Methanol synthesis via direct CO2 hydrogenation in a square duct: A direct numerical simulation study

Methanol synthesis through sorption enhanced carbon dioxide hydrogenation

The influence of Ni load and support material on catalysts for the selective catalytic oxidation of ammonia in gasified biomass

Vanadium magnesium oxide (VMgO) catalysts with different vanadium loadings were synthesized and tested for catalytic activity in the oxidative dehydrogenation of n-hexane. High surface area catalysts were obtained by the wet impregnation technique. Magnesium oxide (MgO) and magnesium orthovanadate [Mg3(VO4)2] were the only phases observed in each catalyst. All the catalysts were tested at 0.6–7.8 % of n-hexane in air within a temperature range of 350–550 °C, varying the gas hourly space velocities. Catalytic testing conducted below the lower flammability limit (0.6 % n-hexane in air) showed only benzene and carbon oxides in the product stream, whereas for experiments done above the upper flammability limit (7.8 % n-hexane in air), hexenes, in addition to benzene and carbon oxides were observed. Decreasing the feed composition from 7.8 to 5.5 % resulted in higher yields towards benzene and total dehydrogenated products. The effect of variations in the gas hourly space velocity investigated using the 19 wt% vanadium catalyst and a feed concentration of 7.8 % showed that the selectivity to benzene increased slightly with an increase in the gas hourly space velocity.

Methanol synthesis from CO2 and H2 in multi-tubular fixed-bed reactor and multi-tubular reactor filled with monoliths

A novel precipitation/digestion route has been developed to synthesize crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO3) by using an equimolar quantity of cerium nitrate (Ce(NO3)3·6H2O) and mixed precipitants (KOH + K2CO3) at room temperature. Nano-sized CeO2 supports could be prepared by the pre-calcination of CHC at 400 °C for 4 h. A highly active water gas shift (WGS) catalyst, 1 wt.% Pt/CeO2 catalyst showed almost equilibrium CO conversion with 100% CO2 selectivity at 320 °C even at the gas hourly space velocity (GHSV) of 45,625 h−1. A novel precipitation/digestion route has been developed to synthesize crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO3) by using an equimolar quantity of cerium nitrate (Ce(NO3)3·6H2O) and mixed precipitants (KOH + K2CO3) at room temperature. Nano-sized CeO2 supports could be prepared by the pre-calcination of CHC at 400 °C for 4 h. A highly active water gas shift (WGS) catalyst, 1 wt.% Pt/CeO2 catalyst showed almost equilibrium CO conversion with 100% CO2 selectivity at 320 °C even at the gas hourly space velocity (GHSV) of 45,625 h−1.

Utilization of CO2 for syngas production by CH4 partial oxidation using a catalytic membrane reactor

Ce0.70La0.20Ni0.10O2-δ catalyst for methane dry reforming: Influence of reduction temperature on the catalytic activity and stability

Hydrogen mordenite catalysts with silicon to aluminum ratios of 11, 39, 73 and 120 were used in this study. Three methods for preparing the hydrogen mordenite catalysts were compared. A 3-cycle alternation of ammonium exchange and calcinations method provided the catalyst with maximum hydrogen content. To obtain the catalysts having precisely required silicon to aluminum ratios the conditions for zeolite dealumination by acid leaching were systematically studies. It was found that the silicon to aluminum ratios depend strongly on acid concentration, temperature and duration of acid treatment. The catalysts were characterized using XRD, 27Al-NMR, NH3-TPD and AAS techniques. The catalysts were tested for their activities in methanol conversion to olefins. Various parameters including time on stream, temperatures (300-500°C) and Si/Al ratios affect the methanol conversion and product selectivity. For example, using a feed of 20% methanol in nitrogen at a gas hourly space velocity (GHSV) of 2000 h-1, the methanol conversion on mordenite catalyst (silicon to aluminum = 120) at 500 °C is 100%, and only little coke formation content leads to higher selectivity to light olefins and less coke deposition on the catalysts. The catalyst lifetime can be extended by reducing of number of acid sites which importantly affects the degree of coke formation.

