Concentration of xylose reaction liquor by nanofiltration for the production of xylitol sugar alcohol

Xylitol, a five-carbon sugar alcohol, is used commercially as a natural sweetener in several food products including soft drinks and confectionery. Xylitol is produced by catalytic dehydrogenation of xylose, an intermediate sugar compound, which is extracted from sugar cane bagasse, corncobs or rice husk. The reaction liquor of xylose contains 1.5-2% of d-xylose besides water as the major constituent. The current process of evaporation for concentration of xylose reaction liquor can be effectively replaced by the more economical nanofiltration technique. Pilot-scale nanofiltration experiments were carried out using a polyamide (PA) spiral membrane module having 300 molecular weight cut-off and 1 m2 effective area. At a feed pressure of 20 bar, xylose was concentrated from 2 to 10% at a reasonably high average flux of 24 l/m2 h and rejection of >99% which indicated negligible losses of the sugar in the permeate. Effect of fouling on membrane performance and life span as well as influence of operating parameters such as feed flow rate and trans-membrane pressure was evaluated. An economic comparison between nanofiltration and evaporation is presented for a feed capacity of 1000 kg of the solution.