Biomass is an alternative energy resource to fossil fuels because of its potential to reduce greenhouse gas emissions. However, ash-related problems are serious obstacles for this development, especially for the use in combustion plants. Thus, design and operation of biomass boilers require detailed understanding of ash transformation reactions during thermochemical conversion. To evaluate ash transformation in silica-rich biomass fuels, rice husk and rice straw were selected because of their abundance, limited utilization conflicts with the food sector, as well as their potential in both energy and material applications. This paper reveals ash transformation mechanisms relevant for the ash melting behaviour of silica-rich biomass fuels considering chemical and phase composition of the ashes. In this regard, several advanced spectroscopic methods and diffractometry were employed to characterize the materials. The ash transformation reactions and the viscosity were simulated using thermodynamic equilibrium calculations and a slag viscosity modeling toolbox. The results illustrate the impact of impurities on the atomic structure of the silica resulting in an altered ash melting behaviour and viscosity of the silica-rich ashes. Chemical water washing, acid leaching, and blending of rice straw with rice husk strongly influenced the chemical composition of the ashes and improved ash melting behaviour. The analysis also revealed the correlation between the crystalline fraction and the porosity in silica-rich biomass ashes, as well as a crystallinity threshold. These findings are highly relevant for future investigations in boiler designs and production of biogenic silica for material applications.

Autoxidation of jet fuels is a complex phenomenon which occurs below 250 C. Caused by naturally dissolved oxygen, the reactions lead to the formation of different oxidation products by a mechanism of degradation which is not yet completely understood. n-dodecane, a linear alkane molecule, has been chosen as a model for jet fuel. The influence of temperature and progress of reactions have been studied using the PetroOXY device, focusing on the beginning of the autoxidation. For the first time, the oxidation products formed in the gas and liquid phases were precisely identified by spectroscopic and chromatographic characterization techniques but also quantified by chemical methods. It was possible to establish the mechanisms involved in the different steps using data from the literature, to propose a new one based on combustion mechanisms and to calculate the kinetic constants of the reactions.

A microanalytical procedure using smartphone-based digital image colorimetry is proposed for determining calcium and magnesium concentrations in biodiesel without analyte extraction. The analytical method relies on the discoloration of an alkaline Eriochrome Black T (EBT) solution because of complex formation with the analytes. Ethanol was used as a mediator solvent for dissolving both biodiesel and EBT. The analytical response was based on the measurement of reflected radiation from digital images captured using a smartphone camera. Photometric measurements were based on the RGB color system, taken R channel values as the analytical signal because of complementarity with the color of the EBT solution. The coefficient of variation (n = 10) and limit of detection were 1.0% and 3 mu mol L-1, respectively. A linear response was observed in the 10-75 mu mol L-1 range, described by the equation R = 0.612C + 93.1 (r = 0.999). The reagent amounts consumed per determination were as little as 25 mu g of EBT and 120 mu g of NaOH, with generation of only 935 mu L of waste. The procedure was selective for calcium and magnesium, without interference of metal ions (Na+, K+, Zn2+, Cu2+, Ni2+, Fe2+, and Fe3+) as well as other sample components (glycerol, methanol, and water) in concentrations higher than those expected in biodiesel. Matrix effects for biodiesel obtained from different raw materials were negligible (recoveries from 90 to 104%), making feasible external standard calibration with aqueous/ethanolic reference solutions. The results agreed with those obtained by ICP OES after sample preparation by emulsion breaking, demonstrating the reliability of the proposed approach.

Chemical looping with iron-based oxygen carriers enables the production of hydrogen from various fossil and biogenic primary energy sources. In applications with real producer gases, such as biogas or gasified biomass, hydrogen sulfide represents one of the most challenging contaminants. The impact of H2S on the reactivity of a Fe2O3/Al2O3 oxygen carrier material in chemical looping hydrogen production was investigated in the present work. First, potential sulfur deactivation mechanisms are discussed in detail on the basis of thermodynamic data. Afterwards, an experimental study in a fixed-bed reactor system gave experimental evidence on the fate of sulfur in chemical looping hydrogen systems. The chemisorption of hydrogen sulfide (H2S) was identified as the main cause for the accumulative adsorption of H2S in the reduction phase and was confirmed by ex-situ ICP-EOS analysis. In the subsequent steam oxidation step, significant quantities of H2S were released resulting in an undesirable contamination of the hydrogen product gas. The reason was found as weakened sulfur bonds through increasing reactor temperatures caused by the exothermic oxidation reactions. In additional air oxidation steps no further contaminants as sulfur dioxide were identified. A profound interpretation was achieved through the fulfillment of the overall sulfur mass balance within a mean deviation of 3.7%. Quantitative investigations showed that the hydrogen consumption decreased by 12% throughout the reduction phase in the event of 100 ppm H2S in the feed gas.

Diesel engines are widely used because of their low fuel consumption, high fuel efficiency, high reliability, and safety. However, the soot particles contained in diesel engine exhaust have become one of the main sources of urban haze, and their elimination has great significance for environmental protection and economics. In the present study, a series of CenMnOx catalysts with different Ce contents and calcination temperatures were successfully synthetized via a simple hydrothermal process, and the physicochemical characteristics of the as prepared catalysts were investigated. That CenMnOx composite oxides were amorphous, contradicting previous reports that manganese and cerium usually form MnxCe1-xO delta with crystalline structures. Due to Ce doping, the amorphous Ce1MnOx catalysts have higher specific surface area, greater porosity, and better ability to activate oxygen species than pure MnOx catalysts. The amorphous catalysts also exhibit good stability, sulfur and water resistance for catalytic combustion of soot particles. Among the prepared catalysts, Ce1MnOx calcinated at 450 degrees C has the best catalytic activity, the values of T-10, T-50 and T-90 were 258 degrees C, 327 degrees C and 370 degrees C, respectively. Based on their simple preparation, low cost, and good catalytic performance, the amorphous CenMnOx catalysts show promise for application in soot combustion.

Due to their excellent fuel properties, butanol and hexanol are considered as two promising renewable fuels for diesel engine applications. The objective of this work is to investigate and compare the spray and combustion characteristics of butanol-diesel and hexanol-diesel blends under high-altitude conditions. A constant volume combustion chamber was used to provide the desired environment. Experiments were conducted under various ambient temperatures ranging from 800 K to 1200 K and various ambient densities ranging from 11 kg/m3 to 15 kg/m3. Fuel blends with 20% blend ratio (B20 and H20) and neat diesel were used as test fuels. The spray and combustion characteristics of the test fuels were analyzed using measured liquid penetration length, ignition delay, combustion duration, flame lift-off length (FLoL), and spatially integrated natural luminosity (SINL). Results revealed that B20 and H20 had shorter liquid penetration length than diesel under low ambient temperature and density conditions due to their higher volatility. The blended fuels showed significantly longer ignition delay than diesel under low ambient temperature conditions, but it could be overcome by increasing the ambient temperature. Adding butanol and hexanol into diesel both extended FLoL especially under low ambient temperature and density conditions, but the effects of hexanol was less dramatic compared to butanol due to its lower latent heat of vaporization and higher chemical reactivity. Both B20 and H20 showed lower SINL than diesel under any conditions, indicating their ability of reducing soot emissions. However, no apparent differences could be found between these two fuels until the ambient temperature dropped to 800 K.