Aromatic Diesel Research Articles

Application of a property prediction model based on the structure oriented lumping method in the fluid catalytic cracking process

Based on the Structure Oriented Lumping (SOL) method and the Artificial Neural Network (ANN) algorithm, a SOL-ANN property prediction model was constructed to predict the properties of molecules and products in the fluid catalytic cracking (FCC) process. The properties of each structural vector in the molecular composition matrices of gasoline and diesel were calculated. The influences of reaction temperature on the properties of gasoline and diesel were investigated from the perspective of molecular composition. When the reaction temperature increased from 490 °C to 510 °C, the content of aromatics and olefins in gasoline and the content of aromatics in diesel increased, resulting in the research octane number (RON) of gasoline increasing by 2.96 units and the cetane number (CN) of diesel decreasing by 1.37 units. Using the molecular composition information of products to calculate the properties of molecules and products could guide the product quality evaluation and process optimization.

Compound specific stable isotope analysis of aromatics in diesel fuel to identify potential cocktailing

Estimates suggest billions of dollars are lost annually in the US due to fuel tax fraud. One method of fuel fraud is called “cocktailing” and involves blending products that are non-taxed, lower value, taxed at a lower rate, or unwanted/less-refined petroleum to diesel fuels. The goal of this study was to investigate compound specific isotope analysis (CSIA) using isotope ratio mass spectrometry (IRMS) for small aromatics contained in diesel fuel to determine whether this approach could be used to identify cocktailing and potentially fingerprint possible sources. However, the high chemical complexity of diesel fuels complicates CSIA owing to the need to fully separate individual compounds for effective isotope analysis. Therefore, different methods were investigated to selectively isolate aromatics for CSIA and evaluate these methods for isotopic fractionation. Analyses indicate that there is enough variability in isotopic ratios (δ2H and δ13C) between toluene samples obtained from different sources to use CSIA to differentiate/identify the origin of potential fuel adulterants. Three isolation methods were identified that provided sufficiently pure aromatic fractions for CSIA: selective solvent extraction, ionic liquid coated solid phase microextraction (SPME), and a combination of the two. However, due to the labor-intensive nature of selective solvent extraction, ionic liquid coated SPME represents the best method to quickly isolate aromatics from diesel fuel, without sacrificing selectivity or sensitivity. All methods tested can result in isotopic fractionation, but this can be compensated for by applying a correction factor. Furthermore, the chemical composition of a sample appeared to be important in the degree to which fractionation occurred during isolation. While the tested approaches for aromatic extraction from diesel showed promise, additional studies are required to refine and validate the methods prior to routine use in fuel cocktailing investigations.

Hydrogen solubility prediction for diesel molecules based on a modified Henry equation

Diesel hydrotreatment removes heteroatoms and polycyclic aromatics in diesel in the presence of high-pressure hydrogen gas. The hydrogen solubility is the basis for hydrogen consumption prediction and process design/optimization. In the presented study, we established a method to predict the hydrogen solubility of diesel molecules and mixture. A modified Henry equation was proposed to illustrate the hydrogen solubility variation among the temperature and pressure. The parameters of the modified Henry equation for typical molecules were regressed from literature data. Then we established an empirical correlation between the parameter and the structure and property of molecules. The method was then combined with a molecular-level compositional model to accurately predict the hydrogen solubility in diesel, illustrating the validity of the method.

Conversion of heavy gasoil into ultra-low sulfur and aromatic diesel over NiWRu/TiO2–γAl2O3catalysts: Role of titanium and ruthenium on improving catalytic activity

