Construction Of Boronate Affinity Absorbents And Their Application In The Preparation Of Tagatose

Tagatose is a functional rare sugar with physiological functions such as weight control,intestinal flora improvement,and blood sugar control.It has a good application prospect in the field of food and medicine.In the commercial production of tagatose,it is necessary to add a large amount of chemical catalyst equal to the mole of the raw material,which downstream processing is difficult.The boronate affinity material has the property of specific and reversible covalent binding to the cis-diol structure,and can selectively bind to tagatose.Taking the advantage of it,this study designed an isomerization system for the conversion of galactose into tagatose by a boronate affinity adsorbent packed column prepared by bulk polymerization,realizing the synchronization of isomerization and purification,improving the isomerization.efficiency,inhibiting side reactions,and achieving multiple recycling of boronate affinity adsorbents.Finally,the granular boronate affinity adsorbent with mesoporous structure was synthesized by the method of inverse-phase suspension polymerization,and the preparation process of the boronate affinity adsorbent was improved.Main contents and results are as following:Firstly,an adsorbent with 3-(acrylamido)phenylboronicacid as the functional monomer and ethylene dimethacrylate as the crosslinking agent was constructed by bulk polymerization.Its physicochemical properties and adsorption-desorption behaviors in the galactose-tagatose system were studied.In the 1:1 galactose-tagatose binary solution,the adsorption capacities for tagatose and galactose were 59.35 mg/g and 3.88 mg/g,respectively.The system has good adsorption selectivity.In pH 1 HCl solution,the adsorbent can be completely desorbed within 5 min.Through a pH-controlled dissociation strategy,>85%high-purity tagatose solution can be purified from 50%pure tagatose solution.Secondly,the constructed adsorbent was applied in the process of adsorbent-assisted isomerization and simultaneous purification to prepare tagatose from galactose in the form of packed column.Using NaOH as catalysis,the optimal conditions for the isomerization of galactose to tagatose were the reaction temperature of 60℃,pH of 12.0,substrate concentration of 50 g/L and reaction time of 50 min.At this time,the yield of tagatose was 25.40%,the byproduct rate is 20.46%.With the adsorbent packed column,the optimal conditions were the reaction temperature of 70℃,pH of 12.0,boronate-sugar ratio of 1:1 and reaction time of 240 min.The yield of tagatose was 52.92%,and the byproduct rate was 15.14%.It shows that the use of adsorbent can significantly improve the yield of tagatose and inhibit the occurrence of side reactions.The adsorbent was used for 10 consecutive adsorption-desorption and 6 adsorbent-assisted isomerization cycle reactions,all of which showed good stability.Finally,the preparation process of boronate-affinity adsorbents was improved using an inverse-phase suspension polymerization method.The bulk polymerization reaction system is used as the dispersed phase,liquid paraffin is used as the continuous phase,and Span 80 and Tween 80 are used as dispersants.Factors such as monomer dosage,water-oil ratio,dispersant dosage,and stirring intensity are optimized.It was determined that the molar ratio of monomer and crosslinking agent was 1:5,the solvent was 5 mL,the water-oil ratio was 1:5,the stirring intensity was 200 r/min for 6 h,the dispersant was 1.5%Tween 80+1%Span 80,and the temperature was 60 ℃.Under the optimal conditions,the adsorption capacity of the adsorbent was 71.14 mg/g for tagatose and 27.90 mg/g for galactose.The physicochemical characterization shows that the adsorbent prepared by inverse-phase suspension polymerization has a good spherical appearance and abundant mesoporous structure.Its adsorption capacity and stability are comparable to the adsorbent prepared by bulk polymerization,indicating its ability to replace bulk polymerization.In the experiment of adsorbent assisted isomerization,the generation rate of tagatose was 54.29%,and the generation rate of byproducts was 16.19%,indicating that it has the same catalytic function as the adsorbent prepared by bulk polymerization.