Pressurized fluidized bed gasification is advantageous for efficient integration with downstream processes operating under pressurized conditions. This study presents a detailed analysis of product gas's composition and yields, using different natural minerals, including magnesite, dolomite, olivine, and silica sand at 8 bar in a pressurized biomass fluidized bed gasifier, investigating the mechanisms of selected natural minerals in catalytic tar-cracking and reforming. The used bed particles were further analyzed and examined using H2-TPR, TPO, and XPS analysis. In comparison with used olivine, the used dolomite exhibited a higher amount of carbon deposited on the surface; however, the carbon starts reacting with H2 at around 550 °C, which could not be observed from the used olivine. The used dolomite contains more C-O on the surface while the used olivine has a relatively higher level of C=O. The non-active chemical status of main elements (Fe, Mg, Ca) on the surface of used olivine was also determined by the XPS analysis. The mechanisms for the evolution of light and heavy hydrocarbons were also elucidated. A linear correlation between the concentrations of benzene and naphthalene was observed in tests using dolomite and magnesite. Dolomite is effective in increasing H2 concentration, which could be attributed to dolomite's catalytic tar cracking capacity. The optimal use of dolomite may be achieved via selecting a proper steam-to-biomass-ratio (SBR) and optimizing the internal circulation and hydrodynamics of bed particles in the pressurized fluidized bed gasifier to continuously converting deposited carbon and regenerating dolomite particles.

Combining CO2 electrochemical reduction (CO2R) and biomass gasification for producing methanol (CH3OH) is a promising option to increase the carbon efficiency, reduce total production cost (TPC), and realize the utilization of byproducts of CO2R system, but its viability has not been studied. In this work, systematic techno-economic assessments for the processes that combined CO2R to produce CO/syngas/CH3OH with biomass gasification were conducted and compared to stand-alone biomass gasification and CO2R processes, to identify the benefits and analyze the commercialization potential of different pathways under current and future conditions. The results demonstrated that the process that combined biomass gasification with CO2R to CO represents a viable pathway with a competitive TPC of 0.39 €/kg-CH3OH under the current condition. For all the combined cases, electricity usage for CO2R accounts for 36–76% of total operating cost, which plays a key role for TPC. Sensitivity analysis confirmed that the process that combined biomass gasification with CO2R to CO is sensitive to the price of electricity, while both CO2R performance and prices of stack and electricity are important for the processes that combined with CO2R to syngas/CH3OH.

Catalyst passivation through carbon poisoning is a common and costly problem as it reduces the lifetime and performance of the catalyst. Adding oxygen to the feed stream could reduce poisoning but may also affect the activity negatively. We have studied the dehydrogenation, decomposition, and desorption of naphthalene co-adsorbed with oxygen on Ni(111) by combining temperature-programmed desorption (TPD), sum frequency generation spectroscopy (SFG), photoelectron spectroscopy (PES), and density functional theory (DFT). Chemisorbed oxygen reduces the sticking of naphthalene and shifts H2 production and desorption to higher temperatures by blocking active Ni sites. Oxygen increases the production of CO and reduces carbon residues on the surface. Chemisorbed oxygen is readily removed when naphthalene is decomposed. Oxide passivates the surface and reduces the sticking coefficient. But it also increases the production of CO dramatically and reduces the carbon residues. Ni2O3 is more active than NiO.

Refuse-derived fuel (RDF) produced from the processing of municipal solid waste is a promising raw material for waste-to-energy processes such as gasification. Several catalysts were used to improve the performance of RDF in this process. The study aims to understand the thermal decomposition of pellets made from a mixture of RDF and biomass in the presence of waste-based catalysts by simulating a CO2 gasification process in a thermogravimetric analyzer (TGA) instrument. Marble and eggshells, which are low-cost bio-based sources of calcium carbonate, were investigated as catalysts. Dolomite was used as a reference for comparison. In general, all samples showed two significant decomposition phases and an attenuated decomposition phase (pyrolysis), between 250 and 700 ºC, corresponding to the degradation of hemicellulose, cellulose, lignin, and mixed plastics, before the onset of gasification. It was concluded that dolomite may degrade more during the pyrolysis compared to the marble and eggshells, as it was not calcined, hindering the gasification reaction, and subsequently resulting in a lower char conversion. The catalysts based on marble and eggshells favored the reactivity of the RDF: B pellets during gasification, resulting in faster decomposition of the char. In general, the waste-based catalysts performed well, suggesting they have potential for application in waste gasification.

In this study time-resolved char conversion and alkali release under steam gasification conditions were investigated using a fixed bed reactor. The behaviour of an industrial char and chars produced from straw and furniture waste was investigated. For woody chars, an increase in gasification reactivity is observed together with a notable alkali release as the gasification approaches completion (degree of conversion > 0.8). In contrast, straw char exhibited a decrease in conversion rate and alkali release throughout the gasification process, attributed to the formation of catalytically inactive potassium silicates inhibiting the catalytic role of alkali. Aerosol particles in the 0.01–22 µm size range are emitted during the char conversion. A fraction is formed by nucleation of alkali compounds and other condensable gases. A wide particle distribution that extends over the whole size range is also observed, and the particles are likely to consist of solid char fragments. The study concludes on the importance of alkali release, illustrating the difference in alkali release pattern for high and low ash char.

