Soon-Haeng Cho

Vacuum swing adsorption process for the separation of ethylene/ethane with AgNO3/clay adsorbent

The performance of the 4-bed and 3-bed VSA process using AgNO3/clay adsorbent for the ethylene separation from C2 fractionator feed (83.56% C2H4, 16.44% C2H6) was investigated experimentally and theoretically. With the 4-bed VSA process, extremely high recovery of ethylene, over 99%, was obtained at ethylene purity of 99.8%. The recovery of the 3-bed process was lower about by 1% than that of the 4-bed VSA process. But, the productivity of the 3-bed VSA was higher about by 33% than that of the 4-bed VSA process. The productivity of the 3-bed VSA process was 3.7 mol/kg/hr at the ethylene purity of 99.8%. Effects of the rinse flow rate in the 3-bed VSA process were investigated by both experiment and simulation. The purity of ethylene was not significantly improved by the increase of the rinse flow rate after it reached 99.8%. At the rinse flow rate where the purity was 99.9%, the recovery became 70%. It might be attributed to the slow diffusion of ethane. According to the simulation, ethylene purity of over 99.9% could be obtained with recovery of over 90% only when the mass transfer rate of ethane is lower than 1.0×10-4 s-1 or higher than 0.2 s-1. The productivity of the process could be improved by increasing the feed flow rate at the expense of the recovery. According to the simulation, at the feed flow rate of 5,000 ml/min, the productivity of 5.2 mol/kg/hr was obtained at the ethylene purity of 99.5%.

Adsorptive ethylene recovery from LDPE off-gas

The objective of this study was to verify experimentally the recovery of high-purity ethylene from LDPE off-gas by a vacuum swing adsorption process. Adsorbent for this purpose was prepared by the impregnation of AgNO3 on Montmorillonite clay. The prepared adsorbent with an original substrate-shaped form shows high adsorption selectivities of light olefins to the corresponding paraffins. A 4-bed vacuum swing adsorption process using the above adsorbent, in which steps comprise adsorption (feeding), cocurrent rinse with ethylene product, countercurrent desorption (production) of ethylene by vacuum pump, pressurization-1 with paraffin stream, pressurization-2 with the rinse off-gas from the other bed and pressurization-3 with paraffin stream, was experimentally applied to recover ethylene from LDPE off-gas. Ethylene product purity of 99.95% could be obtained with the recovery of over 93%. The ethylene productivity of prepared adsorbent was 1.98 mol/kg-hr.

Adsorption Equilibrium and Dynamics of C4 Olefin/Paraffin on π‐Complexing Adsorbent

Abstract Ag+ ion impregnated clay as a newly developed adsorbent was studied for 1‐butene separation from n‐butane. Equilibrium adsorption isotherms of pure components were measured at the temperature range from 25°C to 100°C and pressure up to 1200 mmHg. Experimental data of n‐butane and 1‐butene were correlated with various isotherm models. The best selectivity was shown at 80°C. Equilibrium capacities for 1‐butene and n‐butane at 80°C and 900 mmHg were 0.92 and 0.31 mmol/g, respectively. The average heats of adsorption for n‐butane and 1‐butene were found to be 6.6 and 13.3 kcal/mol, respectively. Diffusion of 1‐butene and n‐butane on this sorbent was fast, with 100% uptake reached within 15 min. The IAS model with Toth isotherm for pure component gave the best prediction results for both the n‐butane and 1‐butene compared to the other models used in the study. Binary adsorption equilibrium was well predicted by the Ideal Adsorbed Solution (IAS) model. The equilibrium adsorption ratio of 1‐butene/n‐butane in binary system was 14.87 and its selectivity was 6.71 at 80°C and 900 mmHg, when the mole fraction of 1‐butene in gas phase was 0.689. Experimental breakthrough curves were well predicted by a mathematical model, and the curves were steep enough to separate 1‐butene from n‐butane. Thus, it can be noted that Ag+ ion impregnated clay can be applied to the adsorptive separation of C4 olefin/paraffin.

Catalytic Composites Based on Yttria Stabilized Zirconia for Oxidative Dehydrogenation of Ethane

LiCl/YSZ is found to be a very effective catalyst for the oxidative dehydrogenation of ethane. LiCl supported on YSZ-MgO composite shows increase in catalytic activity and ethylene selectivity. Addition of Mn and Sn as promoters to this system leads to 85% ethane conversion, 77% ethylene selectivity and 65% ethylene yield at 662 °C. Use of Li2O in the place of LiCl results in lower ethylene yields. Further modification is needed to improve the catalyst stability.

Production of High-Purity Nitrogen from Air by Pressure Swing Adsorption on Zeolite X

Abstract A PSA air separation process for the production of high purity nitrogen is studied experimentally and theoretically. The experimental apparatus is composed of three columns filled with zeolite X. The PSA cycle consists of six steps: pressurization with air, adsorption, recovery, null, high pressure purge with product nitrogen, and desorption. The nitrogen purity analyzed between 95.0 and 99.992%. The effects of adsorption pressure and reflux ratio on the PSA performance are studied experimentally. The productivity is 2.8 NL/(kg·min) and the recovery is 55% at a nitrogen purity of 99.99% and an adsorption pressure of 800 mmHg. The experimental results are compared with the theoretical model, and the effects of the recovery step and the operating variables on the performance are studied theoretically. The recovery step makes the PSA performance favorable, especially in the high product purity region above 99%.

