Pure Syngas Research Articles

The effect of impurities on syngas combustion

The effects of chemical impurities on the combustion of syngas were investigated, focusing on CH4, a common component of syngas, and trimethylsilanol (TMS), an unstudied impurity related to those common to landfill-based syngas. Ignition properties were systematically investigated at high-pressure low-temperature conditions relevant to gas turbine combustor operation using the University of Michigan Rapid Compression Facility. Pressure time history measurements and high-speed imaging of the ignition process in this facility were used to determine auto-ignition delay times and observe ignition behaviors. The four simulated syngas mixtures used were (1) pure syngas: 30% H2, 70% CO fuel volume, (2) syngas with CH4: 27% H2, 67% CO, 6% CH4, (3 & 4) pure syngas with 10 or 100ppm TMS, all with fuel-to-O2 equivalence ratios (φ) of 0.1 at air dilution (i.e. molar O2 to inert gas ratio of 1:3.76), and N2 as the primary diluent gas. The pressures after compression were 5 & 15atm with temperatures of ∼1010–1110K respectively. The results uniquely illustrated the occurrence of two-step ignition behavior at higher pressures, with two distinct regions of heat release and pressure rise. First and second auto-ignition delay times were therefore defined and interestingly the times were affected differently by the addition of impurities. The addition of CH4 consistently increased auto-ignition delay times up to 40% at 15atm, while increasing delay times at 5atm by up to a factor of three. Conversely, the addition of 10ppm TMS impurity addition caused a consistent decrease of ∼10–30% delay times at 15atm with insignificant impact at 5atm, and 100ppm TMS impurity caused consistent decreases of 50–70% at 15atm and 20–30% decreases at 5atm. The marked pressure dependence of the auto-ignition delay time, typical for syngas at these conditions, was virtually eliminated for the 100ppm TMS mixture. Kinetic modeling suggests that the promoting effects of TMS are related to enhanced consumption and/or reduced production of HO2. The impact of TMS is remarkably similar to that for SiH4 in pure H2, suggesting a possible trend for poorly understood Si-based species to promote auto-ignition in syngas and hydrogen mixtures.

Shale gas-to-syngas chemical looping process for stable shale gas conversion to high purity syngas with a H2 : CO ratio of 2 : 1

The shale gas-to-syngas (STS) chemical looping process was conceived by Fan and associates in 2013 for the production of high-purity syngas from shale gas. The STS process producing syngas does not require the use of molecular oxygen from air separation and steam. This paper describes the rationale for the process concept with experimental data that substantiates the process validity. Specifically, the STS process consists of a co-current gas (shale gas)–solid (metal oxides) moving bed contact mode reducer operation with metal oxides for shale gas conversion to syngas. The reduced metal oxides from the reducer operation are regenerated via an oxidation operation with air. Various active metal oxides or metal oxide composites can be utilized. However, it is through the combination of desired metal oxides and co-current moving bed reducer that high syngas purity and a desirable H2 : CO molar ratio of ∼2 : 1 can be achieved. In this study, active iron–titanium composite metal oxide (ITCMO) materials are used as the oxygen carrier for the demonstration of the STS process. The desirable thermodynamic property of ITCMO is a key factor for the generation of high quality syngas. The co-current moving bed provides a desirable gas–solid contacting pattern that minimizes carbon deposition and maximizes the syngas yield. The syngas produced by the STS process can achieve a H2 : CO molar ratio of ∼2 : 1 with little CO2, CH4 and steam, which is required for downstream processes to produce liquid fuels and chemicals. The experimental results for reaction kinetics including oxygen carrier recyclability and pressure effects are obtained by thermogravimetric analysis (TGA), and syngas generation using a fixed bed, a bench-scale moving bed, and a sub-pilot scale moving bed reactor demonstrations are achieved in this study. The bench and sub-pilot demonstrations confirm that the syngas produced by the STS process is close to thermodynamic equilibrium with the reduced ITCMO. Furthermore, simulation studies are conducted to compare the efficiency of the STS process with a conventional autothermal natural gas reforming process.

Rapid bio-methanation of syngas in a reverse membrane bioreactor: Membrane encased microorganisms

The performance of a novel reverse membrane bioreactor (RMBR) with encased microorganisms for syngas bio-methanation as well as a co-digestion process of syngas and organic substances was examined. The sachets were placed in the reactors and examined in repeated batch mode. Different temperatures and short retention time were studied. The digesting sludge encased in the PVDF membranes was able to convert syngas into methane at a retention time of 1day and displayed a similar performance as the free cells in batch fermentation. The co-digestion of syngas and organic substances by the RMBR (the encased cells) showed a good performance without any observed negative effects. At thermophilic conditions, there was a higher conversion of pure syngas and co-digestion using the encased cells compared to at mesophilic conditions.

