Parametric Study of CO₂ Methanation for Synthetic Natural Gas Production

The production of methane by carbon dioxide hydrogenation through optimization of the operating parameters to enhance methane yield and carbon dioxide conversion in a two‐stage fixed bed reactor is investigated. The influence of temperature, gas hourly space velocity (GHSV), and H2:CO2 ratio on the production of methane is studied. In addition, different methanation catalysts in terms of metal promoters and support materials are investigated to maximize methane production. The results show that the maximum methane yield and maximum carbon dioxide conversion are obtained at a catalyst temperature of 360 °C with a H2:CO2 ratio of 4:1 and total GHSV of 6000 mL h−1 g−1catalyst and reactant GHSV of 3000 mL h−1 g−1catalyst. The optimum metal‐alumina catalyst investigated for CO2 conversion and methane yield is the 10 wt%‐Ni‐Al2O3 catalyst. However, reduction in the methane yield is observed with the addition of Fe and Co promoters because of catalyst sintering and nonuniform dispersion of metals on the support. Among the different catalyst support materials studied, i.e., Al2O3, SiO2 and MCM‐41, the highest catalytic activity is shown by the Al2O3 catalyst with 83 mol% CO2 conversion, producing 81 mol% CH4 with 98% CH4 selectivity

Methane Production from the Pyrolysis–Catalytic Hydrogenation of Waste Biomass: Influence of Process Conditions and Catalyst Type

The production of methane through the optimization of various operating parameters and the use of different catalysts has been investigated using a two-stage, pyrolysis–catalytic hydrogenation reactor. Pyrolysis of the biomass in the first stage produces a suite of gases, including CO2 and CO, which undergo catalytic hydrogenation in the presence of added H2 in the second stage. The influence of the biomass pyrolysis temperature, catalyst temperature, and H2 gas space velocity has been investigated for the optimization and enhancement of the methane yield. In addition, different metal catalysts (Co/Al2O3, Mo/Al2O3, Ni/Al2O3, Fe/Al2O3), the influence of different metal loadings, catalyst calcination temperature, and different support materials (Al2O3, SiO2, and MCM-41) were investigated. The yield of methane was linked to the properties of the catalysts including the preparation calcination temperature and support material which influenced the catalyst surface area and metal crystallite particle size by sintering. The highest methane yield of 7.4 mmol g–1biomass was obtained at a final pyrolysis temperature of 800 °C, catalyst temperature of 500 °C, and H2 gas hourly space velocity of 3600 mL h–1 g–1catayst. This optimization process resulted in 75.5 vol % of methane in the output gaseous mixture

Enhanced hydrogen-rich gas production from waste biomass using pyrolysis with non-thermal plasma-catalysis

A pyrolysis-non-thermal plasma-catalytic system for the increased production of hydrogen-rich gas from waste biomass has been investigated. Plasma processing of the hydrocarbon pyrolysis gases produced a marked increase in total gas yield with plasma-catalysis producing a further modest increase. The product gases were mainly composed of H₂ , CO and CO₂ , which were all increased under plasma and plasma-catalyst conditions. For example, H₂ yield increased from 1.0 mmol g −¹biomass in the absence of plasma to 3.5 mmol g −¹biomass with plasma and to 4.0 mmol g −¹biomass with plasma-catalysis. In addition, in the absence of plasma, the hydrocarbon tar content in the product gas was 420 mg m −³ , but, for non-catalytic plasma conditions, this was reduced to 325 mg m −³ and for plasma-catalytic steam reforming, the tar hydrocarbons were markedly reduced to 150 mg m −³ . The effect of increasing input power for the plasma processing (no catalyst) showed a large increase in total gas, H₂ , CO and CO₂ yield and corresponding decrease in hydrocarbon gas concentration. Plasma-catalysis showed that higher power input had only a small effect on gas yield. Plasma-catalysis was shown to produce lower catalyst coke deposition compared to non-plasma catalytic processing

Production and application of carbon nanotubes, as a co-product of hydrogen from the pyrolysis-catalytic reforming of waste plastic

