Study On Catalytic Dehydration Of Lactic Acid And Methyl Lactate To Acrylic Acid And Methyl Acrylate

Dehydration of lactate for acrylate production is an important promising industrial process. Comparing with current industrial production process of acrylates with proplene oxidation, the new process attracts wide attentions because it will use renewable biomass as raw material for lactate fermentation, which is high in carbon atom utilization ratio and will reduce the dependence on the petroleum chemicals. In this thesis, the production of acrylates is evaluated with lactic acid or methyl lactate as raw material, and the zeolites or mixed sulfates are applied as catalyst. After careful design and properties improvement of catalysts, optimization of reaction conditions and reaction kinetics, the conversion of lactate and the yield of acrylate are increased remarkablly.Zeolites catalysts were used in the dehydration reaction for its good catalytic performance. Among various zeolites we prepared, a modified NaY molecular catalyst, the 20%CuO-2%KNaY catalyst, obtained by ion exchanging and oxide blending was selected for evaluation in a fix-bed reactor. With the mixture of methyl lactate and methanol as the starting material and nitrogen as the carrier gas, a combined molar yield and selectivity of acrylic acid and methyl acrylate over the above catalyst was 55% and 62.9% at 275℃with a liquid volume space velocity (LHSV) of 0.3 h^-1. The catalyst characterization indicated that methyl lactate dehydration over the modified NaY catalyst was mainly catalyzed by the weak acid sites of Lewis acid, and the adsorption of reactants and products in the meso and micro pores of modified NaY zeolites resulted in catalyst deactivation.A complex sulfate catalyst was also developed for lactate dehydration for acrylate production. The species and quantities of sulfate and phosphate promoters added to calcium sulfate were optimized. The best mass ratio of components in the catalyst was: CaSO₄: CuSO₄: Na₂HPO₄: KH₂PO₄=150.0:8.8:2.5:1.2. With 60wt% methyl lactate solution as starting material and nitrogen as carrier gas, the combined molar yield of acrylic acid and methyl acrylate reached to 63.9% at 400℃with a LHSV of 0.29 h^-1. Over the same catalyst, with 26wt% lactic acid solution as starting material and carbon dioxide as carrier gas, a acrylic acid yield of 63.7% was gained at 360℃ with the LHSV of 0.29 h^-1. By characterizing the catalyst before and after reaction, the results indicated that the dehydration reactions over the sulfate catalyst were mainly catalyzed by Lewis-acid sites and the deactivation could be owned to the formation of coke on the catalyst surface from low molecular weight lactic acid polymers at high temperature.Based on the investigation of reaction processes, we also suggested a kinetic model of methyl lactate dehydration over sulfate catalyst. The model simulation was in good agreement with the experimental data.