Гидролиз целлюлозы с использованием газовоздушных смесей хлористого водорода

Abstract

Abstract. Microcrystalline cellulose (MCC) is a common product used in pharmaceutical, food and other industries. MCC is obtained by liquid-phase hydrolysis of cotton or wood bleached pulp with diluted 0.5–10.0 % mineral acids at a temperature of 100–140 °C. This process requires significant consumption of acid, water, and heat energy. Production of MCC in general is very expensive, which determines its high cost and the need to find alternative methods of cellulose hydrolysis. It is proposed to hydrolyze cellulose with concentrated hydrochloric acid produced by absorption of hydrogen chloride. We studied the processes of hydrogen chloride adsorption by bleached wood pulp with 8–18 % humidity. It is shown that adsorption of hydrogen chloride is determined by pulp humidity and is 3–5 % of the dry pulp mass. The sorption of hydrogen chloride leads to the formation of hydrochloric acid with a concentration of 25–40 % in the raw material moisture, significant heating of the mass and rapid hydrolysis of the amorphous cellulose fraction. It has been found that the use of pure hydrogen chloride for saturation causes strong darkening and humification of pulp. We recommend the use of hydrogen chloride gas-air mixtures to saturate the pulp, which will significantly reduce the sorption temperature and eliminate the strong darkening of the pulp during hydrolysis. The adsorption of hydrogen chloride by cellulose proceeds at an extremely high rate and is accompanied by the formation of a clearly visible sorption front at a temperature of 45–60 °C. Hydrolysis occurs for 15–30 min at 40–60 °C until the amorphous cellulose fraction is completely decomposed. A very small amount of monosaccharides is formed (4 % of dry pulp). The yield of MCC is high, more than 95 %. These circumstances are probably related to the recrystallization of a part of the amorphous fragments of cellulose macromolecules, which is a characteristic of hydrolysis with concentrated acids. The product obtained by cellulose hydrolysis is identical to MCC according to the data of IR spectroscopy, X-ray diffraction and viscometry. The article shows the high efficiency of cellulose hydrolysis with hydrogen chloride gas-air mixtures compared to traditional methods of MCC production.