Study On Green Preparation Of Granular Active Carbon From Lignite And Its Separation Performance Of CH₄/N₂ By Pressure Swing Adsorption

Coal bed methane is an unconventional nature gas. Because of its planless discharge, there are many environmental and secure problems, and resources is wasted. The utilization of coal bed methane is beneficial to optimization of energy structure and decrease of atmospheric pollution and incidents in our country. The key of utilizing coal bed methane is separation of methane and nitrigen which are the main compositions of coal bed methane. Pressure swing adsorption is one of technologies that separate effectually methane and nitrogen. And adsorbent is one of the most crucial factors which influence pressure swing adsorption performance. Due to the higher pore volume, bigger pore size, faster diffusion rate and neglecting limit of loading capacity, activated carbon is more suitable for separation of coal bed methane by pressure swing adsorption.In this paper, active carbon adsorbents used for concentrating methane from CH₄/N₂ were prepared from lignite by using coal tar, tragantine and PAM as binders, respectively. A comprehensive evaluation system consisted of enviromental index, resources index and performance index is established, and used to evaluate the three binders. The results show that soluble starch is the best binders, and its advantages are low discharge of contamination and high separation effect and strength. On the basic of evaluation results, the effects of technologcial conditions, such as pretreatment methods of lignite, kinds of pore-foaming agents, activation temperature, heating rate, dosage of activation water, on separation performance are discussed. The optimized technics is carbonizing at 600℃for 1 hour, activation at 800℃for 2 hour, heating rate of 10℃/min and activation water dosage of 1.9².0ml/min. While 40g soluble starch is added in 200g lignite, the separation performances of samples prepared by optimized technics are 25³0%.The feasibility study of other starches replacing soluble starch show that duo to lower discharge of contamination, higher strength and better separation performance, sample from starch monoester phosphate is superior to soluble starch sample. In sum, starch monoester phosphate is the top-priority binder, and soluble starch is the second choice when granular activated carbon is prepared from lignite.The influence of binders kinds on physical appearance and surface chemical properties of activated carbons is enormous. The characterizations of samples from differfent binders which have the better separation performance indicate that bulk density, pellet density and strength of GAC-ES（starch monoester phosphate） are higher than other samples while GAC-T（soluble starch） has the maximal micropore volume. The difference of micropore distribution is mainly in 0.45⁰.6nm. The surface oxygen-containing functional groups relative concentrations of GAC-T and GAC-C（coal tar） are greater than GAC-P（polyacrylamide）. In addition, besides the weightlessness in 0¹00℃, GAC-T and GAC-C has another weightlessness in 300℃and 700⁸00℃, respectively.The dosages of binder are obviously influenced the pore structure of samples. Samples from commercial salep as examples, pore structure parameters are to reduce, and then to increase with the raise of salep dosage. The pore distribution difference by DFT method of TS-0.2, TS-0.25 and TS-0.3 is in 20⁵0nm, 2²0nm and 0.4²nm.Because of the differences of pore structure and surface chemical properties, adsorptive properties on CO2, CH₄ and N₂ of GAC-C, GAC-P and GAC-T are discrepant. The contents of C=O from ketone, aldehyde, organic acid, ester and estolide, and phenol C-O are greater, the separation performance of CH₄/N₂ is better. At the same time, it is advantageous to separate CH₄/N₂ that activated carbons have more micropore volume. The results of simulation by 10-4-3 model show that the micropore from 0.6nm to 2.0nm could separate CH₄/N₂, and micropore about 0.7nm is the best pore to separate CH₄/N₂. But, numerical analysis of different range micropore volumes and separation performances indicate the micropore of which pore width is less 0.6nm could also separate CH₄/N₂. The reason is that energy parameters of 10-4-3 model are only correlated with temperature,and influence of pressure is not included. However, Knudsen roles explains best the difference。...