H2S–CO2 Separation Using Room Temperature Ionic Liquid [BMIM][Br]

Solubility and selective absorption of hydrogen sulfide (H₂S) over carbon dioxide (CO₂) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) has been evaluated under ambient temperature and pressure. [BMIM][Br] demonstrated its potential as a solvent for selective removal of H₂S from CO₂/H₂S mixture. Our investigation indicated that H₂S solubility in [BMIM][Br] is comparable to or better than that in commercially available MDEA-based solvents. Meanwhile, CO₂ solubility in [BMIM][Br] is lower than that in the same amine resulting in H₂S/CO₂ absorption selectivity of within 3.5 to 3.75. The solubility behavior is relatively maintained after 4 times absorption-desorption cycles. A computational molecular study suggested that intramolecular hydrogen bonding interaction between anion Br and hydrogen atom of H₂S could stabilize the complex and resulted lower complexation energy than CO₂ interaction with [BMIM][Br]. Based on the experiment results, a separation process employing [BMIM][Br] is proposed to control the CO₂/H₂S ratio existing in a natural gas feed.     

Simultaneous experiments of sulfidation and regeneration in two pressurized fluidized-bed reactors for hot gas desulfurization of IGCC

Hot Gas Desulfurizarion for IGCC is a new method to efficiently remove H2S in fuel gas with regenerable sorbents at high temperature and high-pressure conditions. The Korea Institute of Energy Research did operation of sulfidation in a desulfurizer and regeneration in a regenerator simultaneously at high pressure and high temperature conditions. The H₂S concentration at exit was maintained continuously below 50ppmv at 11,000 ppmv of inlet H₂S concentration. The sorbent had little effect on the reducing power in the inlet gas in the range from 11% to 33% of H₂. As inlet H₂S concentration was increased, H₂S concentration in the product gas was also increased linearly. The sorbent was maintained at low sulfur level by the continuous regeneration and the continuous solid circulation at the rate of 1.58× 10⁻³ kg/s with little mean particle size change.     

The removal of hydrogen sulfide with manganic sorbent in a high-temperature fluidized-bed reactor

The removal of hydrogen sulfide (H₂S) from simulated gas was carried out in a batch type fluidized-bed reactor using natural manganese ore (NMO), which consists of several metal oxides (MnO_x: 51.85%, FeO_y: 3.86%, CaO: 0.11%). The H₂S breakthrough curves were obtained by changing temperature, gas velocity, initial H₂S concentration, and aspect ratio. Moreover, the effects of the particle size and the particle-mixing fraction on H₂S removal were investigated in a binary system of different particle size. From this study, H₂S removal efficiency increased with increasing temperature but decreased with increasing excess gas velocity. The breakthrough time for H₂S decreased as the gas velocity increased, which leads to reducing gas-solid contacting due to gas bypassing in a fluidized bed reactor. Improvement of H₂S removal efficiency in continuous process can be expected from the results of the binary particle system with different size in a batch experiment. The NMO could be considered as a potential sorbent in H₂S removal.     

Mesoporous-molecular-sieve-supported Polymer Sorbents for Removing H2S from Hydrogen Gas Streams

A series of sorbents with a linear polyethylenimine (PEI) supported on the mesoporous molecular sieves, including MCM-41, MCM-48 and SBA-15, have been prepared and used to remove H₂S from a model gas containing 0.40 v% of H₂S and 20 v% H₂ in N₂ gas. The sorption was conducted in a fixed-bed system at a temperature range of 22–75 °C, a GHSV range of 337–1,011 h^?1 and atmospheric pressure. The effects of the operating temperature, GHSV, the amount of PEI loading and the different molecular sieve supports were studied. A reduction in the temperature and GHSV improves the sorption performance of the supported PEI sorbents. A synergetic effect of the SBA?15 support and PEI on the H₂S sorption performance was observed. Loading 50 wt% PEI on SBA-15 gave the best breakthrough capacity, while loading 65 wt% PEI on SBA-15 had the highest saturation capacity. The mesoporous molecular sieve with large pore size and three-dimensional channel structure favors increasing the kinetic capacity of the supported PEI sorbent. In addition, the developed sorbents can be regenerated easily at mild conditions (temperature range of 75–100 °C) and have excellent regenerability and stability. The results indicate that the mesoporous-molecular-sieve-supported polymer sorbents are promising for removing H₂S from hydrogen gas streams.     

