Simultaneously Production of High Quality Tar and CH4 from Catalytic Bituminous Coal Hydrogasification in a Pressurized Fluidized Bed

Coal catalytic hydrogasification (CCHG) is an attractive technique of coal clean utilization, which can simultaneously produce SNG (Substituted natural gas) and aromatic hydrocarbon liquids under mild reaction conditions. This study works on achieving high CH₄ yield, light tar yield and coal conversion through the method of coal catalytic hydrogasification (CCHG) in a pressurized fluidized bed. The effects of catalyst loading (cobalt-calcium dual catalyst), temperature (600–850 °C) and H₂ pressure (0.1–3 MPa) on the formation of gaseous and liquid products were explored. Experimental results showed that carbon conversion and CH₄ yield increased markedly at a given ratio of Co-Ca. The addition of Ca retards Co sintering and more importantly triggers the catalytic conversion of graphite carbon in coal structure. Increasing temperature, especially higher than 750 °C, facilitated the activity of Co-Ca catalyst, making more carbon catalytic hydrogasified with lower activation energy. Nevertheless, elevated temperature was not beneficial for the yield of tar products because of the intensified thermal cracking effect. Elevating H₂ pressure facilitated the depolymerization effect of Co-Ca catalyst on coal during hydropyrolysis and promoted Co-Ca-C-H₂ interaction during hydrogasification, and thus encouraged CH₄ and tar formation. Through one stage CCHG at 850 °C and 3 MPa H₂, the yields of light aromatic hydrocarbons (LHs) and gaseous hydrocarbons (GHs) were 1.47 wt.% (BTX, PCX and naphthalene) and 81.2% wt.% (CH₄ and C₂-C₃), respectively, when using 5%Co-1%Ca as catalyst. Through two-stage CCHG (firstly catalytic hydropyrolysis at 600 °C and 3 MPa H₂, and then catalytic hydrogasification at 850 °C and 3 MPa H₂), good results with LHs yield of 3.36 wt.% and GHs yield of 74.2 wt.% were achieved, which could serve as an alternative way for simultaneously production of LAHs and CH₄ from CCHG.