Synthesis Gas Mixtures Research Articles

Mathematical Modeling of the Hydrodynamic Instability and Chemical Inhibition of Detonation Waves in a Syngas–Air Mixture

This paper presents the results of the two-dimensional modeling of the hydrodynamic instability of a detonation wave, which results in the formation of an oscillating cellular structure on the wave front. This cellular structure of the wave, unstable due to its origin, demonstrates the constant statistically averaged characteristics of the cell size. The suppression of detonation propagation in synthesis gas mixtures with air using a combustible inhibitor is studied numerically. Contrary to the majority of inhibitors being either inert substances, which do not take part in the chemical reaction, or take part in chemical reaction but do not contribute to energy release, the suggested inhibitor is also a fuel, which enters into an exothermic reaction with oxygen. The unsaturated hydrocarbon propylene additive is used as an inhibitor. The dependence of the effect of the inhibitor content on the mitigation of detonation for various conditions of detonation initiation is researched. The results make it possible to determine a critical percentage of inhibitor which prevents the occurrence of detonation and the critical percentage of inhibitor which destroys a developed detonation wave.

INFLUENCE OF THE COMPOSITION OF THE SYNTHETIZED GAS ON THE COMBUSTION PROCESS OF THE MIXTURE IN THE INTERNAL COMBUSTION ENGINE

The article is devoted to the use of low-energy synthesized gas (synthesis gas) as a fuel for internal combustion engines, which in turn transmit mechanical energy to a cogeneration plant (combined production of heat and electricity). Such power plants allow you to achieve high values of total effective efficiency when using a conventional internal combustion engine with spark ignition. The analysed synthetic gases can be obtained by the method of gasification of household waste with access to air. In this work, synthesis gases were obtained in laboratory conditions. The composition of the components of the studied synthesis gases corresponds to several gas mixtures that are created during the artificial gasification of household waste of certain categories. The influence of the composition of the synthesis gas components on the internal parameters of the internal combustion engine was studied. The process of supplying fuel to the engine was controlled by a standard block with several sensors connected to it in the combustion chamber and the exhaust manifold. Engine operation on all synthesis gas mixtures was compared with operation on pure methane mixture. The analysis shows that the drop in efficiency indicators in the form of indicator mean effective pressure (IMEP) ranges from 10% to 40% compared to work on a pure methane mixture. With an increase in the proportion of hydrogen in the synthesis gas, the stiffness of the engine, as well as the rate of heat generation, increases. When the synthesis gas contained a high proportion of carbon monoxide, the stiffness of the engine was the lowest. The main combustion time of synthesis gas is reduced when hydrogen is added to the mixture, and due to an increase in the proportion of methane or carbon monoxide, it increases on the contrary. The presented results make it possible to analyses the processes occurring in the internal combustion engine, as well as the influence of the components of the synthesis gas produced from renewable energy sources. This will make it possible to adjust the gas production process in such a way as to achieve the highest possible energy and economic indicators of its utilization in the cogeneration plant.
 Keywords: internal combustion engine, synthesis gases, analysis of pressure

Electrochemical Cells for Novel Routes to Ammonia

Ammonia is an extremely important chemical compound. The conventional production route is CO2 intensive and almost 2% of global anthropogenic CO2 emissions stems from ammonia synthesis. This will have to change over the coming decades to reduce negative impact on the climate and ensure a green route to ammonia. Here, a novel way to provide the synthesis gas mixture for ammonia synthesis is suggested based on combining an SOEC to provide the hydrogen with a dedicated cell to provide also nitrogen for the process. This is suggested to be achieved by electrochemically pumping out oxygen from an air stream. Cells were successfully developed and characterized for this purpose. Exit streams with more than 98% nitrogen purity were documented and the developed cells were shown to be stable over test periods exceeding 3000 hours of operation.

