Preparation Of P H-responsive Lignin-based Magnetic Particles And Its Application In Cellulase Recovery

In the process of conversion of lignocellulose to ethanol,due to the disadvantages of cellulase such as low production efficiency and high production cost,the large-scale application of the process have been limited.Reducing the cost of cellulase is the key for solving the problem.The application of magnetic particles in the immobilization cellulase provides excellent means for the recovery of cellulase.However,the traditional technological process of immobilizing cellulase by magnetic particles aims to combine the enzyme with the carrier as immobilized enzyme,resulting in decreased enzyme activity and low enzymatic hydrolysis efficiency during the hydrolysis.Therefore,in order to raise the activity of immobilized enzyme,the preparation of new magnetic carrier is the key of cellulase immobilized through molecular design and structural construction.In this paper,sodium lignosulfonate is quaternized and made responsive to p H.Then the p H-responsive lignin can modify the surface of magnetic particles to improve the high aggregation tendency by introducing active functional groups.Under acidic conditions,the surface charges of the particles can be adjusted to achieve the combination of cellulase with the particles through electrostatic attraction and hydrophobic interaction.Also,the cellulase can be desorbed from the particles under alkaline conditions through electrostatic repulsion.Thereby,the enzymatic hydrolysis efficiency of the desorbed enzyme can be improved.The specific results are as follows:First,sodium lignosulfonate?LS?was modified by quaternization to synthesize p H-responsive lignin?LSQA-x?.Based on the analysis of zeta potential,elemental analysis and the force interaction between LSQA-x and Fe₃O₄ in different solution environments,the 80%quaternization-degree lignin?LSQA-80?with an isoelectric point of p H 4.8 was selected to prepare p H-responsive lignin-based magnetic particles?Fe₃O₄/LSQA-80?through chemical co-precipitation.By using FT-IR,XPS,VSM,TEM and other methods,the morphology,structure and magnetisms of the particles were characterized.It was shown that at p H 4.8,the adhesion between LSQA-80 and Fe₃O₄ molecules occurred mainly due to the electrostatic attraction.At p H 6.8,there were interaction forces such as complexation,hydrogen bonding,and electric double layer interaction between Fe₃O₄and LSQA-80.Finally,Fe₃O₄were coated with LSQA-80 on its surface through co-precipitation.The results were shown that Fe₃O₄/LSQA-80 had good p H responsiveness and magnetic responsiveness.Also,the crystal structure of Fe₃O₄/LSQA-80 was inverse-spinel type.Finally,the effects of sample mass ratio,immobilization time,and temperature on the immobilization rate of cellulase were investigated.The effect of solution p H on the desorption ratio,the enzyme activity and hydrolysis efficiency were investigated.The immobilization-desorption behavior of cellulase on Fe₃O₄/LSQA-80 particles was explored by FT-IR,CD characterization methods.It was determined that at p H 4.8,the cellulase immobilization rate was 55.52%under the optimized conditions with a time of 30min,40°C and the mass ratio of2:3.When the p H was adjusted to 6.8,the desorption rate of the immobilized cellulase is 68.27%.After five immobilization-desorption cycles,the relative retention rate of the enzyme activity was about 80%,and the enzymatic hydrolysis efficiency was about 40%as the original.The adsorption and desorption on the particles did not affect the structure of cellulase.By fitting with the adsorption kinetic and adsorption isotherm equation,it was found that the cellulase adsorption process could be described as pseudo-second-order model and Freundlich model.This study not only provided a new idea for the recovery of cellulase,but also further revealed the binding mechanism between lignin and inorganic oxides,broadening the large-scale application of industrial lignin and increasing its extra value.