Highly selective absorption separation of H2S and CO2 from CH4 by novel azole-based protic ionic liquids

Recently, the selective removal of H₂S and CO₂ has been highly desired in natural gas sweetening. Herein, four novel azole-based protic ionic liquids (PILs) were designed and prepared through one-step neutralization reaction. The solubility of H₂S (0–1.0 bar), CO₂ (0–1.0 bar), and CH₄ (0–5.0 bar) was systematically measured at temperatures from 298.2 to 333.2 K. NMR and theoretical calculation were used to investigate the reaction mechanism between these PILs and H₂S. Reaction equilibrium thermodynamic model (RETM) was screened to correlate the H₂S solubility. Impressively, 1,5-diazabicyclo[4,3,0] non-5-ene 1,2,4-1H-imidazolide ([DBNH][1,2,4-triaz]) shows the highest H₂S solubility (1.4 mol/mol or 7.3 mol/kg at 298.2 K and 1.0 bar) and superior H₂S/CH₄ (831) and CO₂/CH₄ (199) selectivities compared with literature results. Considering the excellent absorption capacity of H₂S, high H₂S/CH₄, and CO₂/CH₄ selectivity, acceptable reversibility, as well as facile preparation process, it is believed that azole-based PILs provide an attractive alternative in natural gas upgrading process.     

Estimating solubility of supercritical H2S in ionic liquids through a hybrid LSSVM chemical structure model

Development of a predictive tool for H₂S solubility estimation can be very helpful in gas sweetening industry. Experimental databases on H₂S solubility were rarely available, so as reliable predictive models. Thus, in this study the H₂S solubility database was established, and then a Least-Squares Support Vector Machine (LSSVM) approach based on the established database is proposed. Group contribution method was also applied to eliminate the model's dependence on experimental data. Accordingly, our proposed LSSVM model can predict H₂S solubility as a function of temperature, pressure, and 15 different chemical structures of Ionic liquids (ILs). Root Mean Square Error (RMSE) and coefficient of determination (R²) are 0.0122 and 0.9941, respectively. Moreover, comparison of our model with other existing models showed its reliability for H₂S solubility in ILs. This can be very useful for engineers dealing with gas sweetening process in different applications of analysis, simulation, and designation.     

Adsorption of hydrogen sulphide on molecular sieves: No enrichment in the presence of carbon dioxide

Studies of sorption of binary H₂S-CO₂ gas mixtures on LTA zeolites demonstrated the dual function of zeolites acting both as selective adsorbents and as catalysts for converting H₂S and CO₂ into COS and H₂O with shift of the reaction equilibrium to the r.h.s. products due to preferential sorption of water. These results are opposite to the experience gained from technical desulphurization plants for selective removal of H₂S in presence of CO₂, especially on LTA zeolites. Having used data characteristic of a natural gas and of a technical plant adsorber, the mathematical modelling of the separation process gave evidence of the impossibility of sufficient enrichment of H₂S by means of adsorption on the zeolitic molecular sieves under consideration.     

Sulphur capture during gasification of oil sand cokes

The capture of sulphur via the H₂S-CaO reaction during gasification of delayed coke has been investigated in a 6.4 cm dia. semi-batch stirred bed reactor. Calcines from one of three limestones or a dolomite were mixed with coke which was then gasified in a steam-nitrogen mixture at atmospheric pressure and 930°C. The H₂S content of the gas, and the sulphur content of the sorbent were determined as functions of time. The effects of sorbent surface area, percentage calcination, and the Ca/S ratio on the extent of sulphur capture and the conversion of sorbents were determined. The sulphidation reaction was analyzed using continuous and grain models. After an initial stage of chemical control the reaction appears to be controlled by diffusion through the product layer of the grain.     

Development of silica‐gel‐supported polyethylenimine sorbents for CO2 capture from flue gas

In order to reduce the sorbent preparation cost and improve its volume‐based sorption capacity, the use of an inexpensive and commercially available silica gel was explored as a support to prepare a solid polyethylenimine sorbent (PEI/SG) for CO₂ capture from flue gas. The effects of the pore volume and particle size of the silica gels, molecular weight of polyethylenimine and amount of polyethylenimine loaded, sorption temperature and moisture in the flue gas on the CO₂ sorption capacity of PEI/SG were examined. The sorption performance of the developed PEI/SG was evaluated by using a thermogravimetric analyzer and a fixed‐bed flow sorption system in comparison with the SBA‐15‐supported polyethylenimine sorbent (PEI/SBA‐15). The best PEI/SG sorbent showed a mass‐based CO₂ sorption capacity of 138 mg‐CO₂/g‐sorbent, which is almost the same as that of PEI/SBA‐15. In addition, the PEI/SG gave a high volume‐based sorption capacity of 83 mg‐CO₂/cm³‐sorbent, which is higher than that of PEI/SBA‐15 by a factor of 2.6. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2495–2502, 2012     