Hydrogen production from waste plastics is an important alternative for managing waste plastics. This work addresses a promising technology for co-producing high value carbon nanotubes (CNTs) in addition to the production of hydrogen; thus significantly increasing the economic feasibility of the process. Catalyst design is a critical factor to control the production of hydrogen and CNTs. NiMnAl catalysts, prepared by a co-precipitation method, with different metal molar ratios were developed and investigated using a two-stage fixed-bed reactor. It was found that the NiMnAl catalyst with the higher Mn content produced a higher yield of carbon (57.7 wt.%). Analysis of the carbon on the NiMnAl catalysts showed it to consist of ∼90 wt.% of carbon nanotubes. The CNTs were recovered from the catalyst and added at 2 wt.% to LDPE plastic to form a composite material. The tensile and flexural strength and the tensile and flexural modulus of the CNT composite material were significantly improved by the addition of the recovered CNTs. Thus it is suggested that cost-effective CNTs could be produced from waste plastics as by-product of the production of hydrogen, enhancing the potential applications of CNTs in the composite industry

Pyrolysis-plasma/catalytic reforming of post-consumer waste plastics for hydrogen production

Different types of single waste plastics and a range of real-world mixed waste plastics from several different industrial and commercial sources have been processed in a pyrolysis-plasma/catalytic experimental reactor system for the production of hydrogen. The hydrocarbons produced from the pyrolysis stage were catalytically (Ni/MCM-41) steam reformed in a low temperature, non-thermal plasma/catalytic reactor. The polyolefin plastics, high density polyethylene, low density polyethylene and polypropylene produced the highest yield of hydrogen at 18.0, 17.3 and 16.3 mmol g−1plastics respectively. The aromatic structured polystyrene produced a lower hydrogen yield of 11.9 mmol g−1plastics and polyethylene terephthalate with an aromatic and oxygenated structure produced only 10.2 mmol g−1plastics and a high yield of carbon oxide gases. The real-world mixed plastic waste produced yields of hydrogen in the range of 13.4–16.9 mmol g−1plastics. The lowest hydrogen yield of 13.4 mmol g−1plastics was produced from the mineral water bottle packaging waste due to the high content of polyethylene terephthalate in the plastic waste mixture

Biomass:polystyrene co-pyrolysis coupled with metal-modified zeolite catalysis for liquid fuel and chemical production

Biomass and waste polystyrene plastic (ratio 1:1) were co-pyrolysed followed by catalysis in a two-stage fixed bed reactor system to produce upgraded bio-oils for production of liquid fuel and aromatic chemicals. The catalysts investigated were ZSM-5 impregnated with different metals, Ga, Co, Cu, Fe and Ni to determine their influence on bio-oil upgrading. The results showed that the different added metals had a different impact on the yield and composition of the product oils and gases. Deoxygenation of the bio-oils was mainly via formation of CO2 and CO via decarboxylation and decarbonylation with the Ni–ZSM-5 and Co–ZSM-5 catalysts whereas higher water yield and lower CO2 and CO was obtained with the ZSM-5, Ga–ZSM-5, Cu–ZSM-5 and Fe–ZSM-5 catalysts suggesting hydrodeoxygenation was dominant. Compared to the unmodified ZSM-5, the yield of single-ring aromatic compounds in the product oil was increased for the Co–ZSM-5, Cu–ZSM-5, Fe–ZSM-5 and Ni–ZSM-5 catalysts. However, for the Ga–ZSM-5 catalyst, single-ring aromatic compounds were reduced, but the highest yield of polycyclic aromatic hydrocarbons was produced. A higher biomass to polystyrene ratio (4:1) resulted in a markedly lower oil yield with a consequent increased yield of gas

Pyrolysis-catalytic steam reforming of waste plastics for enhanced hydrogen/syngas yield using sacrificial tire pyrolysis char catalyst

Pyrolysis-catalytic steam reforming of waste plastics to produce hydrogen-rich syngas has been investigated using tire char as a sacrificial catalyst in a two-stage pyrolysis-catalytic steam reforming reactor system. The simultaneous steam reforming of the pyrolysis volatiles and ‘sacrificial’ steam gasification of tire char increased the overall yield of syngas and hydrogen in the gas products. Manipulating the catalyst temperature, steam input, char catalyst:plastic ratio influenced hydrogen yield. The presence of metals such as Zn, Fe, Ca and Mg in tire char, play a catalytic role in steam reforming reactions. The syngas production achieved when the catalyst temperature was 1000 °C and steam weight hourly space velocity was 8 g h−1 g−1 catalyst was 135 mmol H2 g-1plastic and 92 mmol CO g-1plastic. However, increasing the amount of char catalyst (4:1 char catalyst:plastic ratio) enabled hydrogen yields of 211 mmol g-1plastic and total syngas yields of 360 mmol g-1plastic to be achieved

