Carbonylation Of Methanol To Acetic Acid Using Ionic Liquids As Promoting Catalysis

Acetic acid is an important chemical, which can derive a variety of derivativeproducts, such as cellulose acetate, vinyl acetate, terephthalic acid, acetic anhydride,polyvinyl alcohol, chloacetic acid, metal acetate and acetic acid ester. In organicsynthesis, pharmaceuticals, pesticides, printing, dyeing, textile, food, paint, adhesivesand other industrial sectors, acetic acid is used primarily as a raw material. So thedevelopment of acetic acid is closely related to the development of the nationaleconomy. Due to the production status of acetic acid, many countries have paid muchattention on it: economy, green technology research and development are in theascendant.Since Monsanto discovered carbonylation of methanol to acetic acid underrelatively mild conditions （30-60bar pressure and150–200°C）.Due to its obviousadvantages, the Monsanto process has been replaced of other process to acetic acid. Andit has been the basis of most new acetic acid manufacturing capacity. But this processgenerally places a limit on separation of product and catalysis,reuse of the catalyst,higher corrosion rates and so on.Ionic liquid as a new kind of green solvent has been taken great interest by moreand more researchers. ILs have small vapor process, a wide liquid temperature range,large windows of electrochemistry, noncombustible,nonvolatility, adjustability ofchemical physical properties. So they have been described as potential environmentallybeing replacements for volatile organic solvents in a variety of catalysis reactions.In order to explore ionic liquid as an efficient promoting medium for synthesis ofacetic acid by carbonylation of methanol, the major research contents are as follows:Part one. The catalysis of iridium complexes using various ionic liquid asco-catalysis is systematically researched in the reaction of carbonylation of methanol toacetic acid. The presence of ionic liquid containing Cl^-、BF₄^-、OAc^-、I^-anions causedpartial deactivation of the iridium catalyst. The best promoter1-butyl-3-methylimidazoliumbis （trifluoromethanesulfonyl） imide （[BMIM]Tf2N） andN-butylpyridinium bis（trifluoromethanesulfonyl） imide（[BPy] Tf₂N）, which have betterperformance on promoting catalysis for carbonylation methanol has been found.Part two. The influence of reaction pressure, temperature, time, concentration ofcatalyst, amount of CH₃I and amount of ionic liquid were evaluated. While the concentration of iridium was1500ppm, the optimum operating conditions as follow hasbeen obtained: reaction pressure of3MPa, reaction temperature of160°C, reaction timeof2h, Molar of CH₃I of0.064mol, mass of ionic liquid was25%of the whole mass ofthe reaction system. Under this reaction conditions, the conversion of methanol couldachieve100%and the selectivity of HAc could excess98%.Part three. This catalytic system can be reusable for at least four times with slightloss of activity and selectivity of HAc. This gradual decrease in the activities could bedue to the loss of the catalyst during handling and transferring the reaction mixture.Part four. On the base of ionic liquid promoting carbonylation of methanol asdescribed previously, some transition metal salts were used as promoters catalyzedmethanol carbonylation. Fe, Cr and Mn chloride precluded this reaction and notablydecreased the reaction rates of methanol carbonylation. However, Co, Cu, Ru and Znincreased the the reaction rates from9.42mol/L·h to18.70mol/L·h.Part five. The mechanism of carbonylation of methanol has also been discussed. Incomparison with FT-IR and1H NMR spectra of Pure ionic liquids and Ir-ionic liquids,no strong or new peaks appeared. It suggested that there were no strong interactionsbetween the ionic liquids and the iridium complex. We hypothesize that ionic liquidscan increase the solubility of the intermediates and transition states, increase the activitypoint of catalyst, resulting in an increase in the selectivity of the carbonylation.However, the role of ionic liquids in metal complex catalyzed reaction needs to befurther clarified.