Study On Char Catalytic Hydrogasification For Methane By Cu-based Composite Catalyst

With the continuous optimization and upgrading of China's energy industry structure,the contradiction between supply and demand of natural gas has become more prominent,and the coal to substituted natural gas?SNG?technology has been widely concerned and developed rapidly.Coal catalytic hydrogasification?CCHG?technology has been used in recent years due to its high thermal efficiency and simple process flow.At present,the research of catalysts in CCHG mainly focuses on transition metal compounds.However,Co and Ni are too expensive to be suitable for industrialisation.In addition,the current research on catalysts mainly focuses on the behavior change during hydrogasification,and ignores the effective recovery of catalysts after hydrogasification.Therefore,this paper studies the effect of relatively cheap Cu-based catalysts on CCHG in a pressurized fixed-bed reactor,and selectively recovers Cu from hydrogasification residues.Characterization of catalysts and char was analysed by XRD,Raman,XPS,SEM,TEM,and H₂-TPR,and the main results are described in following:1.Study on char catalytic hydrogasification by Cu-Ca catalystThe study of Cu-Ca catalyst for CCHG was carried out in a pressurized fixed-bed reactor,and the effects of reaction temperature and catalyst loading on methane yield and methane formation rate were investigated.The results indicated that the methane yield of char with5.0%Cu-1.0%Ca catalyst was 60.63%under 800°C and 2 MPa H₂ in 450 min.The introduction of calcium not only inhibited the agglomeration of the catalyst,but also improved the dispersibility of it.The effect of catalyst was improved when the loading of calcium was 1%.In the initial stage of the reaction,Calcium captured sulfur and the calcium sulfide reduced the toxic effect of sulfur on the catalyst.Copper interacted with carbon during CCHG,which promoted the break of C-C bonds and increased the reaction rate between hydrogen and carbon.As the reaction proceeds,it improved the specific surface area of the hydrogenation residue owing to the consumption of carbon.The coexistence of copper and calcium inhibited the graphitization degree and increased the active site of char during the hydrogenation reaction,which accelerated the formation of mathane.2.Study of Cu-Ni-Ca composite catalyst for char catalytic hydrogasificationThe effects of Cu-Ni-Ca composite catalysts on CCHG under different temperatures and catalyst loadings were investigated in a pressurized fixed-bed reactor.It was found that the introduction of nickle catalyst significantly increased the activity of Cu-Ca catalyst.The methane yield of char with 2.5%Cu-2.5%Ni-1.0%Ca catalyst was 88.33%under 800°C and 2 MPa H₂ in450 min.The catalytic effect of Cu-Ni-Ca catalyst was significantly higher than that of Co-Ca and Ni-Ca catalysts which were generally considered to have better catalytic activity.XRD characterization showed that the Cu-Ni-Ca composite catalyst could form a Cu-Ni alloy during CCHG when the Cu/Ni ratio was 1:1.The geometric effect between Cu-Ni alloys promoted the dispersion of catalyst,strengthened the interaction between catalyst and carbon,and then accelerated the rupture of C-C bonds and the formation of metal carbides;the hydrogen compensation effect caused by hydrogen spillover between Cu-Ni alloys provided more active hydrogen atoms for the subsequent reaction between carbon and hydrogen,and increased the reaction rate between hydrogen and carbon.The H₂-TPR characterization proved that Cu-Ni-Ca composite catalyst had high reducing ability and strong hydrogenation ability.3.Study on selective recovery process of Cu-based catalystUsing NH₃-NH₄HCO₃ oxidizing ammonia leaching method to recover copper from residue of CCHG could achieve better selectivity and higher Cu leaching rate,and the impurity ion content in the leaching filtrate was very low.Under the condition of the leaching time was 120min,the leaching temperature was 50?,the stirring rate was 200 rpm,the liquid/solid ratio was6:1,the ammonia/ammonium bicarbonate ratio was 3:1,the total ammonia concentration was 6mol/L,and the oxygen partial pressure was 7 bar,the Cu leaching rate reached 94.67%.