Hydrothermal gasification of Rosa Damascena residues: Gaseous and aqueous yields

The gasification of Rosa Damascena residues – by-products of the rose-oil industry – was investigated under hydrothermal conditions at 500 °C and 600 °C, 35–45 MPa pressure with a reaction time of 1 h. The experiments were performed in the absence and presence of catalysts of K₂CO₃ and trona in a batch type reactor. The composition of the gaseous and aqueous products was determined by gas chromatography and high performance liquid chromatography, respectively. H₂, CO₂ and CH₄ are the main gaseous products while carboxylic acids (formic acid, acetic acid, glycolic acid) are the main components found in the aqueous phase followed by furfurals, phenols, aldehyde and ketones. More gaseous products were obtained at the higher temperature of 600 °C. Adding catalyst was found to aid the conversion process but the effect was only slight. Rosa Damascena residues have the potential to be a useful source for H₂ production in the future.     

Pyrolysis of pine wood in a slowly heating fixed-bed reactor: Potassium carbonate versus calcium hydroxide as a catalyst

Catalytic pyrolysis of pine wood was carried out in a fixed-bed reactor heated slowly from room temperature to 700 °C under a stream of purging argon to examine the effects of the physically mixed K₂CO₃ or Ca(OH)₂ on the pyrolysis behaviors. K₂CO₃ demonstrated a stronger catalysis for decomposition of hemicellulose, cellulose and lignin constituents, leading to the reduced yield of liquid product in conjunction with the increased yields of gaseous and char products because of the promoted secondary reactions of liquid product. With the addition of 17.7 wt.% of K₂CO₃, none of saccharides, aldehydes and alcohols was formed and the formation of acids, furans and guaiacols was substantially reduced, whereas the yields of alkanes and phenols were increased. Potassium led to an increase in the cumulative yields of H₂, CO₂ and CO at 700 °C. Ca(OH)₂ somewhat promoted the decomposition of cellulose and lignin constituents, and the effect of Ca(OH)₂ on the yields of liquid and char was opposite to that of K₂CO₃. With the addition of 22.2 wt.% Ca(OH)₂, some groups of liquid product such as acids and aldehydes disappeared completely and the yields of saccharides, furans and guaiacols were somewhat reduced, while the yield of alcohols was remarkably increased in contrast to the result of K₂CO₃. The addition of Ca(OH)₂ did not significantly change the total yield of gaseous product at 700 °C but enhanced the yield of H₂.     

Sulfur removal from coal with supercritical fluid treatment

Conversion and sulfur removal of coal in sub- and supercritical water was studied in a micro reactor in the temperature range of 340-400°C and water density 0-0.27 g/cm³ for 0-90 min under N₂ atmosphere. The experiments were conducted to investigate the effect of reaction temperature, pressure, time and density of water on the sulfur removal in gaseous and liquid effluents, respectively. The results show that supercritical condition is more effective than sub-critical condition to remove the sulfur from coal. It is possible to reduce 57.42% of the original sulfur in coal for the reaction time of 90 min at 400°C and 30 MPa. The main gas containing sulfur in the gaseous effluent is not SO₂ but H₂S, irrespective of operating condition. The sulfur removal in liquid effluents is much greater than that in gas effluents. Compared with temperature, the influence of water density and pressure is less significant.     

Selective Removal of H2S from Gas Streams with High CO2 Concentration Using Hollow‐Fiber Membrane Contractors

Selective and simultaneous separation of H₂S and CO₂ from CH₄ was accomplished in a hollow‐fiber membrane contactor (HFMC). The absorption of both H₂S and CO₂ using an aqueous solution of methyldiethanolamine (MDEA) was almost complete and acid gases were totally removed. Despite the large difference between H₂S and CO₂ concentrations, the rate of H₂S absorption was not significantly influenced by CO₂ absorption. The independent effect and interactions of several process variables on the separation performance of H₂S and CO₂ were investigated. The results indicated that the membrane contactor could be a highly efficient choice for removal of almost all H₂S in the presence of a large CO₂ content even at high gas/liquid flow ratio. The selectivity of H₂S was about three times higher compared to the conventional absorption packed towers.     

