Sulfur in Diesel Fuel: Problem and Solution. Sulfur in diesel fuel: problem and solution Central Federal District

(No. 8 for 2010)
Vladimir SHLYAKHOVOY

Sulfur

Diesel fuel is characterized by a number of rather important parameters, and one of the main among them is the sulfur content. In theory, the presence of sulfur improves the lubricating properties of the fuel, but this is simply nothing compared to the problems that arise when it burns while the engine is running. The resulting sulfur oxides react with water vapor to form sulfuric and sulphurous acids, which, in one amount or another, necessarily enter the engine lubrication system. But, besides, what kind of "Euro" can we talk about if sulfuric acid vapors are being felled from the exhaust pipe? Yes, and exhaust gas neutralization systems, and particulate filters when using sulphurous fuels, they quickly fail. Therefore, simultaneously with the growth of requirements for the purity of exhaust gases, the requirements for the quality of fuel naturally grow. Including the sulfur content in it.

For example, in accordance with current standards, the type of fuel must be indicated, depending on the sulfur content in it. In Russia, since 2005, the standard GOST R 52368-2005 (EN 590: 2004) has been in effect. Diesel fuel EURO. Technical conditions ", and in Ukraine on January 1, 2008, a similar standard DSTU 4840: 2007" Diesel fuel of improved quality. Technical conditions ", corresponding to the same standard EN 590: 2004. However, DSTU 3858-99 “Diesel fuel. Technical conditions ", which replaced GOST 305-82 in Ukraine since 1.09.1999, has not been canceled yet, it will operate along with DSTU 4840: 2007 until the end of 2010.

Table 1. Cetane number and limit sulfur content in different types of diesel fuels, mg / kg, depending on the standard

* Fuel with a sulfur content of not more than 10 mg / kg in accompanying documents may be designated as “sulfur-free”.

Table. 2 Cetane number and sulfur limit in diesel fuels of various environmental norms and standards

* Standard valid in Russia.

** Standards in force in Ukraine.

Thus, in Ukraine it is now possible with equal success to refuel both with diesel fuel of Euro-5 level, containing sulfur in the amount of 10 mg / kg, and “Soviet” diesel fuel, in which the sulfur concentration is 500 (!) Times higher.

Frost resistance

Perhaps the second most important parameter of diesel fuel is its frost resistance, which is inversely proportional to the amount of paraffins in it. When the temperature drops, paraffins tend to crystallize, as a result of which diesel fuel first becomes cloudy, then turns into "jelly", and then completely freezes. Therefore, the inherent characteristics of diesel fuel are its parameters such as cloud point and limiting filterability temperature, which are specific for each type of diesel fuel and are separated from one another by about 10 ºС.

At the same time, both of the above parameters are rather arbitrary, and therefore one should not think that it is possible to painlessly use clouded fuel. Especially if the fuel filters are not heated. Indeed, in this case, their filter elements will very quickly become tightly clogged with paraffin, which can no longer be removed. We will keep silent about the fact that in such a case the further operation of the engine is, in principle, impossible. And to solve the problem, you will have to change very expensive filter elements.

The reason for the turbidity of diesel fuel is the appearance of groups of oriented paraffin molecules, which become centers of crystal formation. At the same time, the minimum allowable temperature for using diesel fuel, at which its normal pumpability through the fuel system through the filter elements is ensured, is at least 2 ºС higher than its cloud point.

As for such a concept as "the limiting temperature of the filterability of diesel fuel", it means the limit at which the cooled diesel fuel is able to pass through a standard filter element at a certain speed. This indicator is used only to determine the ability to start the engine. But if, in this case, use non-heated fuel filters, they will immediately be blocked with paraffin.

To this we can add that a parameter such as the "pour point of diesel fuel" is also normalized, the cause of which is the coalescence of hydrocarbon crystals among themselves into a rigid crystal lattice. The pour point determines the possibility of transportation, refueling, discharge and filling of diesel fuel into tanks and has no practical value for determining the possibility of starting the engine or its operation.

And so that you can easily determine in which temperature ranges a particular diesel fuel can be used, according to the requirements of the standards, its symbol must indicate the grade (depending on the values ​​of the limiting filterability temperature, or class), determined by both the filterability temperature and the temperature clouding.

In this case, the grade is set for fuel intended for use in zones with a temperate climate, and the grade - for the Arctic zones.

