Development Of Tray And Packing Foam Separation Columns And Their Properties Of Enhancing Foam Drainage

Foam fractionation technique has been widely applied in the separation of surfactants,heavy metal ions,dyes,proteins,and other natural products with the advantages of low energy consumption,non-pollution,low investment.However,it is still very important to improve the enrichment ratio by enhancing foam drainage.In this paper,the traditional plates and packing were adopted to the foam separation column in order to enhance the foam drainage.And the performances of this column were investigated in details.Based on the hydrodynamics of rising foam,a foam fractionation column with the traditional sieve tray was developed.By using BSA solution as a model system,the influencing factors to the foam fractionation efficiency were discussed.The results indicated that the sieve tray could effectively enhance the foam drainage,lower the column axial liquid hold up,and thereby increase the enrichment ratio.At the liquid loading volume of 490 m L,initial BSA concentration of 0.1 g/L,and air flow rate of 300 mL/min,the enrichment ratio reached to 7.6 by using 10 stages of sieve trays,which was 1.85 times of that in the control column.By referencing the mechanism of traditional sieve tray for enhancing foam drainage,a modified sieve tray was developed by taking off the two arched angles of the traditional sieve tray.The entrained liquid could drain back to the bulk solution through the arched angles,thereby avoiding the problem of ?on set flooding?.By using SDS solution as a model system,the performance of the modified sieve tray was evaluated at various initial SDS concentrations,and air flow rates with different numbers of trays and tray spacing.The results demonstrated that the modified sieve tray,with simple structure,can be easily scaled at relatively high separation efficiency.A novel foam fractionation column with the wire gauze structured packing was also developed for enhancing foam drainage.The effects of this innovated packing on the bubble size,liquid holdup,enrichment ratio,and recovery percentage were investigated by using bovine serum albumin(BSA)aqueous solution as a model.Under the conditions of the liquid loading volume of 490 mL,air flow rate of 300 mL/min,initial BSA concentration of 0.10 g/L,packing bed height of 300 mm and pH 6.2,the enrichment ratio could reach as high as 21.8,which was 2.45 times of that in the control column.The Teller Rosette,a kind of random packing,was then packed in the foam phase of the foam fractionation column.The drainage efficiency of the Teller Rosette was determined by measuring the liquid holdup at various axial heights with SDS solution as a model system.Under the conditions of the feed flow rate of 50 mL/min,liquid pool height of 300 mm,SDS concentration of 0.3 g/L and the air flow rate of 300 mL/min,the theoretical stages of the packing column for effective separation was 12.3,while that in the control column was 15.5.It is clear that the separation efficiency increased by 20.6%.Based on the concept of continuous operation in the distillation process,a single column with multistage continuous foam separation column was developed.The effects of the feeding concentration and the feed flow rate on the separation efficiency were investigated.The results indicated that the surfactant could be effectively removed at low feeding concentration and low feed flow rate.Moreover,it was necessary to increase the column plate stages to get the ideal separation efficiency while the feeding concentration or the feed flow rate increased.The removal of SDS reached 47.2% when the feeding concentration of SDS was 0.25 g/L and the feed flow rate was 9.5 m L/min.A bubble cap continuous foam fractionation column was also developed and its separation efficiency was evaluated by cetyltrimethyl ammonium bromide(CTAB).The effects of the operation parameters(feed flow rate,feeding concentration,and air flow rate)and the design parameters(tray stages,feeding location,tray spacing,and bubble caps number per tray)on the separation efficiency were studied.The operating zone of the column was then determined.And the theoretical stage number was obtained by the methods of plate to plate calculation and graphical calculation.In conclusion,the sieve tray,modified sieve tray,wire gauze structured packing,and the Teller Rosette,which were developed in this thesis,could effectively strengthen the foam drainage and significantly improve the surfactant enrichment ratio.The single column with multistage continuous foam separation column and the bubble cap continuous foam separation column were developed,the results showed that the columns could maintain the continuous operation of foam separation with high separation efficiency.Thus it has promising potential for industrial application.