Equilibrium conditions for the hydrogen sulfide hydrate formation in the presence of electrolytes and methanol

Natural gas industry encounters systems that consist of gases like CO₂ and H₂S, and aqueous solutions of methanol and mixed electrolytes. A knowledge of the phase behavior of such systems, including hydrate formation, is essential in gas production and the design of facilities for gas transportation and processing. Recently, Dholabhai et al. (1997, 1996) and Bishnoi and Dholabhai (1998) described equilibrium conditions for CO₂ and gas mixtures containing CO₂ in the presence of methanol, electrolytes and ethylene glycol. In the present work aqueous three phase (aqueous liquid solution, vapor and incipient hydrate) equilibrium conditions of H₂S hydrate formation in aqueous solutions of electrolytes and methanol are measured in the temperature range of 272 to 294 K and pressure range of 0.3 to 1.0 MPa. A ‘full view’ sapphire variable volume cell with a movable piston is used to obtain the experimental data.     

Adsorption of hydrogen sulfide,carbon dioxide,methane, and their mixtures on activated carbon

Abstract

H₂S and CO₂ are acid contaminants of natural gas and biogas, which removal have been studied using adsorption data for monocomponent and binary mixtures. However, equilibrium adsorption data for H₂S?+?CO₂ + CH₄ mixture has not been investigated yet. In this work, H₂S and CO₂ partition coefficients (K) and activated carbon (AC) selectivity (S) for H₂S?+?CO₂ + CH₄ mixture separation at high-pressure and different temperatures were determined. To reach this goal, monocomponent isotherms for H₂S, CO₂ and CH₄ on Brazilian babassu coconut hush AC were experimentally determined at different temperatures and pressures. Then, obtained data were correlated by Langmuir and Tóth models, and multicomponent adsorption was predicted using Extended Langmuir, Extended Tóth and Ideal Adsorption Solution Theory (IAST) methods. Results indicate AC captures approximately 26?wt% of H₂S or CO₂. K values for CO₂ and H₂S reached more than 3 and 26, respectively, depending on the predictive model utilized and were higher for diluted mixtures (high CH₄ content in gas phase). S values for CO₂ and H₂S can reach values greater than 25 for Tóth?+?IAST. Furthermore, selectivity toward H₂S is approximately 5.6 times greater than CO₂. The effect of temperature on multicomponent results indicate K and S values decrease as temperature increases. Therefore, results obtained herein show that is possible to separate H₂S and CO₂ from mixture containing CH₄ using this AC as adsorbent and better separation performance was observed for low H₂S and CO₂ concentrations and lower temperatures.     

A model of acid gas absorption/stripping using methyldiethanolamine with added acid

A nonequilibrium stage model was developed for the absorption and stripping of H₂S and CO₂ using aqueous methyldiethanolamine (MDEA). Heat and mass transfer are calculated for each stage assuming the liquid is well mixed and the gas moves in plug flow. The vapour-liquid equilibrium is represented by an empirical expression that was fit to experimental data. The mass transfer enhancement factor for CO₂ is based on the surface renewal theory with approximations made to the reaction term by the method of DeCoursey. Calculation of H₂S absorption assumes an instantaneous reaction rate at the gas/liquid interface and accounts for enhancement by equilibrium chemical reactions. Results were generated at Claus tail gas conditions using available equilibrium and rate data for 50 wt% MDEA. The amount of H₂S in the absorber outlet gas, or H₂S leak, was used to measure system performance. The base case resulted in a H₂S leak of 98 ppm with 20 absorber stages, 25 stripper stages, and a steam rate of 1.7 lb/gal solvent. Adding 0.05 equivalents of acid per mole of MDEA to the aqueous solution reduced the H₂S leak to 6 ppm and the steam rate to 1.2 lb/gal. Reducing the base case stripper pressure of 2.0 atm to 1.0 atm reduced the H₂S leak to 22 ppm. Analysis of McCabe-Thiele plots generated by the model showed that system performance improved after adding acid or reducing the stripper pressure because the H₂S equilibrium in the stripper was linearized.     

