Research On Cellulosic Ethanol Production From Oil Palm Residues

At present, the development and utilization of renewable energy has become the important measures of the world countries to safeguard energy security, strengthen environmental protection and cope with climate change. In recent years, more and more countries have developed biomass energy as an important strategic measure to replace fossil energy, and the use of lignocellulosic raw materials to produce fuel ethanol is one of the most important measures. The production of cellulosic ethanol mainly includes three steps:the pretreatment of the raw materials, the hydrolysis of cellulose and ethanol fermentation. In this paper, palm residues as raw material were researched and analysed by dilute alkali pretreatment, enzymatic hydrolysis, fermentation process. The optimum conditions were determined for cellulosic ethanol from oil palm residues.The effects of the pretreatment of alkali, alkali/H2O2on the composition and enzymatic hydrolysis of palm residues were studied. Through researching the factors of pretreatment time, temperature, sodium hydroxide mass fraction and solid to liquid ratio, the appropriate pretreatment conditions were determined as follows:sodium hydroxide mass fraction of1%, solid to liquid ratio of1:10, at40℃for24h, and then subjected to121℃for30min. The solid samples under the pretreatment concentration were hydrolyzed with5%substrate concentration, and the conversion of glucan and xylan reached84.44%and89.28%respectively, while the conversion of glucan and xylan of the untrated EFB was22.07%and18.39%respectively. The solid samples were observed with scanning electron microscopy (SEM) to analyse the structure changes. The results showed that the surface structure of untrated EFB was tight and well-orgnized, while the surface structure of the solid samples after pretreated by NaOH was rough and porous and increased the valid adsorption site of cellulose, which explained why the effect of enzymatic hydrolysis after NaOH pretreatment was better.The effects of enzyme dosage, temperature, substrate concentration and other factors on the enzymatic hydrolysis of the pretreated solid samples were investigated. The results showed that when the pretreated EFB was hydrolyzed for72h with5%substrate concentration and30FPU/g dry mass (DM) enzyme loading at45℃, the conversion of glucan and xylan was maximum, which reached84.44%and89.28%respectively; when the pretreated EFB was hydrolyzed for72h with25%substrate concentration and30FPU/g dry mass (DM) enzyme loading at45℃, the concentration of glucose and xylose was maximum, which reached47.44g/L and31.43g/L respectively. Adding mixed enzyme, the glucose concentration increased furthest by23.03%and the xylose concentration increased furthest by16.86%. The effects of temperature, inoculum size, substrate concentration and other factors on ethanol simultaneous saccharification and fermentation of the pretreated EFB were investigated. The results showed that when the substrate concentration was5%with the inoculum size of5%at35℃, the ethanol yield was maximum, which reached79.09%of ethanol theory yield; when the substrate concentration was25%with the inoculum size of5%at35℃, the ethanol concentration was35.25g/L, which was maximum. The simultaneous saccharification and fermentation (SSF) was compared with the separated hydrolysis fermentation (SHF), and the ethanol concentration after72h fermentation was almost the same. The SSF process was relatively simple and practical.The composition of the pretreatment liquid was determined and analyzed, and the liquid could be accessed to the fermentation medium as seed culture, which realized the full utilization of the waste and biomass and reduced the pollution to the ecological environment.