Use of a micro-porous membrane multi-tubular fixed-bed reactor for tri-reforming of methane to syngas: CO2, H2O or O2 side-feeding

A one-dimensional heterogeneous model for four configurations of a reactor, three micro-porous membrane reactors with O₂ (O-MMTR), CO₂ (C-MMTR) or H₂O (H-MMTR) side-feeding strategy and one traditional reactor (i.e., multi-tubular fixed-bed reactor (MTR)), was developed to explain tri-reforming of methane to produce syngas. Effect of various side-feeding strategies on reactor performance containing CH₄ and CO₂ conversion, H₂/CO ratio, and H₂ yield was investigated under the same condition and then described by chemical species and temperature profiles. It was found that use of side-feeding strategies could be feasible, beneficial, and flexible in terms of change in membrane thickness and shell-side pressure for syngas production with H₂/CO = 2 which is proper for methanol and Fischer-Tropsch process, and = 1.2 which is suitable for DME direct synthesis. However, the syngas produced by the MTR is only appropriate for the methanol and Fischer-Tropsch synthesis under the base case conditions. Also, the results show that the micro-porous membrane reactors have higher CO₂ conversion, based on the H₂/CO = 1.2; so these strategies are more environmentally friendly compared to the traditional reactor.     

O2, H2O or CO2 side-feeding policy in methane tri-reforming reactor: The role of influencing parameters

Methane tri-reforming is an efficient route to produce syngas. Distributing one component through a micro-porous membrane, namely side-feeding procedure, is an effective method for controlling reactions pathway and achieving the higher performance in membrane reactors. More recently, Alipour-Dehkordi and Khademi (2019) suggested a feasible and beneficial membrane multi-tubular reactor with O₂, H₂O or CO₂ side-feeding policy to describe the methane tri-reforming for producing a suitable syngas for the methanol and dimethyl ether direct synthesis processes. To complete the previous research, a theoretical study was presented to detect the role of effective parameters, including molar flow rate of feed components, membrane thickness, shell-side pressure, and inlet gas temperature on the H₂/CO ratio, CH₄ conversion, H₂ yield, and CO₂ conversion. Several results were observed, however one of the most attractive results was to achieve CO₂ conversion up to 40% in these configurations by controlling the influencing parameters (compared to CO₂ conversion in the conventional tri-reformer (i.e., 11.5%)); that would be favorable for the environment.     

Tri-reforming of methane over Ni@SiO2 catalyst

A nickel-silica core@shell catalyst was applied for a methane tri-reforming process in a fixed-bed reactor. To determine the optimal condition of the tri-reforming process for production of syngas appropriate for methanol synthesis the effect of reaction temperature (550–750 °C), CH₄:H₂O molar ratio (1:0–3.0) and CH₄:O₂ molar ratio (1:0–0.5) in the feedstock was investigated. CH₄ conversion rate and H₂/CO ratio in the produced syngas were influenced by the feedstock composition. Increasing the amount of steam above the proportion of CH₄:H₂O 1:0.5 reduced the H₂:CO molar ratio in produced syngas to ∼1.5. Increasing oxygen partial pressure improved methane conversion to 90% at 750 °C. At low ∼550 °C reaction temperature the tri-reforming process was not effective with low hydrogen production (H₂ yield ∼20%) and very low <5% CO₂ conversion. Increasing reaction temperature increased hydrogen yield to ∼85% at 750 °C. From all the tested reaction conditions the optimal for tri-reforming over the 11%Ni@SiO₂ catalyst was: feed composition with molar ratio CH₄:CO₂:H₂O:O₂:He 1:0.5:0.5:0.1:0.4 at T = 750 °C. The results were explained in the context of characterisation of the catalysts used. The obtained results showed that the tri-reforming process can be applied for production of syngas with composition suitable for methanol synthesis.     

