Sequential Dilute Acid/Alkali Pretreatment Of Corncobs For Bioethanol Production

With the continuous advancement of human civilization and the rapid development of global economy,the consumption of energy has been increased in recent years.Compared with fossil energy,bioethnaol produced by lignocellulosic biomass has the advantages of abundance,renewability,and environmental friendliness,thus has been proposed as a promising alternative to fossil energy for sustainable economic development.In this paper,the processes of ethanol production,including pretreatment,enzymatic hydrolysis and ethanol fermentation of corn cob were systematically investigated.The condition of each process was optimized to increase the conversion rate of sugar and ethanol.The results were summarized as follows:?1?A two-step pretreatment using sequential dilute acid/alkali was applied to improve the hydrolysis of corncobs.First,88.6%of the hemicellulose was selectively removed by dilute sulfuric acid hydrolysis under the optimal pretreatment condition of 120?C,60 min,1:10 solid to liquid and 1%H₂SO₄ solution and the content of cellulose in the pretreated material increased from 40.6%to 63.5%.Then,sodium hydroxide?temperature 60°C,treatment time 2 h,sodium hydroxide loading 0.075 g/g,the ratio of solid to liquid 1:10?used in the second step can effectively extract over 88%of the lignin.The two-step pretreated biomass consisted of 74.4%glucan,which corresponds to a 94.5%recovery.The sequential dilute acid/alkali pretreatment of corncobs was effective in removing hemicellulose and lignin in mild process condition and producing cellulose-enriched material.Meanwhile,it can minimize byproducts produced by acid pretreatment and decrease the inhibitory effect of byproducts on enzymatic hydrolysis and fermentation.?2?The effects of the pH values,cellulase loading,and substrate concentration?solids content?on enzymatic hydrolysis were investigated.The optimal enzymatic hydrolysis conditions were as follows:pH 5.5,enzyme loading 15 FPU/g,solids content 10%.Under this condition,the SED?Substrate Enzymatic Digestibility?of the two-step pretreated material reached 91%.?3?SHF and SSF ethanol fermentation studies were performed based on two-step pretreated material.The ethanol production by SSF reached 52 g/L,which was higher than SHF?41.2 g/L?.The ultimate ethanol yield fermented by SSF was 17.8 g/100 g dry biomass,which is equivalent to a 77.2%theoretical ethanol yield based on the untreated corncob glucan content according to overall mass balance.?4?The effects of non-ionic surfactants?Tween-80 and PEG 6000?,cationic surfactants?CTMAB?,and anionic surfactants?SXP?on the enzymatic hydrolysis of acid and two-step pretreated material and the mechanism of surfactant were investigated.Among them,Tween-80,PEG 6000 and SXP could improve the enzymatic hydrolysis.CTMAB had a strong inhibitory effect on the enzymatic hydrolysis of both materials.