This contribution deals with about selective conversion of heavy gas oils into middle distillates fuels that meet ultra-low sulfur and aromatic compound quality standards by using a novel NiWRu/TiO2–γAl2O3catalyst under typical hydrotreatment conditions. A diesel fuel fraction having sulfur, nitrogen and aromatics compound content of about 50 ppm, 10 ppm and 15 v%, respectively, was obtained when the reactor was operated atT = 370 °C,P = 12.4 MPa, LHSV = 0.5 h−1and H2/hydrocarbon ratio = 800 Nm3/m3. Titanium and ruthenium additives used in the preparation of the NiWRu/TiO2–γAl2O3catalyst, remarkably improved the catalytic activities for the hydrogenolysis, hydrogenation and hydrocracking reactions compared to the reference NiW/γAl2O3catalyst. The coprecipitation of titanium and aluminum hydroxides produced a catalyst support having greater surface area, pore volume and surface acidity. An improvement in mechanical properties of the support extrudates was also observed. Characterization analysis by XPS, AUGER and XRD techniques of the TiO2–γAl2O3support suggested the formation of an aluminum-titanate mixed phase (AlxTiyOz) having a non-well-defined stoichiometry. The NiW/TiO2–γAl2O3and NiWRu/TiO2–γAl2O3exhibited a greater surface dispersion of the supported nickel and tungsten species compared to the NiW/γAl2O3catalyst. The promoter effect of ruthenium on the NiW bimetallic system caused a strong increase in both hydrogenolysis and hydrogenation reactions. Hydrodenitrogenation and hydrocracking reactions were also favored by the increase in the hydrogenation capacity and in the surface acidity of the catalyst. The highest conversion levels for all investigated reactions were obtained when the NiWRu/TiO2–γAl2O3catalyst was prepared by co-impregnation of Ni and Ru in a second step. This catalyst showed sulfur tolerance properties when the reaction was conducted in the presence of different H2S partial pressures. The catalytic behavior of the NiWRu/TiO2–γAl2O3catalyst was explained by the existence of a promoting effect between separated Ni and Ru sulfides species and the NiWS phase (dual mechanism).

Experimental and modeling investigations of the interfacial tension of three different diesel + nitrogen mixtures at high pressures and temperatures

Interfacial tension (IFT) data are reported at temperatures up to 530 K and pressures up to 100 MPa for mixtures of N2 with a highly paraffinic diesel, an ultra-low sulfur diesel, and a highly aromatic diesel. The impact of composition on the IFT is determined by comparing data for each system at the same temperature and pressure calculated from a Tait-like relationship fit to the experimental data. The greatest differences in diesel + N2 IFT values are found near the normal boiling point (Tboil) of each diesel where lower molecular weight diesel components begin to dissolve in the N2-rich vapor phase. IFT data are modeled with density gradient theory (DGT) coupled with the perturbed-chain, statistical associating fluid theory equation of state (EoS). Diesel EoS parameters are calculated using three variations of a pseudo-component technique created from one group contribution (GC) method developed from high-pressure density data and from two other GC methods (S-GC and T-GC) developed from differing sets of pure component vapor pressure and saturated liquid density data. The IFT predictions significantly improve when the DGT influence parameter, cii, is allowed to vary with temperature. The DGT predictions with the B-GC method are in closest agreement with data at temperatures below Tboil, which is attributed to the more accurate representation of liquid phase densities. However, at temperatures above Tboil, where significant amounts of low molecular weight diesel components dissolve in the N2-rich vapor phase, DGT predictions with the S-GC and T-GC methods provide the closest agreement with IFT data.

Impact of alkylbenzenes in formulated surrogate fuel on characteristics of compression ignition engine

Aromatic contents in the fuel significantly affect the exhaust pollutant emissions and performance of compression ignition engines. Alkylbenzenes are dominating aromatics in diesel fuel and have attractive properties as the component of diesel fuel. Therefore, different alkylbenzenes were experimentally investigated using single-cylinder direct-injection compression ignition engine at two different loads and constant speed. Different Alkylbenzenes were blended with low aromatic diesel fuel in three percentages i.e. 5, 10 and 15% by mass. The results showed a slight improvement in brake specific fuel consumption and brake thermal efficiency with high calorific value alkylbenzenes. Moreover, carbon monoxide, nitrogen oxides, particulate matter and smoke emissions were significantly influenced with the aromatic content and their types. The effect on performance and emissions differed from one alkylbenzene to another due to the variation in physicochemical properties of aromatics such as density, hydrogen-to-carbon ratio, etc. Ethylbenzene shows better results in terms of performance and lower pollutant emissions.

