3/2020
Differences between the composition of surface and inner layers of fly ash particles
By studying samples from Czech power plants burning brown coal using X-ray photoelectron spectrometry (XPS) have demonstrated differences in the composition of the ashes in their surface and subsurface layers. The main components of the samples were compounds of aluminum, silicon and oxygen - aluminosilicates. Other elements included sulphur, fluorine and in some cases demonstrably calcium, sodium, magnesium, fluorine and iron. The largest part of the carbon compounds present is the so-called "adventitious carbon", contaminating carbon, i.e. hydrocarbons adsorbed on the surface from the atmosphere. Others come from technology including a small amount of carbides. Distribution of sulphur and iron compounds detected using a short time ion etching is in most cases following: sulphur compounds are concentrated on the surface of ash particles while iron compounds are typically concentrated inside. Differences in composition of surface layers were found to be significant as in the surface composition as in theirs depth profiles. Gas evolution was detected in an ash-water reaction test in which the analysis of the gas has shown that it is mainly about hydrogen and carbon dioxide. Another test with water showed the formation of an incrustation and documented the evolution of gases by the formation of bubbles. The released gases can form explosive mixtures with air, which must be taken into account when removing deposits with a water jet.
Premium biofuels from straw – production of advanced biofuels using the Sylvan process
The increasing demand for transportation fuels, especially middle distillates, stimulates the research of new strategies to obtain or synthesize biofuels. The processing of lignocellulosic biomass (for example straw) is a process of great interest, because after its hydrolysis and subsequent dehydration of the resulting sugar monomers, very valuable substances including furfural are obtained. Then, furfural is selectively hydrogenated to 2-methylfuran, sylvan, that is the basic “building block” in the Sylvan process. This manuscript summarizes the knowledge on Sylvan process as a promising way of biofuels synthesis. By sylvan condensing with aldehydes, ketones or even 2-methylfuran itself, it is possible to prepare C13-C16 oxygenates in high yields up to 100 % under mild reaction conditions (30 - 60 °C) over various heterogeneous catalysts. Based on the overview, the heterogeneous catalysts are preferred and the immobilized sulfonic acids are the most active catalysts, however, expensive. The reaction products then may be hydrodeoxygenated commonly over supported noble metal catalysts to provide premium quality C13-C16 hydrocarbons to produce diesel or kerosene. These fractions have great low-temperature properties such as CFPP (-50 °C) or cetane number (70-72). According to the proposed sustainability prediction, this process could be sustainable in the Czech Republic, where 30 % of produced wheat straw could be used for the production of 130 kt advanced biofuels by Sylvan process required by EU directive RED II. Finally, the future approaches have been suggested.
Reproducibility of PetroOxy and its correlation with the Rancimat method
Bio-oil transformation into 2nd generation biofuels
The article summarized the possible transformations of pyrolysis bio-oil from lignocellulose into 2nd generation biofuels. Although a lot has been published about this topic, so far, none of the published catalytic pro-cesses has found commercial application due to the rapid deactivation of the catalyst. Most researches deal with bio-oil hydrotreatment at severe conditions or its pro-cessing by catalytic cracking to prepare 2nd generation biofuels directly. However, this approach is not commercially applicable due to high consumptions of hydrogen and fast catalyst deactivation. Another way, crude bio-oil co-processing with petroleum fractions in hydrotreatment or FCC units seems to be more promising. The last approach, bio-oil mild hydrotreatment followed by final co-processing with petroleum feedstock using common refining processes (FCC and hydrotreatment) seems to be the most promising way to produce 2nd generation biofuels from pyrolysis bio-oil. Co-processing of bio-oil with petroleum fraction in FCC increases conversion to gasoline and, thus, it could be a preferable process in the USA. Otherwise, co-hydrotreatment of hydrotreated bio-oil with LCO leads not only to the reduction of hydrogen consumption but also to the conversion preferably to diesel. This process seems to be more suitable for Europe. Further research on bio-oils upgrading is still necessary before the commercialization of the bio-oil conversion into biofuels suitable for cars. However, the first commercial bio-refinery that will convert bio-oil into biofuel for marine transport is planned to be built in the Netherlands.
Hydrotreating of middle distillates with addition of pyrolysis oil from depolymerisation of waste plastics
Recent challenges of indoor air quality
Indoor air pollution is a complex issue involving a wide diversity and variability of pollutants that threats human health. In this context, major efforts should be made to enhance indoor air quality. Thus, it is important to start by the control of indoor pollution sources. This review presents a general overview of single treatment techniques such as mechanical and electrical filtration, adsorption, ozonation, photolysis, photocatalytic oxidation, biological processes, and membrane separation. Since there is currently no technology that can be considered fully satisfactory for achieving ‘‘cleaner’’ indoor air, special attention is paid to combined purification technologies or innovative alternatives that are currently under research and have not yet been commercialized (plasma-catalytic hybrid systems, hybrid ozonation systems, biofilter-adsorption systems, etc.). These systems seem to be a good opportunity as they integrate synergetic advantages to achieve good indoor air quality. Review contains more than 150 references.