Membrane filtration process for producing food-grade xylooligosaccharide by taking viscose fiber pressing alkali liquor as raw material

The invention provides a membrane filtration process for producing food-grade xylooligosaccharide by taking viscose fiber pressing alkali liquor as a raw material. The membrane filtration process particularly comprises the following process steps of: A, membrane concentration: firstly pre-filtering pressed liquor produced through a viscose fiber to remove large-granular impurities, circularly concentrating permeating liquid for 2-4 times through a nanofiltration membrane, and introducing a last-time concentrated solution into a diffusion dialysis cation exchange membrane stack to obtain a concentrated solution, namely a concentrated solution of the pressed liquor, in the processes of circularly concentrating for 2-4 times through the nanofiltration membrane, feed liquid is diluted by adding water and then enters the nanofiltration membrane before being filtered every time; B, hemicellulose extraction: neutralizing the concentration solution of the pressing alkali liquor by adding acid to obtain hemicellulose liquid; C, enzymolysis: adding a complex enzyme to the hemicellulose liquid for carrying out enzymolysis reaction to obtain enzymolysis liquid; D, purification: filtering the enzymolysis liquid through a ceramic membrane, introducing the permeating liquid into the nanofiltration membrane for desalination, decoloring the obtained concentration solution through active carbon, carrying out resin-ion exchange to obtain purifying liquid of xylooligosaccharide, and evaporating and drying to obtain the food-grade xylooligosaccharide.