Conversion Of Carbohydrates Catalyzed By Biochar Or Dots And Chromium Assemblies

With the increasing consumption of fossil resources,people pay more and more attention to the use of renewable resources to replace traditional fossil resources.Lignocellulose is the most abundant renewable resource on the world,which can be hydrolyzed and converted into high value-added chemicals and liquid fuels,so it has gradually attracted attention.At the same time,using biomass-lignocellulose as a raw material to prepare carbon-based solid acid to catalyze this hydrolysis conversion reaction process,and can realize multiple utilization of renewable resources.However,this type of carbon-based solid acid is a dense layered non-porous structure which is formed by polymerized aromatic hydrocarbons through the hydrogen bonding with strong edge polar functional groups,and there are still poor acid sites in the process of catalyzing the hydrolysis and conversion of cellulose.The catalytic active sites are difficult to access,and the catalytic activity is not high enough,with low 5-hydroxymethyl furfural(HMF)yield.In view of this,this paper aimed to comprehensively solve these shortcomings of BCSA,and develop the preparation of biomass carbon-based solid acid(BCSA)through carbonization and sulfonation as the raw material of agricultural and forestry waste bamboo powder.New biochar-based catalysts such as carbon sulfonic acid points,biochar-metal assemblies,and biochar-metal complexes were adopted by nitrogen adsorption and desorption(BET),Fourier infrared spectroscopy(FT-IR),transmission electron microscopy(TEM).thermogravimetric analysis(TGA)and other characterization methods to study its structure and physicochemical properties,as well as the catalytic activity factors and laws in the hydrolysis and conversion of carbohydrates.The main content of the paper is as follows:1.A layered densely packed non-porous BCSA was prepared using bamboo powder as raw material,through thermal carbonization and concentrated H₂SO₄ sulfonation.The catalyst BCSA and cellulose were added to the mixed solvent DMSO and H₂O,and the BCSA was stripped by solvothermal and in-situ synthesis of biochar sulfonic acid sites(SCQD),finally realized the high-efficiency catalytic hydrolysis and conversion of cellulose.The DLS and TEM characterization results showed that SCQD had a relatively uniform particle distribution with an average particle size of about 2.4 nm.The catalytic system had the characteristics of pseudo-homogeneous catalysis,which effectively improved the accessibility and mass transfer efficiency of BCSA active sites.Studies had shown that as the solvent ratio was DMSO:H₂O=7:3,the reaction temperature was 170?,the catalytic performance was the best in the cellulose hydrolysis reaction(cellulose:0.4 g,catalyst:0.05 g).Under optimized conditions,the yield of reducing sugar and HMF could reach 64.7%and 28.2%respectively.Compared with the traditional BCSA that catalyzes cellulose hydrolysis under heterogeneous conditions,the catalytic activity was significantly improved.2.In order to improve the activity of BCSA for catalyzing the conversion of carbohydrates to HMF,on the basis of the above research,a series of steps such as stripping of bamboo charcoal into SCQD by alkaline hydrothermal method,acidification,metal particle assembly,etc.were carried out to prepare B acid and L acid dual-function recombinant biochar dot-metal assembly SCQD-Cr catalyst.And BET,TGA,XRD,TEM,SEM,HAADF-TEM-EDS and other characterization methods were studied to reseach its morphology,structure and physicochemical properties.We investigated the preparation conditions of catalyst to explore its one-step conversion of carbohydrates to HMF catalysis active.The results showed that the catalyst SCQD-Cr-2 had abundant micro mesoporous channels,a higher specific surface area(about 201 m²·g^-1)and a higher decomposition temperature of sulfonic acid groups(more than 400?).The metal chromium ion content(21.5%)was high and evenly distributed.Under optimized conditions(glucose:0.2 g,catalyst:0.025 g,solvents:MIBK:Ch Cl saturated solution=8:2,and the reaction temperature:160?,reaction time:3 h),the conversion of glucose to HMF in one step could be catalyzed with a yield of 85.1%.Under optimized conditions(cellulose:0.2 g,catalyst:0.05 g,solvents:MIBK:Ch Cl saturated solution=8:2,reaction temperature:170 ^oC,reaction time:3 h),the yield of reducing sugar and HMF were obtained25.6%and 47.4%respectively along with the high HMF selectivity(64.9%)in cellulose hydrolysis.In addition,the catalytic activity of the catalyst was still keep good after being recycled four times.3.Using bamboo powder as raw material,through thermal carbonization and concentrated H₂SO₄ sulfonation,a layered densely packed non-porous BCSA was prepared,and the BCSA was placed in a certain amount of Cr(NO₃)₃·9H₂O solution for mixed and cooled.After acidification and washing to neutrality,the bifunctional biochar-metal complex BCSA-Cr catalyst that alone with L acid and B acid was obtained.And through BET,TGA,FT-IR,XRD,TEM,SEM,HAADF-TEM-EDS and other characterization methods,its morphology,structure and physicochemical properties were investigated.The catalyst preparation conditions were explored by evaluating the catalytic activity of carbohydrates to HMF in one step.The results showed that the catalyst BCSA-Cr-4 had abundant micro mesoporous channels and a higher specific surface area(about 48 m²·g^-1),a higher decomposition temperature of sulfonic acid groups(more than 425?).The metal chromium ion content(11.5%)was relatively high and uniformly distributed.In the catalytic cellulose hydrolysis reaction,the addition of the surfactant could significantly improve its catalytic activity and the yield of the HMF.Studies had shown that 87.5%HMF yield was obtained in the conversion of glucose under optimal conditions(glucose:0.2 g,catalyst:0.05 g,the mixed solvents(MIBK:Ch Cl saturated solution):8:2,temperature:160 ^oC,the time:2 h).Bedsides,under optimal conditions(cellulose:0.2 g,catalyst:0.1 g,MIBK:SDS solution(0.15 M):6:4,temperature:170 ^oC,time:3 h,the yield of reducing sugars and HMF be up to 31.2%and 62.8%respectively.The catalyst still has high catalytic activity after being recycled five times.