Basic Engineering Research On The Sugar?acid Separation Of The Xylose Hydrolysate

D?Xylose,an important carbohydrate in nature,has a good efficacy of promoting the growth of intestinal bifidobacteria without producing energy in human bodys,and also has been extensively used in the fields of food,medicine industry,etc.The hydrolysate of plant fiber as a raw material via acid catalysis reaction generally contains an amount of mineral acid besides the D?xylose.The acid?base neutralization is usually used to reduce the xylose hydrolysate acidity,however such treatment will undoubtedly increase the workload of the ion exchange section and is unable to properly recycle the mineral acid.The disadvantages mentioned above can be overcomed to some extent by ion exclusion chromatography.Although the related researches on the de?acidification of xylose hydrolysate have been continuously reported,the exploration and improvement of the functional sugar separation with the preparative chromatography remains a long?term and arduous task.This paper is aimed at establishing a green and highly efficient sugar?acid separation method with ion exclusion chromatography theory to remove mineral acid from the hydrolysate.The static and the dynamic mass transfer mechanisms as well as chromatography separation technology are studied systematically,which can lay a foundation for further study on the sugar?acid separation of the xylose hydrolysate in the industrial scale.The following studies were carried out sequentially:Firstly,resins with good separation effect for separating sugar and acid in xylose hydrolysate was selected from nine resins by static adsorption experiments.During this process,the static adsorption isotherm,the static adsorption thermodynamics and the static adsorption kinetics were studied separately.Results indicated that the sugar?acid separation effect of 4 H?type resins including HD?8,D001,001×7 and LS001 performed excellent separation efficiency due to the Donnan exclusion mechanism.Freundlich type isotherm can be a very good description of D?xylose adsorption behavior,which belongs to multilayer adsorption.The positive values of ?H and negative values of ?G indicated that the adsorption of D?xylose on resins was a spontaneous and endothermic process.According to positive value of ?S,it is reasonable to draw the conclusion that freedom degrees of D?xylose increased during the adsorption process.Adsorption of D?xylose on resins were mainly affected by the liquid film diffusion and the kinetic data could be satisfactorily described by the pseudo?second order model.Secondly,the separation effect of four kinds of H?type resins including HD?8,D001,001×7 and LS001 were re?evaluated via the dynamic experiments,the effects of feed concentration,temperature,fixed bed packing height and flow rate in the sugar?acid separation process were studied,and the breakthrough characteristics of D?xylose and sulfuric acid were also investigated.Results indicated that the dynamic separation effect of the LS001 H was better than others according to satisfactory values of separation degree and the D?xylose yield.Furthermore,the separation degree and the recovery rate of D?xylose could reach to 0.83 and 96.24%(66 min)respectively with fixed bed packing height of 50 cm(diameter 2.2 cm),flow rate of 2 mL/min,and column temperature of 50 ?.Among three breakthrough models(Thomas,Yoon?Nelson and Adam?Bohart models),Thomas and Yoon?Nelson models could describe the breakthrough processes of D?xylose and sulfuric acid in the fixed?bed column well.Finally,the lumped kinetic chromatographic model was solved by gPROMS software and the simulated elution curves were verified by experimental data;meanwhile a self?built simulated moving bed was used to continuously separate sugars and sulfuric acid in the actual liquid.Results indicated that the elution profiles matched the experimental data well,which verified the applicability of the lumped kinetic chromatography model.The chromatography separation of D?xylose and sulfuric acid were carried out continuously with the simulated moving bed technology,and the recovery rates of D?xylose and sulfuric acid reached to 42.28% and 35.34%,respectively;meanwhile their separation degree was about 0.55.These results provided good theoretical guidance and technical support for design of simulated moving bed and the industrial scale?up of the chromatography column in future.