Gas Separation & Purification最新文献

The intensification of argon purification from oxygen by cryoadsorption is feasible by cooling the adsorbent in an argon medium and by dehydration under decreased temperature. A modified NaA zeolite is used as an adsorbent. The argon purification process has been investigated at an oxygen concentration of 3% at 90 K and at a degree of purification of 1 ppm. The conditions of the occurrence of argon capillary condensation have been considered. The zeolite modification with the best adsorption performance has been defined and an improved method of argon purification from oxygen has been developed.

The calculated relations for defining the value of the adsorbent dynamic capacitance as a function of the rate of flow, and the argon preadsorption as a function of the adsorbent cooling time have been obtained and a plot has been constructed for defining the coefficient of dynamic capacitance decrease under decreased temperature of dehydration. As a result, a calculation formula is proposed for defining the adsorber protective action time under argon purification from oxygen with allowance for the rate of flow, the argon preadsorption value and the temperature of dehydration.

Four kinds of low-molecular-weight liquid crystals (LCs) (cholesteryl oleyl carbonate (COC), the benzoate-containing mixture LC DYC, p-heptyl-p′-cyanobiphenyl (7CB), p-pentylphenol-p′-methoxybenzoate (5PMB) and four cellulose derivatives (ethyl cellulose (EC), cellulose diacetate, cellulose triacetate, cellulose nitrate) were used to prepare blend membranes of thickness 13–45 μm by a solution casting technique. The oxygen permeability, the oxygen/nitrogen separation factor, the permeation flux Q_OEA and the oxygen concentration Y_O2 of the oxygen-enriched air (OEA) through the cellulose derivative membranes with different LCs were studied by a constant pressure-variable volume method. The experimental results show that the membrane-forming ability, uniformity, toughness and air-separation properties of the cellulose derivatives have been improved by adding no more than 12 wt% LC. The air-separation properties of the resulting membranes vary significantly with membrane composition, temperature and pressure difference. Of all the membranes, the COC/EC(4/96) membrane of thickness 18 μm exhibits the highest Q_OEA value of 1.8 × 10⁻⁴ cm³(STP) s⁻¹ cm⁻² and maintains the Y_O2 value of 38.8% in a single operation.

In this paper, the separation characteristics of polyvinyl alcohol membranes are compared for pervaporation of binary, ternary and multicomponent organic/water mixtures. The analyses were performed as a function of composition at steady-state operating conditions. Results are compared in terms of difference in permeation rate, separation factor, time taken for dehydration and temperature drop across the membrane for the three systems. The separation ability of the membrane is expressed in terms of permeation rate and selectivity. From the results, we found that the permeation rate increased and the separation factor decreased as the water concentration in the feed increased. Furthermore, we noted that the presence of one component affects the rate of transfer of the other. These results confirm that interaction between the feed, the permeate and the polymer plays an important role in pervaporation. For binary and ternary systems, permeate composition remains relatively constant over a wide range of feed concentrations, and, for the multicomponent system, water concentration in the permeate decreases as more alcohol molecules are sorbed into the membrane.

Air-lift reactors are important gas-liquid contactors for gas separation, purification, fermentation and waste water treatment on account of their simple construction and low energy consumption together with high mass and heat transfer rates. Apart from the improved liquid mixing, air-lift reactors have no moving elements and the power requirement comes only from the air supply.

A new air-lift tube (ALT)-type reactor was investigated in laboratory and pilot scale. A study was conducted to measure the effects of liquid properties (such as viscosity and density) on the hydrodynamics of the ALT reactor. The systems used for this study were: air/water, air/sodium hydroxide solution, air/sodium citrate buffer solution and air/glycerine. Pressure drop in the reaction tube, minimum and maximum gas velocities, pressure frequency and recycle liquid velocity in the recycle tube were measured under different experimental conditions using different tube diameters for the recycle and reaction tubes.

