Preparation Of Carbon Molecular Sieves Research Articles

Preparation of carbon molecular sieves and its impregnation with Co and Ni for CO2/N2 separation

The carbon molecular sieves (CMSs) prepared by carbonaceous materials as precursors are effective in CO2/N2 separation. However, selectivity of these materials is too low, since hydrocarbon cracking for developing the desired microporosity in carbonaceous materials has not been done effectively. Hence, in this study, cobalt and nickel impregnation on the precursor was conducted to introduce catalysts for hydrocarbon cracking. Cobalt and nickel impregnation, carbonization under N2 atmosphere, and chemical vapor deposition (CVD) by benzene were conducted on the extruded mixtures of activated carbon and coal tar pitch under different conditions to prepare CMSs. The best CMS prepared by carbon deposition on the cobalt-impregnated samples exhibited CO2 adsorption capacity of 54.79 mg/g and uptake ratio of 28.9 at 0 °C and 1 bar. In terms of CO2 adsorption capacity and uptake ratio, CMSs prepared by carbon deposition on non-impregnated and cobalt-impregnated samples presented the best results, respectively. As benzene concentration and CVD time increased, equilibrium adsorption capacity of CO2 decreased, and uptake ratio increased. Cobalt was found to be the best catalyst for benzene cracking in the CVD process.

Preparation of Carbon Molecular Sieves from Pistachio Shell and Walnut Shell for Kinetic Separation of Carbon Monoxide, Hydrogen, and Methane

In this study, two Carbon Molecular Sieves using Pistachio shell (CMS P) and Walnut shell (CMS W) were prepared by a chemical vapor deposition method and used for pressure swing adsorption and separation of CO/H2 and CO/CH4. Adsorption isotherms of gases obtained for both CMS’s. The Dubinin-Radushkevich isotherm model was used for comparing pore volume of CMS’s. The obtained isotherms for both CMS were compared with Langmuir and Freundlich isotherms. It was observed that Freundlich equation can better correlate the experimental data. The adsorption capacity of each CMS and selectivity of them for separation of CO/H2 and CO/CH4 were obtained with the aid of kinetic studies. In comparison with CMS W, CMS P showed higher adsorption capacity values for gases, but lower selectivity for separation of them. Finally by fitting experimental data to a pseudo second-order equation, adsorption capacities at equilibrium were obtained for abovementioned gases on both CMS’s.

Ultrahigh CO2 adsorption capacity on carbon molecular sieves at room temperature

Although metal-organic framework (MOF) materials have been postulated as superior to any other sorbent for CO(2) adsorption at room temperature, here we prove that the appropriate selection of the raw material and the synthesis conditions allows the preparation of carbon molecular sieves (CMSs) with adsorption capacity, on a volumetric basis, highly exceeding those reported in the literature for MOFs. Furthermore, the excellent sorption properties of CMSs over the whole pressure range (up to 50 bar) are fully reversible after different adsorption/desorption cycles.

Preparation of carbon molecular sieves from carbon micro and nanofibers for sequestration of CO 2

In this study, a hierarchal web of carbon micro and nanofibers was used as a precursor for the synthesis of a carbon molecular sieve (CMS). CMSs were prepared by thermal treatment of carbon fibers using a microwave heating device. The heating power and treatment time were optimized for the maximum performance of the prepared CMS for the separation of CO 2 at low concentrations from the gaseous mixture of CO 2 and air under dynamic (flow) conditions. Based on the experimental data, microwave power input of 240 W and treatment time of 15 min were found to be suitable for the maximum uptake of CO 2 by CMS. Adsorption breakthrough curves were obtained at different gas flow rates and CO 2 concentrations. CMSs prepared from the hierarchal web of carbon micro and nanofibers were found to be superior to those prepared from ACF. The CO 2 uptake was determined to be approximately 0.88 mg/g and 10 mg/g at concentrations of 500 ppm and 5000 ppm, respectively, in air.

Preparation of Carbon Molecular Sieves by Pyrolytic Carbon Deposition

The effect of different preparation parameters (pyrolysis temperature, process time, benzene concentration and residence time) on the properties of carbon molecular sieves obtained by pyrolytic carbon deposition from benzene on a microporous activated carbon, has been studied. For a fixed process time of 2 h, the increase of the pyrolysis temperature from 525 to 700∘C produced a strong increase of the CO2/CH4 selectivity, reaching a maximum value of 13 for pyrolysis at 700∘C. Selectivity also increased with process time (up to 5 h, with the pyrolysis temperature fixed at 650 and 675∘C), yielding values as high as 28. The obtained results have allowed to find the optimal preparation parameters for the preparation of CMS with high selectivity.

