Nitrogen generation by pressure swing adsorption based on carbon molecular sieves

Pressure swing adsorption (PSA) processes based on carbon molecular sieves have been known for more than twenty years. The most important industrial PSA process, the nitrogen PSA process, has been developed during the last ten years into a highly efficient technique for producing nitrogen on site. Nitrogen is currently produced by PSA with impurities down to the ppm level and at flow rates up to 1500 N m³ h⁻¹. The on-site supply of nitrogen using the PSA process is an alternative to cryogenic nitrogen. An overview of the theoretical background, of industrial units including purification by deoxo systems and of the economy of the nitrogen PSA system is presented.     

Kinetische Untersuchungen der adsorptiven Luftzerlegung an Kohlenstoffmolekularsieben

In recent years, the adsorptive air separation was established as one of the most important thermal separation processes for the generation of nitrogen and oxygen from air. Both the effects of equilibrium and kinetics can be applied for the separation of nitrogen and oxygen. Nitrogen can be enriched by an equilibrium effect in the adsorbed phase of zeolites, whereas oxygen remains in the gas phase. In contrast to zeolites, oxygen can diffuse much faster into the pores of carbon molecular sieves resulting in a gas phase enriched with nitrogen. In order to exploit this kinetic separation effect in industrial applications, the properties of carbon molecular sieves, e.g., pore aperture, overall pore volume, or release of heat of adsorption are important. Furthermore, research activities are focused on theoretical approaches to describe the kinetic behavior.     

气体分离用碳分子筛吸附剂的制备研究进展

介绍了作为气体分离用途的碳分子筛（CMS）的典型的和非常规的制备方法及应用。讨论了制备工艺条件对CMS分离气体性能的影响；分析了目前CMS制备工艺中存在的不足，并展望了CMS制备的发展趋势。     

低浓度煤层气提纯的研究现状

煤矿开采过程中排放出大量低浓度煤层气,提纯利用这部分煤层气对我国能源开发利用和环境保护意义重大,其难点是经济高效地分离CH4和N2.本文从CH4/N2分离技术、变压吸附分离CH4/N2吸附剂和制备新型炭分子筛3个方面逐层对低浓度煤层气提纯进行了综述和展望.介绍了CH4/N2分离技术研究进展,对其在低浓度煤层气提纯中的应用前景进行了对比.概述了常用变压吸附剂分离CH4/N2的研究现状,分析了它们在低浓度煤层气提纯应用中的优缺点,并提出了制取适合低浓度煤层气提纯用的新型炭分子筛的方法.     

Modification of pore size in activated carbon by polymer deposition and its effects on molecular sieve selectivity

The separation of air for nitrogen production can be carried out by pressure-swing-adsorption over a carbon molecular sieve. The separation is kinetically controlled, since the equilibrium adsorption of both oxygen and nitrogen is very similar, but the adsorption kinetics for oxygen is faster than for nitrogen. Several methods to prepare carbon molecular sieves are reported. In this work, we synthesized a carbon molecular sieve from a commercial activated carbon. After deposition of polyfurfuryl alcohol, these materials were subjected to carbonization at 800°C under an inert atmosphere. All the microporous materials were characterized by analysis of kinetics and equilibrium adsorption data. The molecular sieve performance was assessed by the O₂/N₂ uptake ratio. The material prepared by two depositions has characteristics similar to those of commercial CMS.     

煤基碳分子筛的制备及CH4/N2分离性能研究

以煤为原料,通过气相碳沉积法制备了CH4/N2变压吸附分离用碳分子筛,研究了苯沉积量对碳分子筛吸附性能的影响。用液氮吸附（77 K）、扫描电镜对碳分子筛孔结构及表面形貌进行了表征,结果表明：制备的碳分子筛（CMS-1）平衡分离系数大于5,比表面积SBET=251.5 m2/g,微孔孔容Vm=0.1178 mL/g,孔径主要分布在0.35~2 nm,能满足CH4/N2变压吸附分离要求。     

气体分离用变压吸附剂的研究进展

介绍了在应用变压吸附生产N2、O2和CO2的生产过程中,沸石分子筛和碳分子筛的吸附分离机理及它们的改性研究,并讨论了国内外目前使用的沸石分子筛和碳分子筛的优缺点,评述了现阶段国内外变压吸附剂的研究现状,进而展望了变压吸附剂的研究和发展趋势。     

