Extractive Adsorption Of Bio-based 1,3-Propanediol

1,3-Propanediol is an important chemical raw material and has a wide range of applications.PTT fiber,as a synthetic raw material,has many excellent properties,but it has not been applied on a large scale.The main reasons are that the production of 1,3-propanediol is not enough,the cost is too high,and the advantages of large-scale production are not obvious.Therefore,it is necessary to study the downstream separation process of 1,3-propanediol and develop a separation method with high efficiency and low energy consumption.For this reason,this paper explored the feasibility of low-speed centrifugation to remove the bacteria and mixed alcohol extraction for desalting,and synthesized a novel resin to try to combine extraction and adsorption for desalting and protein of concentrated fermentation broth.The specific results of the study are as follows.Firstly,low-speed centrifugation was used instead of membrane filtration to remove the bacteriophage from the fermentation broth.The p H was adjusted during fermentation using calcium hydroxide instead of sodium hydroxide to reduce the suspension capacity of the bacterium and facilitate the removal of the bacterium by low-speed centrifugation.Centrifugation conditions were optimized by Box-Behnken experimental design,and 98.7%clarification of the fermentation broth could be achieved at a relative centrifugal force of 2400g and 13 min,while reducing the salt content by 20.6%.The evaporation of the supernatant after low-speed centrifugation was further investigated,and the evaporation intensity was 1.8g/min when the evaporation volume was 80%,while that of the membrane filtered fermentation broth was 2.74 g/min under this condition.the former precipitated calcium salts in the crude fractionation stage,which reduced the subsequent evaporation intensity.Next,the feasibility of mixed alcohol solvent extraction of 1,3-propanediol and removal of proteins and salts was explored.In response to the problem that calcium salt precipitation by low-speed centrifugation reduced evaporation intensity,desalination and deproteinization were carried out by hydrophobic solvent extraction.Extractant screening experiments were conducted first,and alcohols were found to have better results.Then a two-component alcohol solvent mixture extraction was conducted,and it was found that a synergistic extraction effect was achieved when the difference in carbon atomic number between medium-chain alcohols and long-chain alcohols was 3 and the molar ratio was 2:3.The energy of different structures was calculated by molecular mechanics and quantum chemistry,and it was found that the structure was most stable when the medium and long chain alcohols were arranged interphase and the hydroxyl groups were arranged relatively,and the Gibbs free energy was-105.94kcal/mol.Weak interaction analysis and topological analysis were performed on the calculation results,and it was found that there was a strong hydrophobic interaction between the long chain structures of alcohol extractant molecules,and the hydrogen bonding bond energy was calculated by the critical point.The hydrogen bonding energies between medium-chain alcohol molecules and between 1,3-propanediol and long-chain alcohol molecules were-1.435,-2.024,-2.243 kcal/mol,respectively.Then,a three-component solvent mixture extraction experiment was carried out,in which a mixture of octanol,undecanol and tetradecanol with a molar ratio of 15:4:6 was selected as the extractant,and a four-stage extraction of 1,3-propanediol concentrate was carried out.The total yields of 1,3-propanediol,acetic acid and butyric acid were 98.73%,68.52%and 98.10%,respectively,and the removal of protein and inorganic salt were 99.31%and 75.61%,respectively.Finally,extraction and adsorption were combined to develop a new method of extraction and adsorption.Two extractive sorbent resins were synthesized using n-octanol and three-component mixed alcohols as extractants.The absorption peaks of alcohol hydroxyl groups at3500 cm^-1 were determined by infrared spectroscopy,and the hydroxyl groups of the two resins were 7.38%and 6.14%,respectively.Determined by physical chemisorption,the specific surface areas of resin I and resin II were 48.71 and 17.41 m~2/g,respectively,and the average pore sizes were 19.2 and 21.7 nm.The static adsorption capacities of the two resins were 511and 473 mg/g,and the dynamic adsorption capacities were 312 and 266.6 mg/g.The isothermal adsorption curves of the resins were fitted with the Langmuir equation,and the R~2 could reach above 0.98.At 298 K and 1,3-propanediol concentration of 200 g/L,the theoretical static maximum adsorption amounts of resin I and resin II were 777.0 mg/g and 784.4 mg/g,respectively.the free energies of adsorption were-559.9 J/mol and-688.8 J/mol,respectively,indicating that the adsorption process proceeded spontaneously.The theoretical maximum dynamic adsorption capacities of resin I and resin II were calculated to be 318.8 mg/g and 280mg/g,respectively,by fitting the resin penetration curves with Thomas model.93.8%and 90.86%of inorganic salts and proteins were removed by resins I and II,respectively,and 89.7%and92.4%of 1,3-propanediol were still extracted after 10 cycles of recycling,showing a good recycling capacity.The extraction capacity of 1,3-propanediol was 89.7%and 92.4%after 10cycles,which showed good recycling ability.