Table 3. Requirements for low-temperature properties of diesel fuel (GOST R 52368-2005)

* N / N - not standardized.

At the same time, the Ukrainian DSTU 4840: 2007 provides for the same six grades (AF), but only two classes (0-1) of diesel fuel, as GOST R 52368-2005, regulates a lower sulfur content and a higher cetane number (at least 51 ). Whereas DSTU 3868-99, which will operate in Ukraine until 01.01.2011, provides only two brands of diesel fuel: L - summer and Z - winter.

Table 4. DSTU 3868-99 requirements for low-temperature properties of diesel fuel

In this regard, diesel fuel can be labeled as follows:

- "Diesel fuel EURO in accordance with GOST R 52368-2005 (EN 590: 2004), grade A, type I";

- "Diesel fuel of high quality (Euro) class 1, type II in accordance with DSTU 4840: 2007".

In a word, it is quite difficult to understand all this variety of grades, classes and types of diesel fuel. Theoretically, as a substitute for winter and arctic diesel fuel for diesel engines you can use kerosene. But in practice, this cannot be done, since kerosene has two significant drawbacks. Firstly, its cetane number is about 40, which is too low for normal engine operation. And secondly, kerosene, unlike diesel fuel, does not have lubricating properties, therefore, all rubbing parts in the fuel system (high-pressure fuel pump, plunger pairs, etc.) will quickly become unusable.

This is allowed only in exceptional cases and only as a temporary remedy, especially on old engines with a mechanical injection pump. But even in this case, it is necessary to introduce antiwear and cetane-enhancing additives. It is believed that without damage to the engine, it is possible to add up to 20% kerosene to summer diesel fuel to lower its pour point. But this, too, should be considered only as a last resort, unacceptable on modern engines with high injection pressure.

Cetane number

An important indicator for diesel fuel is the cetane number (CN), which characterizes the flammability rate of the fuel - from the moment of its injection into the cylinder to the start of combustion (autoignition delay period). And the higher the CN, the faster the diesel fuel ignites.

The numerical value of CN is equal to the percentage of cetane (C16H34, the CN of which is taken as 100) in its mixture with α-methylnaphthalene (its cetane number is 0), the flammability of which is equivalent to the test diesel fuel. In this case, the CC is determined by a test on a motor installation.

With a cetane number of less than 40, due to the long period of autoignition delay, the fuel in the cylinder has time to warm up well, therefore the ignition is explosive, the pressure in the cylinder rises sharply, which leads to knocking in the engine. Such work of a diesel engine is called hard, since it causes shock loads on the piston and crankshaft bearings, which leads to their accelerated wear.

The higher the cetane number, the shorter the ignition delay, the smoother the fuel mixture burns, the smoother the engine and the more environmentally friendly the exhaust. But this is good up to certain limits. Diesel fuel with a CCH higher than 55, having a short autoignition delay period, having entered the cylinder, does not have time to warm up well, therefore the pressure in the cylinder increases evenly and the engine runs smoothly. However, this worsens the mixture formation process, since the fuel does not have time to mix well with air, which leads to incomplete combustion of the fuel, a drop in engine power and economy, and an increase in exhaust gas smoke. In addition, diesel fuel with a high CN is significantly more expensive. Therefore, unlike the octane number, which the higher the better, the cetane number has its own operating range of 40 - 55 units, the optimum of which is 51 - 53 units.

At the same time, standard diesel fuel is characterized by a cetane number of 40 - 45, and the highest quality fuel has a cetane number of 51 - 55. According to modern standards, the CC number of summer and winter diesel fuel should be at least 49 units. (According to the EN 590: 2004 standard, the CN must be at least 51, and the cetane index (the same, but determined by calculation) - at least 46.)

To this we can add that the cetane number indirectly testifies to the low-temperature characteristics of the fuel - the lower it is, the lower the pour point. Therefore, summer and winter diesel fuels usually have different CCs, while for Arctic diesel fuel it is on the verge of hard engine operation. But here the soft operation of a diesel engine is often deliberately sacrificed for the sake of ensuring its normal start-up and pumping the fuel through filters in severe frosts. At the same time, diesel fuel High Quality lighter, contains more flammable light fractions and therefore more suitable for starting the engine in cold weather. In addition, the ratio of hydrogen to carbon in the light ends is higher, so less smoke is generated when such diesel fuel is burned.