Carbon molecular sieves: production from coal and application in gas separation

Carbon molecular sieves are adsorbents for gas separation processes of increasing importance. A variety of carbonaceous adsorbents, activated carbons and improved carbon molecular sieves, all with different pore size distributions, can be produced, systematically, by using different steps in the manufacturing process. The two types of carbon molecular sieves, CMSN2 and CMSH2, carefully developed by Bergbau-Forschung GmbH, can be distinguished by different separation mechanisms. The procedure of manufacturing the carbon molecular sieves type CMSN2 and type CMSH2 and their application in an air separating process for nitrogen recovery and hydrogen or nobel gas recovery processes, respectively, using different feed gases, is discussed.     

Kinetic separation of carbon dioxide from hydrocarbons using carbon molecular sieve

Experimental results are reported on a pressure swing adsorption (PSA) process using carbon molecular sieve (CMS) for the separation of a gas mixture containing carbon dioxide, hydrocarbons (methane, ethane, propane, etc.) and nitrogen. This PSA process has direct applications in carbon dioxide removal or purification from landfill gas, natural gas processing plants and tertiary oil recovery effluent streams. The CMS-based PSA process separates the carbon dioxide in a single stage by using the differences in component diffusivities. This approach, therefore, provides a significant advantage compared to conventional equilibrium adsorption processes which require one separation stage for removing components such as ethane and propane that are more strongly adsorbed than carbon dioxide and another separation stage for removing components such as methane and nitrogen that are less strongly adsorbed than carbon dioxide. The CMS-based PSA process operates between a feed pressure of 20 to 40 bars and a regeneration pressure of 1.5 bars at ambient temperature and produces a 98+% carbon dioxide product. The PSA process can be integrated with a liquid carbon dioxide plant to produce food grade product.     

煤基碳分子筛的研究进展及应用现状

基于原料煤种分类,简要介绍了煤基碳分子筛的制备工艺和在气体分离方面的应用,详细阐述了国内外煤基碳分子筛的研究状况,分析并展望了煤基碳分子筛的应用前景和今后的发展方向。     

粘结剂对不粘煤制炭分子筛的影响

研究以不粘煤为原料，以煤焦油、Ｒ－树脂以及它们的混合物为粘结剂和调孔剂，制备空分用炭分子筛的工艺方法，考察了粘结剂种类和配比对炭分子筛空分性能的影响。结果表明，Ｒ－树脂的引入改进了工艺条件和炭分子筛性能。适宜的Ｒ－树脂／煤焦油／不粘煤配比为５／２０／１００。     

铁离子改性碳分子筛对氮气/甲烷分离性能的研究

针对碳分子筛对氮气/甲烷分离体系分离比低的问题,采用浸渍法以市售空分碳分子筛（CMS）为基体,制备了分离氮气/甲烷的铁离子改性碳分子筛。通过静态吸附量、分离比、吸附动力学及热力学性质考察了铁离子负载量对碳分子筛吸附分离氮气/甲烷性能的影响。结果表明：铁（Ⅲ）的负载减小了CMS的比表面积、微孔体积和孔径,使CMS超微孔的孔径分布呈现更集中的趋势。这种集中性以动力学性能下降为代价,明显提高了碳分子筛对氮气/甲烷的吸附分离比。在303 K、0.7 MPa条件下,综合性能优异的0.3%铁改性CMS具有6.03的氮气/甲烷吸附分离比。     

Air separation by pressure swing adsorption

The original pressure swing air separation process, developed almost simultaneously by Exxon and Air Liquide, uses a nitrogen selective zeolite adsorbent to produce a high purity oxygen product. The same basic process is still widely used in small scale units although, for larger scale units, many modifications to the cycle have been introduced in order to reduce power consumption. Although nitrogen can in principle be recovered from the blowdown stream of such systems, if high purity nitrogen is the required product, it is more economic to use an oxygen selective adsorbent. Most adsorbents show either no selectivity or preferential adsorption of nitrogen. However, in small pore carbon molecular sieves or 4A zeolite there is a substantial difference in diffusion rates so that an efficient kinetic separation is possible. Somewhat different cycles are generally used in such processes. Progress in modelling the dynamic behaviour of both types of PSA system is reviewed and comparisons between experimental performance and the model predictions are shown. A simple linear driving force model provides a good overall prediction of the effects of process variables but the computationally more cumbersome diffusion model gives better quantitative agreement with experiment. Comparisons are drawn between the performance achieved (in nitrogen production) with two different kinetically selective adsorbents; RS-10 (a modified 4A zeolite) and Bergbau Forschung carbon molecular sieve.     

