Novel Reaction And Separation Processes Based On Ion Exchange Resin

The increasing environmental deterioration and resource-exhausting problems have menaced the survival of human being and the development of society.Therefore,researching and developing new environmentally benign,energy-saving and emission-reduction technologies have priorities in various fields.Under this trend,four studies have been being carried out in our group,they are:1)Preparation and applications of ionic liquids;2)Carbon dioxide capture technology;3)Flue gas desulfurization(FGD)technology and 4)Design and application of efficient catalysts.However,some technical difficulties are always perplexing us during the research,such as:the traditional two-step method for ionic liquid synthesis is very difficult to balance the purity and cost,which limites the industrial scale production of ionic liquids;the commercial liquid amine-based processes for CO2 capture are suffering from high regeneration energy,equipment corrosion,solvent degradation and VOCs emission;the conventional processes of FGD also have some disadvantages,such as a huge amount of gypsum waste,high operation cost,low efficience,etc;and the existing catalysts are not efficient enough for the high utilization of mixed C4 resource;etc.All the problems mentioned above are seriously deviated from the environmental benign,energy-saving and emission-reduction principle.Ion exchange resins represents one of the most important scientific developments in the 20th century.They have wide applications in many fields,such as water softening,environmental remediation,hydrometallurgy,wastewater treatment,chromatography,biomolecular separations,and catalysis.Their general applicability originates from the particular construction,i.e.,functional groups are covalently tethered and highly dispersed the polymeric frameworks,which makes ion exchange resins not only stable but also flexible.Therefore,in addition to their literal meaning--ion exchangers,ion exchange resins can also act as supporters,absorbents and catalysts etc.In the recent years,with growing concern about the environmental and resource issues,ion exchange resins attracted increasing research attentions in relative to the past.In the present work,we introduced ion exchange resins into the above-mentioned four studies.The contents and results are summarized as follows:1)Ion exchange resins act as ion exchangers in the preparation of ionic liquids of high purityA general preparation route consisting of metathesis,ion exchange and acid/base neutralization steps is proposed and developed in this part to prepare ionic liquids of high purity from halide precursors.The reactions in the three steps are investigated systematically.It is illustrated that hydroxide intermediates can be produced easily and conveniently in the metathesis step.However,metal and halide ions with concentrations of up to several mass percents still remain in the solutions.The ion exchange in anion exchange and cation exchange resin columns is vital in removing the metal and halide residues and refining the hydroxide intermediates of purity as high as possible.It is further shown that the solubility of metal halides in ethanol,the ratio of halide precursor to potasium hydroxide,and the amount of ethanol solvent in the first step are the three key parameters affecting the residual concentrations of halide and metal ions,whereas there are four important influencing factors in the second step,including type of resin,concentration of hydroxide,size of cation,and flow rate in the resin columns.The results show that these multiple parameters can be flexibly adjusted according to the purity and cost desired.Two hydroxide intermediates([N2221]OH and[C6mim]OH)of high purity are prepared via metathesis and ion exchange steps,and their neutralization with four different acids is followed to produce a series of ionic liquids.The yields of cations and anions in the ionic liquids,as well as the concentration of impurities in each step,are determined to verify the feasibility of the method proposed in this part.It is demonstrated that the new preparation route is of great potential in obtaining various ionic liquids of high purity.2)Ion exchanges act as support for amino acid in the preparation of carbon dioxide absorbentAmino acids are supported on macroporous anion exchange resins for the removal of CO2 in this part.The resulting samples are characterized by EA,FTIR and TGA,and their CO2 equilibrium and dynamic adsorption performance are investigated.The experimental results show that amino acids can be easily supported by acid/base neutralization with the ratio over 95%.CO2 adsorption capacity of macroporous resins increase significantly after the load of amino acid,and the equilibrium capacity is around 1mmol/g at 10OkPa.Adsorption weakened with increasing temperature,suggesting the suitability in low temperature.Moreover,sufficient regeneration can be achieved by slightly elevating to 60? in inert gas ambient.Six adsorption-desorption cycles show that the adsorbent have an excellent regeneration performance.3)Ion exchange resin act as absorbent for sulfur dioxide removalWeak acid cation exchange resins are alkalized by inorganic hydroxides(NaOH,KOH and NH4OH)to remove SO2 in this part.Obvious swell-shrinking are observed during the transition of ion type of resin,and its influence on SO2 adsorption is investigated.The SO2 adsorption performance are investigated in equilibrium and dynamic method,respectively.The results show that the shrinkages are over 30%when resins are converted from alkali form to H+ form,leading to the squeezing out of liquid and loss of exchange capacity(around 25%).SO2 of low concentration(0.15v/v%)can be effectively removed with a high saturation capacity of 128mg/g.Water content in the resin is vital in the process.Sufficient water vapor should be ensured in the source gas as result.Hydrosulphite solution with high purity is obtained as valuable by-product during the process.The saturated resins can be easily and fully regenerated by fresh inorganic hydroxides solution.The results above suggest the prospect of combination of FGD and the disposal of waste alkaline liquid by this method.4)Ion exchange resin act as strong acid catalyst for the preparation of sec-Butyl AcetateTo make full use of C4 resource,mixed C4 of low cost is directly esterified with acetic acid to synthesize high value-added sec-butyl acetate in this part.Among tested acidic catalysts(three macroporous sulfonic acid ion exchange resins,two inorganic acids and two ionic liquids),ion exchange resins show the best performance.The optimized reaction conditions were reaction temperature of 383.15 K,catalyst loading of 15%w/w and molar ratio of the reactants of 1.64:1.The optimum selectivity of 93%sec-butyl acetate is obtained at a conversion of 65%.