Vanillin sorption by hypercrosslinked polysterene sorbent MN-202
Abstract
During the synthesis of 4-hydroxy-3-methoxybenzaldehyde (vanillin) several byproducts are formed in the reaction mixture, so the development of a method for the end product selective extraction from process solutions is an important stage of the used technology. This task can be solved by non-ionogenic sorbents application. The equilibrium and kinetic characteristics of vanillin uptake by hypercrosslinked non-ionogenic polymer material MN-202 (Purolite International Ltd) are studied. Applying the procedure of variable concentration, hydroxybenzaldehyde sorption isotherm for the studied sorbent has been obtained. It is well described by Langmuir equation with high value of correlation coefficient. In the system of aromatic aldehyde and non-ionogenic sorbent the stacking interactions between benzene ring of hydroxybenzaldehyde and styrene-divinylbenzene matrix have the main impact.
Based on vanillin uptake kinetic curves at various temperatures and initial aldehyde concentration 6 mmol/dm3 the time of equilibrium attainment in the studied system has been determined. It is shown that sorption equilibrium is reached faster with temperature increase but the total capacity regarding vanillin is not changed in the considered temperature range.
The nitrogen adsorption/desorption isotherms for MN-202 polymer have been measured before and after vanillin uptake. The changes in specific surface area and pores volume of the studied hypercrosslinked sorbent after vanillin sorption have been revealed. Pores distribution of non-ionogenic sorbent according to the sizes before vanillin uptake and after its sorption has been evaluated using the method of Barrett-Joyner-Halenda (BJH). MN-202 specific surface area has been calculated using the experimental data by the equation of Brunauer-Emmet-Teller. The represented low temperature (77 K) nitrogen adsorption/desorption isotherms for the sorbent samples before and after vanillin uptake belong to the IV type according to IUPAC classification, common for mesoporous materials. The specific surface area and pores volume of polystyrene polymer decrease significantly after vanillin sorption. At the same time the average size of pores in the structure increases that deals with the filling of considerable part of sorbent micro pores with sorbate molecules.
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References
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