Study On The Production Of Butanol By Hydrolysis And Fermentation Of Gracilaria

Biobutanol is increasingly attracting people's attention as a type of renewable biofuel.However,high cost of raw materials and the complex preparation hampers the economic development and promotion of biobutanol.This thesis proposes the use of a new type of biomass,marine algae,as a potential substrate for butanol conversion.Firstly,the extracting method of agar was optimized by response surface methodology.The optimal results can be achieved when NaOH concentration was 6.25%(m/v),reaction temperature was 77?,and extracting time was 2.16 h.The experiments were carried out in triplicate under this optimized condition,with results of agar yield of 21.42%and the sulfate group content of 1.84%.Secondly,the fermentation process for C.acetobutylicum and C.beijerinckii was optimized,and it was found that the optimal sugar concentration was 60 g/L and pH was 5.5.Moreover,when acetic acid and MES were added to the fermentation broth for 72 hours,the amount of produced butanol increased by 87.26%and 72.06%for C.acetobutylicum and C.beijerinckii,respectively,using glucose as substrate.On the other hand,the amount of butanol produced by fermenting galactose increased by 90.99%and 93.93%for C.acetobutylicum and C,beijerinckii,respectively.At the meantime,the metabolic pathways for fermentation of galactose was speculated.The optimum conditions for dilute sulfuric acid hydrolysis of agar were sulfuric acid concentration of 7.5%(v/v),solid-liquid ratio of 1:50(g/mL),and hydrolysis time of 90 min by orthogonal experiments.Under this optimized condition,the yield of reducing sugar can reach 54.38%.The detoxification was further studied with the hydrolyzate.The results showed that the effect of detoxification was:simultaneous detoxification>rotary evaporation detoxification(87?)>Ca(OH)2 detoxification>activated carbon detoxification(3%).After the freeze-dried agar hydrolysate was treated with simultaneous detoxification,the carbon source was used for fermentation.After 72 hours,the amounts of butanol produced by C.acetobutylicum and C.beijerinckii reached 2.83 g/L and 2.74 g/L,respectively.Although simultaneous detoxification can improve fermentation to some extent,this method can only reduce the inhibitory effect but cannot completely eliminate the inhibitory effect.Finally,the fermentation conditions for C.acetobutylicum and C.beijerinckii using the mixing substrate of glucose and hydrolysate were studied.The results showed that the yield of butanol reached the maximum when the ratio of sugar to water was 3:1.At this time,the yields of butanol produced by C.acetobutylicum and C.beijerinckii were 6.59 g/L and 6.10 g/L,respectively.The amount of butanol produced by C.acetobutylicum and C.beijerinckii using simultaneous detoxification hydrolysate was 2.83 g/L and 2.74 g/L,respectively.It can be found that when C.acetobutylicum and C.beijerinckii fermented the mixing substrate,the yield of butanol increased by 132.86%and 122.63%,respectively,compared with fermenting the hydrolyzate alone.