heat exchange action.

Next, the unsaturated aldehyde absorption step will be described.
The gas after being dehydrated by the latent heat exchange action in the dehydration step is led to the bottom of the unsaturated aldehyde absorption tower in order to obtain the unsaturated aldehyde contained therein as a liquid. The gaseous unsaturated aldehyde-containing organic component can be obtained by a method in which the ascending gas containing the cooled condensed and uncondensed unsaturated aldehyde at the bottom of the unsaturated aldehyde absorption tower is contact-absorbed with the solvent from the top of the tower. it can. The obtained organic solution containing an unsaturated aldehyde is used as a raw material for the oxidative esterification reaction step of the unsaturated aldehyde.
Although this is the outline of this process, the details are as diverse as the operating conditions, the polymerization prevention method, and the impurity suppression method as described below.

As a method for cooling and condensing at the bottom of the tower, a method in which the introduced gas and the circulating liquid are brought into direct contact while circulating the cooled tower bottom liquid into the tower is preferable. In order to cool and condense the unsaturated aldehyde-containing gas more effectively, the circulating column bottom liquid is cooled to −10 ° C. or lower using a heat exchanger. The cooling is preferably −15 ° C. or lower, more preferably −20 ° C. or lower.
The effect of cooling condensation is to lower the gas temperature and thus the operating temperature in the tower, to achieve more favorable operating conditions for gas absorption, and aldehydes are liable to generate peroxides, which is a factor that causes radical polymerization. This is because it can be avoided by cooling.

As a cooling operation method using a heat exchanger, the tower top gas temperature is used as an index, and the tower top gas temperature is adjusted to 0 ° C. or lower. Preferably, it is −5 ° C. or lower, more preferably −10 ° C. or lower. When the column top gas temperature is increased, the vent loss of the active ingredient increases, which is not preferable.
By direct gas-liquid contact between the rising gas and the circulating liquid at the bottom of the column, the sensible heat on the gas side moves to the liquid side and is rapidly cooled. As a result, most of the organic components in the gas containing unsaturated aldehyde are condensed. The circulating liquid receives sensible heat and latent heat of condensation from the gas, and the liquid temperature rises and flows down to the bottom of the tower. After that, the circulating liquid is cooled by a heat exchanger and supplied to the tower again as a circulating liquid.

Further, the operating pressure of the absorption tower can be selected from the range of normal pressure to 20 kg / cm ² G as described in, for example, JP-A-2-256625, and the absorption efficiency is improved at higher pressure conditions. If the pressure is too high, the operation may be dangerous. In addition, not only the absorption tower but also all reactors and other equipment need to be pressure resistant. In order to achieve this, it is not practical in terms of construction costs, such as the need for a high-pressure compressor.
In view of these circumstances, in the present invention, the pressure is preferably from normal pressure to 2.0 kg / cm ² G, more preferably from normal pressure to 1.5 kg / cm ² G.

The uncondensed gas comes into gas-liquid contact with the solvent flowing down from the top of the column, dissolves in the solvent, and flows down to the bottom of the column. Solvents used for absorption (hereinafter referred to as absorption solvents) include liquids containing raw alcohol to synthesize unsaturated carboxylic acid esters that are final products, such as methanol and ethyl methacrylate if the final product is methyl methacrylate. If it is ethanol or n-butyl methacrylate, it may be n-butanol.
As the absorbing solvent, pure alcohol may be newly introduced from outside the process, or the alcohol recovered in the downstream process of this process may be recycled. Alternatively, they can be used in combination. However, the water concentration in the absorbing solvent is 2% by weight or less. Preferably, it is 1% by weight or less, more preferably 0.5% by weight or less. When there is much water in an absorption solvent, the byproduct amount of unsaturated carboxylic acid will increase in an oxidation esterification process, and the production | generation of unsaturated carboxylic acid ester will be inhibited.

  It is also possible to introduce the absorbing solvent from a plurality of locations. In this case, it is better to use the alcohol concentration in the absorbing solvent at a position closer to the tower top. In addition, if there are a lot of unsaturated aldehydes and unsaturated carboxyl compounds, there is a possibility of radical polymerization derived from peroxide, and in order to avoid this, it is important to control the temperature in the tower as described above. However, the present inventors have found not only that, but the importance of controlling the dissolved oxygen concentration in the liquid. Conventionally, it is common knowledge among those skilled in the art to add molecular oxygen directly into, for example, a distillation tower, an absorption tower, or a storage tank in order to prevent polymerization of vinyl compounds. On the contrary, the present inventors have found that the formation of a polymer can be substantially eliminated by setting the dissolved oxygen concentration to 1 mg / L or less, preferably 0.5 mg / L or less. is there.

In addition, since the condensation at the bottom of the absorption tower occurs under a low temperature condition, acids other than the desired unsaturated aldehyde are condensed. As a result, the liquidity becomes an acidic range of 2 to 3 at pH. Under these conditions, it is known that aldehydes react with alcohol to produce acetals.
Many of these acetals have a boiling point close to that of the unsaturated carboxylic acid ester, which is a product of the process, and are difficult to be separated by distillation in the product purification step. It is important to suppress the formation of acetal, because residual acetal leads to a decrease in product purity. As a method for suppressing acetal formation in the process, the present inventors mixed a solution containing alcohol recycled from a step downstream of this step and a solution having a high pH, which is used as an unsaturated aldehyde absorbing solution. It has been found that the formation of acetal can be suppressed by supplying it to the absorption tower as an absorption liquid and adjusting the pH of the tower bottom liquid to 5 or more, preferably 6 or more. Examples of the liquid having a high pH to be mixed include a methanol solution of sodium hydroxide, and preferably, a part of the liquid having a high pH used in the process, for example, an outlet liquid of the oxidative esterification step is recycled. It is preferable to use it.

Condensation and absorption are carried out by a known gas-liquid contact method at the part to be directly contacted and the part to be absorbed by gas-liquid contact, and the apparatus includes a perforated plate tower, bubble bell tower, packed tower, or a combination thereof. Can be used.
In the tower, trays and packings are used. Specific examples of trays include bubble cap trays, dual trays, sheave trays, turbo grid trays, super flash trays, max flux trays, etc., and the presence or absence of overflow weirs or downcomers is not distinguished. In addition, as specific examples of the packing, in addition to conventionally used packing such as columnar, cylindrical, saddle-shaped, spherical, cubic, and pyramidal, it has a special shape as a high-performance packing. Regular packing or irregular packing may be used, and these can be preferably used in the present invention. Regular packing materials include sulzer packing (manufactured by Sulzer Brothers), Sumitomo sulzer packing (manufactured by Sumitomo Heavy Industries, Ltd.), techno pack (manufactured by Mitsui & Co.), etc., MC pack (manufactured by Mitsubishi Chemical Engineering). ), Techno Pack (Mitsui & Co., Ltd.), Mela Pack (Sumitomo Heavy Industries, Ltd.) and other sheet type regular packing, Flexi Grid (Coke) grid type regular packing, and Honeycomb Pack (NGK) Product), Good Roll Packing (manufactured by Tokyo Special Wire Mesh Co., Ltd.), Impulse Packing (manufactured by Nagaoka Co., Ltd.), Gem Pack (manufactured by Glitch Company), and Monz Pack (manufactured by Monz Company). As irregular packing, interlock saddle (Norton), flexi ring (JGC), IMTP (Norton), cascade mini-ring (Matsui machine), rushhi ring, terrarette (Nippon Kayoki) Etc.

