碳分子筛吸附氯气的性能研究

采用P-C-T氯气吸附装置对碳分子筛的氯气吸附性能进行了研究.结果表明,碳分子筛可反复多次吸附氯气,并且结构骨架依然存在,稳定性较好.在273℃、0.332 MPa下,氯气吸附质量分数可达35.92％.     

Adsorption of very low level carbon dioxide impurities in oxygen on a 13X molecular sieve

An experimental study, of selective adsorption of very low level carbon dioxide impurities (in oxygen) on a Linde type 13X molecular sieve, has been described. The adsorption process was studied dynamically using laboratory scale apparatus. Operating parameters were selected to simulate conditions normally employed during the operation of large scale oxygen purifiers. Carbon dioxide impurity levels were nearly constant throughout each adsorption run, but ranged between 10 and 50 ppm from trial to trial. Therefore, the carbon dioxide adsorption capacity of the 13X molecular sieve could be determined as a function of varying, but very low, carbon dioxide impurity concentrations in oxygen.     

Adsorption of propane and propylene onto carbon molecular sieve

Equilibrium data for propane and propylene adsorption on a carbon molecular sieve (CMS) 4A from Takeda are presented in the temperature range 343-423 K and 0-300 kPa pressure. The pellet adsorption loading is 0.9 mol/kg for propane and 1.2 mol/kg for propylene at 100 kPa and 373 K. The equilibrium selectivity for propylene in the low-pressure range are 2.3 (343 K) and 1.7 (423 K). Experimental data were fitted with the Toth and Dubinin models. Zero length column (ZLC) technique has been used to determine the controlling mechanism and estimate the diffusivity parameters. Transport of both hydrocarbons in the pellets is controlled by micropore diffusion. Breakthrough curves were measured in the same temperature range and atmospheric pressure, at the low partial pressure of adsorbate (linear region of the isotherm). Simple models have been used in the simulation of breakthrough curves.     

煤层气在活性炭和炭分子筛上变压吸附分离

变压吸附分离是有效的气体分离提纯方法,采用合适的吸附剂可对煤层气(CH4/N2混合气体)进行高效分离,节约能耗。在单床吸附装置上测量了CH4/N2混合气体在3种活性炭和4种炭分子筛吸附柱上的穿透曲线,并进行实验研究再生条件对吸附剂分离性能的影响。实验结果表明,7种吸附剂均对CH4/N2混合气具有一定程度的分离能力,且高温真空再生后吸附效果更好;但仍需开发出更有效的吸附剂。     

甲烷/氮气分离用碳分子筛的制备

为制备甲烷与氮气分离用碳分子筛,以酚醛树脂基炭化料为基体,利用甲烷为沉积剂,探讨了不同沉积条件对碳分子筛甲烷与氮气吸附量的影响,测试了沉积后样品孔结构性能,并与国内外样品进行了对照。结果表明,最佳沉积温度为850℃,在沉积时间30 min,甲烷流量100 mL/min和氮气流量200 mL/min时,沉积后碳分子筛在孔径0.3～0.67 nm之间孔容为0.083 cm³/g,平均孔径为0.516 nm,吸附甲烷性能低于同类产品,有利于动力学分离。     

Pressure swing adsorption processes to purify oxygen using a carbon molecular sieve

Four different pressure swing adsorption (PSA) cycles using CMS for oxygen purification were developed to produce high-purity oxygen of over 99% with a high level of productivity. The cyclic performances such as purity, recovery, and productivity of the four different PSA cycles were experimentally and theoretically compared under non-isothermal conditions. In addition, one binary (O₂/Ar; 95:5 vol%) and two ternary (O₂/Ar/N₂; 95:4:1 and 90:4:6 vol%) mixtures were used to study the effects of feed composition. The PSA cycles with two consecutive blowdown steps produced oxygen with 98.0-99.9% purity and 56-66% recovery. The PSA cycle with oxygen generation in the second blowdown step produced oxygen with a higher level of purity and productivity. Also, the cycle introducing a pressure equalization step instead of a pure step produced oxygen with about 99.8% purity and 78% recovery. The period for the cyclic steady state of the ternary feed with 1% N₂ was slightly longer than that of the binary feed, while the PSA performance of the ternary feed was similar to that of the binary feed without nitrogen. However, in the ternary feed with 6% N₂, the purity of the O₂ in the purification cycles decreased by up to 97.3%. Therefore, nitrogen played a key role in producing high-purity oxygen in the CMS PSA instead of argon.     