Catalytic activity of potassium halides in water vapour gasification of graphite

The catalytic activity of potassium halides in water vapour gasification of graphite was studied at 900 ° C and pressures up to 2 MPa. The initial step is the hydrolysis of the potassium halide which controls the catalytic activity: KF >KCl >KBr. Main steps of the catalysed gasification reaction are in good agreement with an oxygen transfer mechanism. The following general reaction scheme is proposed not only for the potassium halides, but also for K₂CO₃ and KNO₃. Initial reactions: K₂CO₃ + H₂O → 2KOH + CO₂; KNO₃ + H₂O → KOH + NO_x; KX + H₂O → KOH + HX. Intermediate step: KOH + C, H₂ → K + CO, H₂O. K-catalysed gasification reactions: K + H₂O → K(O) + H₂; K(O) + C → K + CO; K(O) + CO → K + CO₂.     

Kinetic study of hydrogen sulfide absorption in aqueous chlorine solution

Hydrogen sulfide (H₂S) is currently removed from gaseous effluents by chemical scrubbing using water. Chlorine is a top-grade oxidant, reacting with H₂S with a fast kinetic rate and enhancing its mass transfer rate. To design, optimize and scale-up scrubbers, knowledge of the reaction kinetics and mechanism is requested. This study investigates the H₂S oxidation rate by reactive absorption in a mechanically agitated gas–liquid reactor. Mass transfer (gas and liquid sides mass transfer coefficients) and hydrodynamic (interfacial area) performances of the gas–liquid reactor were measured using appropriated physical or chemical absorption methods. The accuracy of these parameters was checked by modeling the H₂S absorption in water without oxidant. A sensitivity analysis confirmed the robustness of the model. Finally, reactive absorption of H₂S in chlorine solution for acidic or circumneutral pH allowed to investigate the kinetics of reaction. The overall oxidation mechanism could be described assuming that H₂S is oxidized irreversibly by both hypochlorite anion ClO⁻ (k = 6.75 × 10⁶ L mol⁻¹ s⁻¹) and hypochlorous acid ClOH (k = 1.62 × 10⁵ L mol⁻¹ s⁻¹).     

Structure of K2Co3-loaded activated carbon fiber and its deodorization ability against H2S gas

Coal tar pitch containing finely dispersed KOH was spun centrifugally, followed by stabilization through heating to 330°C under a (1:1) mixture of air and CO₂ and carbonization/activation by heating to 850°C under CO₂. The activated carbon fiber obtained possessed of a specific surface area of 491 m²g⁻¹ and contained ca. 2% of K as K₂CO₃ over the peripheral region of fiber. The fiber showed high deodorization ability against 30 ppm of H₂S gas in air at ambient temperature. H₂S gas did not diffuse to the most interior parts of the fiber and was oxidized around outer regions of the fiber. Elemental sulphur was deposited in the fiber after H₂S absorption. The deodorization mechanism was discussed. The role and action of the K₂CO₃ supported was explained.     

Production of hydrocarbons by pyrolysis of methyl esters from rapeseed oil

The pyrolysis of a mixture of methyl esters from rapeseed oil has been studied in a tubular reactor between 550 and 850°C and in dilution with nitrogen. A specific device for the condensation of cracking effluents was used for the fractionated recovery of liquid and gaseous effluents, which were analyzed on-line by an infrared analyzer and by gas chromatography. The cracking products in the liquid effluent were identified by gas chromatography/mass spectrometry coupling. The effects of temperature on the cracking reaction were studied for a constant residence time of 320 ms and a constant dilution rate of 13 moles of nitrogen/mole of feedstock. The principal products observed were linear 1-olefins,n-paraffins, and unsaturated methyl esters. The gas fraction also contained CO, CO₂, and H₂. The middle-chain olefins (C₁₀–C₁₄ cut) and short-chain unsaturated esters, produced with a high added value, had an optimum yield at a cracking temperature of 700°C.     

Selective absorption of H2S from CO2 — factors controlling selectivity toward H2S

A novel experimental system was adapted to determine factors controlling selective absorption of hydrogen sulfide (H₂S) from carbon dioxide (CO₂). This work demonstrates that liquid film controlled mass transfer regime and a low value of the liquid side mass transfer coefficient favors selective removal of H₂S from CO₂. By identifying the factor controlling selective removal of H₂S from CO₂, this work lays the basis for the parameter optimization of a process for selective removal of H₂S from CO₂.     