  Subsequently, the oxidative esterification reaction step will be described. This is a process for producing an unsaturated carboxylic acid ester directly from an unsaturated aldehyde, an alcohol and a molecular element without passing through an unsaturated carboxylic acid. The catalyst used in this reaction step is a noble metal-supported catalyst having the formula RrBbNn, wherein R includes at least one of palladium, gold, and ruthenium, and B is at least one selected from Pb, Bi, Tl, Hg, N is one of Mg, K and Na, and is a production method characterized by using a catalyst formed on a spherical carrier having an average particle diameter of 30 to 200 μm. N is usually used in an amount selected from the range of 0.01 to 30% by weight, preferably 0.01 to 5% by weight. Preferred are a palladium / lead-containing supported catalyst and a palladium / bismuth-containing supported catalyst. More preferably, the palladium / (lead and / or) supported composition ratio of the activated palladium / (lead and / or bismuth) -containing supported catalyst is 3 / 0.7 to 3 / 1.3 in atomic ratio, Palladium (lead and / or bismuth) intermetallic compound. For example, in the case of a palladium-lead intermetallic compound, a catalyst having an X-ray diffraction angle (2θ) of (111) plane of 38.55 to 38.70 is preferable.

  In addition to R and B components as catalyst components, different elements such as mercury, thallium, tellurium, nickel, chromium, cobalt, indium, tantalum, copper lead, zirconium, hafnium, tungsten, manganese, silver, rhenium, antimony, tin, Rhodium, ruthenium, iridium, platinum, gold, titanium, aluminum, boron, silicon and the like may be included. These dissimilar elements can usually be in a range not exceeding 5% by weight, preferably 1% by weight. A small amount of these different elements and the above-described N component may enter between crystal lattices, or may be replaced with part of the crystal lattice metal. Further, the N component may be added to a solution containing a palladium compound or a lead compound at the time of catalyst preparation, and adsorbed or adhered to the support, or the catalyst can be prepared using a support that supports these in advance. . It can also be added to the reaction system under the reaction conditions.

R and B components used for catalyst preparation include organic acid salts such as formate and acetate, inorganic acid salts such as sulfate and nitrate, organometallic complexes such as ammine complex and benzonitrile complex, and oxides , And a hydroxide are appropriately selected. For example, palladium chloride and palladium acetate are suitable as the palladium compound, and lead nitrate and lead acetate are suitable as the lead compound, while an organic compound is suitable as the bismuth compound. The N component is also selected from organic acid salts, inorganic acid salts, hydroxides and the like.
The carrier can be widely selected from activated carbon, silica, alumina, silica alumina, silica alumina magnesia, zeolite, zirconia-containing silica, magnesia, magnesium hydroxide, titania, calcium carbonate, and the like. Preferred are chemically stable materials, especially carriers that are stable to acids and bases. It is more preferably selected from those having a specific surface area and a pore structure. Preferred are activated carbon, silica, alumina, silica alumina, silica alumina magnesia, zeolite, and zirconia-containing silica.

In the case where the carrier supports nickel, the supported amount is usually 0.1 to 20% by weight, preferably 1 to 10% by weight, based on the weight of the carrier. When lead is supported, the supported amount is usually 0.1 to 20% by weight, preferably 1 to 10% by weight, based on the weight of the support, but rather than each supported amount of palladium, lead and bismuth. The supporting composition ratio (atomic ratio) of / (lead and / or bismuth) is important.
That is, palladium / (lead and / or bismuth) supported composition ratio (atomic ratio) of the palladium / (lead and / or bismuth) supported catalyst to be activated in the present invention is 3 / 0.1 to 3/10. Although it can be selected from a wide range, it is preferably selected from a range of 3 / 0.1 to 3/3, more preferably 3 / 0.7 to 3/1.
In the case of a palladium / lead catalyst, the X-ray photoelectron spectrum of palladium metal (3d (3/2) + 3d (5/2)) / lead metal (4f (7/2) × 1.75) is more preferable. The intensity ratio is in the range of 1 / 0.2 to 1 / 0.7.

  In the case of a catalyst having an X-ray diffraction angle (2θ) of less than 355, the yield on the basis of alcohol is remarkably reduced, for example, the production of methyl formate is increased. If it exceeds 38.70, the decomposition of the aldehyde becomes remarkable, and the yield based on the aldehyde decreases. In addition, when the amount of supported lead exceeds 1.3 in terms of atomic ratio, the formation of methyl formate becomes remarkable, and when it is less than 0.7, the decrease in MMA selectivity due to decomposition of aldehyde is large. In the case of a palladium / lead catalyst obtained by the activation method of the present invention, more preferable palladium metal (3d (3/2) + 3d (5/2)) / lead metal (4f (7/2) × 1) .75) in the range of the X-ray photoelectron spectral intensity ratio in the range of 1 / 0.2 to 1 / 0.7, both the yields based on aldehyde and alcohol are improved. In order to obtain such a supported catalyst, a catalyst in which the supported amount of lead is controlled so that the palladium / lead supported composition ratio does not exceed 3 / 1.3 in atomic ratio is prepared, and this is activated. It is a preferable method to use.

  Examples of the alcohol used in the production of the unsaturated carboxylic acid ester include aliphatic saturated alcohols such as methanol, ethanol, isopropanol, sec-butanol, isobutanol, t-butanol, cyclohexanol, and octanol, ethylene glycol, and butanediol. Diols, allyl alcohols, methallyl alcohols and other aliphatic unsaturated alcohols, and benzylchols and other aromatic alcohols. These alcohols can be used alone or as a mixture of two or more kinds. There is no particular limitation on the ratio of the amount of aldehyde to alcohol used. For example, the molar ratio of aldehyde / alcohol can be as wide as 10 to 1/1000. Implemented in a range.

