阅读说明：本技术 含钠盐的mma-甲醇混合物的提取处理 (Extraction treatment of MMA-methanol mixture containing sodium salt ) 是由 M·格罗姆皮恩格 S·克里尔 A·黎金 M·卢基科 S·芬格尔 于 2016-09-14 设计创作，主要内容包括：本发明涉及一种用于通过直接氧化酯化甲基丙烯醛来制备甲基丙烯酸甲酯的方法。甲基丙烯酸甲酯大量用于制备与其他可聚合化合物的聚合物和共聚物。另外,甲基丙烯酸甲酯是用于各种基于甲基丙烯酸(MAS)的特殊酯的重要构造单元,所述特殊酯能够通过与对应的醇的酯交换来制备。由此对这种起始材料的尽可能简单经济且环保的制备方法存在很大兴趣。本发明尤其涉及对氧化酯化甲基丙烯醛的反应器出料的经优化的处理,借助于该处理能够最大程度减少工艺排出流并且能够以最优的方式再循环工艺水。此外,最优地回收并同时分离在工艺中产生的丙烯酸或将其转化为丙烯酸烷基酯的有价值材料。此外,此方法的优点是,在设备的装置设计方面需要提出的要求比现有技术中的更少。(The invention relates to a method for producing methyl methacrylate by direct oxidative esterification of methacrolein. Methyl methacrylate is used in large quantities for the preparation of polymers and copolymers with other polymerizable compounds. In addition, methyl methacrylate is an important building block for various special esters based on Methacrylic Acid (MAS), which can be prepared by transesterification with the corresponding alcohol. There is thus great interest in a process for the preparation of this starting material which is as simple, economical and environmentally friendly as possible. The invention relates in particular to an optimized treatment of the reactor output of an oxidative esterification of methacrolein, by means of which the process discharge stream can be minimized and the process water can be recycled in an optimum manner. Furthermore, the valuable materials of acrylic acid produced in the process or its conversion into alkyl acrylates are optimally recovered and simultaneously separated. Furthermore, this method has the advantage that fewer requirements need to be made in the design of the device of the apparatus than in the prior art.)

1. Process for the preparation of MMA, wherein methacrolein is prepared in reactor I in a first reaction stage and is oxidatively esterified in reactor II with an alcohol in a second reaction stage to alkyl methacrylate, characterized in that a low boiling fraction comprising mainly alcohol is taken from a mixture comprising water, the alcohol, at least one alkali metal salt, methacrylic acid and a strong acid in a distillation column IV and the alcohol is reused for the preparation of alkyl methacrylate.

2. The process according to claim 1, characterized in that methacrolein and the alcohol are removed partially from the oxidatively esterified crude alkyl methacrylate in a distillation column III, wherein a stream comprising alkyl methacrylate, water, alkali metal methacrylate and/or methacrylic acid and alcohol is obtained, a strong acid is added and separated in a phase separation and/or extraction into a light phase comprising alkyl methacrylate and methacrylic acid and a heavy phase comprising water, the alcohol, at least one alkali metal salt and methacrylic acid, which heavy phase is conducted directly or indirectly into the distillation column IV.

3. The process according to claim 1, characterized in that a mixture comprising water, the alcohol, at least one alkali metal salt, a strong acid and methacrylic acid is separated in a distillation column IV into a low-boiling fraction comprising the alcohol, a side-stream fraction comprising water and methacrylic acid and a bottom-stream fraction comprising water, the strong acid and its alkali metal salt.

4. The process according to claim 1, characterized in that the strong acid is added to the stream comprising alkyl methacrylate from distillation column III and is conducted to a phase separation, from which the organic phase is conducted to an extraction process and the aqueous phase is conducted to the distillation column IV.

5. The process according to any one of claims 2 to 4, characterized in that the stream comprising alkyl methacrylate from the distillation column III is conducted to a mixer, into which the strong acid and optionally water are transported and mixed with the stream comprising alkyl methacrylate, and subsequently the mixture is conducted to the phase separator and/or the extraction process.

6. The process according to any one of claims 2 to 4, characterized in that the strong acid is directed into the heavy phase of the extraction process directly before the distillation column IV.