Effect of ionic liquid in Ni/ZrO2 catalysts applied to syngas production by methane tri-reforming

This study investigates the influence of ionic liquid in morphology, acid-base properties, metal dispersion and performance of 5%Ni/ZrO₂ catalysts in the methane tri-reforming reaction. Zirconia was prepared by precipitation and the catalysts by wet impregnation. The ionic liquid modified the acid and basic character of the catalysts and positively influenced the methane tri-reforming reaction efficiency. The reaction was evaluated with synthetic biogas and with stoichiometric feed molar ratio (CH₄: CO₂: H₂O: O₂ = 1:0.5:0.5:0.1 and CH₄: CO₂: H₂O: O₂ = 1:0.33:0.33:0.16). The Ni/ZrO₂ prepared with ionic liquid exhibits promising catalytic activity and stability in methane tri-reforming at 800 °C in 4 h run, without coke formation. An increase in the reaction temperature results in an increase of hydrogen yield and the methane conversion, reaching ∼85% at 850 °C. The presented results demonstrate that the tri-reforming reaction could be used for production of syngas with H₂/CO ratio appropriate for methanol synthesis.     

Tri-reformer with O2 side-stream distribution for syngas production

Methane tri-reforming combines steam reforming, dry reforming and partial oxidation of methane in a single reactor. The heat generated by the exothermic partial oxidation of methane can be used to supply the energy for the other two endothermic reactions (dry and steam reforming of methane). The thermoneutral condition allows the use of a tri-reformer with a simpler reactor structure since no external heat supply is necessary. Thermodynamic analysis of the thermoneutral reactor was performed using Gibbs free energy minimization approach. Conventional tri-reformers have heat and mass management problems. We developed a novel tri-reformer concept that utilizes proper distribution of O₂ gas to the reactor to address the problems. The optimization of the proposed reactor was performed with the objective function of minimizing total annual cost. Maintaining the peak temperatures by adjusting the O₂ flow rate at the distribution point along the reactor was shown to provide good load flexibility for the change in methane flow rate.     

Process simulation and economic feasibility assessment of the methanol production via tri-reforming using experimental kinetic equations

The purpose of this paper is to assess via techno-economic metrics the feasibility of a tri-reforming coupled methanol process. The simulation of the tri-reforming reactor considered empiric kinetic equations, developed by our group in previous studies. The flue gas coming from the furnace that provides the energy required by the reforming reactor was also used as feed, in order to reduce the CO₂ emissions. A sensitivity analysis was carried out to determine the influence of the feed composition and temperature in the tri-reforming process results, studying H₂O/CH₄ and O₂/CH₄ ratios (0.5–1.5 and 0.35–0.40, respectively), and varying the temperature between 850 and 1050 °C. The methanol plant was also simulated, and an economical study was carried out to know if the proposed process would be economically feasible. The most relevant economic parameters (including the Net Present Value, the Internal Rate of Return, the Payback Period and the break-even) were calculated, showing a quite robust process from an economical point of view.     

The effect of H2 pressure on the reduction kinetics of hematite at low temperatures

Two novel experimental approaches to study the reduction kinetics of hematite (Fe₂O₃) by hydrogen at low temperatures are presented. Experiments were carried out in batch reactors at 200 °C and at H₂ pressures of 3, 6 and 8 MPa, respectively. Complementary experiments were performed in an open system at atmospheric H₂ pressure and 270 °C. Here the reaction product water in the effluent gas was quantified in short intervals by gas chromatography (Thermal Conductivity Detector; TCD). The mineralogical changes over time were assessed by X-ray powder diffraction with Rietveld analysis, scanning electron microscopy and the measurement of magnetic hysteresis loops.While the phase conversions of hematite $\to$ magnetite $\to$ Fe(0) are occurring consecutively in open systems (p(H₂)$\approx$0.1 MPa), in closed systems at elevated H₂ pressure both reduction products are observed simultaneously. At 200 °C the reaction rates are about one order of magnitude lower than at 270 °C. The conversion rate of magnetite $\to$ Fe(0) is highly sensitive to the hydrogen pressure with a rate increase by a factor of 2.5 upon an increase of p(H₂) from 3 to 6 MPa and by 2.0 between 6 and 8 MPa.