Study On Extraction Of Volatile Fatty Acids From Anaerobic Fermentation Broth

In recent years,the production of volatile fatty acids（VFAs）through anaerobic fermentation methods using organic waste as raw materials has attracted the attention of researchers.VFAs exist in the fermentation broth in liquid form,so how to efficiently separate VFAs in the fermentation broth is still a major technical problem.Based on this,this paper uses liquid-liquid extraction method to carry out related research work on the separation of model solution and fermentation broth.Ionic liquids are added as an extractant to traditional organic solvents,the extraction performance of each extraction system for VFAs was studied and compared,and the extraction process was investigated in detail and optimized.Through infrared spectroscopy,the changes of the organic phase before and after extraction were analyzed.The extraction process at different temperatures was studied,and the corresponding thermodynamic parameters were obtained.On the basis of providing a basis for the subsequent separation of VFAs in the fermentation broth,using kitchen waste as a raw material,an anaerobic fermentation acid production experiment was carried out at different initial pH to produce VFAs,and a carbon chain extension experiment for caproic acid production was carried out at 30℃.Several types of fermentation broth extraction experiment conditions were optimized to improve their extraction rate and selectivity.came to a conclusion:When the extraction time exceeds 120 min,the extraction rate no longer increases with time;in the two ionic liquids,[P_666,14][Cl]system has a higher extraction rate for VFAs and is less affected by pH;in the three diluents（n-octanol,dodecane and mineral oil）,[P_666,14][Cl]+dodecane system extraction The highest rate,[P_666,14][Cl]+mineral oil system has good selectivity to caproic acid;the higher the pH,the lower the extraction rate of VFAs;in multi-stage extraction,[P_666,14][Cl]+dodecane has the highest bearing capacity for VFAs,and the total extraction amounts of acetic acid,butyric acid and caproic acid are respectively 11.5,14.5 and 30.0g/L;the extraction of VFAs by[P_666,14][Cl]is an exothermic process,which can be used at room temperature conduct.In the initial pH-regulated anaerobic fermentation acid production experiment,the highest total VFAs was obtained at pH 11,which was 20.8 g/L;When pH=10,it was acetic acid fermentation,and when pH=7,it was butyric acid fermentation.=11,it is a mixed fermentation;for the[P_666,14][Cl]+dodecane system,the optimum extraction conditions for acetic acid and butyric acid are both at a ratio of 2/1,and the ionic liquid addition amount is 10%.,The extraction rates are 44.3%and 66.0%,respectively;when compared with the model dissolving g/L,the presence of other substances in the fermentation broth will reduce the extraction rate;when the ionic liquid is added at 4%,the extraction is more selective than VFAs,while the ion When the liquid addition amount is 8%,the total extraction rate is higher.For the[P_666,14][Cl]+mineral oil system,the higher the sum of ionic liquids,the higher the extraction rate of VFAs;according to the molar ratio of ionic liquids to VFAs,the VFAs at different concentrations were screened out The best extraction conditions;ethanol and oil have little effect on the separation of caproic acid.The higher the concentration of acetic acid,propionic acid and butyric acid,the more obvious the effect on the extraction of caproic acid.Na Cl inhibits the extraction of caproic acid most significantly;In the model solution,the ratio of 1/1 is conducive to obtaining high-purity caproic acid;for the carbon chain extension fermentation broth,the selectivity is higher when the addition amount is 4%,and the purity of caproic acid is high;when the total amount of VFAs is the target,Using the 8%group extractant,the maximum value of the total amount of VFAs extracted can be obtained.