Research and development of hydrocracking catalysts and technologies in China

Hydrocracking of petroleum feedstock represents a compelling route for the production of industrial clean fuels, which has triggered the continuous research and development of core technology related areas such as catalysts, reaction engineering and engineering design. This review particularly focuses on the research and development of catalysts and catalytic processes for hydrocracking of petroleum feedstock in China. Hydroprocessing technologies of China keep pace with the up-todate progress of the world, and some of the technologies have achieved leading role in the world. It is noted that China Petroleum and Chemical Corporation has a full range of hydroprocessing technologies and provides corresponding “tailor-made” catalysts. Through the efforts of several generations, 20 categories of the catalysts including more than 60 brands have been developed, among which more than 40 brands have been successfully applied for more than 130 times. Importantly, the pivotal technical improvements including the deep drawing vacuum gas-oil (VGO) and de-asphalting oil hydrocracking technology to improve material adaptability, the high value-added hydrogenation technology to convert high aromatic diesel conversion to naphtha, the hydrocracking technology using VGO-catalytic diesel blends, the Fushun Research Institute of Petroleum and Petrochemicals’ diesel to gasoline and diesel hydrocracking technologies, and the Sheer hydrocracking technology to reduce energy are reviewed.

Fuel Industry for Road Transportation in Côte D'ivoire

Cote d'Ivoire is a small mature crude oil producer in West Africa. In 2015, Cote d'Ivoire produced around 27,000 bblsbbl/day (IEA, 2015). Crude oil production started in the early 1980s and peaked in 2006 at 63,000 bblsbbl/day. Today, there are a number of factors which that raise questions regarding the sustainability of the oil industry and energy security of the country: depleting oil reservoirs in expensive offshore locations coupled with low crude oil prices in the spot markets, put pressure on the upstream sector, high dependency on crude oil imports, largely concentrated in geopolitically unstable Nigeria, poses questions regarding energy security, while financial distress in refining activities, ageing infrastructure, domestic demand absorbing refinery production capacity of gasoline and diesel, and high levels of sulfur and aromatics in diesel and gasoline, presenting both environmental and health-related concerns, present serious challenges in the downstream sector that need to be addressed. Biofuels may represent an attractive opportunity to diversify the country's transportation fuels portfolio available at the pump, and improve fuel quality, while rendering the country less dependent on crude oil imports, more energy secured, and more resilient to oil-price shocks.

Hydrocarbons fuel upgradation in the presence of modified bi-functional catalyst

Air pollutants such as NOX and SOX emitted from diesel combustion are one of the major concerns of the environment as well as human health. Aromatics in diesel fuel are one of the major sources of poor cetane number, which is tackled by selective ring opening of diesel to increase the cetane number. The present work's objective was at the ring opening of decalin over mono-functional and bi-functional catalysts. The catalyst, mordenite, is modified by treating with acid to increase its surface area for the better performance by aluminum leaching from its framework. The mordenite is used as support, and different metals like nickel and cobalt are impregnated. These catalysts were characterized, and the results indicate that the dealumination does not affect the structure and maintains its property as observed by X-ray diffraction (XRD) analysis. Brunauer–Emmett–Teller (BET) analysis shows that the surface area of catalyst increased from 342 to 366.3 m2/g due to extraction of aluminum. The morphology of catalysts was also maintained, and Si/Al ratio was increased due to dealumination of catalysts. The ring opening of decalin was examined by gas chromatograph mass spectroscopy (GC-MS) analysis, which indicates that ring opening of decalin with NiCo/dealuminated catalyst has higher conversion of 14.7% at 350 °C than other catalysts. Thus, modified catalyst can be a better source for providing high cetane hydrocarboneous fuels and membrane gas separation applications.

Elimination of by-products of autothermal diesel reforming

This paper outlines the design optimization and operation of the Forschungszentrum Jülich’s ATR 13 autothermal reformer with conventional diesel fuels. The main objective was to eliminate undesirable by-products that can amass in the reformate. The reforming of conventional, highly aromatic diesel fuels with a high final boiling point presents a particular challenge – these fuels are more difficult to evaporate and are prone to coking; tendencies that can damage both the reformers themselves and downstream components. Here, we present several constructive and operational measures to generate a high-quality reformate from the Swedish Test Diesel SD 10 and, moreover, to prevent the formation of short-chain hydrocarbons and aromatic compounds in the reformate. This will enable the stable, long-term operation of fuel cell-based APUs utilizing conventional diesel fuels on board trucks.

