The present invention relates to a method for separating sorbitol, and in particular to a method for separating the product of the in-situ hydrogenation reaction of glucose.
Background technology:
Sorbitol is a very important fine chemical with broad application prospects. It can be used to synthesize vitamin C, nutritional sweeteners, resin plastics, etc. Esters of sorbitol and its derivatives can be used in the pharmaceutical industry as important intermediates and additives. In addition, chemical reforming of sorbitol can produce hydrogen, low-carbon olefins, biogasoline, etc., and dehydration of sorbitol can also produce higher-value isosorbide.
At present, sorbitol is mainly obtained through catalytic hydrogenation of glucose. Common catalysts include Raney nickel alloy catalysts, amorphous alloy catalysts, Ru/C catalysts and some supported non-noble metal catalysts (such as nickel-based catalysts ), such as U.S. Patent U.S. 5543379, which uses Raney nickel catalyst to hydrogenate glucose and adds an appropriate amount of CaO and other additives. At a reaction temperature of 125-150°C and a hydrogen pressure of 5-7MPa, sorbitol can be obtained, but the reaction There are also many by-products in the product. Chinese invention patent CN1120829C discloses a nickel-P-B amorphous catalyst, which can better hydrogenate and convert glucose at a reaction temperature of 90-150°C and a hydrogen pressure of 0.5-2.5MPa, with a glucose conversion rate of 90%. , the sorbitol selectivity reaches about 90%. For supported catalysts, glucose hydrogenation can also be achieved in the presence of high-pressure hydrogen. For example, Romero et al. (Applied Catalysis A: General, 2017, 529: 49–59) reported a supported RuNi/MCM- 48 catalyst is used for glucose hydrogenation. When the reaction temperature is 120-140°C and the hydrogen pressure is 2.5MPa, the glucose conversion rate reaches a maximum of about 95%, and the maximum sorbitol yield reaches 60%. However, for these glucose hydrogenation reactions that require high-pressure hydrogen, most of the reaction products are accompanied by many by-products. It is difficult to select and generate the glucose hydrogenation product sorbitol. At the same time, the catalyst is subjected to high-pressure gas flow and hydrothermal heat during the reaction process. The environment causes problems such as structural instability of the catalyst itself, making it very difficult to separate the glucose hydrogenation product sorbitol. There have been reports on the separation process of sorbitol. For example, Chinese invention patents CN109305882 and CN108863721 can separate sorbitol through crystallization and ion exchange. However, the process is relatively complicated and is greatly affected by the state of the product during the reaction. In order to alleviate the impact of high-pressure hydrogen on the reaction, Chinese invention patent CN109400441 discloses a method for mildly hydrogenating glucose to produce sorbitol. It utilizes in-situ low-temperature hydrogenation of sodium borohydride without the need for additional high-pressure hydrogen. The glucose can be better However, the reaction products are in a state where many species exist, such as sodium metaborate, unreacted glucose and sorbitol, the by-products of sodium borohydride and water to produce hydrogen. How to effectively separate and purify them? This is an important issue, and it also affects the actual production and large-scale application of sorbitol.