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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., QC 20240322

Hydrogen is a versatile energy vector for a plethora of applications; nevertheless, itsproduction from waste/residues is often overlooked. Gasification and subsequent conversion ofthe raw synthesis gas to hydrogen are an attractive alternative to produce renewable hydrogen. Inthis paper, recent developments in R&D on waste gasification (municipal solid waste, tires, plasticwaste) are summarised, and an overview about suitable gasification processes is given. A literaturesurvey indicated that a broad span of hydrogen relates to productivity depending on the feedstock,ranging from 15 to 300 g H2/kg of feedstock. Suitable gas treatment (upgrading and separation) isalso covered, presenting both direct and indirect (chemical looping) concepts. Hydrogen productionvia gasification offers a high productivity potential. However, regulations, like frame conditions orsubsidies, are necessary to bring the technology into the market., QC 20240215

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√3 × 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.

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., QC 20240206

The mineral content of biomass plays an important role in the gasification rate of biomass-derived char. The understanding and quantification of mineral-related phenomena are thus of importance when considering gasification reactor design. In the present work, the potassium-induced catalytic phenomena during gasification of biomass-derived char have been studied. Char samples with similar structure and different intrinsic potassium content were gasified in a steam atmosphere at a temperature range of 700-800 °C. It was found that for all the samples, irrespective of the temperature and the initial potassium content, there is a critical K/C ratio (5 × 10-3), whereafter the catalytic phenomena prevail. The instantaneous conversion rate of the char is positively correlated with the potassium content and the progressively increasing conversion. The application of the modified random pore model was able to capture the later stages of conversion by the introduction of two additional parameters (c and p). It was found that these constants are not just fitting parameters but that there is an underlying physical significance with c being directly related to the intrinsic potassium content while being temperature independent and with p being temperature dependent., QC 20231103

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 compatible 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, Fourier-transform 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, QC 20231101

Heavy-duty transportation is one of the sectors that contributes to greenhouse gas emissions. One way to reduce CO2 emissions is to use drop-in fuels. However, when drop-in fuels are used, i.e., higher blends of alternative fuels are added to conventional fuels, solubility problems and precipitation in the fuel can occur. As a result, insolubles in the fuel can clog the fuel filters and interfere with the proper functioning of the injectors. This adversely affects engine performance and increases fuel consumption. These problems are expected to increase with the development of more advanced fuel systems to meet upcoming environmental regulations. This work investigates the composition of the deposits formed inside the injectors of the heavy-duty diesel engine and discusses their formation mechanism. Injectors with internal deposits were collected from field trucks throughout Europe. Similar content, location and structure were found for all the deposits in the studied injectors. The physical structure was analyzed using a Scanning Electron Microscope with an Energy Dispersive X-Ray (SEM-EDX). Pyrolysis coupled with Gas Chromatography Mass Spectrometry (Py GC-MS) and Fourier-transform Infrared Spectroscopy (FTIR) were also used to determine the composition of the injector deposits. The deposits consist of a mixture of organic and inorganic compounds, indicating that they originate from fuel and engine oil. To further analyze the origin of the formed deposits, samples were collected from various parts of the fuel system. The analysis suggests that the deposits were formed exclusively in the injectors, and by comparing and describing the composition and structure of the deposits from different parts of the injector, a mechanism is proposed., QC 20240418

Elevated exposure to airborne pollutants such as NOx and SOx is known to be damaging to human health. A current approach to deal with such harmful gases is to trap them in ammonium salt particles. The present study presents the sensitivity analysis of the aerosol model for ammonium salt particle formation from NOx and SOx for low-temperature gas cleaning applications developed by Olenius et al. (2021). Starting from the acid gases derived from NOx and SOx (i.e. HNO3 and H2SO4), the model simulates the particle growth phenomena as the acids react with ammonia (NH3). This work presents, for the first time, a global sensitivity analysis of the aerosol model uncertainty. The first-and total-order effects of five different input variables on model outputs such as particle size distribution, pollutant removal effectiveness, ammonia slip, and total run time are reported. Furthermore, the range of input parameters for which the model is tested is made to emulate the conditions experienced by two-stroke marine diesel engine ships. Sources of uncertainty are reviewed in detail to provide a complete view of the knowledge gaps in the particle conversion process. For the conditions studied, we report that variations in particle sizes are influenced by HNO3, H2SO4 and temperature. Similarly, the degree of ammonia slip was observed to be driven by temperature and the ammonia ratio. Additionally, the removal efficiency of HNO3 was reported to be very high (above 99%) for the vast majority of conditions tested, and was not significantly influenced by the concentration of H2SO4. Finally, the model run time variability was observed to depend mainly on variations in temperature, relative humidity and the ammonia ratio., QC 20221111

Electrochemical reduction of CO2 removed from biosyngas into value-added methanol (CH3OH) provides an attractive way to mitigate climate change, realize CO2 utilization, and improve the overall process efficiency of biomass gasification. However, the economic and environmental feasibilities of this technology are still unclear. In this work, economic and environmental assessments for the stand-alone CO2 electrochemical reduction (CO2R) toward CH3OH with ionic liquid as the electrolyte and the integrated process that combined CO2R with biomass gasification were conducted systematically to identify key economic drivers and provide technological indexes to be competitive. The results demonstrated that costs of investment associated with CO2R and electricity are the main contributors to the total production cost (TPC). Integration of CO2R with CO2 capture/purification and biomass gasification could decrease TPC by 28%-66% under the current and future conditions, highlighting the importance of process integration. Energy and environmental assessment revealed that the energy for CO2R dominated the main energy usage and CO2 emissions, and additionally, the energy structure has a great influence on environmental feasibility. All scenarios could provide climate benefits over the conventional coal-to-CH3OH process if renewable sources are used for electricity generation., Validerad;2023;Nivå 2;2023-02-22 (hanlid)

QC 20220503

The formation of soot in a swirling flow is investigated experimentally and numerically in the context of biogas combustion using a CO2-diluted methane/oxygen flame. Visualization of the swirling flow field and characterization of the burner geometry is obtained through PIV measurements. The soot particle size distributions under different fuel concentrations and swirling conditions are measured, revealing an overall reduction of soot concentration and smaller particle sizes with increasing swirling intensities and leaner flames. An axisymmetric two-dimensional CFD model, including a detailed combustion reaction mechanism and soot formation submodel, was implemented using a commercial computational fluid dynamics (CFD) code (Ansys Fluent). The results are compared with the experiments, with similar trends observed for the soot size distribution under fuel-lean conditions. However, the model is not accurate enough to capture soot formation in fuel-rich combustion cases. In general, soot particle sizes from the model are much smaller than those observed in the experiments, with possible reasons being the inappropriate modeling in Fluent of governing mechanisms for soot agglomeration, growth, and oxidation for CH4-CO2 mixtures., QC 20220407