Synthesis Of Levulinic Acid And Furfural Compounds Via The Hydrolysis Of Holocellulose

The search for green renewable resources to replace fossil energy has become a research focus as the exhaustion of fossil resources and increase in environmental pollution.Lignocellulosic biomass is a renewable carbon source and its content is second only to fossil resources on earth.Cellulose and hemicellulose are the most abundant natural carbohydrates in biomass.The conversion of cellulose and hemicellulose into high value-added compounds is believed to be an effective way to solve environmental problems and resource shortages.In this work,the synthesis of levulinic acid（LA）,5-hydroxymethylfurfural（HMF）and furfural（FUR）from holocellulose analogue composed of cellulose and hemicellulose was proposed in the presence of catalyst with acid-base double active sites.The main research contents are as follows:The synthesis of LA from holocellulose was catalyzed by sulfamic acid（NH₂SO₃H）with dual active sites.The effects of solvent type and ratio,the amount of catalyst,reaction temperature and time were investigated by single factor method.The results showed that the solvent had a significant effect on the composition and distribution of the products.LA was the main product in N,N-dimethylformamide（DMF）while furfural compounds was the main product inγ-valerolactone（γ-GVL）.The yield of LA from holocellulose reached 63.9%in DMF/H₂O（19:1,v:v）in the presence of NH₂SO₃H.Response surface analysis with four factors and three levels was used according to Box-Benhnken center combination experiment on the basis of single factor method.The maximum yield of LA at 64.3%was obtained,which was close to that of the factor method.Liquid chromatography-high resolution mass spectrometry（LC-HRMS）was used to qualitatively analyze the reaction products of the holocellulose analogue in DMF/H₂O.And a possible reaction mechanism for the synthesis of LA from holocellulose was proposed.The hydrolysis of holocellulose analogue to produce HMF and FUR was catalyzed by NH₂SO₃H with dual active sites inγ-GVL/H₂O.The effects of catalyst amount,solvent ratio,reaction temperature and reaction time were investigated.The results showed that NH₂SO₃H displayed efficienet performance for the coproduction of HMF and FUR from holocellulose analogue composed of cellulose and hemicellulose.The yields of HMF and FUR at 37.2%and 62.0%were obtained inγ-GVL/H₂O（25:1,v:v）.LC-HRMS was used to qualitatively analyze the reaction products derived from the holocellulose analogue inγ-GVL/H₂O.Based on this,a possible mechanism for the coproduction of HMF and FUR from holocellulose was proposed.H₂N-Ui O-66-SO₃H with acid-base double active sites was synthesized by the reaction of zirconium oxychloride,terephthalic acid and monosodium2-sulfoterephthalate using one-step hydrothermal method.H₂N-Ui O-66-SO₃H was characterized by infrared spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,EDS analysis,thermogravimetry,elemental analysis and N₂adsorption-desorption.The catalytic performance of H₂N-Ui O-66-SO₃H for the hydrolysis of holocellulose to HMF and FUR was further investigated.The effects of catalyst type,the amounts of acid/base groups and catalyst,reaction time and temperature and substrate on the conversion process were also investigated.The yield of HMF and FUR reached 39.1%and 28.2%under the optimized conditions with 0.75 molar ratio of-SO₃H to-NH₂at 190 ^oC for 6 h in the mixture ofγ-GVL/H₂O.The cyclic catalytic performance of the catalyst was also studied.The results showed that H₂N-Ui O-66-SO₃H had good catalytic stability,both the yields of HMF and FUR decreased slightly after 1 cycle.The former changed from 39.1%to 37.5%,and the latter from 28.2%to 27.4%,respectively.