High-efficent Lignocellulose Pretreatment And Cellulase Recovery

The pretreatment and saccharification processes both are the bottlenecks oflignocellulose bio-refining. We designed and examined an efficient combinedpretreatment method to reduce lignocellulose resistance and to enhance the hydrolysisefficiency, and explored a simple and efficient cellulase recovery strategy to reducethe cellulase loading and process cost. The major research conclusions are listed asfollows.(1) Combined pretreatment technology: FeCl3-Ethanol pretreatment was usedto treat corncobs. The effect of different pretreatment conditions, such as theconcentration of FeCl3and ethanol, pretreatment temperature and time, to thechemical compositions and physical structures were investigated through scanningelectron microscope (SEM), X-ray diffraction (XRD) and Fourier infrared spectrum(FTIR). The results suggested that the increase of the concentration of FeCl3andethanol could boost the degradation of hemicellulose and delignification, respectively.The superior conditions: the concentration of FeCl3is0.2mol/L, the concentration ofethanol is60%(v/v),120oC and60min. The hydrolysis yield of pretreatmentcorncobs that pretreated under these optimized conditions at solid concentration of10%was91.6%.(2) The mechanism of combined pretreatment method: The effects ofdifferent kinds of strong acid weak base salt, the concentration and pH onpretreatment and hydrolysis of corncobs were extensively investigated. And we foundthat the solution of FeCl3shows significantly acidic as a strong acid weak base salt. Itpromoted the degradation of hemicellulose when the pH reached a certain degree (pH<2.5).The metal ions could be absorbed by the pyran ring of carbohydrate to formcomplex, which may trigger the degradation of carbohydrates and delignification. Ifthe solution's acidity was weak, the influence of acid radical ion would be higher. Wecould adjust the pH using the acid which composed by the same acid radical ion tointensify the pretreatment. After hydrolyzed at20%(w/v) for110h, the cellulaseloading was30FPU/g glucan, the final concentration of glucose reached80.1g/L.(3) pH-triggered cellulase recovery: We investigated the effects of different pH and temperature to the adsorption-desorption behavior of cellulase, and developed apromising way to recover most of both free and bound cellulases by pH-triggeredadsorption-desorption. Furthermore, the results show that acidic pH (e.g., pH4.8) wasfound to favor adsorption, whereas alkaline pH (e.g., pH10) and low temperature (4–37°C) favored desorption. The adsorption of cellulases reached an equilibriumwithin60min at pH4.8and25°C, leading to approximately50%of the addedcellulases bound to the substrate. By adjusting the pH of eluent (citrate buffer,25°C)from4.8to10, we were able to increase the desorption efficiency of bound cellulasesfrom15%to85%. To recover cellulases after enzymatic hydrolysis, we employedadsorption by fresh substrate and desorption by pH adjustment to recover the freecellulases in supernatant and the bound cellulases in residue, respectively. Therecycling performance (based on the glucose yield) of this simple strategy could reachnear80%.