“Nanowire catalysts for ultra-deep hydro-desulfurization and aromatic hydrogenation”

Here, we report high performance catalysts designed using nanowire supports. Specifically, nickel clusters supported on Zinc Oxide (ZnO) nanowires and γ-alumina found to be highly active for ultra-deep desulfurization and aromatic hydrogenation of diesel. They were also found to be highly active for ultra-deep desulfurization of gasoline and kerosene. The catalysts reduced sulfur from diesel, gasoline, and kerosene fuels containing sulfur as high as approximately 200ppm to less than 1ppm with sustained activity over testing periods of 100–150h. The feed contained some of the most difficult to remove sulfur compounds such as 4-methyldibenzothiophene (MDBT), 4,6-dimethyldibenzothiophene (DMDBT). In addition to activity towards ultra-deep desulfurization, these catalysts have shown to be active towards saturate/hydrogenate aromatics in diesel at moderate reaction conditions (30bar, 290°C, and LHSV 2.2h−1). The active catalytic site was determined to be a super Ni rich NixZny phase which seemed to remain essentially sulfur free during the reaction. The regenerated catalyst showed reasonable activity toward desulfurization of gasoline.

Gaussian fit to the fluorescence spectra for determination of adulteration to diesel by addition of residual oil

This paper describes a methodology for determining non-transesterified residual cooking oil content in aromatic diesel. The procedure consists in fitting multiple Gaussian to the fluorescence spectra of standards and following construction of a graph using as x-axis the values of the concentrations of the standards in the range of 0 to 45 % and as y-axis the values of the area of the Gaussian centered around 513–540 nm. A straight line was obtained rising with R 2 of 0.9837 to the curve of areas of Gaussian × concentration of residual oil in diesel. The results indicate a possibility for development of a sensor device for determining non-transesterified residual cooking oil content in diesel.

Effects of fuels, engine load and exhaust after-treatment on diesel engine SVOC emissions and development of SVOC profiles for receptor modeling

Diesel exhaust emissions contain numerous semivolatile organic compounds (SVOCs) for which emission information is limited, especially for idling conditions, new fuels and the new after-treatment systems. This study investigates exhaust emissions of particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs (NPAHs), and sterane and hopane petroleum biomarkers from a heavy-duty (6.4 L) diesel engine at various loads (idle, 600 and 900 kPa BMEP), with three types of fuel (ultra-low sulfur diesel or ULSD, Swedish low aromatic diesel, and neat soybean biodiesel), and with and without a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF). Swedish diesel and biodiesel reduced emissions of PM2.5, Σ15PAHs, Σ11NPAHs, Σ5Hopanes and Σ6Steranes, and biodiesel resulted in the larger reductions. However, idling emissions increased for benzo[k]fluoranthene (Swedish diesel), 5-nitroacenaphthene (biodiesel) and PM2.5 (biodiesel), a significant result given the attention to exposures from idling vehicles and the toxicity of high-molecular-weight PAHs and NPAHs. The DOC + DPF combination reduced PM2.5 and SVOC emissions during DPF loading (>99% reduction) and DPF regeneration (83–99%). The toxicity of diesel exhaust, in terms of the estimated carcinogenic risk, was greatly reduced using Swedish diesel, biodiesel fuels and the DOC + DPF. PAH profiles showed high abundances of three and four ring compounds as well as naphthalene; NPAH profiles were dominated by nitronaphthalenes, 1-nitropyrene and 9-nitroanthracene. Both the emission rate and the composition of diesel exhaust depended strongly on fuel type, engine load and after-treatment system. The emissions data and chemical profiles presented are relevant to the development of emission inventories and exposure and risk assessments.

Experimental and modeling study of burning velocities for alkyl aromatic components relevant to diesel fuels

