Biotechnology of desulfurization of diesel: prospects and challenges
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Ultra-low-sulfur diesel
With the increasingly strict diesel standards in the countries of the world, deep processing of diesel oil to ultralow sulfur levels is receiving more and more attention. This paper mainly reviews the reaction mechanism, catalysts, and process conditions of diesel hydrodesulfurization, and it provides new research directions for producing ultralow sulfur diesel (ULSD). In terms of mechanism, the sterically hindered sulfides, nitrides, aromatic compounds, and hydrogen sulfide affect the direct desulfurization and hydrogenate pathways of the hydrodesulfurization reaction to varying degrees. In order to eliminate these effects, the properties of high-dispersion active metals, large pore size, high specific surface area, high content of medium-weak acid, and a certain amount of Bronsted acid support are beneficial to further improve the activity of the catalyst, to produce ULSD that meets market demand. This article also reviews the influences of process conditions (for instance, temperature, hydrogen pressure, liquid hourly space velocity, and hydrogen consumption) on the diesel ultradeep hydrodesulfurization reaction, and it finds those moderately high temperatures and high hydrogen partial pressures, as well as low space velocity, to be beneficial. In short, the development of new catalysts is the current research hotspot in the field of ultradeep hydrodesulfurization of diesel, and further research is still needed.
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Ultra-low-sulfur diesel
Sulfidation
Dibenzothiophene
Fuel oil
Hydrodenitrogenation
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This paper briefly introduced diesel hydrotreating combined catalyst system and process developed by Fushun Research Institute of Petroleum and Petrochemicals.Test results of pilot plant showed that compared with applying single catalyst,using this combined catalyst system,under the same process conditions,clean diesel oil with much lower sulfur content could be acquired.Commercial cases of this technology,a 3.3 Mt/a diesel hydrotreating unit in Shanghai Petrochemical Company and a 3.0 Mt/a diesel hydrotreating unit in Zhenhai Petrochemical Company,indicated that FHUDS-2/FHUDS-5 combined catalyst system exhibited excellent deep hydrodesulfurization performance,which could provide diesel oil with sulfur content meeting the requirement of GB Ⅳ emission standard under mild process conditions.
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Ultra-low-sulfur diesel
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Two catalysts,Co-Mo and Ni-Mo-W supported on γ-alumina,were used to evaluate the hydrodesulfurization effect of three typical diesel oils by analyzing their properties including sulfur content,sulfur compound structures and distributions,nitrogen content and aromatic content.Results showed that Co-Mo catalyst was more effective in sulfur removal when treating straight run gas oil.In the case of delayed coker diesel and FCC normal light cycle oils,Ni-Mo-W catalyst showed a better performance for removing benzothiophene,dibenzothiophene and their derivates than Co-Mo catalyst.For secondary processed diesel oils,Ni-Mo-W showed higher ability for denitrogenation and aromatic saturation compared to Co-Mo.
Dibenzothiophene
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Ultra-low-sulfur diesel
Coker unit
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Hydrodenitrogenation
Vegetable oil refining
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In order to adapt for processing high sulfur crude oil and suit the new standards of diesel,a 260 mt/a diesel hydrorefining unit has been built in Maoming refinery of SINOPEC,which adopted FH-UDS deep hydrodesulfurization catalyst newly developed by FRIPP.This article introduces the first time commercial application and analyses the properties and using effects of the catalyst especially the capabilities of deep hydrodesulfurization for diesel.Commercial results indicate that FH-UDS deep hydrodesulfurization catalyst has well HDS/HDN activities and stability and can satisfy demands for producing low sulfur dieslel under high caustical conditions.Via properly adjusting the operating conditions, ULSD of sulfur content less than 10 μg·g-1 could be produced.
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This article examines the hydrodesulfurization process used to produce diesel with low sulfur content in Ecuador. The analysis covers the level of processing in the country, the quality of domestic diesel compared to other nations, and the technical and economic requirements of the process. It also explores the need to modify or upgrade catalysts to achieve deep hydrodesulfurization.. Unfortunately, the review found that sulfur content in Ecuadorian deposits is very high, with 3.53 MMkg produced in 2018. Despite improvements in the country’s refineries, diesel sulfur content has only been reduced to 110 ppm.. Ecuador regulates sulfur emissions through the Ecuadorian standard NTE INEN-1489 (2012). This norm classifies the fuel into three types, diesel #1 (3000 ppm), diesel #2 (7000 ppm), and premium diesel (500 ppm), following the use of diesel both in the industrial and transportation sectors. However, Ecuador seeks to adjust to countries with stricter regulations, such as the European Union. The standard that regulates sulfur emissions in this community is Euro VI, which limits the concentration to 10 ppm. One of the challenges in achieving international standards in the hydrodesulfurization units of the Ecuadorian refineries is to modify or improve the catalytic systems. Trimetallic catalysts, both supported and unsupported, can help overcome this challenge by decomposing the refractory molecules (e.g., dibenzothiophene and 4,6-dimethyldibenzothiophene) found in deep hydrodesulfurization. These catalysts can handle molecules that commonly used catalysts such as CoMo or MoW cannot. Therefore, proposals such as using trimetallic catalysts to achieve deep hydrodesulfurization levels are techno-economic options for Ecuador. Keywords: diesel, sulfur, Ecuador, hydrodesulfurization, refineries, catalyst.