CH4／O2在炭分子筛上的吸附动力学

为消除低浓度煤层气对煤层开采存在的安全隐患,提出了利用甲烷和氧气在炭分子筛上的动力学差异进行脱氧的工艺。采用容积法测定了纯CH4和O2在炭分子筛颗粒上的吸附动力学数据,并利用单床变压吸附装置测定了混合气体在298．15K,各压力下的穿透曲线。研究结果显示：吸附初期,O2在CMS上的扩散速率明显大于CH4;在混合体系穿透曲线上,O2的穿透时间远大于CH4,炭分子筛固定床表现出对O。的优先吸附选择性,可以实现出口直接富集甲烷的目的。0．4MPa时,当产品气中CH4含量为92．44％时,CH4回收率为73．27％。     

炭分子筛CH4/N2吸附分离

煤层气(CBM)是一种非常规天然气。在中国,煤层气在抽采出来时常混有空气。考虑到安全因素,氧气首先应该被去除。之后,煤层气利用的最重要步骤则是甲烷-氮气混合气体的甲烷高效提浓。本文搭建了双床变压吸附(PSA)装置,选择特定的炭分子筛(CMS)进行CH₄/N₂混合物分离实验研究。由于CMS的动力学吸附特性,氮被吸附在CMS上,带有一定压力的甲烷则连续输出。研究了吸附压力、进气速度和循环周期等因素对吸附过程整体性能的影响。从50% CH₄/50% N₂的原料气可以获得95.45%纯度的甲烷产品,而从30% CH₄/70% N₂的原料气可以获得94.89%纯度的甲烷产品。研究表明,以上3个参数都对分离性能有影响,其中后两者的影响更大。在较低吸附压力和较低进气速度时更容易获得纯度90%以上的甲烷产品。另外,循环周期越短,获得的甲烷纯度越高。     

Modelling of a pressure swing adsorption process for oxygen enrichment with carbon molecular sieve

Adsorptive separation of oxygen from nitrogen and argon is carried out during the desorption steps of a pressure swing adsorption (PSA) process which uses carbon molecular sieves developed by Bergbau-Forschung GmbH. The adsorption isotherms of the three main components of air are very similar. On account of the pore size distribution of CMSN2, the diffusion coefficient of oxygen is more than eight times those of nitrogen and argon so that air separation occurs by adsorption kinetics. Experimental results for the individual steps and cyclic operation of the PSA process are presented and compared with the predictions of an isothermal plug-flow model. Adsorption rate is represented by a linear driving force equation. If the diffusion coefficients are adapted separately to every step, a good agreement is observed between the model calculations and experimental results.     

炭分子筛的表征

炭分子筛是浓缩煤层气变压吸附机组的关键材料,性能的好坏直接影响变压吸附机组的性能。通过在77 K下N2的吸脱附等温线对炭分子筛的比表面积、孔径分布进行测定,通过吸附试验对炭分子筛吸附N2,O2,CO2,CH4,H2的能力及N2和CH4在炭分子筛上的吸附速度进行比较,以确定不同炭分子筛分离气体的能力。     

Rate and equilibrium sorption parameters for nitrogen and methane on carbon molecular sieve

Sorption parameters for nitrogen and methane on carbon molecular sieve (CMS) have been obtained using chromatographic, volumetric and gravimetric techniques. The equilibrium parameters-Henry constants, heats of adsorption and Langmuir constants-are consistent with reported literature values. Measurements of adsorption rates using a volumetric apparatus give results inconsistent with the diffusion hypothesis. The phenomena can be explained by the presence of a barrier resistance along with a diffusion mechanism. Analysis of results shows that the resistance measured by the chromatographic method is consistent with the resistance of the combined barrier resistance-diffusion model. The latter two resistances can only be obtained from the volumetric results. The general equation for additivity of resistances of Haynes and Sarma (AIChE J (1973) 19 1043) for breakthrough curves on a chromatogram is modified to account for the barrier resistance.     