This production reaction can be carried out by a known method such as a gas phase reaction, a liquid phase reaction, or an irrigation reaction. Preferably, it is a liquid phase reaction, for example, it can be an arbitrary reactor type such as a bubble column reactor, a draft tube reactor, or a stirred tank reactor.
The oxygen used in the production reaction of the carboxylic acid ester can be in the form of molecular oxygen, that is, oxygen gas itself or a mixed gas obtained by diluting the oxygen gas with a diluent inert to the reaction, such as nitrogen or carbon dioxide gas, Air can also be used. Moreover, when carrying out this reaction continuously, deterioration of the catalyst can be suppressed by performing the reaction while adding a substance containing lead to the reactor. At this time, it is preferable that the oxygen partial pressure on the outlet side of the reactor is 0.8 kg / cm ² G or less because the lead concentration in the raw material liquid supplied to the reactor can be reduced to suppress deterioration of the catalyst. The reaction pressure can be realized in any wide pressure range from reduced pressure to increased pressure, but is usually carried out at a pressure of 0.5 to ²⁰ kg / cm ² G. The total pressure should be set so that the oxygen concentration in the reactor effluent gas does not exceed the explosion range (8%).

  In this carboxylic acid ester production reaction, an alkali metal or alkaline earth metal compound (for example, a substance, hydroxide, carbonate, carboxylate, etc.) is added to the reaction system to adjust the pH of the reaction system to 6-9. It is preferable to hold. In particular, by setting the pH to 6 or more, there is an effect of preventing dissolution of the lead component in the catalyst. These alkali metal or alkaline earth metal compounds may be used alone or in combination of two or more. The oxidative esterification reaction in the present invention can be carried out at a high temperature of 100 ° C. or higher, but is preferably 30 to 100 ° C. More preferably, it is 60-100 degreeC. The reaction time is not particularly limited and is not determined because it varies depending on the set conditions, but is usually 1 to 20 hours.

  Subsequently, an unreacted unsaturated aldehyde and an unsaturated carboxylic acid are produced from a liquid containing an unsaturated carboxylic acid ester, an unreacted unsaturated aldehyde, an unreacted alcohol, a by-product unsaturated carboxylic acid, and water produced in the oxidative esterification step. A method for separating and recovering the acid ester and effectively using it will be described in detail. Conventionally, with respect to the recovery of unreacted unsaturated aldehyde and unreacted alcohol in the oxidative esterification reaction, as shown in JP-A-11-246453, an azeotropic product is used in one distillation column. A method of separation, which is simple in terms of equipment and has few troubles such as polymerization, has been found. In the present invention, the separation can be carried out by the same technique. Japanese Patent Application Laid-Open No. 2000-1458 describes a method of recycling a solution containing recovered unreacted aldehyde to an oxidative esterification step. In the present invention, the recovered unsaturated aldehyde and unreacted Alcohol can be used in a continuous production method of unsaturated carboxylic acid ester using alkane as a raw material.

In order to separate the unsaturated aldehyde and the unreacted alcohol from the oxidized esterification reaction solution, the oxidized esterification reaction solution is supplied to the middle part of the distillation column, and the unsaturated aldehyde and the unreacted alcohol are recovered by distillation separation. Although distillation can be performed by a known technique, for example, it is desirable to perform distillation by a method described in JP-A-11-246453.
That is, in this process, the low boiling point compound generated in the oxidative esterification process is extracted from the top of the column and incinerated. Further, the recovered unsaturated aldehyde and alcohol are mainly extracted as an azeotropic mixture from an intermediate stage of the tower (referring to a stage near the middle of the supply stage and the top of the tower). This can be recycled to the oxidative esterification step. Further, unsaturated carboxylic acid ester, unrecovered unsaturated aldehyde, unrecovered alcohol, and water are mainly extracted from the bottom of the column and used for the next step in order to obtain the unsaturated carboxylic acid ester of the product.

  Next, a process of recovering alkane from a gas containing unreacted alkane from which unsaturated aldehyde is separated will be described. The gas containing unreacted alkane contains oxygen, nitrogen, generated carbon monoxide, carbon dioxide, etc., and in this process, unreacted alkane is used as a raw material gas for the gas phase oxidation reactor. The alkane and other gas components are selectively separated for recycling to the vessel. One of them is an absorption method using an organic solvent. Alkanes dissolve in organic solvents relatively easily, while oxygen, nitrogen, carbon monoxide, carbon dioxide, and the like are based on the principle of low solubility. If this method is used, the organic solvent has a relatively large heat capacity with respect to the gas, and the danger of explosion can be avoided.

As the solvent used for absorption, hydrocarbons, halogenated hydrocarbons, ketones, ethers, etc. can be used, but the selection of the absorbent is extremely important, not to mention the absorption function, but economical It is necessary to decide in consideration of safety and stability. Preferred are hydrocarbons, among which aliphatic hydrocarbons having 6 to 20 carbon atoms, aliphatic cyclic hydrocarbons, and / or aromatic hydrocarbons are preferred.
More preferably, it is an aliphatic hydrocarbon having 7 to 18 carbon atoms, an aliphatic cyclic hydrocarbon, and / or an aromatic hydrocarbon. When the number of carbon atoms is 5 or less, the relative volatility between the organic solvent and the unreacted alkane is small, and when separating and recovering by distillation, a large number of distillation column stages are required and a lot of energy is required. On the other hand, when the number of carbon atoms exceeds 20 or more, the operating temperature of a conventional absorption tower is not preferable because the viscosity becomes high and the absorption efficiency deteriorates. Suitable organic solvents include, for example, hexane, heptane, octane, isooctane, dimethylcyclohexane, trimethylheptane, decane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, eicosane, cyclohexane, methylcyclohexane, dimethylcyclohexane, benzene. , Toluene, xylene, ethylbenzene, propylbenzene, butylbenzene, cymene, deurene, methyltaphthalene, ethylnaphthalene, propylnaphthalene, dimethylnaphthalene, diphenyl and the like, but are not limited thereto.

  These can be used alone or in the form of a mixture. The organic solvent in which impurities have accumulated can also be extracted continuously or intermittently by distillation operation or the like. The contact method with the alkane-containing gas may be a countercurrent type or a cocurrent type, but multistage countercurrent contact is more preferable in order to increase absorption efficiency. The form of the absorption tower can be any form such as a packed tower, a perforated plate tower, a bubble bell tower, and a spray tower. Since the supply amount of the absorption solvent varies depending on the operation temperature, operation pressure, gas amount, and type of the absorption solvent of the absorption tower, it is difficult to define uniquely, but the organic solvent is added to 1 mol of unreacted alkane. 0.5 to 100 mol, preferably 1 to 50 mol, more preferably 2 to 20 mol of the solvent may be supplied.

