| In recent decades,the biorefinery technology that makes crude glycerol as byproduct from the biodiesel industry convert to high value-added 1,3-propanediol（1,3-PD）has attracted a great of attention.However,the separation of 1,3-PD and by-products is faced with many difficulties due to high boiling point and strong hydrophilicity of 1,3-PD as well as multiple components in the fermentation broth.And the separation cost accounts for more than 50%of total cost.To solve the problem,effects of hydrophobic solvents on the partition of 1,3-propanediol,acetic acid（HAc）and butyric acid（BA）were first investigated.And then two-step salting-out extraction technology was adopted to separate the three target products.Based on the deficiency of salting-out extraction the new method combining with microfiltration,ultrafiltration,concentration,pH precipitation,solvent extraction and rectification was put forward.Firstly,the effects of different hydrophobic solvents（e.g.ethyl acetate,ethyl ether,methyl tertiary butyl ether,n-pentanol,isopropyl ether and n-hexanol）on the separation of 1,3-PD,HAc and BA in the concentrated broth were investigated,and ethyl acetate was chosen for further study.The extraction yields of 1,3-PD and HAc were only 18.64%and 67.78%,respectively,and almost all the BA could be extracted by four-stage extraction at 50%（v/v）ethyl acetate/50%（v/v）concentrated broth.Although methanol added into the ethyl acetate as cosolvent could improve the hydrophilicity of the extraction system,the recovery of 1,3-PD changed little,approximately 15%.Secondly,the separation of 1,3-PD,HAc and BA from the fermentation broth by two-step salting-out extraction method were investigated.In the first salting-out extraction,the partition coefficient and recovery of BA reached 42.21 and 96.42%,respectively,under the optimal condition of 25%（w/w）NaH2PO4/30%（w/w）n-butyl acetate.Subsequently,91.28%of BA in the top phase could be recovered through back-extraction when 0.5 volume of sodium carbonate solution were mixed with organic phase,in which the mole ratio of sodium carbonate to organic acids was 3:5.Finally,50%（v/v）ethanol（95%）was added to the bottom phase for the second salting-out extraction.And the partition coefficient and recovery of 1,3-PD were 9.40 and95.50%,and those of HAc were 7.46 and 94.40%.In a scale-up experiment on 500 g,the recoveries of 1,3-PD,HAc and BA reached 91.67%,92.75%and 83.20%,respectively,with the removal of almost all the cells and 97.16%of the proteins after two-step salting-out extraction.At the end,the separation of 1,3-PD,HAc and BA was further investigated by a combination of microfiltration,ultrafiltration,concentration,precipitation with adjustment of pH,extraction and rectification.The final recoveries of 1,3-PD,HAc and BA were 80.76%,40.91%and 74.46%,respectively,after entire operation units.At the same time,99.90%of cells,96.39%of proteins and 79.35%of salts were removed,indicating excellent removal effect on impurities.The distilled water produced during concentration and residual glycerol in the rectifying tower could be reused for fermentation production of 1,3-PD,HAc and BA,which made a contribution to reducing waste emission and lowering cost. |