Coking, ash content and others ...

Other standardized parameters of diesel fuel include its coking capacity, which contributes to the formation of deposits in the combustion chamber and on the piston rings, and ash content, which determines the non-combustible fuel residue. Thus, the coking capacity of the ten percent residue remaining after the distillation of the volatile fractions of diesel fuel should be within 0.3%, and the ash content should not exceed 0.01%, whereas according to previous standards, this value was ten times greater.

As for various additives, they are usually industrially added only to special grades of diesel fuel, primarily in the Arctic. Although sometimes manufacturers also throw out special grades of fuel on the market.

These include, for example, Shell V-Power Diesel.

For the first time this fuel was presented in Italy in 2002. And now it has appeared in Ukraine. At the same time, neither Russian nor Belarusian drivers can yet refuel with such fuel, despite the fact that Shell came to Russia much earlier than to Ukraine. In Belarus, there are no Shell filling stations at all.

The new fuel is produced on the basis of Euro-4 diesel (type II), with the addition of a special detergent additive NEMO 2010. At the same time, as the manufacturer declares, the Shell V-Power Diesel composition helps to remove existing carbon deposits and prevents the formation of new deposits in the combustion chamber of the engine, which contributes to the extension of its resource, stable power and improvement of environmental parameters. This fuel contains no more than 0.05% (50 mg / kg) sulfur, but it also costs like AI-95.

According to the assurances of representatives of the Shell company, a mileage of 2,400 km on Shell V-Power Diesel fuel is sufficient for almost complete cleaning of the combustion chamber and injector. Naturally, the advantages of this fuel can be most pronounced when used on used cars, while on new cars the difference will not be noticeable.

In 2005, in connection with the government's obligations to reduce the environmental load from exhaust gases, as well as the need to comply with the requirements of European customers for export shipments, it was forced to develop a new standard for diesel fuel in Russia.

GOST R 52368-2005 duplicates all the requirements of the European standard EN 590: 2004 (that is why the word "EURO" and a reference to "EN 590: 2004" must be present in the designations of diesel fuel manufactured in accordance with GOST R 52368-2005).

In autumn 2009, a new version of BS EN 590: 2009 came into force in Europe. The main differenceits from the previous standard is the exclusion of types of diesel fuel with a sulfur content of 50 mg / kg. Thus, in the European Union standard there is only one norm for the sulfur content - no more than 10 mg / kg.

In the Russian GOST R 52368-2005, the sulfur content rate of up to 350 mg / kg existed until December 31, 2011, and 50 mg / kg will last until December 31, 2014. Diesel fuel with a sulfur content of 10 mg / kg does not have a release date. limited. So, since 2012, the oil refining industry has been producing diesel fuel with a sulfur content of 10 and 50 mg / kg.

According to GOST R 52368-2005, diesel fuel is classified according to two parameters:

1. Limit sulfur content, reflected in the indicator "TYPE" of the fuel, namely:

type I - sulfur content not more than 350 ppm (mg / kg);

type II - sulfur content not more than 50 ppm (mg / kg);

type III with a sulfur content of less than 10 ppm (mg / kg).

2. Application temperature (climatic zone in which diesel fuel can be used). For a temperate climatic zone, diesel fuel is divided into six grades: A, B, C, D, E, F.

Fuel requirements for temperate climates

For areas with a cold climate, diesel fuel is conventionally divided into five classes: 0, 1, 2, 3, 4.

The term “filterability temperature” was also introduced for the first time by the new GOST R 52368-2005 and denotes the temperature below which diesel fuel does not pass at the required rate (flow rate) through a standard reference filter.

Fuel requirements for cold and arctic climates

It is important to remember: "SORT" or "CLASS" is the parameter of the temperature characteristic, and "VIEW" is the parameter of the sulfur content in diesel fuel.
Here are some examples symbol fuel its decryption.

Example 1. "DT Euro grade F, TYPE II". From this designation, we learn that diesel fuel is intended for a temperate climatic zone (grade F) - a winter grade, and the sulfur content in this fuel is not more than 50 ppm (mg / kg).

Example 2. "Diesel fuel Euro class 2, type I". The word "CLASS" means that this fuel is intended for the cold and arctic climatic zone. Class "2" indicates that the limiting filterability temperature is minus -32 ° C. Type I indicates that the sulfur content is not more than 350 ppm (mg / kg).