By supplying an appropriate amount of the absorbing solvent in this manner, substantially the entire amount of alkane can be recovered. The operating temperature of the absorption tower can be controlled by installing a cooler inside or outside the absorption tower. The alkane absorption tower has a temperature of -20 ° C to 100 ° C, more preferably 0 ° C to 80 ° C. Preferably, it can choose from the range of 20 to 60 degreeC. The operating pressure should not be set only from the optimum conditions of the absorption tower alone, but in order to improve the absorption efficiency of the absorbing solvent, the operating pressure is operated at a pressure of about 0.5 to 10 kg / cm ² G. It is preferable to select within the range. Further, when operating the absorption tower under pressure, it is possible to increase the operation pressure of the absorption tower and increase the operation pressure.

The organic solvent that has absorbed the unreacted alkane is then supplied to a distillation column or a stripping column, where the alkane and the organic solvent are separated, and the alkane is recycled to the reactor. If the alkane to be recycled contains an organic solvent, there is a concern about the loss of the organic solvent and the influence on the reaction. Therefore, the amount of the organic solvent in the gas and / or liquid obtained from the top of the column is suppressed to 1% or less, more preferably 1000 ppm or less, and even more preferably 100 ppm or less.
The distillation or stripping tower can also be operated under pressure. In this case, the absorption tower and, in some cases, the reactor can also be operated simultaneously under pressure, and the entire process is operated under pressure consistently. You can also
Further, as an alkane adsorption separation and recovery method, only alkane is selectively adsorbed and separated from gas containing alkane by a method using pressure swing adsorption (PSA device, pressure swing absorption gas generator) in which a plurality of adsorption units are arranged. . The adsorbed alkane is switched by a valve operation or the like, and the alkane can be desorbed from the adsorption tower by operating the pressure and recycled to the reactor.

Next, the unsaturated carboxylic acid ester purification step will be described.
From the bottom of the unsaturated aldehyde recovery step, a liquid mainly composed of an unsaturated carboxylic acid ester, an unrecovered unsaturated aldehyde, an unrecovered alcohol, an unsaturated carboxylic acid, and water is supplied to the step. The water in the composition is oil-water separated by operations such as stationary separation, centrifugation, and extraction. The crude unsaturated carboxylic acid ester-containing liquid from which moisture has been removed is supplied to a high-boiling separation column, and high-boiling compounds such as unsaturated carboxylic acids are distilled off. From the top of the column, a crude unsaturated carboxylic acid ester is obtained and supplied to a low boiling separation column, and from the bottom of the column, an unsaturated carboxylic acid is obtained and used for an unsaturated carboxylic acid esterification step.
In the low boiling separation column, low boiling point compounds such as unrecovered unsaturated aldehyde, unrecovered alcohol and the like are separated by distillation. Since the low boiling point compound extracted from the top of the column contains an unsaturated aldehyde and alcohol as active components, it can be recovered and recycled to the oxidative esterification step or the unsaturated aldehyde recovery step.
The crude unsaturated carboxylic acid ester separated at low boiling point is supplied to a product column to obtain a product from the top of the column.

Next, the unsaturated carboxylic acid esterification step will be described.
The quenching tower bottom liquid and the high boiling separation tower bottom liquid contain a high concentration of unsaturated carboxylic acid.
These liquids are subjected to an esterification step, and are esterified using a known esterification catalyst such as sulfuric acid or a strongly acidic ion exchange resin. The unsaturated carboxylic acid ester generated in this step is subjected to an unsaturated carboxylic acid ester purification step.
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. Note that the pressure used in the examples and the like is expressed as a gauge pressure and expressed as kg / cm ² G.

[Example 1]
1. Gas Phase Oxidation Reaction Step 144.0 g of molybdenum trioxide, 8.27 g of vanadium pentoxide and 12.5 g of phosphoric acid (85% by weight) are added to a Pyrex (registered trademark) three-necked flask together with 1000 ml of water, and heated for 24 hours. Refluxed. Subsequently, the insoluble component of the aqueous solution was filtered and concentrated to obtain reddish brown crystals. When this crystal was examined by X-ray diffraction, atomic absorption analysis and ³¹ PNMR, it was molybdovanadate (PMo ₁₁ V) having an atomic ratio of P: Mo: V of 1: 11: 1. 1678 g of molybdovanadolinic acid obtained by repeating the above-described operation was dissolved in 1450 (L) of cuprous chloride 49.5 g of water, and 6.4 wt% aqueous ammonium nitrate solution 725 (g The resulting slurry solution is concentrated, then dried at 120 ° C. for 12 hours, and then pulverized to obtain a ring having an outer diameter of 6 (mm), an inner diameter of 3 (mm), and a height of 6 (mm). It was molded into a shape and fired in a nitrogen stream at 450 ° C. for 3 hours and further in air at 350 ° C. for 2 hours. A catalyst having a composition of PMo ₁₁ VCu _0.5 was obtained.

This catalyst was placed in a jacketed stainless steel reaction tube (made of SUS304) having an outer diameter of 48.6 (mm), an inner diameter of 45.0 (mm) and a length of 4.5 (m) from the gas inlet to the outlet. The catalyst layer is divided into two reaction zones, and the catalyst concentration is C1 between 2.3 (m) from the inlet and the catalyst concentration is C2 between 2.2 (m) and 4.5 (m). did. The catalyst concentration C2 was filled with only the ring catalyst. The catalyst concentration C1 was diluted with a porcelain Raschig ring (ring shape with an outer diameter of 6 (mm), an inner diameter of 3 (mm), and a height of 6 (mm)) so that the catalyst concentration C1 was half of the catalyst concentration C2.
The temperature of the heat medium in the jacket was 290 ° C., and a mixed gas of 60 vol% isobutane, 15 vol% oxygen, 5 vol% water vapor, and 20 vol% nitrogen was supplied at a contact time of 3.3 seconds. After 12 hours, the reaction gas was analyzed by gas chromatography. As a result, 8.3% of isobutane was converted, the selectivity of methacrolein was 50.1%, and the selectivity of methacrylic acid was 11.7%.

2. Rapid Dehydration Step and Unsaturated Aldehyde Absorption Step Next, the unsaturated aldehyde absorption step by the quenching tower, the dehydration tower and the absorption tower was carried out as follows with reference to JP-A-11-80077.
Above 1. The gas containing methacrolein and water vapor obtained in this step was introduced into the quenching tower.
The composition of the methacrolein-containing gas to be introduced is as follows: methacrolein is 2.35 mol%, water is 15 mol%, the total of liquid by-products such as acetone is 0.2 mol%, and nitrogen, oxygen, carbon dioxide, carbon monoxide, The total amount of gases such as unreacted isobutane was 82.45 mol%. The gas was cooled to 80 ° C. using quench water to obtain partially dehydrated methacrolein. Moreover, the quenching tower bottom liquid was used for the esterification process.