Aromatic species represent a significant fraction (about one third by weight) of both diesel and gasoline fuels. Much of the aromatics in diesel and gasoline are alkyl-benzene species. Although toluene, the lightest of the alkyl-benzenes, has been the subject of extensive literature investigations, very little experimental data are available for heavier alkyl-benzenes (9–20 carbon atoms) relevant to diesel fuel.In this work, the burning velocity of ethyl-, n-propyl- and n-butyl-benzenes were measured in a premixed flat-flame burner using the heat flux method. The burning velocities were measured as a function of the equivalence ratio at atmospheric pressure and for two unburned gas temperatures (358 and 398K). These new experiments are compared with burning velocities for toluene previously measured by the authors. The comparisons showed that ethyl-benzene has the highest flame speed, followed by n-propyl- and n-butyl-benzenes which have similar burning velocities. Toluene has the lowest flame speed. Excellent agreement was observed between the new measurements and simulations using a mechanism for alkyl-benzenes recently published by Lawrence Livermore National Laboratory (LLNL) and National University of Ireland.Based on the strong correlation between experiments and calculations, different aspects contributing to the burning speed of the fuels (thermal effects, kinetics, …) were analyzed using the model. A sensitivity analysis was used to determine the reaction rate constants that are most important in determining the flame speed. Reaction path analysis and species profiles in the flame were used to identify the key reaction paths that lead to increase or decrease in the burning velocities. Contrary to what is generally observed for alkanes whose flame speed is controlled by small radical fragments, the flame speed of aromatics is influenced by fuel specific intermediates such as phenyl, benzyl, or even heavier species. The new experimental data and modeling insight generated by this work will support the development of models for heavier alkyl-aromatics of great relevance to diesel fuel.

Catalytic Oxidative Desulfurization of Diesel Fuels Using Air in a Two-Step Approach

This study presents a novel approach to fuel desulfurization in two steps where air is used as oxidant for the in situ generation of hydroperoxides from aromatics in diesel fuel and then the sulfur compounds are oxidized by the hydroperoxides to sulfones. Bulk and supported CuO based catalysts were examined for oxidation of surrogate and real diesel fuels for generation of hydroperoxides in situ using air. Among bulk CuO, CuO/Al2O3, CuO/SiO2, CuO/TiO2, and CuO-ZnO/Al2O3 tested, CuO/Al2O3 gave the highest conversion, but the highest yield and selectivity for hydroperoxide was obtained on bulk CuO catalyst for liquid phase air oxidation of isopropylbenzene. H2-Temperature programmed reduction (H2-TPR) revealed the presence of dispersed CuO phase on supported catalysts with bulk CuO as the dominant phase on the unsupported catalyst. Three real diesel fuels were tested for liquid phase air oxidation at 120 °C in the presence of bulk CuO catalyst which revealed different levels of hydroperoxides generation. Th...

Effect of B20 and Low Aromatic Diesel on Transit Bus NOx Emissions Over Driving Cycles with a Range of Kinetic Intensity

This research project compares the emissions of oxides of nitrogen (NOx) from transit buses on as many as five different fuels and three standard transit duty cycles. The objective of the project is to establish if there is a real-world biodiesel NOx increase for transit bus duty cycles and engine calibrations. Prior studies have shown that biodiesel, sometimes called B20, can cause a small but significant increase in NOx emissions for some engines and duty cycles. Six buses that span engine build years from 1998 to 2011 were tested on the National Renewable Energy Laboratory's (NREL) Renewable Fuels and Lubricants (ReFUEL) research laboratory's heavy-duty chassis dynamometer with certification diesel, certification B20 blend, low aromatic California Air Resources Board (CARB) diesel, low aromatic B20 blend, and B100 fuels over the Manhattan, Orange County and the Urban Dynamometer Driving Schedule (UDDS) test cycles. The buses that were selected did represent a majority of the current national transit fleet. The selected buses also included hybrid and selective catalyst reduction (SCR) systems that are increasing in numbers in current transit vehicle fleets. The kinetic intensity of the tested duty cycle being the secondary driving factor, the engine emissions certification level had the dominant effect on NOx. With the exception of the 2008 model year bus, the biodiesel effect on NOx emissions was not statistically significant for most buses and duty cycles for blends with certification diesel. CARB fuel had many more instances of a statistically significant effect of biodiesel by substantially increasing NOx. SCR systems proved effective at reducing NOx emissions to near the detection limit on all duty cycles and fuels, including B100. A hybrid system proved to significantly increase NOx emissions over a same model year bus with a conventional drivetrain and the same engine. Because all but one test bus were equipped with diesel particulate filter after-treatment, particulate matter (PM) emissions were negligible and trends could not be drawn. On the oldest sample bus without after-treatment, PM emissions were reduced with B20 blends. The project shows how fuel economy was not significantly changed by the engine certification level, except that the 2008 conventional bus had the best performance on all cycles while all other buses had very similar results on each cycle. All buses had lower fuel economy with increased kinetic intensity of the cycle.

