Process Intensification And Application Of Extractive Distillation

In this article, process intensification and application of extractive distillation was studied. The process intensification was carried out on the following two ways: solvent screening and flowsheet modification.(1) It has been proved that mixed solvent system exhibited some advantages over single solvent in extractive distillation, but no principles or screening policy for selection of mixed solvent were established. According to the green chemistry 12 principles, solvent used in extractive distillation must be of environmental friendship. In this article, screening principle and policy for selection of mixed solvent were established on the basis of green chemistry principles. The first step was: establishing two potential solvent group: group U1 was of high selectivity and low solvency. Group U2 was of low selectivity and high solvency. The second step is: selecting one solvent apiece from each group to make up of a mixed solvent system; screening the mixed solvent according to selectivity, boiling point and solvency. A solvent system of methyl ethyl ketone(MEK) and N-formylmorpholine(NFM) for separation of butanes and butylenes was selected according to the above principle and policy and its feasibility was tested by vapor and liquid equilibrium experiments.(2) In this article, process conditions and some industrialization related problems of extractive distillation of butanes and butylenes using MEK/NFM as mixed solvent were studied. Several industrial scale equipments have been established and put into production. The total scale was up to 180,000 t/a.(3) As for the process of butylene hydration, the per pass conversion is very low (about 6~7%)。A great deal of butylene is recycled in the hydration section to enhance the total conversion. To deal with the accumulation of inert substances, some tail gas must be let out. Butylene concentration in hydration tail gas is about 89%, which is much more than that of feed concentration of butylene concentrage section. But, in the hydration tail gas there are some components such as sec-butanol, tert-butyl alcohol, butadiene and C5 components. So, it is not feasible to lead hydration tail gas directly into the butylene concentrage section. Otherwise,the extractive distillation solvent could be contaminated by these impurities and also accumulation of C5 in butylene would occur. In this article, a method for disposing of these impurities was proposed and studied. Concentrations of impurities in the clean tail gas were: sec-butanol and tert-butyl alcohol less than 1mg/kg, butadiene and C5 less than 20 mg/kg. The clean tail gas could be leaded into butylene concentrage section. Butylene components in tail...