Study On The Lignin Removal From Prehydrolysis Liquor Of Kraft Based Dissolving Pulp

Holistic using lignocellulose is an alternative approach to face the scarcely of fossil resource and environmental pollution.The kraft-based dissolving pulp process fits well into the biorefinery concept by separating hemicellulose,lignin and cellulose into different streams.However,the valuable utilization of hemicellulose,mainly dissolved in pre-hydrolysis liquor(PHL)was not realized due to the lignin present.Therefore,the Laccase treatment of PHL was carried out in this thesis,followed as adjusting the pH of PHL for lignin removal.Finally,the treatments of PAC,PEO,PAC/PEO,chitosan and lime on PHL were optimated,and coordinated-laccase treatment removal the lignin of PHL.First,laccase treatment method was selected to removal lignin from PHL.The UV and IC were employed to analyze the concentration of lignin and sugar.The results showed lignin removal of 43.69%was achieved under condition of laccase dosage of 2 U/mL,2 h,pH 3.0 and 40~oC.The concentration of xylose and total sugar was 44.05 g/L and 60.49 g/L,respectively,and the xylose and sugar loss was 4.38%and 6.22%after laccase treatmetn.Second,PHL was treated by adjusting pH values.Results showed that the removal of lignin increased at first and then decreased with the increase of pH values.Lignin removal reached the maximum of 26.59%while adjusting the pH of PHL to 10.The contents of sugars kept stable at first and then declined sharply when the pH was above 10.The contents of polysaccharide and monosaccharide were dropped to 30.74 g/L and 22.51 g/L,which declined 11.87%and 10.35%,respectively,compared to the original PHL at pH of 10.Lignin removal of 49.02%was obtained when combined pH adjustment and laccase treatment,which yield sugars,monosaccharide and polysaccharide were dropped to 51.24g/L,21.44g/L and 29.80 g/L,which was decrease of 15.29%,14.62%and 14.56%respectively.Finally,PHL was treated by PEO,PAC,PEO/PAC,chitosan and lime,as well as those combined with laccase treatment.Results showed that the lignin removed 32.5%when the PEO dosage was 400 ppm,and the lignin removed18.8%when the PAC dosage was 400 ppm.When the dosage of PEO and PAC were all 200 ppm during the synergistic treatment of PEO/PAC,the lignin removed22.4%.After optimization,PEO,PAC and PEO/PAC were used to treat the pre-hydrolysate with laccase respectively.The results showed that the removal rate of lignin was 68.7%,48.0%and 54.3%,respectively.The sugars loss was 9.01%,6.99%and 8.43%,respectively.The chitosan and lime were used to treat the PHL assisted with laccase respectively.The lignin removal reached the maximum of 52.65%,while the sugars decreased 19.76%during chitosan assisted laccase treatment.The lignin removal reached the maximum of 63.53%,while the sugars drcreased 23.94%during lime assisted laccase treatment.