Seasonal use of diesel fuels in the regions of the Russian Federation in accordance with the requirements for the limiting temperature of filterability

In accordance with climatic conditions, it is allowed to change the number of days of the spring and autumn transition periods towards winter or summer by agreement of the local administration with the regional services of the Hydrometeorological Center.

The requirements for diesel fuel in accordance with GOST R 52368-2005 (EN 590: 2009) are as follows:

This article was born out of a casual conversation with a colleague, when the phrase was heard that, according to the estimates of representatives of foreign auto-building companies, given the sulfur content that is characteristic of Russian fuel, no diesel engine can travel more than 600 thousand km. But they do! We thought about it, and realized that everything is not as simple as our colleague would like. And in order not to generate speculation and legends, they turned to specialists: Viktor Davidovich Reznikov, already well known to our readers, and his colleague at the VNII NP, specializing in fuel, Arkady Mironovich Bakaleinik.

Sulfur and its compounds as a natural constituent of crude oil are included in the composition of crude oil in the form of elemental sulfur, hydrogen sulfide and various organic compounds (mercaptans, sulfides, disulfides, etc.), while heavier oil distillates contain more sulfur and sulfur compounds than lungs. Elemental sulfur, hydrogen sulfide, mercaptans are highly corrosive; therefore, their presence in gasoline and diesel fuels was not allowed (sulfur and hydrogen sulfide) or strictly limited (mercaptans). The total content of other sulfur compounds in the fuel is limited by the limiting rate of the "mass fraction of sulfur" indicator. Tightening the standards for this indicator requires deeper purification from sulfur and, accordingly, additional costs for fuel production, increases its cost, and reduces resources. Therefore, a certain amount of sulfur is present in all commercial fuels.

Recall that the current standard divides diesel fuel into "sulfurous" and "low-sulfur". These terms have been given different meanings at different times. When equipment manufacturers did not have or had minimal restrictions on emissions of harmful substances, the sulfur content was normalized based on the possibility of ensuring reliable operation of the engine without significantly reducing its resource, but so that this did not reduce the fuel output and did not increase its cost.

At this stage, i.e. in the 50s - 70s, diesel fuel with a sulfur content of about 1.0% was referred to as "sulfurous", and fuel in which it was not more than 0.2% was considered "low-sulfur". The main problem with the use of sulfurous fuels was an increase in the wear of parts of the cylinder-piston group of diesel engines and an increase in the amount of deposits on them under the influence of sulfur combustion products. Most of these products (SO2 and SO3) are emitted into the atmosphere with exhaust gases, but the amount of SO2 and SO3 that forms sulfurous and sulfuric acids with water vapor significantly increases the corrosive wear of cylinders, piston rings and other parts, contributes to carbon formation, which violates heat removal from the piston, piston ring mobility, which reduces compression.

To solve these problems, diesel oils have been imparted with neutralizing properties by means of alkaline detergents. The additives almost completely prevent corrosive wear of engine parts and increased carbon formation. With sufficient alkalinity of the oil (about 8 - 10 mg KOH / g), wear of a set of piston rings when operating on fuels with a sulfur content of 1.0; 0.5% and 0.2% are practically the same if the oil change is done in a timely manner. When operating on fuels with a high sulfur content, the base number of the oil decreases faster and the mileage before oil change is reduced.

Today the situation has changed. Now "sulphurous" is called a fuel containing 0.2% sulfur, and in "low-sulfur" it can contain only 0.035% or less. What is the reason for such drastic changes?

In recent years, due to the severity of the problem of environmental pollution from the operation of a rapidly growing multimillion-dollar fleet of cars, more and more stringent standards have been introduced on the emission of toxic compounds, particulate matter and other air pollutants by cars. Compliance with these standards required manufacturers of equipment to use various emission control systems (afterburners, catalytic converters, filters, etc.) in the design of vehicles, as well as changes in the organization of the combustion process, the introduction of exhaust gas recirculation, and new fuel injection systems.

The presence of sulfur compounds in fuel increases the toxicity of exhaust gases not only directly, by increasing the concentration of sulfur oxides and particulate matter in them, but also indirectly, by reducing the efficiency and reliability of modern exhaust gas composition control systems. Therefore, at present, along with the development and production of equipment that meets new standards for emissions of harmful substances, more stringent restrictions on the sulfur content in automotive fuels are gradually being introduced.