7. The process according to any one of claims 2 to 4, characterized in that the alkali metal salt is sodium sulfate, the alkali metal methacrylate is sodium methacrylate, the strong acid is sulfuric acid, the alcohol is methanol, and the alkyl methacrylate is MMA.

8. Process according to any one of claims 2 to 4, characterized in that the light phase of the extraction process is conducted to at least two further distillation stages and/or crystallization processes and a fraction consisting essentially of methacrylic acid and a fraction consisting predominantly of MMA are obtained simultaneously.

9. The method according to claim 8, wherein the fraction consisting essentially of methacrylic acid is esterified with alcohol to form alkyl methacrylate.

10. Process according to any one of claims 2 to 4, characterized in that only such an amount of the strong acid is added to the respective stream after the distillation column III or during the extraction that the pH during the extraction is always greater than or equal to 3.

11. The process according to any of claims 2 to 4, characterized in that the low boilers of the distillation column III and/or of the distillation column IV are conducted into the reactor II.

12. The process according to any one of claims 2 to 4, characterized in that the low-boiling fraction of the distillation column IV comprises more than 60% by weight of alcohol and less than 20% by weight of water, the bottom fraction comprises more than 60% by weight of water and the side-stream fraction of the distillation column IV comprises more than 80% by weight of water and less than 5% by weight of alcohol.

13. Process according to any one of claims 2 to 4, characterized in that the distillation column IV has a dividing wall in the lower part, the feed to the column being introduced at the upper end of the dividing wall and being withdrawn in liquid form laterally at a point on the other side of the dividing wall where the concentration of the strong acid is less than 0.1% by weight and on the other hand the alcohol content is less than 1% by weight.

14. A process according to any one of claims 2 to 4, characterized in that the bottom stream from the distillation column IV is sent to another separation stage for the recovery of water and methacrylic acid and for the concentration of the brine containing effluent stream.

Technical Field

The invention relates to a method for producing methyl methacrylate by direct oxidative esterification of methacrolein. Methyl methacrylate is used in large quantities for the preparation of polymers and copolymers with other polymerizable compounds. In addition, methyl methacrylate is an important building block for various special esters based on Methacrylic Acid (MAS), which can be prepared by ester exchange with the corresponding alcohol. There is thus a great interest in a process for the preparation of such starting materials which is as simple, economical and environmentally friendly as possible.

The invention relates in particular to an optimized treatment of the reactor output of an oxidatively esterified methacrolein, by means of which the process discharge stream can be minimized and the process water can be recycled in an optimum manner. Furthermore, the acrylic acid produced in the process is optimally recovered and simultaneously separated or converted into valuable materials alkyl methacrylate. Furthermore, this method has the advantage that fewer requirements have to be made in terms of the device construction of the apparatus than described in the prior art.

Prior Art

Currently by means of a slave C₂、C₃Or C₄Methyl Methacrylate (MMA) is prepared in various ways starting from the building block. In one of these processes, isobutene or tert-butanol is oxidized to form methyl by the air oxygen in the gas phase under heterogeneous contactAcrolein is then oxidatively esterified with methacrolein using methanol to obtain MMA. This method developed by ASAHI is described in particular in documents US 5,969,178 and US 7,012,039. The disadvantage of this method is in particular the very high energy requirement. In a development of the process, methacrolein is obtained from propanal and formaldehyde in a first stage. Such a process is described in WO 2014/170223.

Such a process for the oxidative conversion of isobutene or tert-butanol to methacrolein and subsequent oxidative esterification to MMA is described in US 5,969,178. In the second stage, the liquid, water-reduced mixture of methacrolein and methanol is reacted with molecular oxygen and a palladium catalyst, the palladium catalyst being present in most cases as a palladium-lead catalyst on a support. In the first distillation stage, a mixture of methacrolein and methanol is separated from the crude product of the oxidative esterification below the top of the column, while the low-boiling components are removed via the top. The bottom liquid containing MMA is subsequently conducted to a second distillation stage in which the azeotropes of methanol and saturated hydrocarbons are separated via the top. The bottom liquid containing crude MMA is conveyed to further work-up, while methanol is separated from the fraction obtained via the top by means of a phase separator and a third distillation column and is conducted back to the reactor. It is to be noted here that, due to the azeotrope formed, methanol may contain relatively large amounts of water and therefore has to be conveyed to the dehydration process.

