CO-rich Synthesis Gas Research Articles

Circumventing carbon formation in CO2 reforming of methane by an adiabatic post conversion reactor

Feasible process conditions for reforming of gas mixtures of CH4 and CO2 into CO-rich synthesis gas are dictated by the risk of carbon formation. To overcome this risk, a minimum steam requirement exists for the process as determined by thermodynamic considerations. This work describes an approach for using a well-known nickel-based catalyst system to enable production of CO-rich synthesis gas at low steam-to-hydrocarbon-carbon (S/C) ratios. The concept utilizes a two-reactor approach where traditional steam reforming is done initially, followed by CO2 addition to the hot synthesis gas and subsequent conversion in an adiabatic reactor, a so-called Adiabatic POst Converter (APOC). This allows for operating at overall S/C ratios of below 1.5; which is much lower than what is possible in a conventional fired reformer. The central element of the APOC is that the temperature is kept higher than 700–800 °C to circumvent the carbon limits. The process elements were demonstrated by a combination of thermodynamic calculations, process calculations, and laboratory experiments. The concept allows for design of significantly more compact reformers (up to 30 % reduced size), which in turn also reduces firing and thereby CO2 emissions. The concept can also be used in existing plants where the capacity can be boosted by adding an APOC.

An intermetallic Pd2Ga nanoparticle catalyst for the single-step conversion of CO-rich synthesis gas to dimethyl ether

Well-defined Pd/Ga-nanoparticles were prepared and used as a precursor for the methanol active component in a bifunctional syngas-to-dimethyl ether catalyst. In situ X-ray absorption spectroscopy experiments were employed both to unravel the initial formation of the active catalyst phase in reductive H2 atmosphere and to further monitor changes of the nanoparticles under conditions of dimethyl ether synthesis at a pressure up to 20 bar (250 °C). The catalytic studies were conducted using simulated biomass-derived, CO-rich syngas in a continuous-flow reactor, with the bifunctional catalyst offering the two types of active sites, i.e. for methanol synthesis (Pd/Ga nanoparticles) and its subsequent dehydration (γ-Al2O3), in close proximity. As compared to the conventional Cu/Zn-based reference catalyst prepared via a similar procedure, the Pd/Ga-based catalyst showed a promising activity together with a notable stability with time on stream and a high temperature tolerance (up to 300 °C). A kinetic model which considers the individual reactions involved in direct DME synthesis based on power law equations was used to fit the experimental data, and the apparent activation energies were compared to the Cu/Zn-based catalyst.

Bifunctional catalysts based on colloidal Cu/Zn nanoparticles for the direct conversion of synthesis gas to dimethyl ether and hydrocarbons

Hybrid catalysts were prepared using well-defined, colloidal Cu/Zn-based nanoparticles as building units. The nanoparticles were immobilized on acidic supports (i.e., γ-Al2O3, HZSM-5, and HY) to yield a series of bifunctional catalysts with a close proximity of active sites for both methanol synthesis and its further conversion to dimethyl ether (DME) or hydrocarbons (HCs). By this model kit principle, a high comparability of the bifunctional catalysts was ensured. The catalysts were characterized in depth regarding their structure and catalytic performance in the conversion of CO-rich synthesis gas. In situ XAS studies demonstrated the formation of the active phase under reducing conditions. The present study revealed important material parameters to control activity and selectivity of the bifunctional catalysts either towards DME or liquefied petroleum gas (LPG) products in the direct conversion of simulated biomass-derived synthesis gas. In particular, Cu loading, pore structure and Si:Al ratio were investigated.