由灵武煤新法干馏半焦制备炭分子筛的研究

以灵武不粘煤的固体热载体新法干馏半焦为原料，综合使用碳化法和碳沉积法进行了空分富氮用炭分子筛的制备研究，考察了碳化和碳沉积工艺条件对产品空分性能的影响，并用ＦＴＩＲ和ＸＲＤ技术对产品炭分子筛进行了表片。结果表明，灵武煤的新法干馏半焦是制备炭分子筛的优良产；在最佳工艺条件下制得的炭分子筛的空分性能可与进口的同类产品相媲美；炭分子筛是典型的无定形炭，其表面含氧官能团主要是Ｃ－Ｏ键和Ｃ＝Ｏ键。     

Carbon-based oxygen selective desiccants for use in nitrogen PSA

Techniques for the production of composite oxygen selective adsorbents are disclosed. These adsorbents are comprised of a carbon molecular sieve (CMS) which is kinetically selective for the adsorption of oxygen over nitrogen and an agent for the sorption of water such as LiCl or SiO₂. The adsorption properties of the composite adsorbents and results obtained from pressure swing adsorption (PSA) process testing are presented. The composite adsorbents improve the nitrogen PSA process performance (recovery and productivity) over the use of conventional desiccants which do not exhibit oxygen selectivity. Using a standard nitrogen PSA process cycle, replacement of conventional inorganic desiccants like alumina with the current CMS-based desiccants improved air recovery 2 to 4 percentage points and increased nitrogen productivity 15 to 20% at 70°F and a nitrogen purity of 99.5%.     

褐煤两步炭化法制炭分子筛

本文针对高挥发分的褐煤原料，提出两步炭化法制炭分子筛概念，并考察了工艺条件和产品空分性能。结果表明，与一步法相比，两步炭化法制炭分子筛具有易成型、粘结剂用量少，炭分子筛强度高和空分性能好等优点。     

Predictive Dynamic Model of Air Separation by Pressure Swing Adsorption

A general dynamic model is developed for separation of air over a carbon molecular sieve and a zeolite adsorbent for production of nitrogen and oxygen. The proposed model is validated using experimental data from working laboratory scale N₂–PSA and laboratory scale O₂–PSA systems. Simulations studies are performed to investigate the effect of changing various process variables, such as the duration of PSA steps, bed length and feed inlet velocity.     

Preparation of carbon molecular sieves from macadamia nut shells

In this paper, we present a new approach in the preparation of carbon molecular sieves (CMS). Samples of CMS were prepared from macadamia nut shells by a sequence of three stages. First, activated carbon samples were produced by pyrolysis followed by physical activation with carbon dioxide. They were then treated with coke deposition via benzene thermal cracking. It was found that coke deposition in this step occurred mainly at the pore mouths of micropores, leaving most of the pore interior unchanged. The coke deposition process was allowed to proceed until all micropores became inaccessible to nitrogen molecules, resulting in very low BET surface area, contributed mainly by the meso- and macropores. In the third stage, we subjected these samples to an additional activation step, which was necessary to refine the opening of the pore mouth. The CMS samples prepared by this method have a micropore volume of the order of 0.19 cc/g, compared to 0.24 cc/g of the original base activated carbon. They are capable of separating CS₂ from iso-C₅H₁₂, the molecular diameters of which are 3.7 and 4.9 Å, respectively.     

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.     

碳沉积法制富氮用炭分子筛的研究

本文提出的碳沉积法是用煤焦油馏分油的有机溶液浸渍煤炭化物,然后热解以进行“孔调变”。确定了最佳工艺条件,制得富氮性能良好的炭分子筛。并用D-A方程求取了各种样品的微孔结构参数。