Synthesis Of Temperature-responsive Betaine Compounds And Their Application In Cellulase Recovery

The cellulose and hemicellulose in lignocellulose such as crop straws can be converted into sugar compounds by the pretreatment and enzymatic hydrolysis technologies,then biofuels and other chemicals can be obtained from sugar compounds by biological or chemical methods.However,there is still a technical bottleneck problem of low enzymatic hydrolysis efficiency and high cost of enzymatic hydrolysis.A Upper Critical Solution Temperature(UCST)type betaine compounds were added to the lignocellulosic enzymatic hydrolysis system(p H 5.0,50°C),and the enzymatic lignin was removed by filtering or centrifugation after the enzymatic hydrolysis.Then the enzymatic hydrolysate system was reduced to room temperature,and cellulase was recovered by utilizing its temperature response performance.The recovered cellulase was directly added to a new round of enzymatic hydrolysis system to realize recycling cellulase.Firstly,in order to reduce the energy consumption of cellulase recovery process and improve the temperature of cellulase recovery,octadecyl sulfobetaine with the longer hydrophobic carbon chain was used to recover cellulase at room temperature;secondly,in order to further shorten the time of cellulase recovery and reduce the amount of additives,sulfobetaine polymer(PSPE)with different molecular weights were synthesized to recover cellulase at room temperature by utilizing their temperature response performances;finally,in order to make full use of the strong interaction between lignin and cellulase to further improve the cellulase recovery performance,UCST-responsive lignin zwitterionic surfactants,including lignin-grafted sulfobetaine and lignin-grafted phosphobetaine,were synthesized by grafting betaine fragments on the enzymatic lignin,and cellulase was efficiently recovered at room temperature by their utilizing response performances.The main research results were as follows:(1)The UCST response temperature of hexadecyl sulfobetaine was relatively low,and cellulase could be effectively recovered only when the system was reduced to 0°C.It was found that the UCST response temperature of betaine was improved by increasing of hydrophobic carbon chain and improved the hydrophobicity,and the UCST of octadecyl sulfobetaine was 25°C.One times of amount of octadecyl sulfobetaine(the mass ratio to cellulase)was added to the enzymatic hydrolysis system of corncob residue.After the enzymatic hydrolysis,50%of cellulase was recovered after 12 h of precipitation by reducing the system to 25°C.The effects of factors such as p H value,ionic strength,adsorption temperature and urea on the adsorption of cellulase on octadecyl sulfobetaine film were investigated by using the dissipative microcrystalline quartz balance(QCM-D),revealing that octadecyl sulfobetaine and cellulase co-precipitated mainly through the hydrophobic interaction.(2)In order to shorten the time of cellulase recovery and reduce the amount of additives,PSPE with different molecular weight was synthesized by using the aqueous free radical polymerization method,employing N,N-dimethyl(methacryloy-loxyethyl)ammonium as monomer.It was found that the hydrophobicity of PSPE was significantly improved by increasing its molecular weight,so the amount of additives was effectively reduced under the same cellulase recovery rate,and the cellulase recovery time was shortened from 12 h to 3 h.Only 0.4 times amount of PSPE-3(M_w=355.1 k Da)was added to the enzymatic hydrolysis system of corncob residue.After the enzymatic hydrolysis,50%of cellulase was recovered after 3 h of precipitation by reducing the system to 25°C.The effects of factors such as p H value,ionic strength,molecular weight,adsorption temperature and urea on the adsorption of cellulase on octadecyl sulfobetaine film were investigated,revealing that PSPE and cellulase co-precipitated mainly through the hydrophobic interaction.(3)In order to further improve the cellulase recovery performance and make full use of the electrostatic,hydrogen bonding and hydrophobic interaction between lignin and cellulase,and p H response performance of lignin,lignin-grafted sulfobetaine with UCST-response was synthesized by grafting sulfobetaine fragments on the enzymatic lignin.It was found that LSB could efficiently recover cellulase at room temperature by utilizing its sensitive UCST and p H response performances.3.0 g/L lignin-grafted sulfobetaine was added to the enzymatic hydrolysis system of corncob residue(p H 5.0,50°C).After the enzymatic hydrolysis,70%of cellulase was recovered by adjusting the p H value of the system to 4.0 and cooling to 25°C,which was significantly higher than octadecyl sulfobetaine and PSPE.(4)Lignin-grafted phosphobetaine(LPB)were synthesized by grafting phosphatebetaine fragment onto the enzymatic hydrolysis lignin.It was found that LPB not only had sensitive p H response and UCST response,but also significantly improved the enzymatic hydrolysis efficency of lignocellulose.Moreover,with the increase of grafting rate,LPB more significantly enhanced the enzymatic hydrolysis of lignocellulose.The effect of LPB on the adsorption of cellulase on lignin film was studied by using electrophoresis test.It was found that LPB significantly reduced the no-productive adsorption of cellulase on lignin.At the same time,the UCST and p H response of LPB can be used to recover cellulase at room temperature.3.0 g/L LPB was added to the enzymatic hydrolysis system of corncob residue,the hydrolysis efficiency was increased from 69.6%to 85.0%.After the enzymatic hydrolysis,50%of cellulase was recovered by adjusting the p H value of the system to 4.0 and cooling to25°C.By increasing the hydrophobic carbon chain of sulfobetaine,the UCST response temperature of sulfobetaine was improved,and cellulase was recovered at room temperature by adding octadecyl sulfobetaine;The binding force between additives and cellulase was improved by synthesizing sulfobetaine polymer with high molecular weight,resulted in the shorted recovery time and the reduced dosage of additives;lignin-grafted sulfobetaine and lignin-grafted phosphobetaine were synthesized,the recovery of cellulase was further improved and the enzymatic hydrolysis of lignocellulose was enhanced by making use of the strong interaction between lignin and cellulase and the p H response performance.By recycling cellulase,the cost of enzymatic hydrolysis was effectively reduced,and the industrialization process of lignocellulose biorefinery was promoted.