Paliva (Fuels) is a scientific journal issued quarterly by the Faculty of Environmental Technology, ICT Prague. Fuels publishes papers on a broad range of topics covering exploitation, processing, upgrading, and utilization of various types of fuels, and power engineering.
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Differences between the composition of surface and inner layers of fly ash particles

Petr Buryan, Petr Sajdl

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.

Keywords: fly ash, composition
3/2020 - pages 81 - 86DOI: 10.35933/paliva.2020.03.01

Premium biofuels from straw – production of advanced biofuels using the Sylvan process

Jaroslav Aubrecht, David Kubička

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.

Keywords: biofuels; biomass; 2-methylfuran; Sylvan process
3/2020 - pages 87 - 92DOI: 10.35933/paliva.2020.03.02

Reproducibility of PetroOxy and its correlation with the Rancimat method

Karolína Jaklová, Aleš Vráblík
The current trend of reducing greenhouse gas emissions and carbon footprint as well as legislation requirements means an increase in the effort to replace fossil fuels by using renewable sources. One of the possibilities is usage of methyl esters (FAME or UCOME) as a bio-component in diesel fuel. Now the maximum FAME content in diesel is 7 vol% (according to the standard EN590 – B7). Increasing the proportion of FAME means a deterioration in oxidation stability. FAME is produced by the transesterification of the triglycerides present in vegetable oils. A major disadvantage of biodiesel (FAME) is ability to be slowly oxidised by air oxygen. Oxidation products may impair fuel properties, quality and engine performance. This is the reason why the oxidation stability of diesel and biodiesel is an important quality parameter. It could be detected using several methods, for example: Rancimat, PetroOxy or thermal techniques.
The Rancimat method is intended for biodiesel and for diesel with a minimum 2 vol% content of FAME as mentioned in the standards EN 590 and EN 14214. The disadvantage is the time required for this method (more than 8 h for biodiesel and 20 h for diesel).
The PetroOxy is shorter and its results can be converted to Rancimat stability.
The set of 75 samples (40 samples of B7 and 35 samples of FAME) was measured using both mentioned methods. Three values of oxidation stability were determined for all of the analysed samples. In the first laboratory, oxidation stability of the samples was measured using both methods. In the second laboratory, oxidation stability was measured using only the PetroOxy. The PetroOxy results from both laboratories were compared with a high correlation value (R2 = 0,954). In the next step, outliers were removed from dataset. Experimental results of the Rancimat method were correlated with recalculated values of PetroOxy method from both laboratories. Correlation equation provided by the manufacturer of PetroOxy was used for recalculation of PetroOxy results to Rancimat results at first. Measured results were then compared with recalculated results. The largest difference in results was found in the B7 samples.
Because of these differences the correlation equation between PetroOxy and Rancimat was optimized. Two different equation were made (for each laboratory). The recalculated oxidation stability results were compared with the primary results from Rancimat. The newly correlated values showed a higher degree of agreement with the experimental data than when the results were recalculated using the correlation equation provided by manufacturer.
These optimized correlation equation have proven to be more suitable for industrial laboratories.
Keywords: oxidation stability; PetroOxy; Rancimat; FAME; diesel fuel
3/2020 - pages 93 - 97DOI: 10.35933/paliva.2020.03.03

Bio-oil transformation into 2nd generation biofuels

Tomáš Macek, Miloš Auersvald, Petr Straka

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.

Keywords: pyrolysis; bio-oil; catalytic cracking; hydrotreating; 2nd generation bio-fuels
3/2020 - pages 98 - 106DOI: 10.35933/paliva.2020.03.04

Hydrotreating of middle distillates with addition of pyrolysis oil from depolymerisation of waste plastics

Blanka Zbuzková, Karolína Jaklová, Aleš Vráblík, Radek Černý
The research work deals with the influence of the addition of alternative pyrolysis fractions as a component of feedstock processed in the hydrogenation of middle distillates. The alternative feedstocks are middle boiling fractions of oils derived from pyrolysis of sorted waste plastics, namely polystyrene (PyOil-PS) and mixture of polypropylene and polyethylene (PyOil-PP/PE). The down-flow testing reactor was used for simulation of hydrogenation process. The effects of the addition of alternative pyrolysis fractions on the quality of products as well as on the activity of the desulphurisation catalyst were studied.
The testing was divided into three steps. The reaction temperature was subsequently changed to achieve the level of sulphur content of 10 In the first step, the feedstock was changed to the standard feedstock used in the hydrogenation unit. When the required level of sulphur content has been achieved, the feedstock was changed in the second step. The feedstock was changed to a standard feedstock with addition of 5 wt% of the mentioned alternative feedstock. The addition of alterna-tive pyrolysis fractions were compensated by an increase in reaction temperature by 6 °C to achieve the level of sulphur content of 10 In the third step, the feed-stock was changed to the standard feedstock. The addi-tions of recycled alternative materials resulted in higher deactivation of the catalyst, which had to be compensated by an increase in reaction temperature of 3 °C for PyOil-PS oil and 6 °C for PyOil-PP/PE.
Pyrolysis oils used showed to be potential raw material for co-processing with conventional feedstock. The overall effect on activity of catalyst should be verified during long-term testing. Products meet requirements of standard ČSN 590.
Keywords: catalytic hydrotreatment; alternative feedstock, plastic pyrolysis; polystyrene; polypropylene; polyethylene
3/2020 - pages 107 - 113DOI: 10.35933/paliva.2020.03.05

Recent challenges of indoor air quality

František Skácel, Viktor Tekáč

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.

Keywords: indoor air quality; air purification systems; pollutants; PM10, PM2.5
3/2020 - pages 114 - 135DOI: 10.35933/paliva.2020.03.06

technical support editor-in-chief