Gas Separation & Purification最新文献

The separation of air for the production of nitrogen by pressure swing adsorption over a carbon molecular sieve is kinetically based. The basic steps involved in a cycle are typically pressurization, high pressure adsorption, countercurrent blowdown and vent. Simulations studies with DAPS (Dynamic Adsorption Process Simulator) were performed to analyze the effect of the pressurization rate and bed length on the performance of a single bed nitrogen pressure swing adsorption unit in the high purity region. Both specific product and yield improve with the bed length due to the reduction in the axial dispersion effect. A comparison between the predictions of the theoretical model and experimental results was carried out.

This research investigates the effects of relative humidity (RH) on the adsorption of soluble (acetone) and insoluble (benzene) volatile organic compounds (VOCs) with activated carbon cloths (ACC). A gravimetric balance was used in conjunction with a gas chromatograph/mass spectrophotometer to determine the individual amounts of water and VOC adsorbed on an ACC sample. RH values from 0 to 90% and organic concentrations from 350 to 1000 ppmv were examined. The presence of water vapor in the gas-stream along with acetone (350 and 500 ppmv) had little effect on the adsorption capacity of acetone even at 90% RH. Water vapor in the gas stream had little effect on the adsorption capacity of benzene (500 ppmv) until about 65% RH, when a rapid decrease resulted in the adsorption capacity of benzene with increasing RH. This RH was also about where capillary condensation of water vapor occurs within ACC pores. Water vapor condenses within the ACC pores, making them unavailable for benzene adsorption. Increasing benzene concentration can have a significant effect on the amount of water vapor adsorbed. At 86% RH and 500 ppmv, 284 mg/g water was adsorbed, while at 86% RH and 1000 ppmv, only 165 mg/g water was adsorbed. Water vapor was more inhibitory for benzene adsorption as benzene concentration in the gas stream decreased.

This paper presents results of chemical activation of sewage sludge, a waste material generated in sewage treatment processes, to produce an adsorbent for H₂S removal. Dewatered sewage sludge samples were subjected to chemical treatment by sulfuric acid and zinc chloride at various molar concentrations and were then pyrolysed in inert gas atmosphere at various temperatures for different hold times. Resulting adsorbents were characterised in terms of BET surface area, micropore area and pore size/volume distributions. In this study, it was shown that pyrolysis temperature and activation chemicals used significantly affect the surface area development and pore structure evolution. Solution molar concentration of the activating agent is a particularly important factor. H₂S adsorption tests were carried out on the derived adsorbents using a thermogravimetric analyser. Experimental results demonstrate that sewage sludge, a waste material in abundant supply at virtually no cost, is a viable source of activated adsorbents. Its potential use for odour control is reinforced by the need to find environmentally safe disposal alternatives for sewage sludge. From both economics and environmental perspectives, these experimental results warrant further efforts, perhaps in terms of large scale manufacturing and testing.

Type HGR^® activated carbon is frequently employed to protect aluminum heat exchangers in liquefying natural gas. Residual mercury levels in the treated gas are frequently at or near the limits of detection, challenging the analytical methods employed. Additionally, process variables and variations in the testing environment can affect the analytical procedures used to measure low levels of mercury. This paper will describe the analytical procedures used to routinely measure mercury levels to below 0.01 μg/Nm³ under challenging process and field conditions. The impact of process variables on adsorbent performance will also be described.

There is an emergent need to reduce the emissions of toxic volatile organic compounds (VOCs) to the atmosphere. One strategy to reduce the emissions of VOCs from point sources is to use air pollution control devices on the sources' discharge streams. This paper describes the development of a new activated carbon cloth (ACC) adsorption system that is integrated with cryogenic vapor recovery to reduce the amount of VOCs emitted to the atmosphere from point sources and provide for reuse of the VOCs that are recovered. Electrical current is used to regenerate the ACC. ACC adsorption followed by electrothermal regeneration results in formation of a concentrated organic vapor which is cryogenically condensed from the gas phase. Electrothermal desorption allows for careful control of the desorption time and the concentration profile of the desorbed VOC to allow minimal use of cryogen. Adsorption, followed by cryogenic treatment enables VOC sources to meet air quality control regulations while providing a high quality liquid VOC product for reuse.

Granular activated carbons (−20 + 100 mesh; 0.149−0.84 mm) were produced by physical activation and chemical activation with KOH from an Illinois bituminous coal (IBC-106) for natural gas storage. The products were characterized by BET surface area, micropore volume, bulk density, and methane adsorption capacities. Volumetric methane adsorption capacities ($\text{V}{}_{\mathrm{m}}\text{V}{}_{\mathrm{s}}$) of some of the granular carbons produced by physical activation are about 70 cm³/cm³ which is comparable to that of BPL, a commercial activated carbon. ($\text{V}{}_{\mathrm{m}}\text{V}{}_{\mathrm{s}}$) values above 100 cm³/cm³ are obtainable by grinding the granular products to −325 mesh (<0.044 mm). The increase in ($\text{V}{}_{\mathrm{m}}\text{V}{}_{\mathrm{s}}$) is due to the increase in bulk density of the carbons. Volumetric methane adsorption capacity increases with increasing pore surface area and micropore volume when normalizing with respect to sample bulk volume. Compared with steam-activated carbons, granular carbons produced by KOH activation have higher micropore volume and higher methane adsorption capacities (g/g). Their volumetric methane adsorption capacities are lower due to their lower bulk densities.

The fabrication of monolithic activated carbon fibre composites using isotropic pitch based carbon fibres, and phenolic resin as binder, is briefly described. The dimensional changes during drying, curing, baking and activation stages are presented and discussed. Data on other physical properties of the composites including their permeability and surface area are presented. With respect to gas separation, a technique developed to assess the potential of the composites to separate methane and carbon dioxide is described; the effects of some of the fabricating process variables on performance in CH₄/CO₂ separation is presented and discussed. In particular the effect of the extent of weight loss during activation on the final composite's properties is described.

Natural gas storage for natural gas vehicles and the separation and removal of gaseous contaminants from gas streams represent two emerging applications for carbon adsorbents. A possible precursor for such adsorbents is waste tires. In this study, activated carbon has been developed from waste tires and tested for its methane storage capacity and S0₂ removal from a simulated flue-gas. Tire-derived carbons exhibit methane adsorption capacities (g/g) within 10% of a relatively expensive commercial activated carbon; however, their methane storage capacities ($\text{V}{}_{\mathrm{m}}\text{V}{}_{\mathrm{s}}$) are almost 60% lower. The unactivated tire char exhibits SO₂ adsorption kinetics similar to a commercial carbon used for flue-gas clean-up.

A simple model has been created for predicting acid gas vapor-liquid equilibrium (VLE) in alkanolamines. The model is simple enough to use in a hand held calculator, but its structure is derived from theory. Model parameters were obtained by regression of experimental VLE data. The model is valid for total gas loadings from 0.003 to 0.8 and over a wide range of temperatures and amine concentrations. Partial pressure predictions are shown to agree with a more complex model over seven orders of magnitude in pressure. Heat of absorption values derived from the model are also shown to agree with literature sources. Parameters are given for the MDEA-H₂O-H₂S-CO₂ and DEA-H₂O-H₂S systems.