Recovery Of L-arabinose From Xylose Mother Liquor

L-arabinose,a health sugar with a promising application prospect,has a fancy physiological function.Xylose mother liquor,come from the process of D-xylose production,is rich in L-arabinose,while it is sold as byproduct at a low price. Therefor,the separation of L-arabinose from xylose mother liquor has positive social, economical and environmental benefits.Components of xylose mother liquor were analyzed by means of HPLC.Xylose mother liquor consisted chiefly of D-xylose,L-arabinose,D-glucose and D-galactose. The proportion of D-xylose was the highest,followed by L-arabinose.The proportion of D-galactose was the lowest.So D-xylose and L-arabinose were set as the key components.However,D-xylose and L-arabinose are isomers,so their structures are similar,which makes the separation difficult.This paper used the method of chromatography to solve this problem.The typical separation media for separation of sugar alcohols were sulfonated cross-linked styrene divinylbenzene cation exchange resins.This paper systematically studied the influences of ion-exchange resin type,counter-ions fixed on the resin,the degree of cross-linking of the polymer matrix and resin size on the adsorption behavior and separation effect between these two key substances.At the concentration ranges of 0～100g/L,D-xylose and L-arabinose were linearly adsorbed on ion exchangers with a low adsorption quantity.For a same resin,the capacity of the adsorbents in respect to L-arabinose was larger;a lower degree of cross-linking and K-form resin adsorbed more than others;the macroreticular resin adsorbed more sugar than the gel resin.For example,at 25℃,the equilibrium concentration of 80g/L,the adsorption quantity of L-arabinose was 65.92 g/kg on the resin of 001^*6 Ca²⁺,while that of D-xylose was 50.00 g/kg.The adsorption quantities of L-arabinose were 198.80g/kg on the resin of 001^*2 Ca²⁺ and 79.28g/kg on the resin of 001^*6K⁺, both were higher than that on the resin of 001^*6 Ca²⁺.As for the separation effects, Dowex 50 WX4 Ca²⁺,a middle degree(4%),Ca-form and fine gel resin performed better,the resolution of D-xylose and L-arabinose reached 1.0.The influences of operating conditions(velocity of flow,temperature,feed concentration and sample volume) on the fixed bed separation effects were studied here.The result indicated that in the studied range,the resolution decreased as the velocity of flow increased;the optimum temperature was between 50℃and 60℃; feed concentration and sample volumes had little influence on the separation effects.With resin of Dowex 50 WX4 Ca²⁺ as the padding and deionized water as the mobile phase,simulated moving bed(SMB) was used to separate the key components. The effects of flow rate in sectionâ…¡(â…¢),operating temperature,feed flow rate and feed concentration on the operating performance parameters:purity,recovery, productivity and eluent consumption were studied.At the experimental ranges,as flow rate in sectionâ…¡(â…¢) increased,the purity of L-arabinose and eluent consumption increased,and the recovery,productivity of L-arabinose decreased;the operating temperature influenced little on the separation performance,the suitable operating temperature ranges were 50～70℃;the increase of the feed flow rate caused the decrease of recovery and eluent consumption,the increase of purity and productivity;the feed concentration influenced little on the purity and recovery of L-arabinose,the productivity increased and the eluent consumption decreased with the increase of feed concentration.The results of simulation with the software of the instrument and the results of the experimentation fit well.Under the simulative conditions,we separated the xylose mother liquor containing D-xylose of 13.95g/L,L-arabinose of 7.74g/L,D-glucose of 5.32g/L and D-galactose of 3.22g/L in two steps.Firstly,most of D-xylose was separated from the mixed liquor,then D-glucose was separated from L-arabinose.The purity of L-arabinose reached 91.38%.The recovery was 94.02%.The productivity was 0.984 g/(h·L).And the eluent consumption was 2.792(L/g).