Density Functional Theory Study of the Hydrogenation of Carbon Monoxide over the Co (001) Surface: Implications for the Fischer–Tropsch Process

The increasing demand for renewable fuels and sustainable products has encouraged growing interest in the development of active and selective catalysts for the conversion of carbon monoxide into desirable products. The Fischer–Tropsch process consists of the reaction of a synthesis gas mixture containing carbon monoxide and hydrogen (syngas), which are polymerized into liquid hydrocarbon chains, often using a cobalt catalyst. Here, first-principles calculations based on the density functional theory (DFT) are used to investigate the reaction mechanism of the Fischer–Tropsch synthesis over the Co (001) surface. The most energetically favorable adsorption configurations of the species involved in the carbon monoxide hydrogenation process are identified, and the possible elementary steps of hydrogenation and their related transition states are explored using the Vienna Ab initio simulation package (VASP). The results provide the mechanisms for the formation of CH4, CH3OH and C2H2 compounds, where the calculations suggest that CH4 is the dominant product. Findings from the reaction energies reveal that the preferred mechanism for the hydrogenation of carbon monoxide is through HCO and cis-HCOH, and the largest exothermic reaction energy in the CH4 formation pathway is released during the hydrogenation of cis-HCOH (−0.773 eV). An analysis of the kinetics of the hydrogenation reactions indicates that the CH production from cis-HCOH has the lowest energy barrier of just 0.066 eV, and the hydrogenation of CO to COH, with the largest energy barrier of 1.804 eV, is the least favored reaction kinetically.

Quo Vadis Dry Reforming of Methane?—A Review on Its Chemical, Environmental, and Industrial Prospects

In recent years, the catalytic dry reforming of methane (DRM) has increasingly come into academic focus. The interesting aspect of this reaction is seemingly the conversion of CO2 and methane, two greenhouse gases, into a valuable synthesis gas (syngas) mixture with an otherwise unachievable but industrially relevant H2/CO ratio of one. In a possible scenario, the chemical conversion of CO2 and CH4 to syngas could be used in consecutive reactions to produce synthetic fuels, with combustion to harness the stored energy. Although the educts of DRM suggest a superior impact of this reaction to mitigate global warming, its potential as a chemical energy converter and greenhouse gas absorber has still to be elucidated. In this review article, we will provide insights into the industrial maturity of this reaction and critically discuss its applicability as a cornerstone in the energy transition. We derive these insights from assessing the current state of research and knowledge on DRM. We conclude that the entire industrial process of syngas production from two greenhouse gases, including heating with current technologies, releases at least 1.23 moles of CO2 per mol of CO2 converted in the catalytic reaction. Furthermore, we show that synthetic fuels derived from this reaction exhibit a negative carbon dioxide capturing efficiency which is similar to burning methane directly in the air. We also outline potential applications and introduce prospective technologies toward a net-zero CO2 strategy based on DRM.

The Exhaust Emission Characteristics of a Spark-Ignition Engine Fuelled with Gasoline and Synthesized Biogas from Non-Thermal Plasma

This study synthesizes biogas with low methane contents (<50%) to hydrocarbons that form a combustible synthesis gas (syngas) mixture. Conventional methods used for reforming biogas has limitations in terms of fabrication, maintenance, and cost. This is especially true when the biogas’ composition fluctuates. Non-thermal plasma (NTP) is an alternative method to produce combustible syngas for power generation. Thus, the exhaust emissions from a 2 kWe spark ignition (SI) engine fuelled with gasoline and NTP-synthesized biogas is investigated with respect to the type of NTP reactor, plasma power consumption and biogas composition. Two types of NTP reactors are used: a cylindrical reactor where the gas flow path is linear, and a cyclonic reactor where the gas flow path is a curvature, similar to that of a gas-solid cyclone separator. The results show that the NTP reactors produced additional hydrocarbons, decreasing flue gas temperatures by 4°C and reducing NOx emissions by 35%.