Hydrogen production from methane under the interaction of catalytic partial oxidation, water gas shift reaction and heat recovery

Catalytic oxidation is a feasible and affordable technology for solvent emission abatement. However, finding optimal operation conditions is important, since they are strongly dependent on the application area of VOC incineration. This paper presents the results of the laboratory experiments concerning four most central parameters, that is, effects of concentration, gas hourly space velocity (GHSV), temperature, and moisture on the oxidation of n-butyl acetate. Both fresh and industrially aged commercial Pt/Al2O3 catalysts were tested to determine optimal process conditions and the significance order and level of selected parameters. The effects of these parameters were evaluated by computer-aided statistical experimental design. According to the results, GHSV was the most dominant parameter in the oxidation of n-butyl acetate. Decreasing GHSV and increasing temperature increased the conversion of n-butyl acetate. The interaction effect of GHSV and temperature was more significant than the effect of concentration. Both of these affected the reaction by increasing the conversion of n-butyl acetate. Moisture had only a minor decreasing effect on the conversion, but it also decreased slightly the formation of by products. Ageing did not change the significance order of the above-mentioned parameters, however, the effects of individual parameters increased slightly as a function of ageing.

Experimental and modeling investigation on CO2 sorption kinetics over K2CO3-modified silica aerogels

Technologies for reducing hydrodynamic skin-friction drag have a huge potential for energy-savings in applications ranging from propulsion of marine vessels to transporting liquids through pipes. The majority of previous experimental studies using hydrophobic surfaces have successfully shown skin-friction drag reduction in the laminar and transitional flow regimes (typically Reynolds numbers less than ≃106 for external flows). However, this hydrophobicity induced drag reduction is known to diminish with increasing Reynolds numbers in experiments involving wall bounded turbulent flows. Using random-textured hydrophobic surfaces (fabricated using large-length scalable thermal spray processes) on a flat plate geometry, we present water-tunnel test data with Reynolds numbers ranging from 106 to 9 × 106 that show sustained skin-friction drag reduction of 20%–30% in such turbulent flow regimes. Furthermore, we provide evidence that apart from the formation of a Cassie state and hydrophobicity, we also need a low surface roughness and an enhanced ability of the textured surface to retain trapped air, for sustained drag reduction in turbulent flow regimes. Specifically, for the hydrophobic test surfaces of the present and previous studies, we show that drag reduction seen at lower Reynolds numbers diminishes with increasing Reynolds number when the surface roughness of the underlying texture becomes comparable to the viscous sublayer thickness. Conversely, test data show that textures with surface roughness significantly smaller than the viscous sublayer thickness and textures with high porosity show sustained drag reduction in the turbulent flow regime. The present experiments represent a significant technological advancement and one of the very few demonstrations of skin-friction reduction in the turbulent regime using random-textured hydrophobic surfaces in an external flow configuration. The scalability of the fabrication method, the passive nature of this surface technology, and the obtained results in the turbulent regime make such hydrophobic surfaces a potentially attractive option for hydrodynamic skin-friction drag reduction.

Carbon capture and utilization (CCU) has emerged in recent years as a promising decarbonization solution for hard-to-abate industries. Compared to carbon capture and storage (CCS), CCU aims not for the storage of carbon dioxide (CO2) but for its use in the production of synthetic fuels, such as synthetic methanol (MeOH). Synthetic MeOH is produced through CO2 hydrogenation, utilizing green hydrogen (H2). Efficient use of CO2 and H2 feedstocks is essential to maximize the carbon reduction potential and energy efficiency of the process. This study performed an optimization analysis on a small-scale, containerized, and portable CO2 hydrogenation unit with a 5 kg MeOH/h production capacity goal, focusing on carbon conversion efficiency (CCE), MeOH yield, H2 consumption, and MeOH purity. The analysis was conducted using Aspen Plus V12. A single-pass model was used first to evaluate an initial reactor design. The reactor was then re-designed according to the results of the gas hourly space velocity (GHSV). The model was then expanded to include a recycling loop and the final reactor design was validated, aiming to maximize overall efficiency. The effects of the operational parameters including the reactor inlet temperature, reactor pressure, thermal fluid temperature, and condensation temperature were examined. The model was then further expanded to include the MeOH distillation process, and the effect of the distillation temperature was examined. The final product of the analysis was a fully-defined and optimized unit, achieving an 87.97% CCE and an 84.99% MeOH yield, consuming 1.11 kg H2/h for the production of 5.01 kg MeOH/h of 99.86 wt% purity. This study can provide valuable information and guidelines for designing small-scale, containerized, and portable CO2 hydrogenation units, which can serve as alternative solutions to address issues of H2 production and transportation related to large-scale installations.