Impact and Detailed Action of Sulfur in Syngas on Methane Synthesis on Ni/γ-Al2O3 Catalyst

Stability and deactivation phenomena are of utmost importance for metal nanocatalysts from both fundamental and industrial points of view. The presence of small amounts of sulfur at ppm and ppb levels in the synthesis gas produced from fossil and renewable sources (e.g., biomass, coal) is a major reason for deactivation of nickel catalysts for carbon monoxide hydrogenation. This paper addresses reaction pathways and deactivation mechanisms of alumina-supported nickel catalysts for methane synthesis from pure syngas and syngas containing small amounts of sulfur. A combination of SSITKA and operando FTIR is indicative of both reversible molecular and irreversible dissociative carbon monoxide adsorption on nickel nanoparticles under the reaction conditions. Methanation reaction involves irreversible carbon monoxide adsorption, dissociation, and hydrogenation on nanoparticle steps and edges. Hydrogenation of adsorbed carbon species leading to methane seems to be the reaction kinetically relevant step. Molecular forms of carbon monoxide reversibly adsorbed on nickel terraces are likely not to be involved in carbon monoxide hydrogenation. The results suggest a competition between sulfur and carbon monoxide for nickel surface sites. During methanation, sulfur preferentially adsorbs on the sites of reversible molecular carbon monoxide adsorption, whereas the low-coordinated nickel sites responsible for carbon monoxide dissociation and hydrogenation are affected to a lesser extent by sulfur poisoning. The active sites of carbon monoxide hydrogenation are poisoned much more rapidly by sulfur, when the catalyst has been exposed to small amounts of H2S in the absence of methanation.

Carbon nanotubes decorated α-Al2O3 containing cobalt nanoparticles for Fischer-Tropsch reaction

A new hierarchical composite consisted of multi-walled carbon nanotubes (CNTs) layer anchored on macroscopic α-Al2O3 host matrix was synthesized and used as support for Fischer-Tropsch synthesis (FTS). The composite constituted by a thin shell of a homogeneous, highly entangled and structure-opened carbon nanotubes network and it exhibited a relatively high and fully accessible specific surface area of 76 m2·g−1, compared with that of 5 m2·g−1 of the original α-Al2O3 support. The metal-support interaction between carbon nanotubes surface and cobalt precursor and high effective surface area led to a relatively high dispersion of cobalt nanoparticles. This hierarchically supported cobalt catalyst exhibited a high FTS activity along with an extremely high selectivity towards liquid hydrocarbons compared with the cobalt-based catalyst supported on pristine α-Al2O3 or on CNTs carriers. This improvement can attribute to the high accessibility of composite surface area comparing with the macroscopic host structure alone or to the bulk CNTs where the nanoscopic dimension induced a dense packing with low mass transfer which favoured the problem of reactants competitive diffusion towards the cobalt active site. In addition, intrinsic thermal conductivity of decorated CNTs could help the heat dissipating throughout the catalyst body, thus avoiding the formation of local hot spots which appeared in high CO conversion under pure syngas feed in FTS reaction. Cobalt supported on CNTs decorated α-Al2O3 catalyst also exhibited satisfied high stability during more than 200 h on stream under relatively severe conditions compared with other catalysts reported in the literature. Finally, the macroscopic shape of such composite easily rendered its usage as catalyst support in a fixed-bed configuration without facing problems of transport and pressure drop as encountered with the bulk CNTs.

Platinum based core–shell catalysts for sour water–gas shift reaction

Pt@CeO 2 and Pt@Ce 0.67 Zr 0.33 O 2 prepared by microemulsion method were studied for water–gas shift reaction in pure syngas and sour syngas from 573 K to 773 K. Both showed high catalytic activities in pure syngas with CO conversion (X CO ) nearly to equilibrium status at temperature above 723 K, and the side reaction of methanation was inhibited throughout the temperature range. Pt@Ce 0.67 Zr 0.33 O 2 showed lower X CO in pure syngas, but higher in sour syngas than Pt@CeO 2 , indicating that the former is more resistant to H 2 S than the latter. Although a decrease in X CO was observed in sour syngas relative to pure syngas, stability experiments carried out over Pt@Ce 0.67 Zr 0.33 O 2 indicated that the catalytic activity could be recovered after the removal of H 2 S. ► Platinum based core–shell catalysts were firstly studied for sour WGS. ► Core shell shows high activities in pure syngas but no methanation even at 773 K. ► The catalysts deactivation in sour syngas was partly irreversible. ► The reason is mainly due to the absence of surface platinum.

Heating Effect of Plasma Catalytic Reaction on the CH4 Reforming of CO2 over Ni/γ-Al2O3 Catalyst in Dielectric-barrier Discharge Reactor

Abstract CH4 reforming of CO2 reaction for producing synthesis gas (syngas) was performed using dielectric-barrier discharge (DBD) with catalyst. Ni/γ-Al2O3 was used as a catalyst. To investigate the effect of reaction temperature, extra heating was applied outside of the plasma reactor. When supplied extra heating, pure syngas could be obtained only at 573 K. It is a noticeable result comparing with pure catalytic reaction or plasma reaction only.