Oxide materials research for global environment and energy with a focus on CO2 fixation into polymers

Representing the gas, liquid, and solid phase materials on the earth under the standard conditions, CO₂, H₂O, and SiO₂ attract my interest for their natural abundance, chemical stability, and yet fundamental roles in energy and environmental problems. Chemical consideration is made on the utilization of these stable resources for renewable clean energy materials and processes based on a thermodynamic approximation. A general scheme is presented to compare the utilization of CO₂, H₂O, and SiO₂ for such purposes as CO₂ fixation into functional polymers, photosynthesis of carbohydrates from CO₂ and H₂O, and solar silicon production from SiO₂. Focused is CO₂ copolymerization, since it is originated from our discovery of alternating CO₂–epoxide (oxirane) copolymer in 1968 and it has been revived by the recent industrialization of this unique bio-degradable polymer in China. New ideas of using combinatorial chemical technology and soft plasma processing for fixing CO₂ into polymers are proposed together with some preliminary experimental results.     

Oxidation of low concentrations of hydrogen sulphide: Process optimization and kinetic studies

Low concentrations (e.g. < 3) of H₂ S in natural gas can be selectively oxidized over an “granular Hydrodarco” activated carbon catalyst to elemental sulphur, water and a small fraction of by-product sulphur dioxide, SO₂. To optimize the H₂ S catalytic oxidation process, the process was conducted in the temperature range 125—200 °C, at pressures 230—3200 kPa, with the O/H₂ S ratio being varied from 1.05 to 1.20 and using different types of sour and acid gases as feed. The optimum temperature was determined to be approximately 175 °C for high H₂ S conversion and low SO₂ production with an O/H₂ S ratio 1.05 times the stoichiometric ratio. The life of the activated carbon catalyst has been extended by removing heavy hydrocarbons from the feed gas. The process has been performed at elevated pressures to increase H₂ S conversion, to maintain it for a longer period and to minimize SO₂ production. The process is not impeded by water vapour up to 10 mol% in the feed gas containing low concentrations of CO₂ (< 1.0). A decrease in H₂ S conversion and an increase in SO₂ production were obtained with an increase in water vapour in the feed gas containing a high percentage of CO₂. The process works well with “sour natural gas” containing approximately 1% H₂ S and with “acid gas” containing both H₂ S and CO₂. It gives somewhat higher H₂ S conversion and low SO₂ production with feed gas containing low concentrations of CO₂. A kinetics study to determine the rate-controlling step for the H₂ S catalytic oxidation reaction over “granular Hydrodarco” activated carbon has been conducted. It was concluded that either adsorption of O₂ or H₂ S from the bulk phase onto the catalyst surface is the rate-controlling step of the H₂ S catalytic oxidation reaction.     

Carbon dioxide absorption in a cross-flow rotating packed bed

This work investigates the feasibility of applying the cross-flow rotating packed bed (RPB) to the removal of carbon dioxide (CO₂) by absorption from gaseous streams. Monoethanolamine (MEA) aqueous solution was used as the model absorbent. Also, other absorbents such as the NaOH and 2-amino-2-methyl-1-propanol (AMP) aqueous solutions were compared with the MEA aqueous solution. The CO₂ removal efficiency was observed as functions of rotor speed, gas flow rate, liquid flow rate, MEA concentration, and CO₂ concentration. Experimental results indicated that the rotor speed positively affects the CO₂ removal efficiency. Our results further demonstrated that the CO₂ removal efficiency increased with the liquid flow rate and the MEA concentration; however, decreased with the gas flow rate and the CO₂ concentration. Additionally, the CO₂ removal efficiency for the MEA aqueous solution was superior to that for the NaOH and AMP aqueous solutions. Based on the performance comparison with the conventional packed bed and the countercurrent-flow RPB, the cross-flow RPB is an effective absorber for CO₂ absorption process.     

Vapour liquid equilibrium calculations for dilute aqueous solutions of CO2, H2S,NH3 and NaOH to 300°C

Henry's law constants for aqueous CO₂, H₂S and NH₃ up to 300°C have been recalculated from literature vapour pressure, enthalpy and heat capacity data. The high vapour pressure of water above 150°C causes significant solute-water interactions in the gas phase, which were calculated using the Peng-Robinson cubic equation of state. The results were combined with selected ionization constant data to derive a vapour-liquid equilibrium model for dilute solutions. The model reproduces experimental data for binary systems at solute molalities of up to 0.5 m at 100°C, 1.0 m above 250°C and ionic strengths below about 0.1 m.     

