Study On Catalyst System For The Production Of Acetic Acid By Methanol Carbonylation

Under appropriate catalyst, methanol can directly carbonylate to acetic acid, which compared with synthetic routes of oil, regardless of the source of raw material or the economic benefits, is obviously superior than the route of oil. Among the catalysts, iridium catalyst due to its mild reaction condition, high aetivity and high selectivity have been studied extensively. It had been succeeded in achieving industrialization.Iridium catalyst system with methyl iodide as the cocatalyst, can greatly improve the catalytic reaction rate, but the loss of catalyst caused some environmental pollution, and it is not conducive to industrial production and application. In this paper, iridium catalyst system was selected, using autoclave to carbonylation test and the proeess parameters were investigated(such as temperature, pressure, reaction time, catalyst concentration). ionic liquid containing iodine was synthesized to solve the problem of the loss of catalyst, and the effect of ionic liquid on the catalytic reaction was studied. The major research contents are as follows:(1) Using precious metals iridium as the main catalyst, we also add methyl iodide as catalyst promoter. Catalyst appearance of dark brown solid, iridium content: 400～300 ppm(wt.), methyl iodide: 5¹0%(wt.). The catalyst system has high catalytic activity.(2) An analysis method for the methanol carbonylation is explored through experiments. with thermal conductivity detector(TCD),Φ3 mm×2 m stainless steel packed column(stationary phase: Porapak-Q, 80 100 mesh), the products were analyzed qualitatively by retention time comparison with standard material, and separation are greater than 1.5; the products were analyzed quantitatively by peak area normalization method, and the quality correction factor of each components was determined: water——0.1927, methanol——0.3604, acetone——1.0000, methyl acetate——0.8175, acetic acid——1.4512.(3) Under the reaetion temperature 190℃, the pressure 3.5 MPa, the residence time 300 min, raw material composition (mole ratio) H₂O:CH₃OH:CH₃COOH:CH₃COOCH₃=11:159:12:3 methyl iodide 7.9%(wt.), Catalyst 800 ppm(wt.).carbonylation product by methanol, conversion rate of methanol 99.85%, seleetive of acetic acid is 67.26%.(4) 1-Butyl-3-methylimidazolium iodide ionic liquid (IL-I) was synthesized by the reaction of 1-methylimidazole (MLD) and n-Butyl iodide (BI) through microwave enhanced.The optimum conditions were as follows:microware power of 160W, microwave enhanced time of 30 min, the mole ratio of 1-methylimidazole to n-Butyl iodide of 1:1.09, the yield was 96.66%. The structure of the ionic liquid was characterized by UV and IR. The ionic liquid is hydrophilic, which is similar to [Bmim][BF4].(5) Ionic liquid of different type has some effects on the selectivity of the product in the carbonylation reaction. When cationic group of the ionic liquid is the same, anionic group of halogen type has favorable effect on improving the selectivity of acetic acid, while some other larger anionic group has the opposite effect.(6) Through the experiments, it is obtained that 1-Butyl-3-methylimidazolium iodide ionic liquid could enhance the selectivity of acetic acid and reduce the selectivity of methyl acetate under lower pressure in the range of 1.0 MPa and 2.0 MPa, so it is advisable to utilize ionic liquid to improve the selectivity of acetic acid under lower pressure. At the same time, ionic liquid of this kind could stabilize the catalyst to some degree and make it possible that catalyst used in the catalytic reaction could be recycled.