Sugaring-out Extraction Combining Crystallization For Recovery Of Succinic Acid

Succinic acid is a valuable four-carbon platform chemical.It has important applications in food,medicine,chemical materials and other fields.It is widely used in biodegradable polymers?PBS?,green solvents,dyes,cosmetics,food additives and solubilizers.The production of succinic acid by microbial fermentation is more environmentally friendly and meets the needs of sustainable development.However,the separation of succinic acid from fermentation broth makes 50-60%of processing costs in bio-succinic acid production.The separation technologies of succinic acid are mainly focused on precipitation,membrane separation,ion exchange and extraction,etc.The extraction technologies include complexation extraction,reactive extraction,salting-out extraction,and sugaring-out extraction,etc.Compared with other extraction technologies,sugaring-out extraction has the unique advantages of rich source of raw materials,mild environmental protection,low waste water discharge,and reuse of extractant phase fermentation,which can be used for the separation of bio-based chemicals.Firstly,screened for the optimal succinic sugaring-out extraction system.The binodal curves were used to investigate the phase-forming ability of different sugars and different organic solvents.The effects of different sugaring-out extraction systems on the partition behavior of succinic acid were compared.The results showed that the order of the phase-forming ability of different sugars and different organic solvents was:t-butanol>n-propanol>isopropanol and galactose>glucose>fructose>mannose?sucrose>xylose.Hydrophilic organic solvents were more conducive to the distribution of succinic acid in sugaring-out extraction systems.From the different sugaring-out extraction systems investigated,t-butanol/glucose system showed the potential superiority in the partition behavior of succinic acid,glucose and solvent.Secondly,based on the phase diagram,the effects of system parameters on the distribution of succinic acid in t-butanol/glucose sugaring-out extraction system were investigated.The system parameters influencing the extraction efficiency,such as tie line length,system pH,temperature,glucose,t-butanol and succinic acid concentration were evaluated.At the same glucose concentration,with the increase of t-butanol concentration,the study found that the phase ratio showed an increase in the same rate,the yield of succinic acid was basically stable and the partition coefficient increased rapidly.At the same t-butanol concentration,with the increase of glucose concentration,the study found that the phase ratio decreased,the partition coefficient of succinic acid increased greatly and the yield increased slowly.The results showed that partition coefficient and yield of succinic acid increased linearly as tie line length increased.The closer system pH was to the pKa of organic acids,the more easily the organic acids existed in molecular form,the easier it was to extract to the upper phase.The higher the succinic acid concentration,the more favorable the distribution of succinic acid.The effect of temperature on succinic acid extraction was negligible.Salts-assisted sugaring-out extraction of succinic acid in t-butanol/glucose system was also investigated.With the increase of?NH₄?₂SO₄ concentration,the partition coefficient and yield of succinic acid increased from 4.725 and 86.96%to 5.69 and 89.23%.Compared with the results of KH₂PO₄ and NaH₂PO₄,the higher gibbs free energy of hydration of inorganic salts,the more favorable the distribution of succinic acid.The optimized composition and extraction conditions were as follows:40%t-butanol/27%glucose?w/w?,pH=3 and room temperature.The optimal system phase ratio was 1.436,the partition coefficient of succinic acid was 4.725,and the yield of succinic acid was 86.96%.Finally,a process for the separation and purification of succinic acid by t-butanol/glucose sugaring-out extraction system and gradient crystallization was developed.The effect of gradient crystallization,stirring crystallization,and direct crystallization on the yield and purity of succinic acid was investigated.The optimal crystallization process and conditions of succinic acid was as follows:pH<2,gradient stirring crystallization?5 ^oC/h?,washing crystals and drying.The total yield and purity of the final succinic acid reached 72.51%and 97.96%.