Diesel fuels in Russia are currently produced in accordance with GOST 305-82 and more than thirty technical conditions (TU). According to these documents, diesel fuels are produced not only for vehicles, but also for agricultural machinery, construction and road vehicles, diesel locomotives, ships, etc. In accordance with GOST 305-82, 80-85% is now produced in Russia, i.e. the main volume of diesel fuel. The sulfur content of 0.2% can be considered a baseline for Russia. In diesel fuel of type 2, according to this standard, even a sulfur content of up to 0.5% is allowed. However, this norm is being revised towards stricter sulfur content, and fuel with a limit of 0.05% is also being introduced.

For use in large cities or regions with a difficult environmental situation, technical conditions have been developed for diesel fuel with improved environmental properties - urban (TU 38.401-58-170-96) with a sulfur content of no more than 0.05% and "environmentally friendly" fuels (TU 38.1011348 -99), providing, among other restrictions, for the production of fuels with a sulfur content of not more than 0.035%.

Since November 1, 2001, TU 38.401-58-296-2001 “Automobile diesel fuel. Technical conditions ", developed on the basis of an authentic translation of EN-590-2000 with a sulfur content standard of not more than 0.035%, for vehicles that meet Euro-3 requirements. By 2003 - 2005 it is planned to harmonize domestic standards for gasoline and diesel fuel with European requirements for cars of Euro-3 level. This means limiting the sulfur content in gasoline to 0.015%, and in diesel fuel to 0.035%. But the introduction of such standards will not mean a simultaneous transition to new requirements: the process will continue for at least 5 years. During this period, the "old" and "new" requirements will operate simultaneously.

Diesel fuels with a sulfur content of less than 0.035% have poorer lubricating properties. Their use leads to a significant increase in the wear of the high-pressure pump plungers and a decrease in the uptime of other fuel equipment units. It became necessary to introduce additives into fuels to improve their lubricating properties. In Russia, such additives are not yet commercially produced. And this is not the only problem associated with the transition to new standards.

Unfortunately, at our filling stations there is still no separate sale of diesel fuels of different grades, differing in their sulfur content and other indicators characterizing their environmental friendliness. This urgent task must be solved, since the mixing of fuels in one tank of a gas station leads to a deterioration in the quality of environmentally friendly varieties. But this is already a matter of infrastructure reform, which will take a long time.

Diesel fuel is obtained by refining petroleum, therefore sulfur compounds remain one of its components. Although there is no pure sulfur in the fuel, its derivatives are still present in a fairly large amount (up to 7%). To remove some of the sulfurous substances and improve the environmental friendliness of diesel fuel, various types of cleaning are used - hydrocracking and alkaline treatment with caustic soda.

The reasons for limiting the sulfur content in fuel are:

1. corrosive effect on piston elements;
2. the appearance of carbon deposits and deposits;
3. premature wear of the fuel and exhaust system;
4. exhaust smoke;
5. emission of sulfur compounds and other harmful substances into the atmosphere;
6. non-compliance with standards, which limits the use of cars.

To extend the life of diesel engines and avoid environmental pollution, limits have been adopted on the sulfur content of diesel fuel.

Effect of Sulfur in Diesel Fuel on Engine

The current standards strictly regulate the fractional composition of fuel, including sulfur compounds. However, a certain percentage of such substances still remain, despite the purification and processing of the feedstock. It is very expensive and unprofitable to completely remove sulfides and other sulfurous elements.

The presence of such sulfurous substances when interacting with water vapor leads to the formation of sulfurous and sulfuric acid. As a result, corrosion of metal parts of the piston group, fuel and exhaust systems appears. The formation of deposits impairs heat dissipation, reduces compression, and limits the mobility of the rings.

The effect of sulfur on fuel properties limits and specifications the diesel engines themselves, namely:

• power decreases;
• fuel consumption increases;
• power and acceleration characteristics deteriorate.

Due to the high sulfur content in marine fuel or fuel for other diesel engines, the combustion process of the mixture itself changes. As a result, a loss of power, a decrease in efficiency and a deterioration in the dynamics of the diesel engine is possible.

It should be borne in mind that low sulfur content is also not very good for a diesel engine. With a decrease in sulfur compounds below 0.035%, the lubricating properties of the fuel deteriorate. As a result, premature wear appears and the life of the fuel system is reduced. To eliminate this problem, special additives are used.

