Preparation Of Phenylborate Acid-based Adsorbent And Its Application In The Preparation Of Lactulose

Lactulose is a functional lactose derivative,which has many functional properties such as low calorie,prebiotics,treatment of constipation and hepatic encephalopathy,and has a wide range of applications in the fields of health food and clinical medicine.The existing commercial lactulose is prepared by chemical isomerization of lactose in a high temperature and strong alkaline environment.The addition of soluble borate can effectively increase the yield of lactulose,but the removals of boric acid and by-products are very complicated,which not only causes environmental pollution,but also has potential safety hazards,limiting the further development of chemical isomerization.Based on the reversible covalent interaction between the phenylboronic acid group and the compound containing the cis-dihydroxy structure,this study prepared a phenylboronic acid polymer adsorbent with high adsorption specificity for lactulose,large adsorption capacity,and renewable recycling.And then established two auxiliary lactose chemical isomerization modes,aiming to optimize the traditional chemical isomerization method of lactose and realize the green and efficient production of lactulose.Firstly,the adsorbent is prepared by dispersion polymerization.Acetonitrile（ACN）is used as the continuous phase,3-acrylamidophenylboronic acid（AAPBA）as the functional monomer,ethylene glycol dimethacrylate（EGDMA）as the crosslinker monomer and polyvinyl-pyrrolidone（PVP）as the dispersant.In this paper,the monomer dosage,the type of continuous phase and the synthesis temperature in the synthesis formula were optimized.The optimal polymerization conditions were determined to be the molar ratio of AAPBA to EGDMA of 1:2,the monomer concentration of 13.64 g/L,and the synthesis temperature of55^oC.Further analysis of the physicochemical properties of the phenylboronic acid-based polymer,surface morphology,pore structure,Fourier transform infrared（FTIR）and X-ray photoelectron spectroscopy（XPS）measurements show that the carbon-carbon double bond（C=C）of AAPBA and EGDMA was successfully polymerized,and the average pore diameter of the adsorbent was 13.57nm,which was rich in mesopores and micropores.The adsorption experiment showed that at pH 11.0,the adsorption capacity of the polymer carrier for lactulose reached 112.02 mg/g,while the adsorption capacity for lactose was only 6.35 mg/g,indicating that the polymer carrier has good adsorption selectivity.The adsorption behavior of the adsorbent to lactose and lactulose conforms to the quasi-first-order kinetic model and the quasi-second-order kinetic model,respectively,indicating the difference in binding affinity of the adsorbent to the two sugar molecules.There is a stronger chemical covalent bond between the adsorbent and lactulose.The lactulose adsorbed on the polymer carrier can be quickly（<15 min）and almost completely desorbed in the desorption solution of pH=1.0（desorption rate is 98.73%）.Operational stability experiments show that the regeneration efficiency of the adsorbent is still above 85%after ten batches of alkali adsorption-acid desorption cycles.Subsequently,the reaction conditions of the traditional chemical isomerization method were optimized.The optimal isomerization conditions were Na₂HPO₄+Na OH as the basic catalyst,the isomerization pH was 11.0,the isomerization temperature was 50^oC,and the lactose concentration was 50 g/L.The phenylboronic acid-based adsorbent was applied to the chemical isomerization of lactose by adopting two modes:batch-assisted and synchronous-assisted respectively.Under the above optimal conditions,the isomerization reaction occurred for 250 minutes.The conversion rates of lactose obtained by traditional chemical isomerization,batch adsorption-assisted isomerization and synchronous adsorption-assisted isomerization were 69.04%,89.37%and 79.20%,respectively.The lactulose production rate was 16.70%,51.60%and 50.92%,respectively.The yields of by-products were 54.46%,38.34%and 25.88%,respectively.The addition of phenylboronic acid adsorbent increased the yield of lactulose by 34.90%and greatly reduced the yield of by-products.In addition,the phenylboronic acid-based adsorbent can be separated from the isomerization system by simple filtration.Both the filtrate and the desorbed and regenerated adsorbent can be reused.The desorbed lactulose solution has high purity,and the procedure for obtaining high-purity lactulose syrup downstream is simple.Phenylboronic acid-based adsorbent assisted chemical isomerization of lactose is a green and clean lactulose production model with application potential.