H2S absorption at high pressure using hollow fibre membrane contactors

In this article, the removal of H₂S from natural gas at high pressure using hollow fibre membrane contactors and water as the absorbent solvent was described and validated by a 2D comprehensive mathematical model. The modelling predictions were in a good agreement with the experimental data at low pressure of 1 bar under non-wetting conditions. However, the experimental behaviour at high pressure in the range of 10–50 bar was always lower than the modelling predictions. And thus, a sensitivity analysis was carried out to study the influence of gas, liquid, membrane diffusion and solubility coefficients of H₂S at high pressure upon the modelling behaviour compared with the experimental trend. The modelling results confirmed that these parameters were still insensitive as the model predictions changed slightly with altering these coefficients. Conversely, membrane wetting was confirmed to be an important factor even for small ratios, i.e. pseudo-wetting (1–3%). The model was able to predict the absorption of H₂S at higher pressures under 3% pseudo-wetting. Although the type of membranes used in this study was highly hydrophobic (ePTFE) and thus membrane wetting was not expected, pseudo-wetting phenomenon was confirmed to be an important factor at high pressure.     

Effect of dissolved gases on subcooled flow boiling heat transfer

The influence of various dissolved gases (He, N₂, Ar, CO₂, C₃H₈) on subcooled boiling heat transfer was investigated for flow of water and of heptane in an annulus with a heated core. Flow velocity, liquid bulk temperature, system pressure, gas partial pressure and heat flux were all varied over a wide range.In comparing the measured heat transfer coefficients with those for subcooled boiling of the corresponding degassed liquids, it was found that the coefficients were always increased owing to the desorption of the dissolved gases. The extent of the increase depended on the solubility of the given gas in the given liquid and could be as much as several hundred per cent. In addition, the solid surface temperature required for the inception of bubble formation was reduced considerably, in some cases far below the saturation temperature of the pure liquid.Attempts were made to extend the prediction of incipient boiling temperatures to cases where gases are dissolved in the liquid.     

Separation and Recovery of Uranium from Wastewater Using Sorbent Functionalized with Hydroxamic Acid

A newly developed hydroxamic acids functionalized acrylic based solid phase sorbent, named as poly-acryl hydroxamic acid (PHOA) is used as an extractant for the recovery of uranium from nuclear waste solution. Various parameters such as sorbent solubility in different medium, effect of various cations on U(VI) sorption, desorption performance of different eluents with respect to U(VI) sorption has been investigated in detail. U(VI) sorption behaviors of the sorbent were studied in different concentration of competitive ions such as Mg²⁺, Fe³⁺, and NO₃^? and it was found that the sorbent was capable of removing the U(VI) efficiently in the presence of high concentration of these ions.     

Sorption properties of lithium carbonate doped CaO and its performance in sorption enhanced methane reforming

In-house prepared lithium carbonate doped CaO was tested for its CO₂ sorption properties and suitability as a CO₂ sorbent for sorption-enhanced reforming of methane. The new material demonstrated CO₂ capacity at the temperatures above the equilibrium for CaO recarbonation reaction. However, the capacity was unstable and decreased during carbonation–regeneration cycles. After sufficiently large number of cycles Li dopant escaped from the sorbent and its sorption behavior resembled to that of CaO. The main route of escape is, probably, a crossover of liquid Li₂CO₃ onto crucible in TG experiments and onto catalyst in SER tests. Sorption enhanced methane reforming at 2 bar pressure, 750 °C and H₂O to CH₄ ratio of 4 using novel sorbent yielded as high as 99.8 vol% pure hydrogen during the first cycle. In subsequent cycles the hydrogen purity drastically decreased as a result of severe catalyst poisoning by Li.     

Integrated combined cycle from natural gas with CO2 capture using a Ca–Cu chemical loop

The integration in a natural gas combined cycle (NGCC) of a novel process for H₂ production using a chemical Ca–Cu loop was proposed. This process is based on the sorption‐enhanced reforming process for H₂ production from natural gas with a CaO/CaCO₃ chemical loop, but including a second Cu/CuO loop to regenerate the Ca‐sorbent. An integration of this system into a NGCC was proposed and a full process simulation exercise of different cases was carried out. Optimizing the operating conditions in the Ca–Cu looping process, 8.1% points of efficiency penalty with respect to a state‐of‐the‐art NGCC are obtained with a CO₂ capture efficiency of 90%. It was demonstrated that the new process can yield power generation efficiencies as high as any other emerging and commercial concepts for power generation from NGCC with CO₂ capture, but maintaining competing advantages of process simplification and compact pressurized reactor design inherent to the Ca–Cu looping system. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2780–2794, 2013     

Effect of sulfidation/oxidative regeneration cycle on the solid structural changes of sorbent for high-temperature removal of H2S

In order to investigate the effects of sulfidation/oxidative regeneration cycle on the change of structural properties and removal capacity of sorbent, sulfidation/regeneration cycle was carried out up to 15 times in a fixed-bed reactor. The effluent gases from the fixed-bed reactor were analyzed by gas chromatography, and XRD, SEM, and liquid nitrogen physisorption method were used to characterize the reacted sorbents. The sorbent treated first sulfidation/regeneration cycle exhibited maximum specific surface area and the highest H₂S removal capacity. Hysteresis of adsorption isotherm of the regenerated sorbent reflected the growth of pores of fresh sorbent and pore size distribution confirmed this fact. Furthermore constant H₂S removal capacity was maintained up to 15 times of sulfidation/regeneration cycle.     

