The current status and progress of vinyl acetate technology

Vinyl acetate is widely used in the production of polyvinyl acetate, polyvinyl alcohol, paints, slurries, adhesives, vinylon, films, vinyl copolymer resins, acetal resins, and the like.

At present, there are two kinds of vinyl acetate production processes: ethylene and acetylene. Among them, the ethylene process occupies a dominant position due to its good processability and economy. In the United States in the 1970s, the conversion of acetylene to ethylene was completed. The acetylene method includes both liquid-phase and gas-phase methods. The liquid phase method has been eliminated. The gas phase method uses desulfurization, dephosphorization of calcium carbide, acetylene, and acetic acid as raw materials. The catalyst is zinc acetate-activated carbon, and added with cesium carbonate promoter. The reaction temperature is 170-200° C. and the pressure is normal pressure. Acetylene process has been gradually replaced by ethylene because of the high cost of raw materials, but it still occupies an important position in China.

Ethylene-based ethylene gas-phase process catalysts are mainly Pd-An, Pd-Pt and Pd-Cd supported catalysts, mainly silica gel and alumina. The two main factors affecting the catalyst are the coordination ability of Pd and the ability of acetic acid or acetate to oxidize Pd. Vinyl acetate produced by ethylene and acetylene has a vinyl acetate content of more than 99.5% and contains slightly different impurities. Acetylene vinyl acetate in the aldehyde content is much higher than the ethylene method, although the absolute content of these aldehydes is not much, but have a greater impact on the polymerization reaction. Therefore, for the production of vinyl acetate as the final product of vinyl acetate, ethylene quality is better than the acetylene method.

Although the ethylene production of vinyl acetate has been greatly improved in technology compared to the acetylene process, and the ethylene catalyst has been continuously improved, the selectivity and yield have been continuously improved. However, due to the insurmountable disadvantages of using fixed bed technology, scientists Later, a new method of fluidized bed vinyl acetate was developed.

In 1998, foreign companies announced the new process of ethylene-based fluidized-bed vapor-phase vinyl acetate. The new fluidized bed reactor system and catalyst are used in this process to reduce equipment investment costs. The product yield is 99% for acetic acid and 92% to 94% for ethylene, which is significantly higher than that of fixed bed technology.

Compared with the fixed bed process, the advantage of adopting a fluidized bed process to produce vinyl acetate is that the catalyst is continuously and uniformly mixed in the reactor, which can significantly improve the uniform addition of the co-catalyst and keep the concentration of the co-catalyst unchanged; the operation of the fluidized bed. The deactivated catalyst can be continuously removed and the new catalyst replaced; the fluidized bed is operated in an isothermal environment, minimizing the deactivation of the catalyst due to overheating. Foreign companies try to use acetic acid as the sole raw material for the production of vinyl acetate. During the three-step liquid phase reaction, acetic acid is first cracked to form ketene, ketene is hydrogenated to acetaldehyde, and acetaldehyde is reacted with the added ketene to generate acetic acid. Ethylene. It is said that the yield of vinyl acetate monomer obtained by this method is as high as 95%.

Production of vinyl acetate in China began in the 1960s. Beijing Organic Chemicals Plant first introduced the acetylene fluidized bed technology from Japan. Later, Shanghai Petrochemical Plant and Sichuan Vinylon Plant successively introduced ethylene and natural gas acetylene plants. China currently has 17 sets of vinyl acetate production facilities with an annual production capacity of nearly 800,000 tons. It is expected that the demand for vinyl acetate in China in 2005 and 2010 will be 840,000 tons and 1 million tons respectively.

China's vinyl acetate production has made many significant advances based on the introduction of technology digestion and absorption. The CT series of catalysts jointly developed by the Shanghai Petrochemical Research Institute and the Shanghai Petrochemical Plant has been used in the introduction of devices and has increased the production capacity of the devices by 10%. At present, the Shanghai Science and Technology Development Corporation of Shanghai Petrochemical Co., Ltd. is conducting a single-tube test of CTV-III vinyl acetate catalyst. In addition, the acetylene catalyst has been replaced with coconut coal as the raw material for the activated carbon carrier as a raw material, and has been industrially applied.