Biodiesel Blend Level Detection Using Ultraviolet Absorption Spectra

Biodiesel is often blended with regular U.S. No. 2 diesel. The blending level influences engine performance, emissions, and fuel cold-flow properties. In this article, ultraviolet (UV) absorption spectroscopy is presented as a reliable and affordable technology for blend level detection based on the absorbance patterns of the aromatic compounds in the proposed spectrum. Blends of biodiesel from six different feedstocks and U.S. No. 2 diesels from five different sources were used to test the robustness of the method. Since the absorbance of undiluted samples was too high to measure reliably, the samples were diluted with n-heptane. It was found that the feedstock and alcohol used (methyl or ethyl) did not make a significant difference in the absorbance of diluted biodiesel in the 245 to 305 nm range, while absorbance from 254 to 281 nm was correlated with blend level with R2 > 0.99. It was also observed that if the absorbance of the diesel source was known, then a single wavelength could be used to detect the biodiesel blend level. However, a single wavelength was inadequate when the diesel source was unknown because of variation in the level of aromatics in diesel fuel. Absorbances at 265, 273, and 280 nm were used to calculate the absorbance index, which was found to be independent of the diesel fuel used. Using three wavelengths captured the shape information of the absorbance curve and eliminated the variation from the aromatics content. The root mean square error in determining blend level with this method was estimated to be 2.88%, and the R2 for the linear model was 0.99. The method worked well with biodiesel from the different feedstocks tested in this research and was independent of the diesel fuel used.

Catalyst for ultra-low sulfur and aromatic diesel

A WNiPd/TiO 2·Al 2O 3 new catalyst with improved desulfurization and hydrogenating capabilities was tested to produce ultra-low sulfur and aromatics diesel oil. The removal of the sterically hindered sulfur and nitrogen containing polyaromatic molecules is studied. It was observed that the new catalyst surface structure promotes the hydrogenating and ring opening of poly-alkyl-poly-aromatics that are less limiting step than that with conventional catalyst. The catalyst characterization indicated the possible formation of metallic acid sites that contribute to the ring opening reactions. The catalyst study using the extracted aromatics and the raffinated product indicated a large improvement in hydrogenation and a reduction in hydrodealkylation functions for converting these sterically hindered aromatics. The reduction in aromatics families improves diesel engine emissions.

Local round robin test for determination of aromatics in diesel fuels by HPLC.

Determination of aromatics in diesel fuels by HPLC is covered by European Standard EN 12916 (April 2000). The Standard is based on former standards IP 391/90 and IP 391/95. The method used for measurements is NP HPLC and separation is performed on silica or modified silica columns with RI detection. The precision of the method was checked by determining the repeatability and reproducibility. The content of aromatics was measured in a number of commercial samples. The measurements have been performed in three different laboratories and under different working and instrumental conditions. Satisfactory agreement was established for repeatability and was slightly poorer for reproducibility. The content of polyaromatics is within the tolerance range (IP 590/99) and the content of tricyclic and higher aromatics (tri+) is close to the limit of quantitition in some samples. Clear differences in the content of polycyclic aromatics in domestic diesel and eurodiesel fuels were observed. The results have confirmed the ruggedness and robustness of the measuring method.

Kinetic behavior of hydrogenation of aromatics in diesel fuel over silica–alumina-supported bimetallic Pt–Pd catalyst

The kinetics and long-term stability test of the aromatic hydrogenation of diesel fuel were studied on SiO 2–Al 2O 3 supported bimetallic Pt–Pd catalyst. The tests on the influence of operating parameters and kinetics studies were carried out using Pt (0.5 wt.%)–Pd (1.0 wt.%)/SiO 2–Al 2O 3, which provided the highest catalytic activity in a previous paper [Applied Catalysis A: General, 192 (2000) 253] with hydrotreated light cycle oil (LCO)/straight-run light gas oil (SRLGO) feedstocks containing 30 vol.% aromatics/100 wppm sulfur and 34 vol.% aromatics/420 wppm sulfur under numerous conditions. The results on this catalyst obtained at different LHSV showed an excellent fit to first-order kinetics. The apparent activation energy was determined to be 92 kJ/mol. Long-term stability test demonstrated the excellent stability of this catalyst. The products during the long-term stability test are of good quality, with the upgraded color, the increased cetane index, and sufficiently decreased sulfur content.