The conversion of biomass-derived oxygenates over zeolite catalysts constitutes a challenge for the efficient production of bio-based chemicals and fuels due to difficulty in controlling the selectivity and high coke formation of such reactions. This is partly attributed to the microstructure of zeolite catalyst which affects the conversion and selectivity of products derived from biomass-derived oxygenates. In this study, the conversion and deactivation characteristics of three different model oxygenates found in biomass bio-oil (namely, acetol, furfural and guaiacol) over ZSM-5 zeolites of varying acidity, pore and crystal size prepared with bottom-up and top-down approaches were evaluated using a fixed bed microreactor at atmospheric pressure and a space velocity of 5 h−1 at a temperature range of 450–650 °C. Analysis of the experimental results indicates that the optimum temperature for such conversions is in the vicinity of 600 °C allowing for complete conversion of the compounds and high resistance to coking. The mechanisms of those conversions are discussed based on the obtained results. In general, crystal size and mesoporosity induce easier access to active sites improving mass transfer but also alter the location type, and strength of acid sites allowing for higher yields of primary and intermediate products such as olefins.

 The formation of deposits in the fuel systems of heavy- duty engines, using drop-in fuels, has been reported in recent years. Drop-in fuels are of interest because they allow higher levels of alternative fuels to be blended with conventional fuels that are ompatible with today’s engines. The precipitation of insolubles in the drop-in fuel can lead to clogging of fuel filters and internal injector deposits, resulting in increased fuel consumption and engine drivability problems. The possible mechanisms for the formation of the deposits in the fuel system are not yet fully understood. Several explanations such as operating conditions, fuel quality and contamination have been reported. To investigate injector deposit formation, several screening laboratory test methods have been developed to avoid the use of more costly and complex engine testing. To further evaluate and understand the formation of internal injector deposits in heavy-duty engines, a thermal laboratory test method has been developed. The test method is called Thermal Deposits Test (TDT) and it is inspired by Jet Fuel Thermal Oxidation Test (JFTOT) method. This test unit can be used to study in applications where a fluid is in contact with a hot surface. The method uses common laboratory hardware and readily available off-the-shelf parts, making it inexpensive to build and very flexible to operate. Deposits are collected on a metal foil, which makes it easier to analyze. This paper describes the construction of the apparatus and its performance. Experimental tests with diesel fuel, doped with soap-type soft particles, which contain typical particles that can form deposits, are performed, and compared with JFTOT results. Analytical techniques, such as Scanning Electron Microscopy with Energy Dispersive X-Ray, Fouriertransform Infrared Spectroscopy, and Pyrolysis coupled with Gas Chromatography-Mass Spectroscopy and Ellipsometry were used. Conclusions about the performance of the doped fuel are drawn from the test. Future plans are to study the mechanisms behind the formation of internal diesel injector deposits. 

In the present study, an improved understanding of dynamic temperature and differential pressure phenomena during pressurized biomass gasification in a bubbling fluidized bed is used to develop a method for the early detection of bed defluidization. Experiments with silica sand as a bed material and three different biomass feedstocks, namely, birch chips, grot chips, and pine pellets, were conducted. For comparison, experiments using magnesite and dolomite as the bed materials were also conducted. The main variables potentially influencing bed fluidization, including K content and K/Si ratio in fuel feedstock, bed temperature, steam, and fluidization velocity, were considered in relation to their effect on bed defluidization time. Correlation of differential pressure and temperature at different positions in the bed with fluidized bed changes, such as char accumulation, sticky coating formation on particles, and char consumption, was evaluated and identified. The study demonstrates that under the operating conditions investigated, it is possible to determine the bed defluidization tendency fairly accurately using a combination of bed temperature deviation and the deviation of two series of dynamic differential pressure signals, measured at different bed positions.

There are several difficulties when experimentally determined reaction mechanisms are applied from model systems to real catalysis. Besides the infamous pressure and material gaps, it is sometimes necessary to consider impurities in the real reactant feedstock that can act as promoters or catalyst poisons and alter the reaction path. In this study, the effect of sulfur on the dehydrogenation of naphthalene on Ni(111) is investigated by using X-ray photoelectron spectroscopy and scanning tunneling microscopy. Sulfur induces a (5 root 3 x 2) surface reconstruction, as previously reported in the literature. The sulfur does not have a strong effect on the dehydrogenation temperature of naphthalene. However, the presence of sulfur leads to a preferred formation of carbidic over graphitic carbon and a strong inhibition of carbon diffusion into the nickel bulk, which is one of the steps of destructive whisker carbon formation described in the catalysis literature.

Alkali-associated problems are key issues for the efficient use of straw that is available as a major renewable energy resource worldwide. The effects of six bed materials commonly used in fluidized bed reactors on straw pyrolysis and char gasification were evaluated using online monitoring of alkali release and thermogravimetric analysis. Scanning electron microscopy with energy dispersive spectroscopy was used to determine the elemental composition of the char surface. In the straw pyrolysis stage, alkali release is reduced by the addition of dolomite and silica due to alkali adsorption on the bed materials, and enhanced by the addition of alumina because of its high sodium content. In the char gasification stage, silica, sea sand, olivine, and ilmenite reduce the char reactivity and alkali release, which is attributed to transfer of Si and Ti from the bed materials to the char and reaction with alkali to form stable and catalytically inactive compounds. Alumina also reduces the char conversion rate by transfer of Al to the char and formation of K-Al-Si and Ca-Al-Si compounds, while alkali release from the straw and alumina blend remains high due to the high Na content in alumina. Dolomite initially appears to increase the char gasification reactivity, but the results are affected by conversion of volatile matter that deposited on the dolomite in the straw pyrolysis stage. Dolomite also significantly increases the alkali release, which is attributed to Ca reactions with aluminosilicate compounds that allow potassium to remain in volatile form. Fresh bed materials are concluded to have significant effects on straw conversion depending on their chemical composition, and the results can contribute to the understanding required for efficient use of straw in commercial applications of biomass thermochemical conversion.