The Research Of Key Points On Biobutanol Production Using Corn Stover

Corn stover is a by-product of agricultural production, which can be thought as a renewable resources. One of the key procedures is the process of acid-catalyzed hydrolysis of corn stover to produce fermentable sugar in the production of bioethanol and biobutanol, in which one of the main costs is from the consumption of acid itself. In this study, a new process was developed in which the hemicellulose was firstly hydrolyzed to produce furfural by using formic acid as catalyst. Then cellulose and lignin were separated by dissolving most of lignin from the corn stover residues by using butanol or ethanol as extractant which were actually the final products of the whole process. Finally cellulose was hydrolyzed to produce glucose by using sulfuric acid as catalyst by a two-step hydrolysis. Moreover, acid and sugar in the hydrolysate mixture were separated by using acid retardation process. Finally, the eluents were deeply concentrated and detoxified by using multiple-effect membrane distillation(MEMD) process. The concentrated aqueous acid solution could be reused as catalyst and the purified and concentrated aqueous sugar solution was then used in fermentation to produce butanol or ethanol.Experimental results demonstrated that acid retardation process provided effective separation of acid and sugar by using a strong basic anion exchange resin, and the separation effect of sulfuric acid and sugar was better than that of hydrochloric acid and sugar. The recovery rate of sugar was as high as 94.3%~99.2% while the recovery rate of sulfuric acid was 92.4%~98.9%. The eluent I(dilute aqueous sulfuric acid solution) was further concentrated by using MEMD and MED and then reused. When a solution of 2 wt% sulfuric acid was concentrated up to ca. 30 wt% by using MEMD, the maximum value of permeation flux(Jw) and gained-output-ratio(GOR) was 5.52 L/(m2h) and 12.00, respectively, which corresponded to the energy saving effect of a conventional fifteen-effect evaporator. Even when sulfuric acid was concentrated to 30 wt%, the value of Jw and GOR kept as high as 3.80 L/(m2h) and 8.16, respectively, which corresponded to the energy saving effect of a conventional ten-effect evaporator. Meanwhile, when the eluent II(dilute aqueous sugar solution) were concentrated 20-fold to a final sugar concentration of ca. 497.6 g/L by using MEMD process, the final value of Jw and GOR was still 2.01 L/(m2h) and 7.2, respectively, which corresponded to the energy saving effect of a conventional nine-effect evaporator.When the combined process of acid retardation and MEMD could be used in separation and concentration of hydrolysate, they had the detoxification effect to the dilute aqueous sugar solution. For instance, the removal rate of inhibitors such as formic acid, acetic acid, levulinic acid, furfural, 5-hydroxymethyl furfural and phenolic compounds by MEMD process was 86%, 82%, 54%, 86%, 57%, 19%, respectively, when the hydrolysate was concentrated for 5 times. The non-volatile phenolic compounds inhibitors had been effectively removed in advance by acid retardation. Therefore, the key detoxication procedure had been included in the acid/sugar separation step and in the concentration step, which thus simplified the production process and reduced the cost.These results shows that the novel combined process, which has integrated hydrolyzing hemicellulose by using formic acid as catalyst, dissolving lignin by using final product solvent as extractant, hydrolyzing cellulose by using sulfuric acid as catalyst, separating acid/sugar mixture by using acid retardation process, concentrating and detoxing the eluents by using MEMD process, can be effectively used to the production of biofuel with the corn stover.