Diesel fuel environmental standards

A certain balance between the sulfur content and the environmental friendliness of the fuel was achieved with the advent of the corresponding standards (Euro 0-6). These standards regulate the emission of harmful elements and the technical characteristics of diesel fuel. The last adopted options are Euro 5 and 6 (2009 and 2015, respectively), according to which harmful emissions should not exceed the following values:

1. carbon monoxide - 0.5;
2. nitric oxide - 0.18 - 0.08;
3. suspended particles - 0.005.

Hydrocarbons and VOCs are not allowed at all.

Diesel fuel specifications

Cars, trucks, buses and special equipment are refueled in accordance with climatic conditions. There are summer, winter and arctic fuels. According to the temperature of use, the fuel is divided into grades (A-F) and classes (0-4). Such fuel is distinguished by the following indicators:

• cetane number 45-51;
• sulfur content in diesel fuel Euro 5 and 6 - no more than 10 mg;
• filtration temperature - up to -55 ° С;
• density within 0.830-0.860 g / cm 3.

According to Russian GOST, the sulfur content in diesel fuel should also not exceed 10 mg.

If you liked our article and we somehow were able to answer your questions, then we will be very grateful for a good review of our site!

Continuous improvement of technology and tightening of environmental standards lead to increased requirements for fuel quality ... Much attention is paid to sulfur content in petroleum products and oil... This parameter is necessarily reflected in the quality certificate.

Sulfur impurities are present in any grade of oil and in all petroleum products, ranging from 0,05 before 6% from the total mass. Sulfur compounds are unevenly distributed over all fractions, even in highly purified distillates. High sulfur content in fuels is undesirable for many reasons:

• sulfur is toxic and causes an unpleasant odor of petroleum products,
• reduces the resistance of gasoline to detonation,
• provokes increased gum formation during cracking,
• increases corrosiveness,
• vapors of sulfur compounds irritate the human respiratory tract and worsen the condition of plants.

However, it is not yet possible to completely eliminate sulfur from the fuel. For example, if the sulfur content in diesel fuel is below 0.035%, then its lubricity is significantly deteriorated, which leads to accelerated wear of the elements of the vehicle's fuel system. To prevent this, additives are added to the diesel oil to improve the lubricating properties. But they are still inaccessible, since mass production has not yet been established. The only way out is to reduce the amount of sulfur in petroleum products by setting strict standards.

Sulfur classification of oil

GOST R 51858-2002 defines oil classes by sulfur content:

• Class 1 - low-sulfur - sulfur in the total mass of 0.6%.
• Class 2 - sulfurous - sulfur in the total mass is up to 1.8%.
• Class 3 - high sulfur - sulfur in the total mass is up to 3.5%.
• Class 4 - especially high-sulfur - sulfur in the total mass is above 3.5%.

Oil usually contains pure sulfur (there is little of it) and its derivatives. V quality certificate the proportion of total sulfur (pure sulfur + sulfur-containing impurities) is indicated. The higher the sulfur content in oil, the lower its cost.

The main share of sulfur compounds (50-80%) in oil products is represented by almost neutral sulfides and disulfides. The most "unpleasant" sulfur derivatives are mercaptans. It is they that cause a pungent odor and more than others provoke corrosion and the formation of resins. The content of mercaptans is limited to a few hundredths of a percent, depending on the type of fuel and is indicated separately in the quality passport.

Sulfur content standards for different types of fuel

Sulfur standards are set for all fuels. The most stringent requirements apply to motor gasoline and jet fuel... The permissible sulfur content in them is from 0.02 to 0.1%. The same requirements apply to solvent gasolines.

Diesel fuel in terms of sulfur content is divided into environmental classes... For today in Russia, the release and use of only Diesel fuel of Euro-5 class with a sulfur content of less than 10 mg / kg.

How to reduce sulfur content

The removal of sulfur from fuel is carried out in refineries in two ways:

The oil is preliminarily passed through filters to free it from mechanical impurities. And then it is processed by catalytic hydrogenation at high temperature. The cost of sweet oil is about twice the cost of the initial feedstock, but this way you can get oil with a sulfur content of up to 1%.

The second method involves the removal of sulfur from part of the heavy oil fractions using vacuum distillation. Then these fractions are subjected to hydrogenation with hydrogen. The resulting sulfur-free raw material is mixed with the bulk, and the total sulfur content is reduced by 80-95%.