CO₂ Removal From Biohvthane With Amine Based Solid-liquid Phase-changing Absorbent And Ionic Liquids Loaded On Porous Materials

Desulfurated biohydrogen(mixture of hydrogen and methane produced by biomass waste)can be prepared as vehicle gas after CO2 removal,which is of great significance for energy saving and low carbon economy.The traditional amine aqeoues solution for CO2 capture have high energy consumption of regeneration and strong corrosivity to equipment,as a result,ionic liquids with low corrosion and amine-based phase-changing absorbents have attracted a wide attention.In this paper,ionic liquids loading on porous materials(such as molecular sieve and graphene)and a new type solid-liquid phase-changing solution(ethylenediamine/N,N-Dimethylformamide,EDA/DMF)wes proposed to capture CO2 efficiently from biohythane.Ionic liquid(IL)[P66614][2-Op],which absorbed CO2 efficiently through multiple-site cooperative interactions,was loaded on molecular sieve MCM-41(using impregnation method)to capture CO2 and the CO2 adsorption rate of loaded[P66614][2-Op]was about 2 times as high as that of a pure IL.N2 adsorption analyzer,scanning electron microscope(SEM)and high-resolution transmission electron microscope(HRTEM)were used to characterize the pore structure,morphological structure and pore length of 4 kinds of mesoporous molecular sieve SBA-15 with different pore lengths.The effects of pore lengths on CO2 absorption by SBA-15 loaded[P66614][Triz]were revealed and found the molecular sieve SBA-15(with the shortest pore length of 120 nm)loaded with 50%[P66614][Triz],which was called hybrid sorbent SBA-15(4.3)-50%IL,exhibited the fastest CO2 absorption rate and the shortest equilibrium time,which was approximately one-third of the equilibrium times of the other three hybrid sorbents.In addition,ionic liquid(IL)[P66614][Triz]with low regeneration temperature was also loaded on graphene nanoplatelet(GNP)and reduced grapheme oxide(RGO)to accelerate CO2 absorption rate.CO2 absorption capacity(63.6 mg CO2/g IL)and absorption peak rate(22.4 mg CO2/(g IL-min)of IL loaded on GNP were increased by 8.2%and 72.3%respectively,compared with those of neat IL.Moreover,13C NMR and Mulliken atomic charge calculated by Gaussian were used to support the CO2 absorption mechanism.A new type solid-liquid phase-changing solution(ethylenediamine/N,N-Dimethylformamide,EDA/DMF)was proposed to capture C02 efficiently from biohythane.In this EDA/DMF solution,only the precipitate product EDA-carbamate which was formed after CO2 absorption needed to be regenerated,avoiding high energy consumption of amine aqueoues solution.The C02 absorption capacity of solid-liquid phase-changing solution EDA/DMF was 13.9 mg/g absorbent,which was 30%higher than that of the EDA/water solution.And also performed better than the CO2 absorption capacity of the solid-liquid phase-changing solution piperazine/N,N-Dimethylformamide(PZ/DMF)with 11.7 mg/g absorbents.The CO2 peak absorption rate of EDA/DMF solution(0.97 mg CO2·9-1 absorbent·min-1)was 67%higher than that of the EDA/water solution.Besides,this also performed better than CO2 peak absorption rate of solid-liquid phase-changing solution N-methyl-1,3-diaminopropane/N,N-Dimethylformamide(MAPA/DMF)(0.94 mg CO2·g-1 absorbent·min-1)and that of PZ/DMF solution(0.89 mg CO2·g-1 absorbent·min-1).More CO2 molecules involved in reaction in these phase-changing solutions than in amine aqueous solutions,which attributed to the higher physical dissolution of CO2 in DMF(3.0 mg/g solvent in this work)than in water(1.7 mg/g solvent in this work).The two type of precipitate products EDA-carbamates in EDA/DMF system and ethylenediamine/N,N-Dimethylacetamide(EDA/DMA)system were characterized using X-ray diffraction(XRD).Although the molecular structures of the two EDA-carbamates were same,their molecular arrangements were different(their unit cell dimensions ?=90°and ?=95.8° respectively),resulting in the two EDA-carbamate crystals having different spatial groups and belonging to different crystal systems(monoclinic and orthorhombic).The reaction mechanism between EDA and C02 in solid-liquid phase-changing solution was revealed.The decomposition activation energies of monoclinic and orthorhombic EDA-carbamate crystals were 63.6 kJ/mol and 91.2 kJ/mol,respectively.the regeneration heat of MAPA/DMF and PZ/DMF were 2.95 and 2.77 GJ/t CO2 respectively.The electrochemical corrosion experiments tested the corrosion current of carbon steel in PZ/DMF solution was 0.57,far lower than that in PZ/water solution(993 ?A).