Adsorption equilibria for oxygen and nitrogen gas mixtures on 5a molecular sieves

Equilibria data for the adsorption of oxygen, nitrogen and binary mixtures of these gases are determined on 5A molecular sieve pellets. Pure component isotherms are presented at pressures up to 9 bar and at 278.15, 293.15 and 303.15 K. The binary equilibria are presented at the same temperatures and at pressures of 1.7 and 4.4bar. The binary data have been examined against values predicted by various models using regression parameters obtained from the pure component isotherms. For these systems the ideal adsorbed solution theory, Cook and Basmadjian model and the statistical thermodynamic model gave the best representation of the experimental data.     

Physical aging in carbon molecular sieve membranes

This paper considers physical aging in carbon molecular sieve (CMS) membranes. Moreover, the performance of stabilized membranes under practical operating conditions is discussed. Physical aging has been studied extensively in glassy polymers, but aging in CMS membranes has previously focused primarily on adsorption: either chemisorption of oxygen, or physical adsorption of water and organics in the pore structures. Experimentally, in this study, for the samples considered, all of the above adsorption-induced aging mechanisms were excluded as significant factors through thoughtful experimental design. Physical aging appears to be the primary cause for rapid changes of transport properties in early stages after membrane fabrication for samples derived from high fractional free volume precursors. The CMS pores are believed to age analogously to the “unrelaxed free volume” in glassy polymers. Over time, these pores tend to shrink in order to achieve thermodynamically more stable states. Results of sorption tests in CMS also support the above hypothesis. The significance of physical aging phenomena on membrane testing protocols, structural tailoring, and performance evaluation are discussed. A long term permeation test demonstrated excellent stability of stabilized CMS membranes under realistic conditions.     

Nonlinear kinetics of oxygen and nitrogen sorption on carbon molecular sieves

Equilibrium and kinetics of oxygen and nitrogen sorption in two different carbon molecular sieves (CMS) have been modeled. In both CMS materials, equilibrium characteristics are adequately described by the Langmuir model. However, for kinetics of sorption, one CMS followed classic Fickian diffusion, while the other sample did not. A mathematical model was developed which accurately describes both pure component as well as binary uptakes in both materials. Simple manipulation of the boundary condition of the diffusion process allows the model to accurately predict both Fickian and surface barrier diffusion. All parameters needed to estimate binary uptake rates are obtained from pure component uptakes and isotherms. In addition, the model predicts both pure component and binary diffusion rates with diffusion coefficients which are not concentration dependent.     

Generalization of effect of oxygen exposure on formation and performance of carbon molecular sieve membranes

Previously, a pyrolysis method was developed to control separation performance of carbon molecular sieve (CMS) membranes by doping with trace oxygen. This method involved oxygen exposure during pyrolysis to tune the selective pore windows. During the development, it was observed that oxygen concentration in inert gas, rather than the total amount of oxygen exposed controls performance. In this study, we hypothesized that mass transfer of oxygen in CMS membranes during pyrolysis is governed by chemical reaction at critical pore opening. Effect of thermal soak time, inert flow rate, and precursor thickness were conducted to test this hypothesis with 6FDA/BPDA-DAM and Matrimid® polymer precursors. Results of oxygen consumption from pyrolysis process and CO₂/CH₄ separation performance showed that the process is likely governed by reaction kinetics. This observation implies simplicity and easy scale-up for the oxygen “doping” method on CMS formation by tuning the oxygen concentration in the pyrolysis atmosphere.     

炭分子筛膜的制备与改性

炭分子筛膜足近年来发展起来的高效、新型气体分离膜,具有良好的气体分离选择性,高的热和化学稳定性,但其气体分离选择性与气体渗透通量却不能同时达到很高的要求.综述了炭分子筛膜的制备材料,重点讨论了化学方法和物理方法对制备炭膜的前驱体进行改性,展望了炭分子筛膜的未来发展方向.     

蜂窝状块体硅胶/分子筛复合物吸附性能

采用静态法测定了蜂窝状块体硅胶/分子筛复合物的吸附性能,并采用吸附床结构模拟转轮除湿过程,测定了复合物动态吸附性能;探讨了复合物在吸附过程中温、湿度分布;研究了处理风参数（风速,进口温度、湿度）对块体吸附剂吸附性能的影响。结果表明：块体硅胶/分子筛复合物的除湿性能明显高于硅胶,尤其在较高温度和较低湿度条件下。在处理风温度较低、风速较小及处理风湿度较大的前提下,块体复合物除湿性能较好。