Hydrogen/Syngas Production from Different Types of Waste Plastics Using a Sacrificial Tire Char Catalyst via Pyrolysis–Catalytic Steam Reforming

Single plastics and mixed waste plastics from different industrial and commercial sectors have been investigated in relation to the production of hydrogen and syngas using a pyrolysis–catalytic steam reforming process. The catalyst used was a carbonaceous char catalyst produced from the pyrolysis of waste tires. Total gas yields from the processing of single plastics were between 36.84 and 39.08 wt % (based on the input of plastic, reacted steam, and char gasification) but those in terms of the gas yield based only on the mass of plastic used were very high. For example, for low-density polyethylene (LDPE) processing at a catalyst temperature of 1000 °C, the gas yield was 445.07 wt % since both the reforming of the plastic and also the steam gasification of the char contributed to the gas yield. The product gas was largely composed of H2 and CO, i.e., syngas (∼80 vol %), and the yield was significantly increased as the char catalyst temperature was raised from 900 to 1000 °C. Hydrogen yields for the processing of the polyolefin single plastics were ∼130 mmol gplastic–1 at a catalyst temperature of 1000 °C. The pyrolysis–catalytic steam reforming of the industrial and commercial mixed plastics with the tire char catalyst produced hydrogen yields that ranged from 92.81 to 122.6 mmol gplastic–1 and was dependent on the compositional fraction of the individual plastics in their mixtures. The tire char catalyst in the process acted as both a catalyst for the steam reforming of the plastics pyrolysis volatiles to produce hydrogen and also as a reactant (“sacrificed”), via carbon-steam gasification to produce further hydrogen

High-value resource recovery products from waste tyres

A novel process has been developed which enables the production of high-value carbon nanotubes (CNTs) and hydrogen-rich syngas from the two-stage pyrolysis–catalysis of waste tyres. The waste tyre samples originated from truck tyres and from car tyres. In addition, three of the main rubber elastomers used in tyre manufacture, polybutadiene rubber, styrene–butadiene rubber and natural rubber, were also investigated. The waste car tyres produced a syngas yield of 30·2 wt%, which was composed largely of hydrogen (53·8 vol%) with a calorific value of 18·8 MJ/m3. Increasing the tyre:catalyst ratio increased the yield of hydrogen. The component rubber elastomers produced much higher yields of syngas and hydrogen gas concentration. The carbon deposited on the catalyst during reaction was found to be mostly composed of graphitic CNTs. Changing the process conditions in terms of tyre:catalyst ratio could increase the yield of the carbon deposited on the catalyst to up to 14 wt%

Hybrid plasma-catalytic steam reforming of toluene as a biomass tar model compound over Ni/Al₂O₃ catalysts

In this study, plasma-catalytic steam reforming of toluene as a biomass tar model compound was carried out in a coaxial dielectric barrier discharge (DBD) plasma reactor. The effect of Ni/Al2O3 catalysts with different nickel loadings (5–20 wt%) on the plasma-catalytic gas cleaning process was evaluated in terms of toluene conversion, gas yield, by-products formation and energy efficiency of the plasma-catalytic process. Compared to the plasma reaction without a catalyst, the combination of DBD with the Ni/Al2O3 catalysts significantly enhanced the toluene conversion, hydrogen yield and energy efficiency of the hybrid plasma process, while significantly reduced the production of organic by-products. Increasing Ni loading of the catalyst improved the performance of the plasma-catalytic processing of toluene, with the highest toluene conversion of 52% and energy efficiency of 2.6 g/kWh when placing the 20 wt% Ni/Al2O3 catalyst in the plasma. The possible reaction pathways in the hybrid plasma-catalytic process were proposed through the combined analysis of both gas and liquid products