Crystal growth of clathrate hydrate formed with H2\u2009+\u2009CO2 mixed gas and tetrahydropyran

Hydrate-based gas separation technology is applicable to the CO2 capture and storage from synthesis gas mixture generated through gasification of fuel sources including biomass. This paper reports visual observations of crystal growth dynamics and crystal morphology of hydrate formed in the H2 + CO2 + tetrahydropyran (THP) + water system with a target for developing the hydrate-based CO2 separation process design. Experiments were conducted at a temperature range of 279.5–284.9 K under the pressure of 4.9–5.3 MPa. To simulate the synthesis gas, gas composition in the gas phase was maintained around H2:CO2 = 0.6:0.4 in mole fraction. Hydrate crystals were formed and extended along the THP/water interface. After the complete coverage of the interface to shape a polycrystalline shell, hydrate crystals continued to grow further into the bulk of liquid water. The individual crystals were identified as hexagonal, tetragonal and other polygonal-shaped formations. The crystal growth rate and the crystal size varied depending on thermodynamic conditions. Implications from the obtained results for the arrangement of operating conditions at the hydrate formation-, transportation-, and dissociation processes are discussed.

Catalytic Conversion of CO and H2 into Hydrocarbons on the Cobalt Co(111) Surface: Implications for the Fischer–Tropsch Process

The Fischer–Tropsch (FT) process consists of the reaction of a synthesis gas (syngas) mixture containing carbon monoxide (CO) and hydrogen (H2), which are polymerized into liquid hydrocarbon chains, often using a cobalt catalyst, although the mechanistic pathway is not yet fully understood. Here, we have employed unrestricted density functional theory calculations with a Hubbard Hamiltonian and long-range dispersion corrections [DFT+U−D3−(BJ)] to investigate the reaction of syngas and the selectivity toward the hydrocarbons formed on the cobalt Co(111) surface. The single CO and dissociated H2 molecules prefer to adsorb at two different types of trigonal surface sites, and we discuss how the interatomic distances, fundamental vibrational modes, charge transfers, surface-free energies, and work functions are modified by the adsorbates. The coadsorption of the syngas molecules in close proximity provides enough energy for the system to cross the saddle points on the minimum energy pathway (MEP), leading to the catalytic hydrogenolysis of the C–O bond. The adsorbed CO, alongside the intermediates CH and OH, are further stabilized when the ratio of equilibrium coverage (C) is CH/CCO,CH,OH > 6:1 under the temperature conditions required for the FT process. We propose several mechanistic pathways to account for the formation of ethane (C2H6), as a model for long-chain hydrocarbons, as well as methane (CH4) which is an undesirable product. The MEPs for these processes show that the coupling of the C–C bond followed by hydrogenation is the most favorable process, which takes precedence over the production of CH4. The termination reaction suggests that water (H2O) remains weakly physisorbed to the surface, allowing the reutilization of its catalytic site. The simulated fundamental vibrational frequencies and scanning tunneling microscopy images of the surface-bound intermediates are in agreement with the available experimental data. Our findings are important in the interpretation of the elementary steps of the FT process on the Co(111) surface.

NOx, CO and HC emissions and thermodynamic-energetic efficiency of an SI gas engine powered by gases simulated from biomass gasification under different H2 content

This work explored the problem of using gaseous biofuels with different content of hydrogen and carbon monoxide in a three-cylinder naturally aspirated spark-ignition (SI) engine under laboratory conditions. The tests investigated the combustion process of simulated gases, whose composition was similar to the syngas generated from biomass gasification processes. During the lab tests, the engine operated at a constant speed and wide-open throttle. The engine control parameters and syngas composition influence on the combustion process, performance, as well as its harmful effects on the environment were analysed. The assay also focused on the fast-changing combustion parameters (heat release rate - HRR, mass fraction burned - MFB and combustion duration) based on in-cylinder pressure measurements. Gaseous fuels using during the tests were free from contamination and moisture. A clear impact of the molar fraction ratio H2/CO in the syngas mixture on the internal parameters of the tested engine could be observed. Syngas with higher hydrogen content required the use of slightly lower ignition advance to get the maximum value of Indicated Mean Effective Pressure of the engine - IMEP. The lower heating value of the syngas fuel did not directly affect the indicated efficiency of the engine. The decisive influencing factor indeed was the type and molar fraction of combustible and inert components at the syngas mixture. For syngas mixtures with higher H2 content, increasing the excess gas ratio increased the indicated efficiency. A clear correlation was found between the carbon monoxide content of the synthesis gas mixture and the specific emission of CO in the engine exhaust gas. Nevertheless, keeping the carbon monoxide content constant and increasing the hydrogen content in the syngas mixture resulted in a decrease of specific CO emissions.