Passivation and reactivation of catalyst systems for the single step synthesis of dimethyl ether from CO-rich synthesis gas

A methanol catalyst based on Cu/ZnO/Al2O3 (CZA) was prepared and mixed with four different solid acids, a pure γ-Al2O3, a SiO2-doped γ-Al2O3, an AlPO4-doped γ-Al2O3 and the zeolite H-MFI 400, respectively. These admixed catalyst systems were tested in the direct synthesis of dimethyl ether from CO-rich synthesis gas (CO:H2=1), which is typical for biomass-derived synthesis gas. Reactions were carried out in a laboratory plant at 250°C and 51bar for 120h time-on-stream followed by catalyst passivation with O2 and regeneration by hydrogenation. After catalyst regeneration, the reaction was run again for another 72h. The catalyst system containing the zeolite exhibited highest CO-conversion. However, all catalysts showed a drop of activity after the passivation- and regeneration-process and the system with the SiO2-doped γ-Al2O3 showed the lowest loss of activity. Investigation of the catalysts after reaction by N2O-pulse chemisorption and XRD revealed that agglomeration of catalyst species took place leading to an increased Cu0-particle size for all systems. This phenomenon was less pronounced in the case of the system containing the SiO2-doped γ-Al2O3. Thus, the main cause of catalyst deactivation was found to be sintering of the catalytically active components.

Detailed H2 and CO Electrochemistry for a MEA Model Fueled by Syngas

SOFCs are capable of directly oxidizing CO in addition to H2, which allows them to be coupled to a gasifier that converts coal, biomass or other carbonaceous fuels to synthesis gas. Most membrane-electrode-assembly (MEA) models neglect CO electrochemistry because H2 oxidizes more readily and most CO presumably shifts to H2 by the water-gas-shift reaction in the presence of H2O. In this paper we examine this assumption, especially at conditions of high current density and high CO-content syngas. The comprehensive 1D-MEA model presented here incorporates detailed mechanisms for both H2 and CO oxidation. The rate parameters and rate-limiting steps for the H2 mechanism are selected by fitting the model to experimental porous anode data for H2/H2O mixtures. The kinetic parameters of the CO mechanism were determined by matching the data to EIS measurements. The anode’s physical parameters, triple-phase-boundary length and nickel pattern width, are then determined by fitting the CO mechanism to porous anode data for CO/CO2 mixtures. The resulting H2 and CO mechanisms are then combined, along with surface reforming kinetics, into a single model that iterates through anode activation overpotential to resolve the individual current contributions of each fuel. We find that the model under-predicts experimental data for H2/CO mixtures when CO electrochemistry is neglected, but fits the data well at high current densities when CO oxidation is included. Furthermore, the combined model fits H2/CO data best when a single charge-transfer step in the H2 mechanism is assumed to be rate-limiting over the full range of current densities. This single rate-limiting step assumption for H2/CO mixtures differs from a previous finding that the H2 adsorption step becomes rate-limiting at high current densities for H2/H2O mixtures. This implies that adding CO to the fuel stream can fundamentally alter the H2 oxidation process. The individual H2 and CO current contributions for CO-rich syngas confirm that the addition of CO oxidation can delay H2 current saturation at high anode activation overpotentials, hence improving cell performance. These results indicate that CO oxidation cannot be neglected in MEA models running on CO-rich synthesis gas, and further studies are needed on the combined CO and H2 mechanism on Ni-YSZ.

Zeolite-based bifunctional catalysts for the single step synthesis of dimethyl ether from CO-rich synthesis gas

Zeolite-based bifunctional catalysts for the production of dimethyl ether (DME) from CO-rich synthesis gas (H2:CO=1) were prepared via various preparation methods including co-precipitation–impregnation, impregnation, co-precipitation sedimentation and oxalate co-precipitation. The catalysts comprise a Cu/ZnO/Al2O3 component for methanol formation and zeolite H-MFI 400 as acidic component for methanol dehydration to DME. An admixed catalyst system was used as reference and all catalysts were characterized by SEM-EDX, XRF, N2-physisorption, XRD, H2-TPR, NH3-TPD, N2O-pulse chemisorption and TEM. The catalysts were tested in a continuously operating laboratory plant and the experiments revealed that the synthesis strategy strongly influences catalyst properties and hence catalyst activity. Especially a bifunctional catalyst prepared via oxalate co-precipitation proved to be highly active and could compete with conventional admixed catalyst systems. High CO-conversion and a high DME-selectivity could be reached. Catalyst characterization revealed that high Cu surface areas, small Cu particle sizes and a high number of moderate acidic sites are crucial to achieve maximum catalytic performance.