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Production of clean diesel fuel with a low even ultra-low sulfur content and high cetane number is becoming an urgent task for refineries over the world.Among the various methods for producing clean diesel fuel,improving catalytic activity of hydrotreating catalysts is the most effective and economical one.Starting from the active phase theory for transition metal sulfide hydrotreating catalysts and the pathways of hydrodesulfurization and hydrodearomatization reactions,this review summarizes various approaches to improving the activity of hydrotreating catalysts to meet the needs of diesel fuel deep hydrodesulfurization and hydrodearomatization.The methods reviewed include:(Ⅰ)enhancing hydrogenation performance of active species;(Ⅱ)introducing acidic centers with moderate acidity;(Ⅲ)weakening metal-support interaction;(Ⅳ)improving the dispersion of active species.We conclude that developing a new support with high surface area and moderate acidity and exploring new catalyst preparation methods to increase the dispersion of active species without strengthening metal-support interaction are two of the main routes to further increase performance of diesel hydrorefining catalysts.
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Diesel hydrotreating (DHT) or catalytic hydrogen treating is mainly to reduce undesirable species from straight-run diesel fraction by selectively reacting these species with hydrogen in a reactor at elevated temperatures and at moderate pressures. With the advent of ultra-low-sulfur fuel regulations ushering in the first decade of the twenty-first century, however, it was required for hydrotreating (HDT) research and development to deliver quantum improvements in catalyst performance and process technology. In order to successfully produce ultra-low-sulfur diesel (ULSD), essentially all of the organo-sulfur species must be removed including the substituted dibenzothiophenes (DBTs) and other refractory sulfur species. Multiple reactions occur in parallel on the HDT catalyst surface including hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and aromatic saturation/hydrogenation (HDA). Feeds for DHT unit typically have a nominal distillation range of 300-700 °F. Different process design and flow schemes can be employed for DHT depending on the process objectives and characteristics of the feed being processed.
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Lowering sulfur content of diesel fuel has an important significance on improving the quality of tail gas exhausted from automobiles and protecting the environment.The production of ultra low sulfur diesel mainly depends on hydrodesulfurization and non-hydrodesulfurization technologies.The mechanism of deep hydrodesulfurization and brings forward research gaps needed to be resolved is outlined.The deep hydrodesulfurization of diesel fules requires the decomposition of refractory compounds such as 4,6-dimethyldibenzothiophene(4,6-DMDBT).Design approaches to the catalysts of deep hydrodesulfurization are discussed.New research development in recent years on catalysts and processes of diesel deep hydrodesulfurization are also introduced.Moreover,the non-hydrodesulfurization methods by adsorption,oxidation,or biology are presented.The organic combination of hydrodesulfurization and non-hydrodesulfurization technologies has a promising prospect in the production of ultra low sulfur diesel.
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Fuel oil
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In this thesis, the hydrodesulfurization process to obtain diesel with low sulfur content was analyzed in a general way, the level of processing in Ecuador, the quality of domestic diesel compared to other countries, the technical and economic needs of the process, in addition to the change or improvement of the catalysts to achieve deep hydrodesulfurization. In the bibliographic review it was found that, unfortunately, the sulfur content is very high in Ecuadorian deposits. In 2018, Ecuador produced 3.53 MMkg of sulfur from the processes. However, despite the improvements in the country's refineries, the sulfur content in diesel has only been reduced to 110 ppm. Currently, Ecuador regulates sulfur emissions through the Ecuadorian standard INEN 1489 (2012), this standard in accordance with the use of diesel and the permitted limit of sulfur content classifies the fuel into three types, Diesel No. 1 (3000 ppm), No. 2 Diesel (7000 ppm) and Premium Diesel (500 ppm). However, Ecuador seeks to adjust with the countries that have stricter regulations, such as the European Union, the standard that regulates sulfur emissions in this community is Euro VI, which limits the concentration to 10 ppm.
Some of the changes to reach international standards in the hydrodesulfurization units of the Ecuadorian refineries is to modify the catalytic systems or better them. One of these advances is the use of supported and unsupported trimetallic catalysts. These catalysts manage to decompose the so-called refractory molecules (for example, Dibenzothiophene and 4,6-Dimethyldibenzothiophene) that are found in deep hydrodesulfurization, and that normally used catalysts such as CoMo or MoW cannot do so. An instance of the capacity of these catalysts was the laboratory-scale evaluation of a catalyst made up of NiMoW supported in Al2O3-Ga2O3, Dibenzothiophene was used as a model molecule to evaluate its catalytic capacity through the concentration of S on it. Therefore, proposals such as the use of trimetallic catalysts to achieve deep hydrosulfurization levels are a very viable option for Ecuador. Given that at this time the country is trying to improve its refining processes and is likewise planning to build a new hydrodesulfurization plant and a fuel processing unit under the BOT modality (build, operate and transfer) in Manabi.
Ultra-low-sulfur diesel
Dibenzothiophene
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