Effect of hydrogen concentration on CVD synthesis of graphene

The paper is devoted to the study of AP-CVD synthesis of graphene on a copper substrate. In this work, the effect of hydrogen concentration in the synthesis gas mixture on the growth of a graphene coating is studied experimentally. Two series of experiments with methane concentrations of 0.02% and 0.05% are presented. It is shown that a change in concentration of hydrogen has a nonmonotonic effect on the degree of substrate covering with graphene. This indicates that hydrogen is involved in several competing processes. One of these processes is stabilization of the edges of growing graphene domains. Another is etching of the forming graphene structures and reduction of hydrocarbon radicals on the copper substrate surface and in the bulk. It is shown that an increase in methane concentration leads to an increase in the rate of graphene crystal growth. To preserve the kinetics of graphene domain growth, it is necessary to reduce the H2/CH4 coefficient in the working mixture.

Dynamic changes of Au/ZnO catalysts during methanol synthesis: A model study by temporal analysis of products (TAP) and Zn LIII near Edge X-Ray absorption spectroscopy

Small gold nanoparticles supported on ZnO have been identified as highly active and selective catalysts for the green synthesis of methanol from CO2 and H2. Furthermore, they can serve also a model system for the mechanistic understanding of methanol synthesis on the industrial Cu/ZnO catalyst. The dynamic changes in the structure of Au/ZnO upon exposure to methanol synthesis gas mixtures were studied using a combination of TAP reactor and near edge X-ray absorption spectroscopy (XANES) measurements at the Zn LIII edge, both in CO2/H2 and CO/H2 gas mixtures. TAP measurements indicated that CO can create significant amounts of O-vacancy defects in ZnO at 240°C, while CO2 can re-oxidize a pre-reduced catalyst or maintain this state in the presence of strongly reducing gases (CO and H2). Furthermore, CO2 present as reactant or resulting from the reactive removal of surface lattice oxygen by interaction with CO can be deposited on the pre-reduced Au/ZnO surface as stable adsorbed carbon containing species, e.g., as surface carbonates, which decompose at T≥250°C. In situ XANES measurements at the Zn LIII edge revealed that ZnO is significantly reduced during reaction, both in CO2/H2 and CO/H2 gas mixtures, but with the extent of the reduction being more pronounced in CO/H2 than in CO2/H2. These results will be critically discussed in the light of previous findings on the role of ZnO reduction in the activity of methanol synthesis catalysts.

NiMo-ceria-zirconia-based anode for solid oxide fuel cells operating on gasoline surrogate

A multi-functional NiMo-ceria-zirconia composite was developed as an anode for a solid oxide fuel cell (SOFC) running on isooctane, a commonly used gasoline surrogate. The anode layer was fabricated on an electrolyte-supported single cell using yttria-stabilized zirconia (YSZ) as the electrolyte and La0.6Sr0.4Co0.2Fe0.8O3-δ as the cathode. Our results indicate that the single NiMo-ceria-zirconia layer possesses a dual-functionality: firstly to internally convert complex hydrocarbons into synthesis gas with a high resistance to coking and secondly to electrochemically oxidize the synthesis gas mixture for electric power generation. Compared with the conventional Ni-YSZ anode single cell, the application of the ceria-zirconia in the anode significantly suppresses carbon deposition and improves the performance stability of the single cell. Furthermore, the addition of Mo in the Ni-ceria-zirconia appears to facilitate a higher degree of sintering for the anode, which increases the electronic conductivity and maximum power density of the single cell. Consequently, at 800 °C the single cell with 5 wt.% Mo in the Ni-ceria-zirconia-based anode displayed a higher maximum power density of 212 mW cm−2 at 0.48 V and significantly enhanced performance stability than the conventional Ni-YSZ anode single cell in the isooctane/air operating mode.