Partially dehydrated methacrolein-containing gas was supplied at a flow rate of 5.0 Nm ³ / hr to the bottom of a tray-type dehydration tower equipped with a sieve tray having an inner diameter of 12 cm, a height of 5 m, and a real number of 30 plates. From the uppermost stage of the dehydration tower, a solution obtained by adding 100 wt ppm of hydroquinone to liquid methanol was supplied at 200 g / hr. The gas temperature in the dehydration tower was controlled at 80 ° C. at the bottom and 18 ° C. at the top, and the liquid methanol temperature was controlled at 18 ° C. The pressure at the bottom of the dehydration tower was controlled at 1.5 kg / cm ² G. The partially dehydrated mixed gas was further dehydrated under the above conditions, and a dehydrated mixed gas containing methacrolein and methanol gas was obtained from the top of the dehydration tower. The obtained dehydrated mixed gas was supplied to the tower bottom gas phase part of a tower type absorption tower equipped with a sieve tray having an inner diameter of 10 cm, a height of 5 m, and an actual number of 30 stages. The bottom liquid temperature in the absorption tower was controlled at 8 ° C, and the uppermost gas phase temperature was controlled at -12 ° C. At the bottom of the absorption tower, the introduced gas was condensed while returning to the inside of the tower while cooling and circulating the bottom liquid to −25 ° C. with a refrigerator. From the top of the column, a solution obtained by adding 100 ppm by weight of hydroquinone to liquid methanol was supplied at 650 g / hr to absorb uncondensed methacrolein.

  Furthermore, the 15th stage from the tower top was supplied with a liquid adjusted to pH 7 to 8 by mixing the reaction liquid of the oxidative esterification step described later, and the pH of the tower bottom liquid was adjusted to 6.5. Under the above conditions, substantially all of the methacrolein gas and methanol gas in the dehydrated mixed gas were obtained from the bottom of the absorption tower by condensation and absorption. The composition of the obtained liquid mixture was 35.5% by weight of methacrolein, 64.1% by weight of methanol, 0.2% by weight of water, and 0.1% by weight of by-products such as acetone.

3. Unreacted alkane recovery step Unreacted alkane was recovered with reference to Example 1 of JP-A-3-176439. In other words, unreacted isobutane, oxygen, carbon dioxide, and other nitrogen-containing gas was introduced at 5 Nm ³ / hr from the bottom of the tower into an absorption tower packed with Dixson Packing and having a diameter of 15.84 cm and a packing height of 2 m. From the top, n-paraffin was fed at 47 kg / hr. The n-paraffin was a mixture of decane, undecane, and dodecane, and the contents were 22, 52, and 26% by weight, respectively. When a refrigerant at −12 ° C. was circulated in the mantle of the absorption tower and operated at normal pressure, 99.5% of unreacted isobutane could be recovered. The absorption liquid thus obtained was introduced from the upper part of the diffusion tower, and it was possible to recycle almost quantitatively using a part of the gas used for the gas phase oxidation reaction from the lower part.

4). Oxidation esterification step The catalyst used in this step was prepared and prepared as follows.
As a silica sol aqueous solution, Stex N-30 (manufactured by Nissan Chemical Co., Ltd., SiO ₂ min: 30% by weight), aluminum nitrate and magnesium nitrate were Al / (Si + Al) = 10 mol% and Mg / (Si + Mg) = 10 mol%, respectively. After adding and dissolving as described above, a spherical carrier having a particle system of 60 μm was obtained by spray drying with a spray dryer set to a temperature of 130 ° C. After calcining at 300 ° C. and then at 600 ° C., this was loaded with palladium chloride and lead nitrate as palladium, lead content of 5 parts by weight and 6.5 parts by weight per 100 parts by weight of the carrier, and then hydrazine To obtain a catalyst (Pd _5.0 Pb _6.5 / Mg, expressed as Al—SiO ₂ ). The obtained supported catalyst had a Pd / Pb supported composition ratio of 3 / 1.95 in atomic ratio, an X-ray diffraction angle (2θ) of the (111) plane of the palladium / lead intermetallic compound was 38.745 °, The intensity ratio of the X-ray photoelectron spectrum of (3d) / lead (4f) was 1.24. Next, 800 g of this catalyst was charged into an external circulation type stainless steel bubble column reactor equipped with a catalyst separator and having a liquid phase part of 3.5 liters, and the catalyst was activated. When the activation treatment was completed in 50 hours and the catalyst was analyzed, the Pd / Pb supported composition ratio (atomic ratio) was 3 / 1.09, and the X-ray diffraction angle (2θ) of the (111) plane of the palladium / genus compound was Was 38.634 degrees. The intensity ratio of the X-ray photoelectron spectrum of palladium (3d) / lead (4f) was 1 / 0.597.

990 g of this catalyst was equipped with a catalyst separator and charged into an external circulation type stainless steel bubble column reactor having a liquid phase part of 5.0 liters to carry out the reaction. A 37% by weight methacrolein / methanol solution was continuously supplied to the reactor at 1.6 liter / hr and an NaOH / methanol solution at 0.06 liter / hr, the reaction temperature was 80 ° C., the reaction pressure was 5 kg / cm ² G. Then, the MMA formation reaction was carried out while adjusting the amount of air so that the outlet oxygen concentration was 4.0% (corresponding to oxygen partial pressure 0.2 kg / cm ² G). After 10 hours, methacrolein conversion was 60 The selectivity for methyl methacrylate was 91.2%.

5). Unsaturated aldehyde recovery step The unsaturated aldehyde recovery step was carried out with reference to Example 1 of JP-A No. 11-246453. Step 4 above. The liquid containing the reaction mixture consisting of methacrolein, methyl methacrylate, water, methacrylic acid and methanol obtained in the above and the methyl methacrylate obtained in the unsaturated carboxylic acid esterification step was 10 cm in diameter, 6 m in height, and the actual number of stages 45. Was supplied at a rate of 1943 g / hr from the top of a tower column type distillation column equipped with a sieve tray.
From the top of the column, hydroquinone was supplied so that the concentration of the polymerization inhibitor in the falling liquid in the column was 100 ppm or more. At the top of the column is a device having a column top condenser that can be drained even under reduced pressure, and at the bottom of the column is a device that can withdraw the bottom liquid under reduced pressure controlled by a reboiler and a level gauge. The top temperature of the distillation column is 31 ° C., the bottom temperature is 84 ° C., the temperature at the 6th stage from the bottom is 81.4 ° C., the pressure at the top is 650 torr, and the middle stage of the 15th stage from the top. 700 g / hr of liquid was obtained.

