Effect Of Resin Properties On The Absorption Of Caffeine

Caffeine production using chloroacetic acid as a raw material is a process troubled by complex recovery and refining.This paper first analyses the resin structures and functional groups and then explores the potential of industrial application by studying some basic and theoretical data acquired on macroporous resin's adsorption of caffeine.Six types of styrene-divinylbenzene based macroporous resin were examined and compared for their adsorption of caffeine in a static adsorption and desorption test.It was found that XDA-200 macroporous resin comes with excellent adsorption performance.It was shown that the optimal dosage of resin was 60 g/L,the optimum pH was 6,and the 80% ethanol solution could be used for desorption.Based on the static adsorption test data at different temperatures and caffeine concentrationson the XDA-200 macroporous resin,it was observed that the isotherm was a typical type ? adsorption isotherm,and the lower temperature was more favorable for the adsorption of caffeine;Meanwhile,the study of the thermodynamic models and mechanism of adsorption revealed that the Freundlich model can better describe the adsorption process of caffeine on the XDA-200 macroporous resin,this process:(1)was a multi-layered and preferential absorption process;(2)?G <0,?S> 0 suggested that the adsorption process was spontaneous,during which the disorder increased at the solid-liquid interface;(3)?H,ranging from 8 to 40 kJ/mol,was greater than 14 kJ/mol,which indicated that hydrogen bonds were involved in the adsorption process;(4)An examination of the kinetic data at different temperatures unveiled that the second-order kinetic model can better describe the adsorption process which was rapid.Fitting of the kinetic data to the intraparticle diffusion model indicated that this adsorption process was controlled by multiple adsorption processes.FTIR and XPS were conducted for the analysis of the surface chemical structure before and after adsorption.From the O(1s)spectra,the electron binding energy of O(1s)increased by 0.5eV,and the absorption peak width and peak area of phenolic hydroxyl vibration at 3446.20cm-1 in FTIR also increased,further indicating that the adsorption process was involved by hydrogen bonds.Experiments were undertaken investigate the single factor's influece on the dynamic adsorption and desorption,and also measured the overall mass transfer coefficient,mass transfer zone length,theoretical plate number and theoretical plate height.Thus,the optimum dynamic absorption data including bed depth of adsorption column(20 cm),concentration of caffeine feed(10 mg/m L)and feed rate(3BV/h)were obtained;The ethanol solution with 80% mass concentration was used to desorb the samples at 70?,the highest desorption efficiency was acquired at the feed rate of 4BV/h and the resolution could reach 92.10%.The dynamic adsorption data acquired from different bed depth were fitted with the BDST model to investigate a linear relationship between the service time(t)and the depth of adsorbent bed(Z)when Ct/C0 was set as 0.2,0.6 and 0.8 respectively.The result showed that the correlation coefficient was above 0.98,demonstrating a good correlation.From the BDST plot assuming Ct/C0 to be 0.8,the breakthrough time was computed at different bed depth.And the parameters obtained from the plot were later exploited to calculate the breakthrough time at different caffeine feed rate and initial concentration.The data from the model agreed very well with the practical experimental results,suggesting that the model can accurately describe the dynamic adsorption of caffeine solution by XDA-200 macroporous adsorption resin.XDA-200 macroporous resin was used to improve the pre-treatment process of caffeine crude: the crude caffeine was first dissolved in water at a concentration of 11.0 mg/mL before it was adjusted at p H 1-2 with the HCL solution.Activated carbon with 0.5% solution mass fraction was added to pretreat the solution then filter after intensive mixing;the pH of the filtrate was adjusted to 6.After the dynamic adsorption was completed,through the process of evaporation,crystallization,drying of the desorption solution,the caffeine purity could be above 98.74%,reaching the levels of refined caffeine.