Production of biochar from rice husk: Particulate emissions from the combustion of raw pyrolysis volatiles

Increasing energy demands and waste management concerns have motivated agricultural producers to consider the decentralized conversion of agricultural by-products for energy and value-added product (biochar) generation. Due to the variability of fuel properties, direct combustion of agricultural by-products with high ash contents, such as rice husk, may suffer from increased fouling and slagging issues with high particulate matter (PM) emissions. Combustion of the raw pyrolysis volatiles (bio-oil and synthesis gas (syngas) mixtures) produced from pyrolysis with the inherent separation of ash in the biochar may potentially mitigate these issues. In this study, PM emissions from the combustion of the raw pyrolysis volatiles derived from the pyrolysis of rice husk were evaluated at laboratory scale by using a combined pyrolysis and combustion facility. Pyrolysis temperatures ranging from 400 °C to 800 °C were used to generate raw pyrolysis volatiles with differing bio-oil to syngas ratios which were then combusted at 850 °C. It was found that bio-oil dominated the higher heating value of the raw pyrolysis volatiles produced at low pyrolysis temperatures. The combustion of such raw pyrolysis volatiles with high bio-oil content substantially increased the yields of PM10 and PM2.1. Linear dependence was observed between PM emissions and bio-oil fraction in the raw pyrolysis volatiles. Nevertheless, the pyrolysis-combustion process, with >96% of the ash retained in biochar prior to combustion, is more favorable than direct combustion for high ash biomass as far as PM emissions are concerned.

Electroreduction of CO2 to Synthesis Gas and Hydrocarbons on Doped Carbons

Strategies to close the anthropogenic carbon cycle through a renewable energy-driven efficient chemical conversion of CO2 into usable chemical feeds have become a scientific priority. Conversion of CO2 rich streams from steel mills, concrete- or coal-fired power plants, into syn-gas alcohols or hydrocarbons is of tremendous interest for industry. Of all chemical ways to convert CO2 into hydrocarbons, the electrocatalytic coupling of water splitting and CO2 reduction appears attractive, as it is a one-step process step, occurs at ambient temperature and pressures, involves solely water and CO2 as reactants, and may involve renewable electricity from wind, solar or hydro power plants. CO2 electroreduction is typically carried out on the surface of metal catalysts. Cu catalysts generate various gas products such as H2, CO, methane and ethylene, while Au and Ag are the catalysts of choice for the selective electroreduction of CO2 into CO/H2 synthesis gas mixtures. On all metal catalysts the CO2 electroreduction suffers from prohibitively high kinetic overpotentials and limited product selectivity. This is why the identification of new catalysts or new catalyst formats, such as nanoparticles or core shell architectures, with reduced overpotentials combined with the exploration of new strategies to control and improve product selectivities has become the two key goals for CO2 reduction.In this contribution, we share recent work on the electroreduction of CO2. In particular, we discuss a family of heteroatom-doped carbon catalysts for the generation of synthesis gas. We show evidence that carbon catalysts meet and exceed the activity and selectivity of traditional Au catalysts providing an intriguing cost-effective alternative.