6). Oil / water separation step Step 5 above. The column bottom liquid obtained in step 1 was extracted at 1180 g / hr, adjusted to pH 2 to 3, and supplied to an oil / water separation centrifuge. The oil layer was subjected to the next high boiling separation step.
7). High boiling separation step With reference to Example 1 of JP-A-11-302224, the high boiling separation step was carried out as follows. 5. The above step 6 on the 20th stage from the top of a tower column type distillation column equipped with a sheave tray having an inner diameter of 10 cm and an actual stage of 30 stages. The oil layer separated by oil and water was supplied at 1000 g / hr. At the top of the column, there is an apparatus having a column top condenser that can be drained under reduced pressure. At the bottom of the column is a reboiler and a device that can extract the column bottom liquid under reduced pressure controlled by a liquid level gauge. While supplying hydroquinone from the top of the tower so that the concentration of the polymerization inhibitor in the down stream in the tower is 100 ppm or more, the reflux rate is 1000 g / hr, the top pressure is 150 mmHg, the top temperature is 45 ° C., the bottom temperature is 70 ° C. Continuous distillation was performed under the above conditions to obtain a column top liquid and a column bottom liquid. The column top liquid was sent to the next low boiling point separation step, and the column bottom liquid was subjected to an esterification step.

8). Low-boiling separation step With reference to Example 1 of JP-A-11-35523, the low-boiling separation step was performed as follows. The condensate obtained in Step 7 was supplied at 920 g / hr to the 20th stage from the top of a shelf type distillation column equipped with a sieve tray having an inner diameter of 10 cm and an actual stage of 60 stages. At the top of the column is provided a device having a brine cooler that can be drained under reduced pressure, and at the bottom of the column is a reboiler and a device that can withdraw the bottom solution under reduced pressure controlled by a liquid level gauge. While supplying hydroquinone from the top of the tower so that the concentration of the polymerization inhibitor in the down stream in the tower is 100 ppm or more, the reflux amount is 400 g / hr, the top pressure is 250 mmHg, the top temperature is 45 ° C., the bottom temperature is 80 ° C. Distilled continuously under the following conditions. The crude methyl methacrylate as the tower bottom liquid was sent to the next methyl methacrylate purification step.

9. Step of purifying methyl methacrylate The above step 8. The column bottom liquid extracted in step (b) was fed at 688 g / hr to the bottom of a tray column type distillation column equipped with a sieve tray having an inner diameter of 10 cm and a plate number of 30. At the top of the column is provided a device having a brine condenser that can be drained under reduced pressure, and at the bottom of the column is a reboiler and a device capable of withdrawing the bottom liquid under reduced pressure controlled by a liquid level gauge. Continuous distillation was performed under the conditions of a reflux rate of 225 g / hr, a tower top pressure of 140 mmHg, a tower top temperature of 55 ° C., and a tower bottom temperature of 80 ° C. From the top of the column, 588 g / hr of purified methyl methacrylate was obtained.
The obtained purified methyl methacrylate had an APHA of about 3, and its purity was 99.90% by weight or more. The yellowness YI of the methyl methacrylate polymer produced using the polymer was 3.5, and excellent evaluation was obtained for both the monomer and the polymer.
The methyl methacrylate obtained in the above steps was 44.5% yield from the charged isobutane.

[Example 2]
As an oxidation catalyst, ammonium heptamolybdate as Mo raw material, nitrate as Fe, Co, Bi, Rb, Cu, In raw material, antimony oxide as an antimony was pulverized to 1 micron or less, and each aqueous solution was mixed and slurried. . The obtained slurry solution was concentrated, then dried at 120 ° C. for 12 hours, then pulverized, molded into a ring shape having an outer diameter of 6 (mm), an inner diameter of 3 (mm), and a height of 6 (mm). An oxidation catalyst having a composition of Mo ₁₂ Fe _1.2 Co ₆ Bi _2.4 Sb _1.3 Cu _1.2 In _0.3 Rb _0.15 was obtained by calcination at 2 ° C. for 2 hours.
This catalyst was placed in a jacketed stainless steel reaction tube (made of SUS304) having an outer diameter of 48.6 (mm), an inner diameter of 45.0 (mm) and a length of 4.5 (m) from the gas inlet to the outlet. The catalyst layer is divided into two reaction zones, and the catalyst concentration is C1 between 2.3 (m) from the inlet and the catalyst concentration is C2 between 2.2 (m) and 4.5 (m). did. The catalyst concentration C2 was filled with only the ring catalyst. The catalyst concentration C1 was diluted with a porcelain Raschig ring (ring shape with an outer diameter of 6 (mm), an inner diameter of 3 (mm), and a height of 6 (mm)) so that the catalyst concentration C1 was half of the catalyst concentration C2.

As a dehydrogenation catalyst for isobutane, a catalyst molded into a spherical shape of 6 mmφ using activated carbon as a main raw material was packed. Isobutane was passed through a dehydrogenation reactor having a reaction temperature of 550 ° C. with a contact time of 3 seconds, and the dehydrogenated gas was introduced into the next oxidation reactor together with oxygen, water vapor, and nitrogen.
The temperature of the heat medium in the jacket of the oxidation reactor is 350 ° C., and oxygen is supplied to the oxidation reactor, and the composition at the time of passing through the oxidation reactor is isobutane 40 vol%, oxygen 15 vol%, water vapor 5 vol%, and nitrogen balance. The mixed gas was supplied at a contact time of 3.3 seconds. After 12 hours, the reaction gas was analyzed by gas chromatography. As a result, 30% of isobutane was converted, methacrolein selectivity was 65.3%, and methacrylic acid selectivity was 2.7%.

[Example 3]
1290 g of niobic acid containing 80.2% by weight as Nb ₂ O ₅ and 4905 g of oxalic acid dihydrate [H ₂ C ₂ O ₄ .2H ₂ O] were mixed in 8450 g of water. The molar ratio of the charged oxalic acid / niobium is 5.0, and the charged niobium concentration is 0.532 (mol Nb / Kg solution).
This solution was heated and stirred at 95 ° C. for 1 hour to obtain an aqueous solution in which niobium was dissolved. The aqueous solution was allowed to stand and ice-cooled, and then the solid was separated by suction filtration to obtain a uniform niobium mixed solution. The molar ratio of oxalic acid / niobium in this niobium mixed solution was 2.32 according to the following analysis.
10 g of this niobium mixed solution was precisely weighed in a crucible, dried overnight at 95 ° C., and then heat-treated at 600 ° C. for 1 hour to obtain 0.864 g of Nb ₂ O ₅ . From this result, the niobium concentration was 0.65 (molNb / Kg solution).

3 g of this niobium mixture was precisely weighed into a 300 ml glass beaker, 200 ml of hot water at about 80 ° C. was added, and then 10 ml of 1: 1 sulfuric acid was added. The obtained solution was titrated with 1 / 4N KMnO ₄ under stirring while maintaining the liquid temperature at 70 ° C. on a hot stirrer. The end point was a point where a faint pale pink color by KMnO ₄ lasted for about 30 seconds or more. The concentration of oxalic acid was 1.51 (mol oxalic acid / Kg) as a result of calculation according to the following formula from titration.
2KMnO ₄ + 3H ₂ SO ₄ + 5H ₂ C ₂ O ₄ → K ₂ SO ₄ + 2MnSO ₄ + 10CO ₂
+ 8H ₂ O
The obtained niobium raw material liquid was used as the following niobium raw material liquid (N) for catalyst preparation.