Design correlations for the above-mentioned parameters were developed by computer program in order to design an ALT reactor for gas-liquid reactions. The correlations are valid in the range 0.1–1400 m³ h⁻¹ of the gas stream.

In oil fields, separators are used to separate oil and gas contained in the crude oil pumped from the wells before processing. Although there are many factors influencing the performance of these separators, one of the crucial problems is the formation of foam due to the impurities present in the crude. Another operating problem is carry-over, which occurs when free liquid escapes with the gas phase. Of the several methods used to control foam, chemical control by use of antifoam agents is very important. In this work, the main objective is to study the poor separation of oil and gas due to foaming and the carry-over problem in separators observed in one of the oil fields in Kuwait. Studies were also conducted on the effect of a silicone antifoam agent used to control foaming in order to increase the separation efficiency and thereby increase the production capacity.

The absorption of SO₂ from an SO₂/air mixture into CaCO₃ slurry or NaOH aqueous solution was carried out using a new model of an air-lift tube (ALT)-type reactor in laboratory scale and in pilot scale. The aim of the study was to improve the efficiency of these processes, widely applied in industry, to find the optimal operation conditions in the new reactor type. The SO₂-removal efficiency was measured by varying the gas velocity, the SO₂ concentration and either the CaCO₃ or the NaOH concentration according to experimental design. A computer program (Statgraphics/experimental design) was used to calculate the mathematical models of the SO₂-removal efficiency, and the economic aspects of the two processes were compared.

The purpose of this work is to propose a method of global characterization of the behaviour of pressure-swing-adsorption (PSA) cycles based on statistical experiments design, the ‘experiments’ being actually numerical (simulation). The result of that procedure presented here is a set of polynomials describing the performances of the PSA cycles (purity, yield, productivity) as functions of operating or design variables (flow rates, pressures, composition, bed length, step durations). These polynomials represent the sensitivity of the process to fluctuations, perturbations or intentional changes of process variables, and can be used, within their range of validity, as a fast aid to operators, and as a tool for design and optimization. The specific case investigated is a PSA cycle for pure hydrogen production from a mixture with CO₂, CH₄, CO and N₂ obtained by cracking natural gas. The process comprises two adsorbent beds, each containing a zeolite layer on top of an active carbon layer.

Measurements have been made of the permeability of nitrous oxide (N₂O), carbon dioxide (CO₂) and oxygen (O₂) through silicone rubber and cellulose acetate membranes using a flat sheet permeator. Measurements have also been made of individual gas permeabilities from a mixed feed stream. N₂O had the highest permeability when using the silicone rubber membrane, followed by CO₂, with O₂ an order of magnitude less. All three gas permeability coefficients were independent of feed pressure for this membrane and N₂O and CO₂ permeability coefficients were temperature independent. For the cellulose acetate membrane, N₂O and CO₂ permeabilities varied with feed pressure and all three gases gave positive temperature coefficients. No separation of CO₂ from N₂O could be achieved under any conditions with the cellulose acetate membrane.

Today structured packing is commonly applied in cryogenic air separation plants. Packing is typically characterized by a high surface-to-volume ratio. Owing to the large surface of packing in comparison to common sieve trays — provided equal amounts of oil are attached to surfaces — more organic material may be present within a low-pressure column of an air separation plant. Since an enrichment of organic material in an air separation plant or in liquid oxygen is a principal hazard, and a major accumulation of organic material magnifies this risk, experimental tests were conducted to determine whether chipping of oil at cryogenic temperatures is possible.

Tests are discussed where single sheets of a packing segment had been coated with an oil film of definite thickness. The oil-coated sheets were rinsed by moving them up and down in liquid nitrogen or in liquid oxygen. After fixed time intervals the oil content of a single sheet was determined.

It was concluded that the original oil residue on the sheets up to 250 mg m⁻² remained attached to the packing surface and no decrease of oil was found within the accuracy of the oil determination method.