Synthesis of high-molecular-weight hydrocarbons from CO and H2 over a cobalt catalyst

Hydrocarbon synthesis from CO and H2 over a cobalt catalyst has been carried out, and the dependence of the selectivity and productivity of the process on process parameters, namely, temperature, pressure, GHSV, and synthesis gas composition has been investigated. Raising the temperature by 17°C decreases the high-molecular-weight hydrocarbon (C35+) selectivity of the process by 24% at GHSV = 60 h−1 and by 69% at GHSV = 100 h−1. Raising the pressure from 0.1 to 2.0 MPa improves these characteristics of the process, and increasing the GHSV from 60 to 300 h−1 diminishes them. Concentrated synthesis gas mixtures should be used to obtain C35+ hydrocarbons (ceresin). The actual composition of the resulting hydrocarbon mixture differs from the theoretical composition calculated using the Anderson-Schulz-Flory molar mass distribution equation, suggesting that, under real synthesis conditions, the molar mass distribution is described by more complicated relationships. This study is an applied one, and its results are planned to be used in the design of a pilot plant for ceresin (brand 100) production.

Catalytic reforming of hydrocarbon feedstocks into fuel for power generation units

The feasibility of realization of the multifuel operation principle, specifically, production of a hydrogen-containing gas from various types of hydrocarbon feedstocks using the same catalyst under similar reaction conditions is considered. The steam reforming of two types of hydrocarbon mixtures, namely diesel fuel satisfying GOST (State Standard) R 52368-2005 (EN 590:2004) and a methane-propane mixture imitating the composition of associated petroleum gas, has been investigated to clarify this issue. These hydrocarbon feedstocks were chosen for the reason that they are universally used as a fuel for various types of power generation units. Experiments have been carried out in a catalytic flow reactor at 250–480°C (for the methane-propane mixture) and 500–600°C (for diesel fuel) and pressures of 1–15 atm using a nickel-containing catalyst (NIAP-18). This catalyst has been demonstrated to ensure conversion of different types of hydrocarbon feedstocks into synthesis gas and methane-hydrogen mixtures usable as a fuel for power generation units based on high-temperature fuel cells and for spark-ignition, diesel, and gas-diesel engines.

Homogeneous charge compression ignition engine operating on synthesis gas

Mixtures of hydrogen and carbon monoxide were used to simulate the fuel component of synthesis gas and operate a single cylinder engine in homogeneous charge compression ignition (HCCI) mode. The engine was originally an air-cooled direct injection (DI) compression ignition (CI) engine. The original diesel fuel injection system was removed and a port fuel injection (PFI) system with intake air heating was added. The engine speed was maintained at a constant 1800 RPM.Three synthesis gas fuel compositions were tested, which comprised of 100% H2, 75/25 H2/CO ratio, and 50/50 H2/ CO ratio, by volume. These compositions were investigated at an equivalence ratio (EQR) of 0.26 and 0.30. In-cylinder pressure and H2/CO emissions measurements were made at all conditions.To achieve peak indicated mean effective pressure (IMEP) at a given equivalence ratio, the intake air temperature had to be increased with increasing CO fraction in the synthesis gas mixture. For the EQR = 0.26 conditions, the intake air temperature required for best IMEP was 78 °C, 84 °C, and 98 °C, for 100% H2, 75/25 H2/CO ratio, and 50/50 H2/CO ratio, respectively. For the EQR = 0.30 conditions, the intake air temperature requirements were 62 °C, 71 °C, and 81 °C, for the same respective H2/CO proportions. The peak in-cylinder temperatures for all conditions tested ranged from roughly 1200 K–1500 K depending on intake air temperature, mixture concentration, and fuel composition. The combustion event was short, with the rapid burn angle ranging from 9.5 CAD to 11.5 CAD for all conditions tested, and the synthesis gas mixture composition did not change this significantly. The combustion efficiency was between 83% and 88% for the peak IMEP conditions tested.