(Preparation of dry powder)
Mixing composition formula was produced by dry powder comprising an oxide catalyst represented by _{Mo 1 V 0.22 Nb 0.10 Sb 0.26} O n / 45wt% SiO 2 as follows.
In 4750 g of water, 909.1 g of ammonium heptamolybdate [(NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O], 131.7 g of ammonium metavanadate [NH ₄ VO ₃ ], antimony trioxide [Sb ₂ O ₃ 149.5 g were added and heated at 90 ° C. for 2.5 hours with stirring to obtain a mixed solution (A).
44.8 g of antimony trioxide [Sb ₂ O ₃ ] was added to 786.6 g of the niobium mixed liquid (N). While stirring under ice cooling, 185.5 g of hydrogen peroxide containing 30 wt% as H ₂ O ₂ was slowly added. Then, it stirred and mixed and it was set as the liquid mixture (B).
After cooling the obtained mixed liquid (A) to 70 ° C., 2941.2 g of silica sol containing 30.6 wt% as SiO ₂ was added. Further, 173.9 g of hydrogen peroxide containing 30 wt% as H ₂ O ₂ was added and mixed with stirring at 50 ° C. for 1 hour.

Next, the mixed liquid (B) was added to obtain a raw material preparation liquid.
The obtained raw material mixture was supplied to a centrifugal spray dryer and dried to obtain a microspherical dry powder. The dryer inlet temperature was 210 ° C and the outlet temperature was 120 ° C.
The above operation was repeated 5 times, and the dry powder was collected and used in the following firing examples. When storing the dry powder, a sealed container was used so as not to absorb moisture.
480 g of dry powder is filled in a SUS fired tube with a diameter of 3 inches, heated to 340 ° C. over 1 hour while rotating the tube under a nitrogen gas flow of 5.0 NL / min, and held at 340 ° C. for 4 hours. did. Thereafter, the temperature was raised to 640 ° C. over 1 hour, held at 640 ° C. for 2 hours, and calcined to obtain a catalyst.
This catalyst was reacted in the same manner as in Example 1. After 24 hours, the reaction gas was analyzed by gas chromatography. As a result, 8.3% of isobutane was converted, the selectivity of methacrolein was 50.1%, and the selectivity of methacrylic acid was 11.8%.

[Comparative Example 1]
A crystal 2370 (g) of 12-molybdophosphoric acid (H ₃ PMo ₁₂ O ₄₀ .30H ₂ O: Nippon Inorganic Chemical Co., Ltd.) and cuprous chloride 50 (g) were dissolved in 20 (L) of water. Add 100 wt.% Ammonium nitrate aqueous solution (100 g), stir well, concentrate the resulting slurry solution, dry at 120 ° C. for 12 hours, pulverize, outer diameter 6 (mm), inner diameter 3 (mm ), And molded into a ring shape with a height of 6 (mm), which was fired in a nitrogen stream at 450 ° C. for 3 hours and further in air at 350 ° C. for 2 hours. Thus, a catalyst having a PMo ₁₂ Cu _0.5 composition was obtained.
Using this catalyst and the same reactor as in Example 1, a gas phase oxidation reaction was performed under the same conditions. However, the yield of methacrylic acid was increased by recycling the produced methacrolein. After 12 hours, the reaction gas was analyzed by gas chromatography. As a result, 8.3% of isobutane was converted, methacrolein selectivity was 11.3%, and methacrylic acid selectivity was 40.7%.
Furthermore, the methyl methacrylate obtained through the steps 2 to 9 in Example 1 was a yield of 40.4% from the charged isobutane.

[Comparative Example 2]
12 molybdophosphate: crystal 2370 (g) and niobium mixed solution used in Example 2 of _{(H 3 PMo 12 O 40 ·} 30H 2 O Nippon Inorganic Color & Chemical) (N) (niobium concentration 0.65 (mol-Nb / Kg solution)) 384.7, chromium (III) nitrate nonahydrate 100.1 g, potassium nitrate 101.2 g, and 1300 g of quinoline and 20 L of water were added to this solution, and the resulting slurry was stirred. Concentrated. Then, after drying at 120 ° C. for 12 hours, pulverized and molded into a ring shape having an outer diameter of 6 (mm), an inner diameter of 3 (mm), and a height of 6 (mm). Furthermore, it baked at 350 degreeC in the air for 2 hours. A catalyst having the composition P ₁ Mo ₁₂ Nb _0.1 Cr _0.25 K ₁ was obtained.
The same experiment as Comparative Example 1 was performed except that the catalyst obtained here was used. After 12 hours, the reaction gas was analyzed by gas chromatography. As a result, 8.3% of isobutane was converted, methacrolein selectivity was 13.7%, and methacrylic acid selectivity was 30.2%. Furthermore, the methyl methacrylate obtained through the steps 2 to 9 in Example 1 was 33.7% yield from the charged isobutane.

  The present invention relates to a method for obtaining an unsaturated carboxylic acid ester by catalytically oxidizing an alkane raw material with molecular oxygen, and by selecting a catalyst and conditions for producing a large amount of unsaturated aldehyde, the target unsaturated carboxylic acid ester The yield of can be increased.

It is the schematic which shows an example of the system for implementing this invention.

Explanation of symbols

a Raw material alkane
b Molecular oxygen-containing gas
c Unsaturated aldehyde, unsaturated carboxylic acid-containing gas d Unsaturated carboxylic acid removal gas e Unsaturated carboxylic acid-containing waste water f Alcohol g Unsaturated aldehyde-containing dehydrated gas h Alcohol i Recycled alkane-containing gas j Unsaturated aldehyde / alcohol solution k molecular oxygen-containing gas l oxidative esterification reaction liquid m recovered unsaturated aldehyde, alcohol n low boiling waste oil o unsaturated carboxylic acid ester / water-containing liquid p crude unsaturated carboxylic acid ester-containing liquid q unsaturated carboxylic acid ester r Saturated carboxylic acid-containing liquid s Crude unsaturated carboxylic acid ester-containing liquid (1) Gas phase oxidation reaction step
(2) Rapid cooling process
(3) Dehydration process
(4) Unsaturated aldehyde absorption step (5) Unreacted alkane recovery step
(6) Oxidation esterification process
(7) Unsaturated aldehyde recovery step (8) Oil-water separation step
(9) Unsaturated carboxylic acid ester purification process (including high boiling separation, low boiling separation, product tower)
(10) Esterification step of unsaturated carboxylic acid

