Synthesis And Performance Of Typical ZIFs With Different Pore Window Based On Adsorption And Separation Of Biobutanol

With the increasing shortage of fossil resources and the worsening environmental pollution,biomass energy has attracted widespread attention from countries around the world.Bio-butanol is close to the heating value and octane value of gasoline,and it is a new biofuel with potential.The production of bio-butanol is the traditional ABE fermentation.The characteristics of bio-butanol fermentation broth are low concentration aqueous solution and by-products which are main acetone and ethanol.The adsorptive separation method has the advantages of low energy consumption and high selectivity,and is particularly suitable for the separation of low-concentration multi-component.A new type of Zeolitic Imidazolate Frameworks（abbreviated as ZIFs）has the same topology as zeolite.Its composition unit of imidazole is larger than Si and O in zeolite,so that it has a large pore volume to ensure adsorption capacity,and at the same time,the rich composition of imidazole groups can adjust the pore surface and structural parameters,thereby regulating its hydrophobic/philophilic component performance and mass transfer performance.Therefore,ZIFs meet the design requirements of low-concentration multi-component separation adsorbents.The research model object is the adsorption and separation of low concentration butanol,acetone and ethanol.From the comprehensive properties of target molecule size,polarizability and dipole moment,the adsorption of multi-component target molecules is regulated by the change of the ZIFs pore window potential energy,thereby achieving the adsorption and separation of multi-components.Therefore,for the adsorption separation of bio-butanol,the core is to establish the relationship between the ZIFs pore window and the multi-component adsorption separation performance,and obtain the key structural parameters to determine the performance.The main research contents and conclusions are as follows:（1）Through the same topological groups to regulate the size of ZIFs.Screening and synthesizing ZIFs with different apertures through data mining.Based on the same RHO topology,through different imidazole groups to adjust the size of ZIFs pore window,three ZIFs with different pore window sizes were synthesized:ZIF-11,ZIF-71 and MAF-6,and the pore size was gradually increased through measurement,respectively.They are:3.1（?）,5.1（?）and 7.4（?）;the cage diameters are 14.3（?）,15.4（?）and 18.9（?）,and are relatively close,respectively.（2）The relationship between ZIFs materials adsorptive separation performance with different pore windows and low concentration ternary-component（butanol/acetone/ethanol-water）was studied.From the single-component dynamic column of butanol,acetone and ethanol(20,10 and 5 g L^-1):With the increase of the pore window,the adsorption amount of butanol increased,The adsorption capacity of ZIF-11,ZIF-71 and MAF-6 for butanol are162.8,231.5 and 280.0 mg g^-1,respectively.With the increase of the pore window,the adsorption capacity for acetone decreased,and the adsorption capacity of ZIF-11,ZIF-71 and MAF-6 for acetone are 98.0,72.0 and 19.0 mg g^-1,respectively;with the increase of the pore window,the adsorption capacity of ethanol decreases,and the adsorption capacity of ZIF-11,ZIF-71 and MAF-6 for ethanol are 44.7,7.0 and 2.9 mg g^-1,respectively.Therefore,the adsorption amount of ZIFs to butanol is proportional to its specific surface and pore volume,but the increase of the pore window of ZIFs reduces the adsorption potential of highly polar acetone and highly water-soluble ethanol.Further ternary-component dynamic column showed that the butanol/ethanol selectivity of ZIF-11,ZIF-71 and MAF-6 were15.1,16.6 and 16.0,respectively;and the adsorbed ethanol was easily replaced so butanol/ethanol selectivity is relatively close;but ZIF-11,ZIF-71,and MAF-6have the butanol/acetone selectivity of 2.4,4.4,and 8.4,and the more polar acetone adsorbed by the small pore ZIFs is not easily replaced.Therefore,for the enrichment and separation of low-concentration ternary-component bio-butanol,MAF-6（7.4（?））which has a large pore window is the best.（3）Co-adsorption phenomenon of MAF-6 with large pore window.In the single-component dynamic column of acetone and ethanol(10,5 g L^-1),the adsorption amount of MAF-6 is 19.0 and 2.9 mg g^-1,respectively.However,in the ternary-component butanol/acetone/ethanol(20/10/5 g L^-1)dynamic column,the adsorption amount of MAF-6 adsorbed 39.3 and 7.3 mg g^-1 before replace.The adsorption capacity increased instead.Therefore,the preferential adsorption of butanol leads to a reduction of the pore window,while the small pore window is advantage for the adsorption of acetone and ethanol.（4）The relationship between ZIFs materials of acetone adsorptive separation performance with different pore windows and low concentration binary-component（acetone/ethanol-water）was studied.With the increase of the pore window,the adsorption capacity of ZIF-11,ZIF-71 and MAF-6 to acetone and ethanol decreased,but the difference between the adsorption capacity of the medium pore window ZIF-71 to acetone and ethanol and the difference of the breakthrough time is maximum.Further combined with acetone/ethanol binary-component dynamic column,it was found that the selectivity of ZIF-71 with medium pore window for acetone/ethanol is largest 8.8.Therefore,for the separation of acetone/ethanol in low-concentration binary-component,the ZIF-71（5.1（?））adsorptive separation effect of medium windows is the best.（5）The relationship between ZIFs with different pore windows and the adsorptive separation performance of low concentration ethanol was studied.The single-component batch adsorption curves at the initial ethanol concentration range of 0-50 g L^-1 shows that as the pore window increases,the affinity of ZIFs for ethanol gradually weakens,so the affinity between ZIF-11 with smaller pore windows and ethanol molecules is bigger among them.At a concentration close to the ethanol concentration in the ABE fermentation broth(5 g L^-1),the dynamic adsorption capacity of ZIF-11,ZIF-71 and MAF-6 for single-component ethanol was 44.7,7.0 and 2.9 mg g^-1,respectively.ZIF-11（3.1（?））with smaller pore windows has the largest adsorption capacity for ethanol.Therefore,for the enrichment of low-concentration ethanol,ZIF-11（3.1（?））which has a small pore window is undoubtedly a suitable adsorbent.（6）The relationship between the pore windows of ZIFs and the adsorptive separation performance of ternary-component butanol is established.For the ternary-component separation of bio-butanol,MAF-6 with a large-pore window was used to separate butanol from ethanol and acetone first;then,the acetone/ethanol were separated through the medium pore window ZIF-71,and the ZIF-11 enrich the ethanol and finally,achieve the separation of ternary-component.In addition,compared with the traditional adsorbent zeolite molecular sieve,for the ternary-component butanol adsorptive separation,the large pore window MAF-6 adsorptive separation performance is more excellent.