Sulfur tolerant PdAu and PdAuPt alloy hydrogen separation membranes

Abstract Palladium (Pd) based alloy membranes of PdAu and PdAuPt were fabricated using magnetron sputtering. Membranes ranging in thickness from 9 to 33 μm were tested under pure gas and mixed gas conditions including U.S. Department of Energy (DOE) specified simulated synthesis gas mixtures containing H2, H2O, CO and CO2, and up to 75 ppmv H2S. In pure hydrogen gas, the PdAu alloy exhibited higher permeabilities than pure Pd in agreement with published values for cold rolled and electrodeposited membranes of similar compositions. The addition of Pt in concentrations ranging from 4.3 to 12.9 mass% lowered the permeability in pure hydrogen gas to slightly below pure Pd. For thicker (25–33 μm) PdAuPt membranes pretreated in air (versus nitrogen) at 400 °C before exposure to hydrogen, an increase in permeability of 10–20% was observed, which is lower than that reported in the literature suggesting that some surface properties of thinner foils may boost permeability. A thick (33 μm) Pd–10Au–10Pt foil evaluated under the DOE conditions, showed good recovery in flux after exposure to syngas containing sulfur. The flux dropped from 0.212 to 0.167 mol m−2 s−1 when 20 ppmv of H2S was added to the gas mixture. When the H2S was removed from the gas mixture the flux returned to its original value of 0.212 mol m−2 s−1. However, in the presence of H2S the permeate purity somewhat degraded over time. The hydrogen permeability, as observed for other membranes, was depressed both by water-gas shift mixtures (with or without H2S) but it appears that either high quantities of Au or the presence of Pt, or both, are inhibiting sulfide formation, thereby improving both permeability and stability under mixture gas conditions with H2S.

Experimental analysis of soot abatement in reducing syngas for high temperature fuel cell feeding

The present work proposes a novel approach for the removal of soot from a synthesis gas mixture for fuel cell applications, based on reactions between the particulate and syngas in a wall-flow filter, while respecting the constraints of an SOFC (solid oxide fuel cell) and avoiding excesses of trap backpressure. The experiments were performed on a test-rig with a TPOX (thermal partial oxidation) reformer and a wall-flow soot-trap. The operating range varied from 3 to 8 kW of thermal load and from 0.40 to 0.50 of air-to-fuel ratio. The work shows that is possible to establish an equilibrium between the soot that enters the filter and the soot that is gasified, in order to avoid backpressures due to particle deposition in the channels, by running the reformer at specific air ratio conditions along the power load and without the addition of oxygen. The capacity of the synthesis gas mixture to regenerate the trap has appeared to be directly related to the thermal load. The final part instead presents results concerning the effects of lambda and air pre-heating, analysed separately, in order to evaluate the effect of each one on the kinetics of the filter regeneration. The tests showed how high lambda leads to a faster gasification rate of soot. A positive effect could also be achieved by increasing the air pre-heating temperature that enters the reactor, but this parameter does not appear to be as effective as the previous ones.

Separation and capture of carbon dioxide from CO 2/H 2 syngas mixture using semi-clathrate hydrates

The relation between anthropogenic emissions of CO 2 and its increased levels in the atmosphere with global warming and climate change has been well established and accepted. Major portion of carbon dioxide released to the atmosphere, originates from combustion of fossil fuels. Integrated gasification combined cycle (IGCC) offers a promising fossil fuel technology considered as a clean coal-based process for power generation particularly if accompanied by precombustion capture. The latter includes separation of carbon dioxide from a synthesis gas mixture containing 40 mol% CO 2 and 60 mol% H 2. A novel approach for capturing CO 2 from the above gas mixture is to use gas hydrate formation. This process is based on selective partition of CO 2 between hydrate phase and gas phase and has already been studied with promising results. However high-pressure requirement for hydrate formation is a major problem. We have used semiclathrate formation from tetrabutylammonium bromide (TBAB) to experimentally investigate CO 2 capture from a mixture containing 40.2 mol% of CO 2 and 59.8 mol% of H 2. The results shows that in one stage of gas hydrate formation and dissociation, CO 2 can be enriched from 40 mol% to 86 mol% while the concentration of CO 2 in equilibrium gas phase is reduced to 18%. While separation efficiency of processes based on hydrates and semi-clathrates are comparable, the presence of TBAB improves the operating conditions significantly. Furthermore, CO 2 concentration could be increased to 96 mol% by separating CO 2 in two stages.