Claims (13)

A method for continuously producing an unsaturated carboxylic acid ester using an alkane as a raw material, wherein an alkane and oxygen are contacted with a catalyst in a gas phase, and the resulting unsaturated aldehyde, an alcohol, and a gas containing oxygen are mixed with a catalyst in a liquid phase. A continuous production method of an unsaturated carboxylic acid ester characterized by synthesizing an unsaturated carboxylic acid ester by catalytic reaction. The method for continuously producing an unsaturated carboxylic acid ester using an alkane as a raw material, comprising the steps of recovering unreacted alkane and recycling the recovered alkane to a gas phase oxidation reactor. Manufacturing method. A method for continuously producing an unsaturated carboxylic acid ester using an alkane as a raw material, and separating and recovering an unreacted unsaturated aldehyde from a reaction solution containing the unsaturated carboxylic acid ester generated in the step of synthesizing the unsaturated carboxylic acid ester, The manufacturing method of Claim 1 which has a process of recycling unsaturated aldehyde in an oxidation esterification reaction process. A method for continuously producing an unsaturated carboxylic acid ester using an alkane as a raw material, comprising a step of recovering by-product unsaturated carboxylic acid and synthesizing an unsaturated carboxylic acid ertel using an unsaturated carboxylic acid and an alcohol as an acid catalyst. The manufacturing method according to claim 1. A continuous production method of an unsaturated carboxylic acid ester using an alkane as a raw material, comprising a process comprising the following (1) to (10).
(1) Gas phase oxidation reaction step: a reaction step in which a gas containing at least alkane and oxygen is brought into contact with a catalyst in a gas phase at a temperature of 250 ° C. or higher to produce an unsaturated aldehyde and an unsaturated carboxylic acid.
(2) Quenching step: The reaction gas obtained in the step (1) is rapidly cooled to a temperature of 200 ° C. or lower, and a condensate mainly containing unsaturated carboxylic acid, an unsaturated aldehyde, water, and unreacted alkane from the reaction product. The process of isolate | separating the component which contains.
(3) Dehydration step: a step of selectively removing water by bringing a system containing water, an unsaturated aldehyde and an unreacted alkane into contact with an organic solvent containing alcohol.
(4) Unsaturated aldehyde absorption step: The gas containing the dehydrated unsaturated aldehyde and the unreacted alkane is cooled to recover the condensed unsaturated aldehyde, while the uncondensed unsaturated aldehyde contacts the organic solvent containing alcohol. Process to recover.
(5) Alkane recovery and recycling process: a process of recovering unreacted alkane and recycling the recovered alkane to the gas phase oxidation reaction process of (1) again (6) oxidative esterification reaction process: A process of synthesizing an unsaturated carboxylic acid ester by using an alcohol solution containing a saturated aldehyde as a raw material and bringing it into contact with a gas containing oxygen in the presence of a catalyst. (7) Recovery of unreacted unsaturated aldehyde: produced by oxidative esterification reaction From a reaction liquid containing unsaturated carboxylic acid ester, water, unsaturated carboxylic acid and unreacted unsaturated aldehyde, residual alcohol, and a high boiling point composition having a low boiling point component, an unreacted unsaturated aldehyde and a distillation composition mainly containing alcohol. Separated into a distillation composition containing mainly unsaturated carboxylic acid ester, unsaturated carboxylic acid and water as components, the low boiling point component is The step of recycling to 4).
(8) Oil / water separation step: Step of separating the liquid containing the high boiling point component of (7) above into oil / water (9) Step of purifying unsaturated carboxylic acid ester: Unsaturated carboxylic acid contained in the oil layer obtained in (8) above A step of purifying an unsaturated carboxylic acid ester from a solution containing the ester and impurities to obtain a highly pure unsaturated carboxylic acid ester.
(10) Unsaturated carboxylic acid esterification step: A liquid obtained by separating unsaturated carboxylic acid from a liquid containing unsaturated carboxylic acid separated in (2) and unsaturated carboxylic acid contained in (9) impurities. A step of synthesizing an unsaturated carboxylic acid ester with an alcohol in the presence of an acid catalyst. The alkane is propane, the unsaturated aldehyde obtained by the gas phase oxidation reaction is acrolein, the obtained unsaturated carboxylic acid is acrylic acid, and the unsaturated carboxylic acid ester obtained by the oxidative esterification reaction is acrylic acid ester. The manufacturing method according to claim 1. Alkane is isobutane, unsaturated aldehyde obtained by gas phase oxidation reaction is methacrolein, unsaturated carboxylic acid obtained is methacrylic acid, and unsaturated carboxylic acid ester obtained by oxidative esterification reaction is methacrylic acid ester The manufacturing method according to claim 1. The alcohol is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, t-butanol, cyclohexanol, and 2-ethylhexanol, and used alone or in combination. The manufacturing method of unsaturated carboxylic acid ester of claim | item 1-3. The reactor used for the gas phase oxidation reaction is a heat exchanger type fixed bed reactor, and the pressure loss at the reaction condition gas linear velocity is 70% or less when a cylindrical catalyst is used in the reactor. 4. The production method according to claim 1, wherein a designed and molded catalyst is used. 4. The process according to claim 1, wherein the reactor used for the gas phase oxidation reaction is a fluidized bed reactor, and a spherical catalyst containing 30 to 70% by weight of silica and having an average particle diameter of 30 to 100 μm is used. Method. A noble metal-supported catalyst in the step of producing an unsaturated carboxylic acid ester by an oxidative esterification reaction from an unsaturated aldehyde, an alcohol and oxygen, wherein R is at least one of palladium, gold and ruthenium, and B is At least one selected from Pb, Bi, Tl, and Hg, N is one of Mg, K, and Na, and uses a catalyst that is supported on a spherical support having an average particle size of 30 to 200 μm. A featured manufacturing method. This is a continuous process for producing unsaturated carboxylic acid esters using alkane as a raw material, and a hydrocarbon-based organic solvent having 6 to 10 carbon atoms is brought into contact with a gas mixture containing unreacted alkane to absorb and recover unreacted alkane. Then, the unreacted alkane absorption liquid is separated into alkane and a hydrocarbon organic solvent having 6 to 10 carbon atoms by distillation operation or stripping operation by gas supply. Recycle as a raw material to a gas phase oxidation reactor. A continuous process for producing an unsaturated carboxylic acid ester using an alkane as a raw material, wherein a gas mixture containing unreacted alkane is supplied to an adsorption separation and recovery step formed from at least two adsorption towers. After the alkane is adsorbed and recovered, the adsorbed alkane is released again by temperature swing, pressure swing, gas supply, or the like, and this alkane is used again as a raw material and recycled to the gas phase oxidation reactor.

Images