Distillation Dry Goods 46 | | Case Sharing - Catalytic Distillation Hydrolysis of Methyl Acetate

Keywords

Methyl acetate; reactive distillation; hydrolysis; catalysis

Case Background

Polyvinyl alcohol (PVA) will produce a large amount of methyl acetate (MA) by-products in the production process. If an enterprise produces 33,000 tons of PVA per year, there will be 54,000 tons of MA output per year. For the utilization of MA, various PVA manufacturers currently use it to generate acetic acid and methanol through hydrolysis reaction as raw materials for the production of PVA. The traditional method of this hydrolysis process is to use a fixed bed hydrolysis process with cation exchange resin as a catalyst. The disadvantage is that the hydrolysis rate of MA is only 23% to 25%. A large amount of unhydrolyzed MA needs to be separated by rectification and then recycled for hydrolysis, resulting in huge equipment and high energy consumption. In this case, a new process of MA catalytic distillation hydrolysis is used to replace the old process of fixed bed hydrolysis, and industrial tests are carried out on the basis of the success of small-scale and pilot-scale studies to improve the hydrolysis rate, which can effectively solve the above technical problems.

Catalytic distillation technology

Catalytic distillation technology is a new chemical engineering technology that couples the catalytic reaction and distillation separation of chemical engineering. The reactant is separated from the product while the reaction is carried out, which not only increases the concentration of the reactant in the reaction zone and increases the reaction rate, but also makes the product leave the reaction zone in time and inhibits the progress of the reverse reaction. When this technology is applied to the hydrolysis process of methyl acetate, although the hydrolysis equilibrium constant of the ester is very small, the reaction product is separated in time, which is conducive to the hydrolysis reaction.

Technical Solutions

Raw materials : Methyl acetate (approx. 8% water) and process water

Catalyst : Cation exchange resin

Industrial test equipment : several sets of tower equipment, the catalyst filling method is shown in Figure 3. In addition, several sets of storage tanks, condensers, reboilers, pumps and meters are matched with the tower equipment.

Process flow :

Project implementation results

Using the above technical scheme and process flow, a laboratory test and an industrial test were carried out on the catalytic distillation hydrolysis of methyl acetate. The results of the industrial test are as follows:

1. Steam consumption: The energy saving effect of the new process reaches 27.97%. Since the steam consumption of the methyl acetate hydrolysis process accounts for most of the energy consumption of the PVA production process, it can save 90,000 tons of steam per year based on the annual output of 23,000 tons of PVA.

2. The new process more than doubles the hydrolysis rate of methyl acetate and the processing capacity of the reactive distillation column.

3. The new process can significantly reduce the amount of catalyst. Based on the annual output of 23,000 tons of PVA, 25 tons of ion exchange resin catalyst are required per year, while the new process only requires 5 tons.

Technical Highlights

• Greatly increase the one-way hydrolysis rate of methyl acetate (MA) from 23% to at least 60%;
• The catalyst loading method can provide a good vapor-liquid contact interface while playing a good catalytic role;
• The steam-liquid load of the catalytic distillation column is stable, the pressure drop of the column is small, and the service life of the catalyst package is long (more than 4 years);
• Due to the use of high-efficiency tower internals, the entire system operates stably, has a large elastic range, and saves energy;
• Different process components can be provided according to user needs.

Industrialization promotion and application

In May 2006, TPT Petrochemical Company of Thailand undertook the MAH project with a treatment capacity of 4000t/a. The project started operation successfully on December 12, 2006, producing qualified acetic acid and first-grade methanol.

☺ In 2007, this achievement was applied in the polyvinyl alcohol production unit with an annual output of 33,000 tons to 60,000 tons in Fujian textile chemical fiber group company. The hydrolysis rate of MA was increased from 23% to more than 60%, which was more than 30% energy saving than the old process.

☺ In 2007, this achievement was applied to the polyvinyl alcohol catalytic distillation transformation project of Sinopec Group Shanghai Petrochemical Company. After comparing the achievement with the technology of Swiss Sulzer Company, it was decided to use the technical achievement in this case, and it was completed in early 2008 and entered normal operation.

In 2008, it undertook the Chongqing Pengwei Petrochemical MA hydrolysis project.

In 2009, it undertook the MA hydrolysis project of Zhejiang Yisheng Petrochemical Co., Ltd.