Biogas Upgrading: By Steam Electrolysis or Co-Electrolysis of Biogas and Steam

Biogas can be upgraded by means of SOEC technology. Steam added to biogas and the CO2 content can be co-electrolyzed generating a CO rich synthesis gas. Alternatively hydrogen from steam electrolysis can be added to the biogas. In both cases thesynthesis gas is methanated. Waste heat from the methanator is used as feed for the SOEC. The paper will compare the energy and exergy efficiency as well as the economics of the two routes in future energy scenarios with a large power fraction from wind.

Combinations of CO/CO2 reactions with Fischer–Tropsch synthesis

The combination of CO/CO2 shift reactions with Fischer–Tropsch synthesis offers the possibility to produce hydrocarbons from CO-rich syngas (from biomass or coal gasification) and from H2/CO2 mixtures. In the case of CO-rich synthesis gas, the H2/CO ratio needs to meet stoichiometric requirements for the low-temperature Fischer–Tropsch synthesis and therefore the CO is shifted to CO2 to form additional H2. Mixtures of H2/CO2 require the shift of CO2 into CO, which acts as intermediate in the production of short-chain hydrocarbons via high-temperature Fischer–Tropsch synthesis. The present work analyzes based on validated kinetic models how the shift reaction affects the FT reaction under operation conditions of interest and how both FT and shift reactions can be optimized to maximize hydrocarbon production.

Effect of carbon monoxide, hydrogen and sulfate on thermophilic (55 degrees C) hydrogenogenic carbon monoxide conversion in two anaerobic bioreactor sludges.

The conversion routes of carbon monoxide (CO) at 55 degrees C by full-scale grown anaerobic sludges treating paper mill and distillery wastewater were elucidated. Inhibition experiments with 2-bromoethanesulfonate (BES) and vancomycin showed that CO conversion was performed by a hydrogenogenic population and that its products, i.e. hydrogen and CO2, were subsequently used by methanogens, homo-acetogens or sulfate reducers depending on the sludge source and inhibitors supplied. Direct methanogenic CO conversion occurred only at low CO concentrations [partial pressure of CO (PCO) <0.5 bar (1 bar=10(5) Pa)] with the paper mill sludge. The presence of hydrogen decreased the CO conversion rates, but did not prevent the depletion of CO to undetectable levels (<400 ppm). Both sludges showed interesting potential for hydrogen production from CO, especially since after 30 min exposure to 95 degrees C, the production of CH4 at 55 degrees C was negligible. The paper mill sludge was capable of sulfate reduction with hydrogen, tolerating and using high CO concentrations (PCO>1.6 bar), indicating that CO-rich synthesis gas can be used efficiently as an electron donor for biological sulfate reduction.

The Synergy Effect of Process Coupling for Dimethyl Ether Synthesis in Slurry Reactors

The synergy effect of process coupling of reaction-reaction and reaction-heat transfer for dimethyl ether synthesis has been studied. The theoretical and experimental analyses show that the synergy of reaction-reaction is prominent and that the synergy of reaction-heat transfer is also feasible. Due to the synergy effect, CO-rich synthesis gas can be used for dimethyl ether synthesis and higher once-through conversion of CO can be obtained. Recycling and compression of the unreacted synthesis gas can be minimized considerably. Accordingly, savings will be made in energy consumption and the water gas shift reaction system, and the entire investment and production cost will decrease.