Preparation of carbon molecular sieves by carbon deposition from methane

To prepare carbon molecular sieves (CMSs), methane was pyrolyzed in an attempt to deposit fine carbon particles on the micropore mouths of the carbon substrates being heated; the carbon substrates included grain-based activated carbons and commercial activated carbons. To explore the effects of heat treatment alone, blank experiments were conducted by heating the samples in N 2. The resultant products were characterized by N 2-adsorption at 77 K. Methane failed to deposit carbon at 800 °C. The porosity of activated carbons, however, was substantially influenced by heat treatment alone. The surface areas and micropore volumes of the activated carbons from grain sorghum decreased by 39.32% and 36.84%, respectively, upon heat treatment alone; this is attributable to the destruction of pore structure by sintering. In contrast, the corresponding values of the commercial activated carbons increased by 59.86% and 62.16%, respectively, upon heat treatment alone; this can be attributable to the development of microporosity.

A scanning tunnelling microscopy insight into the preparation of carbon molecular sieves by chemical vapour deposition

A direct visualization of the changes induced by chemical vapour deposition (CVD) on the micropore mouth structure of an activated carbon is provided by scanning tunnelling microscopy (STM). Micropore mouth narrowing after CVD treatment leading to an effective carbon molecular sieve (CMS) has been confirmed.

Preparation of carbon molecular sieves for gas separations by modification of the pore sizes of activated carbons

Two activated carbons of different texture were modified by carbon deposition from the pyrolysis of benzene, in an attempt to obtain carbon molecular sieves of high adsorption capacity and selectivity for the separation of O 2/N 2 mixtures by pressure swing adsorption (PSA). The results show that these objectives can be attained when the carbon precursor has been activated only to a limited extent, and when carbon deposition is carried out in the proper kinetic regime.

95/05994 Preparation of carbon molecular sieves from char derived from non-caking coal

95/05994 Preparation of carbon molecular sieves from char derived from non-caking coal

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 CS 2 from iso-C 5H 12, the molecular diameters of which are 3.7 and 4.9 Å, respectively.

Preparation of carbon molecular sieves, I. Two-step hydrocarbon deposition with a single hydrocarbon

A process is described for preparing a carbon molecular sieve that is suitable for the kinetic separation of gases, such as oxygen from nitrogen. The process involves modifying a carbon support, having a majority of micropores with an effective pore size of about 4.5 to 20 Å, using a two-step process in which the sieve is contacted with two different concentrations of a volatile carbon-containing organic compound. The concentration of the carbon-containing compound used in the first step is larger than that in the second step, so that the pore openings of the micropores of the support are narrowed successively in two distinct steps without excessively filling the micropores themselves.

Preparation of carbon molecular sieves by propylene pyrolysis over nickel-impregnated activated carbons

Exploratory runs have shown it to be possible to produce a sieve for the separation of O 2 from Ar by depositing carbon from propylene in or over an activated carbon (AC) previously impregnated with Ni. It is thought that preferential cracking of propylene at the Ni sites within the pores of the AC particles and/or at the particle exterior surface introduces apertures of size 0.54–0.57 nm—the size required for this separation.

Preparation of carbon molecular sieves by propylene pyrolysis over microporous carbons

Modification of the pore structure of microporous carbons by depositing carbon from pyrolysis of C 3H 6 between 973–1123 K was investigated in regard to development of molecular sieving properties for separation of O 2 and Ar. Excellent adsorption kinetics and selectivity for separation of O 2 and Ar were achieved by depositing carbon on a substrate carbon that contains pores of a narrow size distribution. Activated carbons showed no useful development of molecular sieving characteristics after carbon deposition. This is attributed, primarily, to their containing too wide a size distribution of micropores.

The preparation of carbon molecular sieves by pore blocking

The gaseous adsorption properties of a carbon have been modified by the deposition of further carbon, produced by the pyrolysis of benzene, in the pores. Conditions have been established where carbon is deposited in the pore mouth, decreasing the entrance diameter from ca. 0.6 nm to ca. 0.3 nm. The resulting material is a molecular sieve, in which nitrogen and oxygen adsorbs to different extents. Conditions of pyrolysis are carefully selected to minimise both pore blocking and deposition over the whole of the pore, which would have the effect of reducing adsorptive capacity.