Research On Hydrolysis Of Cellulose With Strong Adsorption Boron-Containing Carbon-Based Solid Acid

Cellulose,as a abundant and renewable resource,can be hydrolyzed into platform compound—glucose,a series of important chemicals.Carbon-based solid acid?CSA?exhibits good activity in cellulose hydrolysis.It has advantages of high acid density,good stability,easy separation from products,non-corrosiveness to reaction equipment,which make CSAs have great application potential and development prospect.Previous studies have shown that phenolic–OH as an adsorption group can increase the accessibility of catalyst to cellulose,break the intramolecular and intermolecular hydrogen bonds of cellulose,and ultimately increase the hydrolysis activity of cellulose.Our group has doped Cl and S into CSAs,and achieved good hydrolysis activity.The doping of Cl and S improve the adsorption capacity of CSAs and promote cellulose hydrolysis in varying degrees.Therefore,we try to dope boron with lower electronegativity than carbon into CSA to further improve the adsorption capacity.In this paper,two kinds of inorganic substances?borax and boric acid?with low cost and high boron content were co-carbonized with cellulose,and then sulfonated to prepare CSAs,which were applied to cellulose hydrolysis.The structure and element content of boron-containing CSAs were analyzed by BET,XRD,FT-IR,XPS and methylenimine-H spectrophotometry.The effects of carbonization temperature and doping ratio on the structure of CSAs were investigated,and the effects of boron doping on adsorption capacity and hydrolysis activity were also discussed.It was found that the CSAs prepared by doping cellulose with borax have a small amount of boron,up to 0.0027 mmol/g,this small amount of doping has a great impact on CSAs.Borax doping is beneficial to the formation of–SO₃H and–COOH,but has little effect on phenolic–OH.Compared with cellulose-based CSA,the adsorption capacity and reducing sugar yield of CSA by borax doping increased 189.29%and 32.68%,respectively.The aromaticity of CSAs increases,the boron content and–SO₃H density increases first and then decreases,–COOH and phenolic–OH both decrease,the adsorption capacity and reducing sugar yield increase first and then decrease with the increase of carbonization temperature.When carbonization temperature is 425^°C and doping proportion is 1:1,the CSA has the highest–SO₃H density,adsorption capacity and reducing sugar yield.The boron content of CSA prepared from boric acid mixed with cellulose is up to 0.023 mmol/g,which is about 10 times higher than that of borax-doped CSAs.The doping of boric acid significantly increased the specific surface area and pore volume?806.53 m²/g and 0.494 cm³/g?,compared with cellulose-based CSA and borax-doped CSAs.In addition,the total acid density?especially–SO₃H and–COOH?,adsorption capacity and reducing sugar yield of CSAs by doping boric acid were increased 55.08%,225.45%and 39.62%,respectively.The–SO₃H density and adsorption capacity of boric acid-doped CSA are 48.49%and 224.20%higher than those of borax-doped CSA,respectively.With the increase of carbonization temperature,the specific surface area and pore volume of CSAs first increased and then decreased,the boron content and adsorption capacity gradually increased,the acid density gradually decreased,and the reducing sugar yields first increased and then decreased,up to 82.75%at 500^°C.The high reducing sugar yield is mainly attributed to the strong adsorption capacity caused by boron doping.Furthermore,a chemisorption besides hydrogen bond adsorption was proposed,and the strong adsorption obviously promoted the hydrolysis of cellulose.