CO2 valorization is a key measure to reach climate neutrality. Thermodynamics suggest direct conversion of CO2 into dimethyl ether (DME) to have greater potential than the indirect route via methanol synthesis, followed by purification of methanol and then a separate dehydration into DME. In this work, we introduce heteropoly acids as a capable class of dehydration catalysts for direct DME synthesis from CO2 and H2. To clarify if direct DME synthesis is in fact superior to sole MeOH synthesis, accurate thermodynamic equilibrium calculations are performed and pose as the base of our argumentation. An efficient Cu/ZnO/ZrO2 (CZZ) methanol catalyst is used to compare the methanol synthesis using a feedstock with stoichiometric CO2/3H2 mixture against bifunctional catalysts, containing CZZ and a dehydration component. The dehydration components include a commercial ferrierite (FER) and heteropoly acid (HPA) coated alumina and zirconia. For direct DME synthesis, the CO2 feed gas at gas hourly space velocities (GHSVs) between 1,250 and 158,400 NL kgcat–1 h–1, at temperatures of 210–270 °C and 40 bar pressure, was investigated. Based on the wide parameter window investigated, the following can be concluded at 250 °C: under a thermodynamic regime, CO2 conversion is close to the theoretical limit (30%exp/32%theo) and the direct DME synthesis is superior to sole methanol synthesis (+20%exp/+33%theo). The amount of valuable products (methanol, DME) profits significantly more (+70%exp/+88%theo) from the direct DME synthesis than CO2 conversion indicates. Under a kinetic regime, HPA-coated catalysts show superior apparent activation energies for DME production than the widely used ferrierite (HPA: 45 kJ mol–1/FER: 80 kJ mol–1), making HPA coatings a great option for highly capable dehydration catalysts under CO2- and water-rich conditions.

Plastic waste, particularly low-density polyethylene (LDPE), poses severe environmental challenges due to its low bio-degradability and limited recycling potential. In this study, a solvent-assisted catalytic steam reforming approach is investigated, in which LDPE is finely dispersed in ethylene glycol (EG) to enable homogeneous feed delivery for hydrogen production. Steam reforming experiments were conducted over 20 wt% Ni-Co/Al2O3-ZrO2 catalyst synthesized via sol-gel and wet impregnation methods. The bimetallic catalyst exhibited high surface area (136 m2 g- 1), strong metal-support interaction (SMI), and improved thermal stability confirmed through characterization techniques including XRD, BET, FESEM, FTIR, and TGA-DSC analyses. Systematic optimization of operating parameters such as metal loading, steam-to-carbon ratio (S/C), gas hourly space velocity (GHSV), and temperature revealed optimal conditions at S/C = 9, GHSV = 810 h- 1, and 500°C. Under these conditions, it achieved 95% feed conversion, 92.72% hydrogen yield, and 97.6% selectivity. The synergistic interaction between Ni and Co enhanced reforming kinetics and suppressed coke formation, enabling stable operation. Compared to previous reports on ethylene glycol or PET reforming, the current work improved hydrogen yield by 5-10%, validating its potential for direct plastic-to-hydrogen conversion. Overall, the results demonstrate the potential of solvent-assisted reforming as a controlled platform for hydrogen generation from waste polymer-derived carbon.