关键词: 植物油抽提溶剂, N-甲基吡咯烷酮, 结焦, 保护气体

Abstract: In order to solve the problem existing in the N-methyl pyrrolidone (NMP) extractive distillation system, such as reducing processing capacity, blocking of reboiler inlet tube, unstable operation and product quality, investigation on NMP extractant was carried out. It was found that compared with fresh NMP extractant the properties of used NMP extractant were changed including boiling range, pH value, color and some black coke-like deposits were formed. Tests of heating NMP extractant under air and pure nitrogen were carried out respectively, and the results showed that keeping NMP extractant away from air was a good way to prevent its degradation. Therefore, an air leak into the vacuum operation system during unit shutdown was the main cause for the changing of NMP extractant. Field application was conducted using natural gas as a protective gas to prevent NMP extractant contact with air during unit shutdown, since then the processing capacity of the unit increased almost 50% and the product quality was stable, which indicated that this anti-coking technology, i.e. using natural gas as a protective gas during unit shutdown, is feasible.

Key words: Solvent for vegetable oils extraction, N-methyl pyrrolidone, Coking, Protective gas