| In recent years,climate and environmental problems caused by the global greenhouse effect have become gradually serious.Under the current"dual carbon"policy,CO2 capture is of prime significance.In addition,clean energy such as H2 and CH4 are play a vital role in the future global energy system.The purification of coke oven gas to produce hydrogen and the efficient separation of CH4/N2 from coalbed methane remain a key challenge.Absorption-adsorption hybrid method is a new green gas separation technology,which provides a new application mode for porous adsorbents by suspending porous materials in solvents to prepare slurries for separation.Metal-organic frameworks（MOFs）have the advantages of adjustable pore shape,host-guest force,high specific surface area,and structural flexibility,give the opportunities for the development of new and efficient slurry systems.From the perspective of industrial application,this paper carries out the experimental and simulation study of Zn-based MOFs slurry systems for CO2 capture,hydrogen purification（CH4/H2）and coalbed methane concentration（CH4/N2）,which provides a theoretical foundation for the design,development and industrial application of the new separation technology.（1）Study on gas separation performance of ZIF-8/isoparaffin C16 slurry system.Considering the shortcomings of the existing ZIF-8 slurry such as low boiling point,slow sorption speed and low solubility,a green,stable,low-cost,and high boiling point hydrocarbon solvent-isoparaffin C16 is selected to form a slurry.Based on the mechanism of physical absorption and adsorption,ZIF-8/isoparaffin C16 slurry was adopted to separate IGCC syngas（CO2/H2）at medium and high pressure.The sorption kinetics and viscosity of slurries with different solid ratios were studied to optimize the ZIF-8 content.The separation and regeneration properties of slurry were investigated,and compared with traditional commercial solvents such as polyethylene glycol dimethyl ether（DEPG）and propylene carbonate（PC）.The results showed that the slurry exhibit low viscosity,high sorption speed,low CO2 sorption heat,and excellent CO2 solubility and separation factor,which were significantly higher than DEPG and PC.In addition,the slurry system shows excellent desorption performance,can recover 98%of the sorption capacity by vacuuming for 5 minutes without heating.According to the principle of similar miscibility,ZIF-8/isoparaffin C16 slurry was employed to separate the gas mixture containing CH4 to improve the solubility and velocity of CH4 in water-based slurry.The adsorption performance of methane in slurry was explored and compared with water-based slurry.The results showed that the isoparaffin C16-based slurry had a higher methane sorption capacity and faster sorption speed.Moreover,the sorption rate of CH4in ZIF-8 slurry exceeded that of pure solvent,indicating that the adsorption process of ZIF-8 enhanced the gas-liquid two-phase mass transfer.The influence of sorption temperature,pressure and feed gas composition on CH4 sorption capacity and selectivity was systematically investigated,and ZIF-8/isoparaffin C16 slurry showed high CH4/H2 and CH4/N2 selectivity.It indicates that the slurry system has great application prospects.（2）Study on gas separation performance of CUPMOF-1/NMP porous slurry system.In order to achieve efficient CO2 capture at low pressure,the current benchmark MOF material CUPMOF-1 is compounded with the physical solvent NMP to form a slurry.The adsorption performance and viscosity of slurries with different solid content rates were studied,the solid-liquid ratio was optimized,and the effects of different desorption time and temperature on the regeneration cycle performance of slurry were investigated.It was found that CUPMOF-1 slurry with a solid content of 40 wt%had a strong ability to capture CO2 at low pressure,low viscosity and high capture rate.At the same time,the slurry has low desorption heat（33.45 k J/mol）,can be regenerated under mild conditions,and the circulating adsorption amount can reach 1.15 mol/L/bar after 15 min of vacuum desorption at 40°C.Then,the adsorption capacity of CUPMOF-1 dispersed in the slurry was investigated,and the mixed gas separation experiment was carried out,and it was found that the slurry enhanced the separation selectivity of dry materials.In order to improve the adhesion performance of ZIF-8 slurry system to CH4,CUPMOF-1/NMP slurry was used to separate CH4/N2 mixture.The aspiration isotherms of CH4 and N2 in CUPMOF-1/NMP slurry were determined,and the separation performance of dry CUPMOF-1 and CUPMOF-1 slurry on CH4/N2 mixture was investigated.The results showed that the CH4 solubility of CUPMOF-1 slurry was significantly higher than that of ZIF-8 slurry.Moreover,the separation factor of the slurry can reach 8.95,which is 2.4 times that of the dry material,and the slurry strengthens the separation selectivity of the dry material for CH4/N2.In addition,CUPMOF-1/NMP slurry has excellent stability and regeneration properties.（3）Development and verification of absorption-adsorption coupling phase equilibrium model.The gas-liquid-solid three-phase equilibrium process is divided into three parts to construct the model:（1）the phase equilibrium model of solvent absorption,based on the Peng-Robinson（PR）equation and van der Waals mixing rule,the binary interaction parameters of the model are fitted by correlating the gas-liquid phase equilibrium data of gases in solvents,and the average deviation of the calculation is within3%.（2）The phase equilibrium model of solid adsorption uses the Langmiur and Langmuir-Freundlich equations to describe the adsorption equilibrium of pure gas and gas mixture on dry materials,and the equation parameters are fitted,and the average deviation between the calculated value of the adsorption amount and the experimental value is less than 5%.（3）Absorption-adsorption coupling phase equilibrium calculation.The lever rule was used to predict the dissolution equilibrium of the absorption-adsorption coupling process,and the solubility of pure gas in the slurry was calculated,and the average relative deviation was less than 6%,and the prediction effect was good.Based on this model,the phase equilibrium of CO2/H2,CH4/H2 and CH4/N2 binary mixtures in slurry was predicted,and the average relative errors were 1.82%,5.82%and 4.77%,respectively.The above results prove the rationality and applicability of the proposed model.（4）Process modeling,simulation and multi-objective optimization of slurry-based separation process.Based on the thermodynamic model established in this paper,the simulation and optimization method of gas separation in slurry system is further established,and the process simulation and multi-objective optimization of separating CH4/H2 and CH4/N2 mixtures by ZIF-8/isoparaffin C16 slurry are carried out to determine the optimal operating conditions,flow characteristics and energy consumption per unit product.For CH4/H2 separation,two processes were designed:（1）Process A adopts decompression for slurry desorption;（2）Process B uses a combination of decompression and hydrogen gas stripping for desorption to purify H2 with purities of 99.5 mol%and99.99 mol%,respectively.The results show that the H2 recovery of process A reaches99.70%,and the total energy consumption per unit is 0.3876 k W·h/Nm3.Process B can reach 99.47%and 0.4608 k W·h/Nm3.Under the same process configurations,four various scenarios of CH4/N2 mixture separations were modeled and optimized.The results show that for medium and high concentrations of coalbed methane,the CH4concentration is 70 mol%,and a methane product with 99 mol%purity can be obtained,the recovery is 98%,and the unit energy consumption is 0.3173 k W·h/Nm3,which is only50～60%of the energy consumption of the cryogenic separation process.The slurry-based process has great energy-saving potential.The simulation and optimization results provide a theoretical fundations for the process design of ZIF-8 slurry method for CH4/H2and CH4/N2 separation. |
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