The Law And Mechanism Of Dynamic Supercritical CO₂ Fluid On Coal Adsorption Performance Under The Condition Of Entrainer

The glo bal war ming issue ar is ing fro m massive r elease o f c arbo n dio xide?CO₂?,a paramount anthropogenic greenhouse gas,has caused the negat ive effect for natural eco logical balance and sustainable development of human societ y.Thus,the human societ y has to take action to reduce CO₂ emissio n.For CO₂ emissio n reduct ion techno logy,CO₂ sequestration in unmineable deep coal seams wit h enhanced coal-bed methane?CH₄?recover y?CO₂-ECBM?cannot only store CO₂ in geo logic t ime but also get CH ₄ resources.Therefore,this work focuses on CO₂-ECBM.Previous research showed that CO₂ exists in supercr it ical state under the practical coal reser vo ir condit io ns.Fluid-so lid interact ions other than adsorptio n do exist between supercr it ical CO ₂ fluid and coals,which will change the phys ichemical properties o f coals and further influence their adsorption per for mance.In addit io n,invest igat ions have confir med that the introduction o f entrainer can enhance extraction effic iency o f supercr it ical CO₂ fluid.Based o n the researc h background abo ve,influence and mechanism o f adsorption per for mance of coa l under supercr it ical CO ₂ fluid blended wit h ethano l?Eth-SCF?will be addressed in this work.The conclusio ns drawn fro m this work will provide valuable implicat ion s for CO₂-ECBM.The main conclusio ns in this work are summar ized as below:To start with,based on dyna mic supercr it ical CO ₂ fluid extraction plat for m,the influence o f Eth-SCF on physicochemical pr operties deter ming adsorptio n capabilit y of coals,including pore structure and oxyg en-containing funct io nal groups,is studied.The result s show that:?1?Eth-SCF extract ion can change the pore structure?pore volume and specific sur face area?and pore shape o f coal.Tipically,wit h regard to coal samples after the extract ion of Eth-SCF(R_o,_max 0.72,0.93,and 1.23),the micropore specific sur face area and pore volume o f the aforement io ned coa l sample s increase,and the pore shape of coal sample s wit h R_{o,ma x}=0.88 and R_{o,ma x}=0.93 change.Wit h regard to coals with R _{o,ma x} o f 0.77,0.88 and 2.62,the extract ion of Eth-SCF decreases the micropore specific sur face area and pore volume of coal samples.?2?T he coal samples with R_{o,ma x} of 0.72,0.88,0.93 and 1.23display an increase in the total amount of sur face oxygen-containing funct iona l groups?-C=O and-COOH?after Eth-SCF treatment,while coal samp les wit h R_{o,ma x},ma x of 0.77 and 2.62,t he total amount of sur face oxygen-co ntaining funct io nal groups decreases.To sum up,both the extraction of Eth-SCF and the chemical adsorptio n between CO₂ and coals lead to changes in the pore structure and sur face chemistr y on the coal samples.Further more,the effects o f Eth-SCF on the adsorption static and dynamic behavior of CH₄ of var ious coal samples were also studied.?1?Static studies show that the adsorption property of coals is strongly dependent on their heterogeneit y.Specifically,aft er the extraction o f Eth-SCF,the adsorptio n propert y of coal sample s with R _{o,ma x},ma x of 0.72,o.77 and 1.23 increase;however,that of t he coal samples wit h R_{o,ma x} of 0.88,0.93 and 2.62 decrease.Furt her analysis indicates that the cha nge in the adsorption propert y o f CH₄ is clo sely related to the change o f pore structure and sur face oxygen-containing funct ional groups of coal samples.?2?The bid isper se diffusio n model wit h high fitt ing accuracy was selected to descr ibe the adsorptio n kinetics o f CH₄ o f coals.Result s confir m that the extractio n of Eth-SCF can increase the effect ive diffusio n coefficients o f CH ₄?mecro/macroporous and microporous effective diffusio n coefficients?wit hin coals,which also indicate that the increase in CH₄ diffusio n coefficient s may be related to the change of the pore structure and the oxygen-containing funct ional groups of coal samples.Finally,the effect s of Eth-SCF on the adsorption stat ic and dynamic behavior o f CO₂ of var ious coal samples were discussed.?1?Static studies show that the adsorption property o f coals wit h R _{o,ma x},ma x o f 0.72,0.93 and 1.23 increa se after the extract ion of Eth-SCF,while the opposite trend is found for other coal samples.?2?Kinet ic studies indicate that after the extractio n of Eth-SCF,the effect ive diffusio n coeffic ients of CO₂ wit hin coals displa y different trend.Wit h regard to the var iat ion of macropore diffusio n coefficient s,the coals with R_{o,ma x} of 0.72,0.77,0.88 and 2.62generally increase,but the coals wit h R_{o,ma x} of 0.93 and 1.23 decrease.Other than the coal wit h R_{o,ma x} of 1.23,the micropore diffusio n coeffic ient s of other coals show an incr easing tendency.Based on what have been addressed above,introduction o f entrainer is helpful to enhance both the amo unt of CO₂ storage and CH₄ recover y for target coal reser vo ir s wit h a certain metamorphic grades of coals.