Absorberentwurf für Anlagen zur Behandlung von sauren Erdgasen: Einfluss Prozessparameter auf Betriebsführung und ProzesswirtschaftlichkeitAbsorber design in sour natural gas treatment plants: Impact of process variables on operation and economics

Two models of absorber have been developed which describe the absorption of H₂S and CO₂ from natural gases by aqueous di-isopropanolamine (DIPA) or methyl-di-ethanolamine (MDEA) solutions. In these models mass transfer, reaction and equilibrium processes as they prevail in conventional tray absorbers and in cascades of trickle bed reactors are incorporated. Owing to the better mass transfer characteristics of the latter type of absorber, i.e. the larger ratio between the gas phase and liquid phase mass transfer coefficients, k_g/k_?, higher selectivities for the absorption of H₂S from sour natural gases are realized.The influence of variation of a number of operation and design parameters on tray absorber performance, H₂S selectivity and solvent flowrate is demonstrated.The economics of the above type of absorbers together with a solvent regenerator, sulfur recovery unit and tail-gas unit are explained in detail. From the point of view of the economics trickle bed absorbers are very attractive owing to lower investment costs and higher selectivities, which result in lower operating costs than for tray absorbers under identical conditions.     

Conversion of yeast by hydrothermal treatment under reducing conditions

In the work reported here, baker’s yeast (Saccharomyces cerevisiae) was used as feed for the production of liquid biofuels in a continuous one-step process under hydrothermal conditions in the presence of excess hydrogen and K₂CO₃. The yeast conversion experiments were performed in an up-flow reactor under near-critical water conditions (T 330–450 °C, p 20–32 MPa). The products consisted of three phases, an oil-like organic phase, a gaseous phase, and an aqueous phase. Higher concentrations of organic carbon in the process resulted in a higher product yield. The heating value of the organic phase was up to 38.6 MJ/kg. Liquefaction of yeast without any addition of K₂CO₃ also resulted in liquid oil, but the quality and the yield of the oil product were lower. A reaction temperature of 400 °C was found to be optimal for the oil yield and quality.     

Effect of alkali metal catalysts on gasification of coal char

A detailed study has been conducted of the effects of LiCl, NaCl, KCl, RbCl, CsCl, KOH, and K₂CO₃ on the steam gasification of char produced from a western sub-bituminous coal. Initial screening of results revealed that K₂CO₃ had the greatest catalytic activity for a fixed cation content in the char. Subsequent experiments were performed to determine the effects of K₂CO₃ loading and gasification temperature on the rate of gasification and the product-gas composition. The results show that gasification rate is enhanced with increasing K₂CO₃ loading and reaction temperature. Increasing K₂CO₃ loading causes CO to be formed in preference to CO₂ and H₂ and suppresses the production of CH₄. Increasing temperature also causes CO to be formed in preference to CO₂ and H₂ but enhances the production of CH₄. These results are discussed in the light of a mechanism to explain the unique catalytic behaviour of K₂CO₃.     

油气田CO2/H2S共存腐蚀与缓蚀技术研究进展

CO₂/H₂S是油气田采集、运输、处理过程中主要的腐蚀介质，由其引起的管道设备的腐蚀问题变得越来越严重，腐蚀和防腐已经成为研究热点。分别对近年来国内外开展的有关CO₂和H₂S共存腐蚀及缓蚀技术的研究进行综述。CO₂/H₂S共存腐蚀研究主要依靠试验手段，但目前的研究结果有很大的离散性，根据不同的试验条件会产生不同的研究结果。分压比是国内外大多数学者研究CO₂/H₂S腐蚀规律的切入点，但关于两者主导腐蚀的分压比界限划分现有研究存有争议。缓蚀技术研究讨论了缓蚀剂作用机理，评述了抑制CO₂/H₂S共存腐蚀常用的酰胺类、咪唑啉衍生物类、季铵盐类和Schiff碱类缓性剂在国内外的研究与应用现状，展望了这一领域的研究前景及发展方向。