Carbon monoxide hydrogenation over molybdenum carbide catalysts

Supported and unsupported molybdenum and molybdenum carbides have been studied as catalysts of CO-H2 reactions at 570 K and atmospheric pressure. The initial turnover rates of these catalysts were comparable to those of the more active group VIII elements. However, all molybdenum-based catalysts showed a hydrocarbon product distribution different from those for typical group VIII metals. Furthermore, production of a large amount of CO2 (instead of water) and a high paraffin/olefin ratio reflected high activities of these catalysts for the water-gas shift reaction and hydrogenation, respectively. The high water-gas shift reaction activity allowed a CO-rich synthesis gas to be used efficiently over Mo-based catalysts. The CO-H2 reactions appear to be structure insensitive on molybdenum carbide catalysts, since the rates were independent of particle size and crystal structure of unsupported catalysts and of metal loading of supported catalysts.

Highly Active and Stable Iron Fischer−Tropsch Catalyst for Synthesis Gas Conversion to Liquid Fuels

A precipitated iron Fischer−Tropsch (F−T) catalyst (100 Fe/3 Cu/4 K/16 SiO2 on mass basis) was tested in a stirred tank slurry reactor under reaction conditions representative of industrial practice using CO-rich synthesis gas (260 °C, 1.5−2.2 MPa, H2/CO = 2/3). Repeatability of performance and reproducibility of catalyst preparation procedure were successfully demonstrated on a laboratory scale. Catalyst productivity was increased by operating at higher synthesis pressure while maintaining a constant contact time in the reactor and through the use of different catalyst pretreatment procedures. In one of the tests (run SA-2186), the catalyst productivity was 0.86 (g hydrocarbons/g Fe/h) at syngas conversion of 79%, methane selectivity of 3% (weight percent of total hydrocarbons produced), and C5+ hydrocarbon selectivity of 83 wt %. This represents a substantial improvement in productivity in comparison to state-of-the-art iron F−T catalysts. This catalyst is ideally suited for production of high-quality d...

Methanation of synthesis gas in a solar chemical heat pipe

The reversible reaction CH 4 + CO 2 = 2 H 2 + 2 CO is under investigation as a chemical heat pipe for storage and transport of solar energy. In this paper, the study of the back exothermic reaction, the methanation of CO-rich synthesis gas, is reported. Three different methanators were constructed and operated in a closed-loop, with the reforming products from the reaction carried out in the solar furnace. The best performance was obtained with a six-stage adiabatic methanator. The experimental results are compared with computer calculations, assuming equilibrium at each stage. The agreement between experimental and calculated results is satisfactory. Scale-up work on a 400 kW unit is in progress.

Iron-based catalysts for slurry-phase Fischer-Tropsch process: Technology review

The slurry-phase reactor system is of interest in Fischer-Tropsch synthesis owing to the ability of the reactor system to efficiently remove the heat produced by the exothermic reaction. Iron-based catalysts are active for Fischer-Tropsch synthesis and for the water-gas shift reaction, and, in addition, are inexpensive. Hence, they have been examined in slurry-phase Fischer-Tropsch synthesis with CO-rich synthesis gas. The role of promoters, carbide phases, and oxide phases in iron-based catalysts is not well understood. The article reviews current knowledge of iron-based catalysts with reference to their application in slurry-phase Fischer-Tropsch synthesis. Areas of investigation requiring further research are identified.

Enhancement of activity for hydrocarbon synthesis from synthesis gas over molybdenum/SiO2 catalysts by treatment with CO-rich synthesis gas.

Reduced Mo-KCl/SiO2 catalysts were effectively activated for synthesis of C1-C9 hydrocarbons with CO-rich (CO/H2=3/1) synthesis gas at 573K. This treatment, which caused but slight change in alcohol productivity, was contrasted with the treatment with CO/H2=1/1 synthesis gas, that was effective in enhancing selective alcohol synthesis; the CO/H2 ratio of the synthesis gas used for pretreatment was crucial to determining hydrocarbon/alcohol selectivity. The enhanced activity for hydrocarbon synthesis might be related with the formation of MoC. This activation treatment proved to be much more effective than the n-C4H10/H2 treatment.