Experimental Study On Adsorbing Material Prepared By Highly Lignin Waste And Its Functional Adsorbing Performance Of CH₄/CO₂

In this paper, highly lignin waste-furfural residue was used as raw material to prepare CH₄/CO₂ functional separation activated carbon by phosphoric acid activation method. Firstly, The preparation conditions of furfural activated carbon was optimized through orthogonal test, which could establish the mathematical relationship and contour map between specific surface area, the most probable pore size of the activated carbon and preparation conditions. Then, the physical and chemical properties such as structure and morphology, specific surface area and aperture, and surface functional group analysis of furfural activated carbon were characterized by scanning electron microscopy （SEM）, Brunauer-Emmett-Teller （BET specific surface area analyzer）, and Fourier transformed infrared （FT-IR）, respectively. Finally, the CH₄/CO₂ pressure swing adsorption （PSA） experiment was applied to obtain the adsorption-separation performance parameters of furfural activated carbon on CH₄/CO₂ mixed gas, and obtain the mathematical relationship between the adsorption, separation degree, coupling degree of CH₄/CO₂ mixed gas and preparation conditions. This study could provide theoretical basis for the preparation of CH₄/CO₂ functional separation activated carbon and adsorption-separation performance on mixed gas.Orthogonal experiment was used to optimize the preparation condition of furfural activated carbon by phosphoric acid activation method. The influences of concentration of H3PO4, impregnation ratio （mass of H3PO4:furfural residue）, activate temperature and activate time on the properties were investigated in orthogonal experiment. According to the test results, the preparation conditions of activated carbon that owned the largest specific surface area were determined. The mathematical relationship and contour map between specific surface area, most probable pore size of the activated carbon and preparation conditions were established through response surface methodology. The experimental results showed that the optimum conditions for preparing activated carbon was that phosphoric acid concentration was 60%, impregnation ratio was 1.5:1, activation temperature was 400℃ and activation time was 120 min. BET surface area and the most probable pore size of furfural activated carbons under the optimized conditions was as high as 1166.952 m2/g and 0.6205 nm, respectively. According to the mathematical relationship and contour map, it could be clearly seen the influences of phosphoric acid concentration, impregnation ratio, activation temperature and activation time on specific surface area, the most probable pore size of furfural activated carbons.SEM showed that the surface of furfural activated carbons was roughness with rich convex, fold and micropores. This structure could produce high specific surface area that provided a good foundation of physical adsorption performance. Nitrogen adsorption curves exhibited that the nitrogen adsorption isotherm of furfural activated carbon products were Ⅱ type, which indicated that the nitrogen adsorption of furfural activated carbon depend on the quantity of micropores to a large extent. The analysis of fourier transform infrared spectra showed that when the raw material and activating agent were the same, the kinds of functional groups on surface of activated carbon had no big differences under different preparation conditions. However, the number of oxygen containing functional groups, such as hydroxyl. carbonyl. ether and hydroxybenzene on the surface of activated carbons with large specific surface area were significantly more than those of small specific surface area.The adsorption-separation performance of activated carbon products （furfural residue as raw material, phosphoric acid as activating agent） on CH₄/CO₂ mixed gas was tested by PSA experiment and then established mathematical relationship between the adsorption, separation degree, coupling degree of CH₄/CO₂ mixed gas and preparation conditions. In the range of experimental conditions, results showed that the larger the specific surface area, the greater adsorption capacity of CH₄/CO₂ mixed gas. It could be concluded that the relationship between the surface area and the adsorption amount possess a positive correlation. Among the samples, activated carbon product with the biggest specific surface area of 1166.952 m2/g owned the best adsorption-separation performance, and the results were listed as follows:the maximum absorption capacity for CO₂ was 65.185 cm3/g and the minimum absorption capacity for CH₄ was 7.171 cm3/g, the corresponding separation degree and coupling degree of CH₄/CO₂ mixed gas were 5.829 and 0.937, respectively.