Study On Key Process Of Biomethane Conversion From Corn Stover

The conversion of corn stover to biogas with industrial scale is an effective way to supplement the deplet of fossil energy,solve the environmental problems caused by burning it in the open air,and to achieve high valuable and clean ulilization of it.However,there are problems such as low fermentate rate,low biogas yield and inefficient utilization rate while using corn stover directly in the anaerobic digestion to produce biogas.From the perspectvie of whole process from harvesting to biogas production of corn stover,the three key unit processes of the conversion of corn stover to biogas production were explored to improve the utilization efficiency.The relationship between the rate of water loss and the change of biochemical content was found.A method of joint utilization of iron ions in hydrothermal reaction and fermentation,co-digestion of corn stover and biological sludge was explored.The method of losing water rapidly was proposed to inhibit the physiological activity of enzyme,so as to reduce the consumption of nutrients,slow down the process of lignocellulosic,and improve the efficiency of subsequent hydrolysis.The effect of water loss rate on the composition of corn stover and the hydrolysis by dilute sulfuric acid was investigated.It was found that the degree of lignocellulosic fibrosis for corn stover with water losing rapidly was lower than slowly dehydrated corn stover,and cellulose and hemicellulose were more susceptible to the hydrothermal reaction.The total sugar yield of the former with 1%H₂SO₄ pretreated at 120°C for70 min was 14.8%higher than the latter under the same condition.XRD analysis showed that the crystallinity index of corn stover with water losing rapidly was lower than the other one.FTIR analysis revealed that the crystalline cellulose content of fast dehydrated corn stover was lower than that of slow dehydrated corn stover,but the content of amorphous cellulose was higher than the latter.The degree of linkage between lignin and hemicellulose of fast dehydrated corn stover was lower than the slow degydrated corn stover.The corn stover stored after rapid water loss is more conducive to subsequent hydrolysis utilization.FeCl₃ was used as a catalyst to improve the hydrolysis of corn stover at high temperature.The optimal pretreatment coditions were obtained by response surface methodology,which were 0.1 mol/L FeCl₃ at 143°C for 21 min.Under this condition,the content of total reducing sugar was 35.56 g/L,and the content of furfural and hydroxymethylfurfural was 2.76 g/L in the liquid fraction.The hydrolysis kinetics of hemicellulose during hydrothermal reaction of corn stover catalysted by FeCl₃ could be predicted by Saeman model.The activation energies of xylose and arabinose in hemicellulose were 112.59 and 75.23 kJ/mol,calculated by the Arrhenius equation.The biogas yield increased from 114.2 mL/gVS to 123.9 mL/gVS after FeCl₃pretreatment,increased by 8.45%.The co-digestion of FeCl₃ pretreated corn stover and low energy density ultrasonic/alkali pretreated biological sludge were investgated on the basis of the previous experiments.Co-digestion improved the bigas yield.The cumulative methane yield reached 89.7%of the theoretical maximum cumulative methane yield with a maximum of 130.5 mL/gVS,when the TS ratio of the pretreated corn stover and sewage sludge was 2:1.The FeCl₃ pretreated corn stover and low density ultrasonic/NaOH pretreated sewage sludge had synergistic efficiency of13.4%⁸4.8%in the co-digestion.At the same time,co-digestion improved the buffering capacity and stability of the system.Fe³⁺increases the biodegradability of corn stover,and it is also used as a trace element by anaerobic microorganisms.In addition,the cumulative methane yield was 17.5%higher than that of the slow dehydrated corn stover when codigested with the ultrasonic/NaOH coupling treated biological sludge for fast dehydration corn stover.