Synthesis Of Metal-Organic Frameworks(MOFs)/Porous Composite Materials And Their Performance In Adsorptive Desulfurization

In these last two centuries of human economic development,fossil fuels have played an important role in the development of energy sector in many countries and they are still leading among other energy sources world widely.Owing to this global standpoint,liquid fuels are currently being seen as an important driving force for the development of many sectors of economy such as air transport,marine transport,railway and road transportation,industrial production processes etc.However,these liquid fuels contain toxic organic sulfur containing compounds(SCCs)which contain a high concentration of sulfur content.High sulfur content in liquid fuels presents itself as a serious threat to global environmental safety.This is because the combustion of sulfur leads to toxic sulfur oxides(SOx)that are gradually released in the atmosphere and pollute the environment through acid rain formation and heavy traffic smog in big cities.In the last few decades,a lot of research has been conducted with the aim of finding better and suitable techniques for desulfurization of liquid fuels using monoporous materials,zeolites,activated carbon etc.Recently,new directives have been oriented towards the use of Metal-Organic Frameworks(MOFs)in adsorptive desulfurization of liquid fuels under mild reaction conditions of ambient temperature under atmospheric pressure.For this reason,the adsorptive desulfurization of liquid fuel is simple and cost effective.In this perspective of finding better MOFs with great potential for adsorption desulfurization,two different MOFs namely Europium metal organic framework(Eu-MOF)and Cu-BTC MOF were synthesized using Europium and Copper as metal ion centers and 1,3,5-trimesic acid(H3BTC)as organic ligand under hydrosolvothermal conditions.The synthesized MOFs were characterized using X-ray diffraction(XRD),Fourier transform infrared(FT-IR),Scanning electron microscope(SEM),Transmission electron microscope(TEM)and Brunauer-Emmett-Teller(BET)method.The adsorption desulfurization performance of these MOFs materials was investigated using a solution of thiophene/n-octane as sulfur containing model oil.The results have shown that Cu-BTC MOF has better adsorption desulfurization performance than Eu-MOF under optimum desulfurization conditions of model oil/adsorbent mass ratio of 100:1 and reaction temperature of 30 ?.After 4 h of desulfurization reaction,the maximum adsorption desulfurization capacity for Cu-BTC and Eu-MOF were 27.43 mgS/g(MOF)and 24.59 mgS/g(MOF)respectively.This shows that the optimal adsorption desulfurization time was 4 hours.In order to enhance and improve the adsorptive desulfurization of the traditional Cu-BTC MOF,we have immobilized Cu-MOF on different porous material supports namely:gamma alumina(?-Al2O3),bentonite clay(Al-Si-Mg-O)and activated carbon(AC)to make metal organic frameworks/porous material composites.Using hydrosolvothermal method,Cu-BTC/?-Al2O3,Cu-BTC/Clay and Cu-BTC/AC composite porous materials were synthesized with 30%,40%and 50%wt of Cu-BTC content.The newly synthesized composite materials were characterized using previous characterization methods:X-ray diffraction(XRD),Fourier transform infrared(FT-IR),Scanning electron microscope(SEM),Transmission electron microscope(TEM)and Brunauer-Emmett-Teller(BET)method.The characterization results revealed that Cu-BTC/porous composite materials maintained the features of a typical metal-organic framework material and thus dispersion of Cu active sites on supports improved the adsorption desulfurization performances of MOF composite materials.The investigation of the adsorptive performance for MOFs composites for the adsorptive removal of thiophene from thiophene/n-octane model oil was carried out as in previous experiments under mild reaction conditions.Experimental results have shown that Cu-BTC/?-Al2O3 composites material have better adsorption desulfurization performance compared to other MOF composite materials.The embedment of supports into precursors of Cu-BTC MOF has considerably improved the adsorption desulfurization performance for thiophene removal from thiophene/n-octane.After 6 hours of desulfurization,under adsorption temperature of 30 ?,model oil/adsorbent ratio of 100:1,the adsorption rate has reached the maximum adsorption rate of 78%while the adsorption capacity was 29.71 mgS/g(MOF)for 40%Cu-BTC/?-Al2O3 sample.Under the same desulfurization conditions,the adsorption desulfurization rate for 40%Cu-BTC/Clay and 50%Cu-BTC/AC has reached 76%and 74%respectively.The adsorption capacity for 40%Cu-BTC/Clay was 28.95 while that of 50%Cu-BTC/AC reached 28.19.Reusability and adsorption kinetics behaviors were also studied for samples with better adsorptive desulfurization performance.The results have showed that MOFs and MOF/composite materials can be reused for at least 5 consecutive rounds with a slight decrease in their performance.Results from the adsorption kinetics studies have revealed that the pseudo first order and pseudo second order rate equations can both be satisfactory models to represent the adsorption kinetics behavior of Eu-MOF,Cu-BTC and all Cu-BTC porous composite materials.However,the adsorption behavior of thiophene over 40%Cu-BTC/?-Al2O3 composite sample responded more appropriately to the pseudo-first-order kinetic model than the pseudo-second-order kinetic model.