Conversion Of Biomass Into Furfural And 5-Hydroxymethylfurfural Using Carbon-based Solid Acids

Furfural and 5-hydroxymethylfurfural(HMF)derived from renewable biomass can synthesize a wide variety of value-added chemicals and biofuels;by virtue of the above,both furfural and HMF have been listed as the top platform compounds in biorefinery processes by the US Department of Energy.However,the current production of furfural and HMF has problems of low production efficiency and low cost-effective,and the reaction mechanisms of furfural and HMF preparation are not very clear.Carbon-based solid acids have relatively strong Bronsted acid sites,and it are easy to realize volume production with relatively low cost;if carbon-based solid acids could efficiently produce furfural and HMF,then it will have a huge positive impact on the high-value utilization of biomass resources.Therefore,this study mainly focused on the preparation of carbon-based solid acid and its catalytic activities for producing furfural and HMF from biomass and its derivates.First,sucrose-derived disorded mesoporous carbon(C-CCA)was successfully sulfonated(SC-CCA)by NaNO2/HCl-assisted sulfanilic acid sulfonation,and the catalytic activities of SC-CCA for the conversion of xylose and corn stover to furfural were investigated.Then the sulfonation method was improved,isoamyl nitrite was used to assist the sulfonation of C-CCA(using sulfanilic acid,and the obtained carbon solid acid was named as ISC-CCA),the catalytic performance of ISC-CCA in the corn stover-furfural conversion was obviously better than SC-CCA.Based on the above study,it was found that the acidic sites in the pores of multi-mesopore carbon-based solid acid could not be fully utilized,therefore,the p-hydroxybenzenesulfonic acid(PHSA)-formaldehyde resin solid acid SPFR was prepared in this study;the catalytic reactivity of SPFR in furfural production was much higher than that of SC-CCA and ISC-CCA.In view of the high catalytic activity of SPFR in furfural preparation,a modified SPFR(MSPFR)was also synthesized and used to catalyze fructose and glucose-HMF conversion;the MSPFR could effectively catalyze the dehydration of fructose,but the conversion efficiency on glucose-HMF is relatively poor.A further modification of SPFR by introducing Al3+ was implemented(Al-SPFR);compared with MSPFR,the reactivity of Al-SPFR for glucose-HMF conversion significantly increased,but the space for improvement is still huge;to further improve the HMF yield,p-toluenesulfonic acid-polyformaldehyde resin solid acid(PTSA-POM)was used together with Lewis acid catalyst Sn-P,Bronsted/Lewis acids synergistic catalysis significantly improved glucose-HMF conversion efficiency.The main conclusions of this study are as follows:(I)An equal mass of sucrose was first loaded onto y-Al2O3 by impregnation;and then,the SC-CCA was obtained through calcinations,acid washing,and sulfonation with sulfanilic acid(using NaNO2/HCl as the diazotization agent);SC-CCA showed a good activity for the production of furfural,and the furfural yields obtained from xylose and corn stover were 76.5%and 60.0%,respectively;in addition,The recyclability of SC-CCA for the reaction of xylose dehydration was good.(2)In order to investigate the effect of carbonaceous supports with different pore structures on the preparation of sulfontaed carbon solid acids,C-CCA,ordered mesoporous carbon CMK-3,glucose-based hydrothermal carbon and activated carbon were chosen as carbonaceous supports,sulfanilic acid and isoamyl nitrite were respectively used as sulfonating and diazotization agent;it was found that carbonaceous supports with high specific surface area,multi-mesoporous and large-scale polycyclic aromatic carbon structure could be successfully sulfonated through covalent attachment of benzenesulfonic acid groups;ISC-CCA with the highest sulfonic acid group content exhibited the optimal reactivity for furfural production,and the yield of furfural obtained from xylose and corn stover were 74.4%and 70.2%,respectively;Compared to SC-CCA,ISC-CCA had significantly higher sulfonic acid group content.(3)Using chitosan that dissolved in an acetic acid solution as a template,by virtue of its activity of absorbing p-hydroxybenzenesulfonic acid(PHSA)and cross-linking with formaldehyde,PHSA-formaldehyde resin solid acid(SPFR)was synthesized.The sulfonic acid groups in SPFR makes it has a relatively high catalytic activity for the reaction of furfural production,and the furfural yield obtained from corn stover was up to 50.3%;besides GVL,using 1,4-dioxane and tetrahydrofuran as the solvents could also achieve relatively high furfural yield;the recyclability of SPFR for xylose dehydration was good,but due to the complex composition of corn stover and its lignin-cellulose-xylan three-dimensional network structure,the recyclability of SPFR for corn stover decomposition was far worse than the dehydration of xylose.(4)The MSPFR was prepared by adjusting the order of drying and washing in the SPFR synthesis process;the characterization analysis showed that both the adjustment of the post-treatment steps of the resin acid synthesis and changing the dosage of PHSA had great influence on the micromorphology and structure and acid properties of the obtained catalyst;MSPFR-0.38(using 3.1 g PHSA hydrate)was far superior to MSPFR-0.26(using 2.1 g PHSA hydrate);MSPFR-0.38 could effectively catalyze the dehydration of fructose,the HMF yield was as high as 82.6%,and the recyclability of MSPFR-0.38 for fructose dehydration was fairly good;Although MSPFR-0.38 almost did not have Lewis acidity,the HMF yield of 33.0%was still obtained from glucose.(5)Al-SPFR was prepared by introducing AlCl3·6H2O into the process of SPFR synthesis.The characterization analysis showed that the specific surface area,pore volume,sulfonic acid group content and amount of strong acid sites of Al-SPFR were significantly better than SPFR and MSPFR.The chelation effect between Al3+ion and the amino group and hydroxyl group of chitosan partially limited the function of chitosan as a template,which may be the main cause for above phenomenon;Al-SPFR showed higher activity for the production of HMF from glucose than MSPFR-0.38,and the optimal HMF yield was up to 47.4%;In a five-cycle experiment,the decreasing trends of HMF yields were similar to the loss trends of sulfonic acid group,which may indicate that the loss of strong acid sites was the main reason for partial deactivation of reused Al-SPFR.(6)PTSA-POM and zeolite molecular sieve Sn-β that prepared by seeding method were used together to catalyze glucose-HMF conversion,and it was found that the Br(?)nsted-Lewis acid synergy of PTSA-POM/Sn-β could efficiently convert glucose to HMF,and a fairly high yield of 60.1%was achieved;using PTSA-POM/Sn-β as the catalyst,the concentration of water in GVL/H2O mixed-solvent had an important influence on glucose-HMF conversion,neither low nor high concentrations of H2O in GVL/H2O could obtain a desired HMF yield;the excessive addition of Sn-β resulted in the decrease of HMF yield,indicating that the Lewis acidic site in Sn-P could also promote the occurrence of polymerization side reactions;the stable structure of cellulose that formed through β-1,4 glycosidic bonds and hydrogen bonds caused the difficulties that associated with the depolymerization of cellulose into glucose,thereby resulting the low HMF yields.