A TWO STAGE PSA FOR ARGON AND HYDROGEN RECOVERY FROM AMMONIA PURGE GAS

Abstract A two stage PSA process for argon and hydrogen recovery from ammonia purge gas was developed. Appropriate adsorbents were selected by considering adsorption equilibrium and regeneration possibility. A continuous process, which can treat about 100 Nm3/h of ammonia purge gas, was designed by applying the adsorption equilibrium and breakthrough test results. The continuous process consists of 2 stage PSA with 4 beds respectively. Product hydrogen (>99%) can be obtained from the first stage during first period of adsorption step, and also from the second stage. An intermediate product, argon and hydrogen mixture, is obtained from the first stage during the second period of adsorption step, and this is sent to the second stage to be separated into high purity argon and hydrogen respectively. From the raw purge gas containing about 6% argon, argon is concentrated upto 14% through the first stage, and upto 97% through the second stage PSA.

A Parametric Study of Pressure Swing Adsorption for the Recovery of Carbon Dioxide from Flue Gas

Recovery of carbon dioxide from a binary mixture (N2/CO2) simulating flue gas was performed by pressure swing adsorption (PSA) using zeolite-X. One PSA process consists of three adsorption beds. The process was tested by varying the operation parameters: pressures of adsorption and vacuum evacuation steps. As a typical result, a high purity CO2 (~99%) can be produced with recoveries of 20% and 53% from feed gases containing 15 and 25 vol.% CO2, respectively. By the other process of two stage PSA, CO2 can be concentrated from feed gas to a product of 99% with much higher recovery.

PSA Processes for Recovery of Carbon Dioxide

Publisher Summary Carbon dioxide is considered the main cause of global warming. For sustainable development, efforts are being undertaken to mitigate the emission of CO 2 to the atmosphere. The pressure swing adsorption (PSA) process is a highly efficient gas separation process and also applied for the removal of carbon dioxide from various gas mixtures PSA processes are studied for the recovery of carbon dioxide from various sources including steel mill offgas, petrochemical waste gas, and combustion flue gas. The 1-stage PSA process is applied when the concentration of CO 2 is higher than 25% like the steel mill off-gas and petrochemical waste gas. The 1-stage PSA process generally consists of four steps; pressurization with feed gas, adsorption, high pressure rinse with product CO 2 , and evacuation. Especially, when the feed contains about 25% CO 2 , performing low pressure purge and recycling the effluent to the feed inlet greatly enhances the process performance. In a typical run, a high purity CO 2 of 99% is produced with recovery of 80% from feed gas containing 25% CO 2 . The 2-stage PSA process is more efficient than 1-stage PSA when the concentration of CO 2 is low. At the first stage of the 2-stage PSA, CO 2 is concentrated to 40-60% from the feed of less than 15% CO 2 and then concentrated to 99%, at the second stage. With the 2-stage PSA process composed of 2-bed for each stage, 99% CO 2 is recovered with 80% recovery from the feed containing 11% CO 2 .

Analysis of Equilibrium PSA Performance with an Analytical Solution

Five-step PSA cycles consisting of pressurization with product, adsorption, co-current depressurization, blowdown, and purge steps have been analyzed with equilibrium model assuming uncoupled linear isotherms and isothermal condition. Unlike the previous models, the proposed model is not restricted to the operating conditions that ensure a complete shock transition of concentration profile at the end of the high pressure adsorption step. The operating conditions could have two classifications: one is utilizing the column completely before blowdown, and the other is not. As the selectivity increases, it is more difficult to utilize the column completely before the blowdown step. There is an optimum co-current depressurization pressure which maximizes the recovery at the given extent of purge. The optimum co-current depressurization pressure decreases as the purge quantity decreases. On the less selective adsorbent, the recovery at the optimum co-current depressurization pressure increases with the decrease of purge quantity without much sacrifice of the throughput. But, on the highly selective adsorbent, there is an extent of purge and corresponding value of cocurrent depressurization pressure below which the recovery is not greatly improved while the throughput decreases rapidly, which limits the number of pressure equalization steps can be included.

ISOBUTANE PURIFICATION BY PRESSURE SWING ADSORPTION

This study is on the development of high-purity isobutane production from isobutane-enriched stream by gaseous adsorption technology. Isobutane purification from C4 mixture, in which not only isobutane, but also n-butane and several kinds of CJ olefins in small or in trace are involved, is very difficult by a traditional distillation method because of their close relative volatilities between constituting components. The continuous layered 3-bed process in which was comprised of six steps as follows; pressurization-1 by the cocurrent effluent gas from the other bed, pressurization-2 by isobutane product, adsorption, wcurrent depressurization, countercurrent blowdown, and low pressure purge by isobutane product, was applied. From the experiment, isobutane product with over 99.9% purity and with the trace levels of olefin components could be obtained at ambient temperature. Silver impregnated clay prefers to CMS for the removal of C4 olefins