Optimal temperature of fixed-bed reactor for high temperature removal of hydrogen sulfide

To find optimal temperature of the reaction between H₂S gas and ZnO-5 at% Fe₂O₃ sorbent, the effluent gas from a fixed-bed reactor was analyzed by gas chromatography. The experimental results showed that H₂S removal efficiency of sorbent was maximum at 650°C and EDX data were in accordance with this feature. XRD analysis exhibited intriguing phenomenon in that different mechanisms were observed at different temperatures. Chemisorption and chemical reaction was considered to be the main mechanism of H₂S removal at 600 C and 650°C, respectively. SEM photographs supported this interesting phenomenon, but unfortunately TGA and DTA results could not distinguish it. To investigate the effect of sorbent deactivation on the reaction rate, deactivating factor was considered.     

Development of a Scalable Method for Manufacturing High‐Temperature CO2 Capture Sorbents

An engineered process for scalable manufacture of a calcium aluminum carbonate CO₂ sorbent with production amounts of about 1000 g per hour has been developed. The process includes mixing and heating, solid‐liquid separation, drying and extrusion, crushing and conveying, and calcined molding steps. The sorbent preparation involves the coprecipitation of Ca²⁺, Al³⁺, and CO₃^2– under alkaline conditions. By adjusting the Ca:Al molar ratio, a series of Ca‐rich materials could be synthesized for use as CO₂ sorbents at 750 °C. A calcium acetate‐derived sorbent exhibited better cyclic stability than sorbents originating from CaCl₂ and Ca(NO₃)₂. The initial sorption capacity increased with CaO concentration. High stability of more than 90 % was maintained by the Ca:Al sorbents after 40 looping tests.     

The effect of CO<Subscript>2</Subscript> or steam partial pressure in the regeneration of solid sorbents on the CO<Subscript>2</Subscript> capture efficiency in the two-interconnected bubbling fluidized-beds system

The effect of CO₂ or steam partial pressure in the regeneration of CO₂ solid sorbents was studied in the two-interconnected bubbling fluidized-beds system. Potassium-based dry solid sorbents, which consisted of 35 wt% K₂CO₃ for CO₂ sorption and 65 wt% supporters for mechanical strength, were used. To investigate the CO₂ capture efficiency of the regenerated sorbent after the saturated sorbent was regenerated according to the CO₂ or steam partial pressure in the regeneration, the mole percentage of CO₂ in the regeneration gas was varied from 0 to 50 vol% with N₂ balance and that of steam was varied from 0 to 100 vol% with N₂ balance, respectively. The CO₂ capture efficiency for each experimental condition was investigated for one hour steady-state operation with continuous solid circulation between a carbonator and a regenerator. The CO₂ capture efficiency decreased as the partial pressure of CO₂ in the fluidization gas of the regenerator increased, while it increased as that of steam increased. When 100 vol% of steam was used as the fluidization gas of the regenerator, the CO₂ capture efficiency reached up to 97% and the recovered CO₂ concentration in the regenerator was around 95 vol%. Those results were verified during 10-hour continuous experiment.     

Sorption, diffusion, and permeation of light olefins in poly(ether block amide) membranes

Sorption, diffusion, and permeation of three olefins (i.e., C₂H₄, C₃H₆, and C₄H₈) in poly(ether block amide) (PEBA 2533) membranes at different temperatures and pressures were investigated. This is pertinent to olefin recovery from resin off gas in polyolefin manufacturing. The relative contribution of solubility and diffusivity to the preferential permeability of olefins over nitrogen was elucidated. It was revealed that the favorable olefin/nitrogen permselectivity was primarily attributed to the solubility selectivity, whereas the diffusivity selectivity may affect the permselectivity negatively or positively, depending on the operating temperature and pressure. The olefin permeability is in the order of C₄H₈>C₃H₆>C₂H₄, the same order as their solubility in the membrane. In general, a low temperature favors both the permeability and selectivity. With an increase in pressure and/or a decrease in temperature, the sorption uptake of the olefin in the membrane increases progressively, and the diffusivity and hence the permeability are also enhanced because of the increased membrane plasticization/swelling caused by the penetrant sorbed in the membrane. At a given temperature, the pressure dependence of solubility and permeability could be described empirically by an exponential function. The limiting solubility at infinite dilution was correlated with the reduced temperature, and the hypothetical diffusivity at zero pressure was related to temperature by the Arrhenius equation.