Intensification Of Foam Drainage In The System With A High Viscosity By Vertical Sieve Tray And Its Application In Foam Fractionation

Foam fractionation is a promising separation technology and it uses bubbles as media for achieving the separation of trace surface-active materials based on their differences in adsorption capacity on the gas-liquid interface.However,it is extremely difficult to separate the desired product from its solution with a high viscosity using foam fractionation because of the weak foam drainage.This could extremely limit the industrialization of foam fractionation in purification of bio-surfactant,food engineering and wastewater treatment.In this work,a novel foam fractionation column with vertical sieve tray(VST)internal in the foam phase was developed for strengthening foam drainage in the system with a high viscosity.The effects of the VST internal and the operation parameters on the foam drainage properties and the separation characteristics were evaluated,using the yam starch processing wastewater and the mixed solution of xanthan gum and yam mucin as the model viscous system,respectively.In the experimental column,the foam film could be partially wiped off as the foam squeezed through the sieve pores,and the inclined motion track could decrease the contact time of the countercurrent between the foam and the entrained liquid and facilitate the release of the entrained liquid within the foam.Meanwhile,the successive contraction and expansion further accelerated the rejection of the entrained liquid.As a result,the VST performance in strengthening foam drainage and decreasing the foam liquid holdup were identified.Under the design parameters of number of trays 5,the number of vertical sieve caps 4 and the number of sieve pores in each cap 28,the superficial liquid velocity and foam liquid holdup in the experimental column decreased by 12.71%and 12.63%,respectively.The yam starch processing wastewater was adopted as the viscous system in which the viscosity of the solution mainly depended on the concentration of yam mucilage.Under the suitable operating conditions of temperature 25~oC,volumetric air flow rate 50 mL/min,pore diameter of gas distributor 125?m and loading liquid volume 500 mL,the enrichment ratio and recovery percentage of yam mucilage in the experimental column were 5.70 and91.21%,respectively,which were 3.77 and 1.55 times higher than those in the control column.Regarding the mixed solution of yam mucin and xanthan gum as the high viscosity model system,in which the viscosity of a solution mainly provided by the non-surface active material and yam mucin only identified as a foam former.Under the conditions of the xanthan gum concentration 0.50 g/L,volumetric air flow rate 50 mL/min,loading liquid volume 450 mL,the enrichment ratio and recovery percentage of yam mucin in the experimental column were 3.86 and 74.56%,respectively,which increased by 64.96%,49.57%compared with those obtained in the control column.In short,it was effective for the VST internal to strengthen foam drainage of the system with a high viscosity and improve the foam fractionation performance of the surface-active materials.