Production Engineering Research Of The Chemical Alcohol Made Of Straws

Ethylene glycol and propylene glycol are important chemicals.At present,ethylene glycol and propylene glycol are mainly produced from petroleum in industry.With the depletion of petroleum resources,this method has been more and more limited.With social progress and economic development of China,the contradiction of energy shortage has become increasingly prominent.Compared with traditional petroleum technology,using renewable biomass as raw materials to produce ethylene glycol and propylene glycol has broad prospects for development.Corn straw is the main by-product of agricultural cultivation and a renewable biomass raw material.The components of straw are cellulose,hemicellulose and lignin.Hemicellulose and lignin are covalently linked to form a network structure.Crystalline cellulose is embedded in it.Cellulose is a polymer of glucose.Glucose can be obtained by enzymatic hydrolysis of cellulose.When glucose is further processed,products such as ethylene glycol and propylene glycol can be produced.The enzymatic hydrolysis of cellulose can only be carried out by pretreatment of straw and destruction of the original network structure of straw.Sodium carbonate is one of the most common pretreatment methods for straw.In this paper,besides sodium carbonate method,a biological solvent method is also introduced.In the range of 140 ~190℃,a set of comparative experiments of sodium carbonate method and bio-based solvent method were carried out at every 10℃elevation.Comparing the results of enzymatic hydrolysis after pretreatment with two methods,it was found that the yield of glucose in straw sugar mixture reached 85.56%after pretreatment with bio-based solvent at 180℃.It was concluded that the pretreatment of straw with Dacheng’s self-produced bio-based solvent at 180 C was better than that with sodium carbonate method.After enzymatic hydrolysis of straw cellulose,straw sugar mixture was formed.The mixture contains glucose,xylose and trace polysaccharides.These sugars can be hydrogenated to produce ethylene glycol,propylene glycol,1,2-butanediol and other polyols under the action of catalysts.However,in addition to glucose and xylose,the mixture also contains impurities such as protein,organic acid and metal ions.These impurities reduce the activity of the catalyst.Therefore,before hydrocracking,straw sugar should be purified to remove harmful impurities.For the process of straw sugar purification,the author first used activated carbon,tubular membrane,ceramic membrane and nanofiltration membrane to purify straw sugar mixture.The decolorization and protein removal effects of each experiment were studied,and the nanofiltration membrane M8-11 was determined as the optimal initial refining scheme.After that,the author screened different ion exchange resins,and finally decided touse decolorization resin(LS-808B)-cation exchange resin(C150S)-anion exchange resin(A103S and A500S)-mixed bed(LS resin)process.This process can effectively remove protein,pigment,metal ions and other impurities in straw sugar solution,so that straw sugar solution can meet the requirements of catalytic cracking.The refined straw sugar was hydrocracked at different temperatures,pressures and feed concentrations.Through comparative experiments,the optimum hydrocracking conditions were determined as follows: the temperature is 230℃,the decompression pressure is 10 MPa,the feed concentration is 55%.Under these conditions,the conversion of glucose was the highest.The product after pyrolysis is a mixture of polyols.The main components of the mixture are propylene glycol,ethylene glycol and1,2-butanediol.Finally,the following experiments were carried out: the first step was to distill the mixture of pyrolyzed polyols at 180 C and-98 KPa to remove glycerol,sorbitol and lactate.In the second step,2,3-butanediol was removed from the deweighted polyol mixture by distillation at-90 KPa and 120 ℃.In the third step,propylene glycol,ethylene glycol and 1,2-butanediol were separated by distillation using azeotropic solvent;in the fourth step,high purity(over 99%)propylene glycol and ethylene glycol products were prepared by vacuum distillation.