As an alternative to this method, US 5,969,178 discloses a process in only one column, wherein the inlet must be located above the bottom liquid during the process. The low boilers in the reactor output are removed from the column via the top. A mixture of crude MMA and water remains in the bottoms liquid, which is sent to further processing. Via side flow (the exact position of which must first be determined and this can be achieved by adding different sieve platesSet) and finally the mixture of methacrolein and methanol intended to be fed back into the reactor is withdrawn from the columnAnd taking out. US 5,969,178 teaches that such processes are difficult to carry out due to different azeotropes. In addition, methacrylic acid, in particular, which is always present as a by-product, plays an important role here. According to this method, although US 5,969,178 does not make explicit, it is possible to separate the methacrylic acid in such a way that it remains in the phase to be transported to the disposal process and can only be worth separating to a limited extent. However, this reduces the overall yield of methacrylic product from the process.

A slightly different treatment of the reactor output of oxidative esterification is disclosed in US 7,012,039. In this case, methacrolein is distilled off overhead in the first distillation stage via a sieve plate and the aqueous MMA-containing mixture is introduced from the bottom into a phase separator. The mixture is adjusted to a pH of about 2 in the phase separator by adding sulfuric acid. The separation of the sulphated water from the organic or oily phase is carried out by means of centrifugation. This oil phase is separated in a further distillation into the high-boiling components and the MMA-containing phase withdrawn overhead. The MMA-containing phase is then separated from the lower boiling components in a third distillation. Followed by a fourth distillation for final purification.

The problem with this process is that the sulfuric acid which has to be added in large amounts and which may act corrosively on the plant components. Accordingly, these components, such as in particular the phase separator or also the second distillation column, must be manufactured from suitable materials. In addition, US 7,012,039 also does not teach how to work up the methacrylic acid produced simultaneously or the residual methanol remaining in the product. It is to be concluded, however, that the former is simultaneously separated off in the distillation stage, whereas methanol can be obtained and returned only partly together with methacrolein, with the residue possibly being lost in the third distillation stage.

WO 2014/170223 describes a process similar to US 7,012,039. The only difference is that in the actual reaction the pH is adjusted by adding a methanolic solution of sodium hydroxide in the circulation loop. This is particularly useful for protecting the catalyst. In addition, separation of the aqueous phase in phase separation is made easier by the salt content. However, this also results in the methacrylic acid produced being present as the sodium salt and later being separated from the aqueous phase and discarded. In the variant in which sulfuric acid is added in the phase separation, the free acid is recovered, but for this purpose sodium (hydr) sulfate is produced, which may lead to further problems in disposal.

In summary, the method according to the prior art improves in the following respect (in particular in combination with one another):

as high a yield as possible

By-products occurring as methacrylic acid are obtained and separated off or returned to the oxidative esterification process

As high a degree of recycling of unreacted methanol as possible

Reducing the amount of sulfuric acid and water added

As pure a treatment stream or exhaust as possible

Object of the Invention

In view of the prior art, it was therefore an object of the present invention to provide a technically improved process for the oxidative esterification of methacrolein which does not have the disadvantages of the conventional processes.

It is an object of the present invention, inter alia, to provide an improvement in the work-up of the crude product from the oxidative esterification of methacrolein with methanol to MMA and thereby improve the overall yield of the process over the prior art.

Furthermore, it is an object to recycle as much as possible of the unreacted reactants or by-products or intermediate products formed in the process, in particular methanol, methacrolein, methacrylic acid and water, and to convert them into the desired product in the process, or optionally to isolate methacrylic acid as such.

It is also an essential object of the invention to separate or recycle methacrylic acid from the system using as small an amount of acid added as possible. Here, the local concentration and the total consumption of the acid should be kept as low as possible.

In addition, the object of the invention is to design the treatment process such that as few contact sites with strong and therefore corrosive acids as possible exist in the apparatus. Furthermore, the object is to design the entire plant with a corresponding acid protection in terms of material only to a limited extent.

In particular, it is also an object to provide a process which can be operated with as little disposal costs as possible, in particular by a lower occurrence of organic constituents and acids in the discharge stream.

In addition, the method should be inexpensive compared to the prior art, in particular with regard to the materials used in the construction of the installation.