摘要
由于石油能源的耗尽和价格的不断抬高,作为下一代石油能源替代品的生物能源引起了学术界和工业界的注意。与生物乙醇、生物柴油等生物能源相比,生物丁醇表现出了很多优良性能。本文以丙酮和丁醇的水溶液分离体系作为分离对象,合成了HTPB-PU和PDMS/PVDF复合膜,并考察了对丙酮和丁醇水溶液的分离效果。同时,将PDMS/PVDF复合膜应用于渗透汽化分离耦合丙酮丁醇发酵。
主要内容如下:
1.HTPB-PU膜
将HTPB-PU膜应用于丙酮-水、丁醇-水、丙酮-丁醇-水的分离。考察了料液温度、料液浓度对膜分离性能的影响。通过溶胀性能、渗透系数和活度系数等方面分析了两组分体系和三组分体系之间渗透汽化性能的差异。结果表明,对于丙酮-丁醇-水,40℃,丙酮和丁醇的浓度分别由1.5和3.0 wt%浓缩至11.9 wt%和43.5 wt%。此外,HTPB-PU膜分离丙酮丁醇发酵液的分离性能优于等浓度下的丙酮-丁醇-水的分离性能。在45℃条件下,对于丙酮-丁醇发酵液,丙酮和丁醇的浓度分别从0.5 wt%和1.1 wt%浓缩至8.7 wt%和16.4 wt%。
2.PDMS/PVDF复合膜
分别以正硅酸乙酯和辛基三乙氧基硅烷为交联剂,制备了PDMS/PVDF复合膜,并将其应用于丙酮-丁醇-乙醇-水的分离,考察了料液温度、料液浓度、料液pH值及交联剂等因素对膜分离性能的影响。结果表明,PDMS(tetraethylorthosilicate)/PVDF复合膜的渗透通量大于PDMS(triethoxyoctylsilane)/PVDF复合膜的渗透通量,但是有机物相对于水的分离因子则相反。PDMS(tetraethylorthosilicate)/PVDF复合膜分离丙酮-丁醇发酵液的分离性能优于HTPB-PU膜的分离性能。在45℃条件下,对于丙酮-丁醇发酵液,渗透总通量为96.7 gm~(-2)h~(-1),丙酮和丁醇相对于水的分离因子分别达到19.1和22.2,总浓度浓缩至21.7 wt%。
3.丁醇发酵与分离耦合反应体系的设计和构建
以PDMS(tetraethyl orthosilicate)/PVDF为基质的膜组件分别与丙酮-丁醇间歇发酵和流加发酵耦合,考察膜分离消除丙酮-丁醇发酵产物抑制作用、膜分离对于丙酮丁醇发酵的糖利用率、溶剂产率和溶剂产量等方面的影响。结果表明,在39℃条件下,渗透汽化-间歇发酵耦合的透过液总溶剂浓度为20 wt%左右;与间歇发酵相比,耦合分离反应体系的总溶剂产率从0.19gl~(-1)h~(-1)提高到0.44gl~(-1)h~(-1)。而渗透汽化-流加发酵耦合,在39℃条件下连续发酵98.5h,透过液的总溶剂浓度为28 wt%左右,发酵分离耦合过程的总溶剂产率0.58gl~(-1) h~(-1)。
Due to extensive oil depletion and its increasing price trend over the past decades, the use of biofuels as a partial replacement for fossil fuels has attracted both academic and industrial attentions.Among alternative biofuels,biobutanol is expected to play an important role in the next generation of biofuels.In this paper,HTPB-PU membrane and PDMS/PVDF membrane have been prepared for recovery of acetone and butanol from dilute aqueous solutions.Furthermore,potential of the membrane for separation of organics from fermentation was also studied by testing the pervaporaton performance.The main contents of this work were as follows:
1.HTPB-PU membrane
Hydroxyterminated polybutadiene-based polyurethaneurea(HTPB-PU) pervaporation membranes were prepared and used for recovering acetone and n-butanol from dilute aqueous solutions.The effects of operation temperature and feed composition on the pervaporation performance were investigated.The differences of separation performance between ternary mixture and binary mixture were also studied through evaluating permeability coefficient,swelling degree of membrane and activity coefficient.The results indicated that the pervaporation performance for ternary mixture was superior to that for binary mixture because of the permeant-permeant and permeant-membrane interactions.A high selectivity towards acetone and n-butanol was obtained.Acetone and butanol were condensed from 1.5 to 11.9 wt%and 3.0 to 43.5 wt%at 40℃for the ternary mixtures,respectively. Furthermore,potential of the membrane for separation of organics from fermentation was also studied by testing the pervaporaton performance,and acetone and butanol were condensed from 0.5 to 8.7 wt%and 1.1 to 16.4 wt%at 45℃,respectively.
2.PDMS/PVDF membrane
PDMS/PVDF composite membranes were prepared with the crossing-agent (tetraethyl orthosilicate or triethoxyoctylsilane) and used for separating acetone-butanol(AB) from its dilute aqueous solution to evaluate pervaporation separation performance at various feed concentrations,operating temperatures and feed pH.Furthermore,potential of the membrane for separation of organics from fermentation was also studied by testing the pervaporaton performance,and separation factor of acetone and butanol were 19.1 and 22.2 at 45℃,respectively.
3.Pervaporation integrated with fermentation
PDMS(tetraethyl orthosilicate)/PVDF membrane was integrated with acetone-butanol fermentation and fed-batch fermentation.Effect of pervaporation for the acetone-butanol fermentation was investigated.The results showed that the total solvent concentration of permeant was about 20 wt%for pervaporation-batch fermentation system at 39℃.Comparing with batch fermentation,solvent production rate increased form 0.19g l~(-1) h~(-1) to 0.44 g l~(-1) h~(-1).For pervaporation-fed-batch fermentation system,the total solvent concentration of permant was about 28 wt%, and during the total solvent yield of coupling separation process(63.5 h-74 h) is up to 0.58 g l~(-1) h~(-1).
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