RU2482162C1 - Method of deep oxidation-absorption desulphurisation of liquid hydrocarbon fuels, and sorbents for its implementation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to petrochemistry, and namely to the process of deep desulphurisation of diesel hydrocarbon fuels. The invention refers to the method of deep oxidation-absorption desulphurisation of liquid hydrocarbon fuels, which involves preparation of a loose sorbent by mixing high-porous absorbents with nitric-acid salt of metal and further treatment of liquid hydrocarbons with the above sorbent, in which the sorbent can contain the binding agent as well, at that, the high-porous absorbent has been chosen from the group of bentonite, montmorillonite, absorbent carbon or high-porous silicon, and nitric-acid salt of metal has been chosen from the group of ferric nitrate, nickel nitrate, copper nitrate; prior to the treatment of liquid hydrocarbons, mixture of the sorbent ingredients is granulated to the particle sizes of 1-5 mm with specific sorbent surface of 50-600 m²/g; at that, treatment is performed by passing the flow of liquid hydrocarbons through a layer of granulated sorbent with volumetric velocity of not more than 100 h^-1. The invention also refers to compositions of sorbents used for the method's realisation.

EFFECT: increasing the efficiency of liquid hydrocarbon fuel cleaning from sulphur containing compounds and providing the continuous process.

5 cl, 1 dwg, 1 tbl, 8 ex

Description

The invention relates to petrochemistry, in particular to a process for the deep desulfurization of diesel hydrocarbon fuels.

Currently, the solution of problems associated with the deep desulfurization of hydrocarbon fuels is very relevant in connection with the growing requirements to reduce the sulfur content in fuels. According to the norms of the European standard EN590, since 2008, the sulfur content in diesel fuel should not exceed 50 ppm. Such sulfur limits are not only associated with the need to reduce pollution from engine exhaust in the form of SO _x compounds. The development of research in the field of deep desulfurization is primarily stimulated by the need to eliminate the harmful effects of sulfur-containing compounds for fuel cells, as well as for the processing of hydrocarbons using sulfur-sensitive catalysts. Since sulfur is a poison for reforming catalysts, as well as for catalysts in fuel cells, the sulfur content of liquid hydrocarbons must be reduced to an ultra-low level, preferably up to 10 ppm for solid oxide fuel cells and less than 1 ppm for membrane polymer electrolyte fuel cells. Liquid hydrocarbon fuels usually contain sulfur compounds, as well as aromatic hydrocarbons in an amount of from 0.1 to 0.3 wt.%. It is known that during hydrodesulfurization of straight-run fractions on the latest generation catalysts, aromatic and aliphatic thiophenes and sulfides are easily removed. With a residual sulfur content in diesel fuel after hydrodesulfurization of less than 100 ppm, sulfur is predominantly in the form of alkyl substituted dibenzothiophenes, since derivatives of dibenzothiophene and 4,6-dimethyldibenzothiophene cannot be removed by catalytic dehydrodesulfurization at elevated hydrogen pressures and temperatures above 350 ° C. The presence of difficult to remove sulfur compounds makes it impossible to use such fuel in fuel cells.

Hydrodesulfurization of hydrocarbon fuels occurs in the presence of hydrogen and a catalyst at a pressure of 3.0-9.0 MPa and a temperature of 315-400 ° C and leads to the conversion of sulfur compounds to H ₂ S. This process removes sulfur-containing compounds such as sulfides, thiophenes. However, alkyl substituted dibenzothiophenes and in particular 4.6-dimethyldibenzothiophene and similar compounds are quite stable and cannot be removed by this technology. Therefore, this process usually removes sulfur to 500-300 ppm, but in order to reduce the sulfur content by this method to 70-50 ppm, it is necessary to significantly increase the hydrogen pressure and temperature. The use of more active and expensive catalysts is also necessary. An increase in hydrogen pressure and temperature necessitates the use of more expensive equipment, and energy costs also increase. Nevertheless, alkyldibenzothiophenes by this method cannot be removed in principle, and they can remain between 50-200 ppm.

For this purpose, the method of oxidative adsorption is most promising, when polar products obtained by the oxidation of hard-to-remove organosulfur compounds such as dibenzothiophenes can be easily separated from hydrocarbons by selective adsorption. The adsorption of alkyl dibenzothiophenes themselves is ineffective for the removal of these compounds. Therefore, for the isolation of alkyl dibenzothiophenes, it is necessary to convert them to more active polar compounds by selective oxidation. The resulting polar compounds — sulfones or sulfoxides — are well adsorbed and can also be separated by extraction with polar solvents. In this case, deep desulfurization of diesel fuel is carried out without the use of hydrogen, while the degree of purification increases to almost 100% and the octane number of the fuel does not decrease. Various methods of oxidation using various oxidizing agents and the isolation of the resulting products are also used. The resulting sulfones and sulfoxides of alkyl dibenzothiophenes are isolated using liquid phase extraction and adsorption. The most promising is the method of oxidative deep adsorption desulfurization, in which both oxidation and adsorption are carried out simultaneously in one stage.

A known method of removing sulfur compounds from hydrocarbon fuels, including the oxidation of high-boiling organosulfur compounds in sulfones and sulfoxides, using activated carbon, silica gel and alumina, an oxidizing agent, which is a complex compound of the composition LMeO (O ₂ ), deposited on porous media such as Me - metal peroxide of the group Mo, W, Cr, a L - hexamethyl triamide phosphate (US Patent No. 5958224, 1994).

Peroxide compounds formed by the interaction of hydrogen peroxide with various catalytic systems are widely used for oxidative desulfurization. However, such catalytic systems are expensive, in addition, peroxide compounds containing both metals and organic peroxides are environmentally hazardous and difficult to synthesize.

A known method for the desulfurization of hydrocarbons, which uses hydrogen peroxide, ozone, nitrogen dioxide and tert-butyl hydroperoxide as a selective oxidizing agent in the process of oxidative desulfurization. In this case, the obtained oxidation products are easily separated from hydrocarbon fuel by liquid extraction with alcohols, amines, ketones or aldehydes (U.S. Patent No. 3847800).

The use of extraction to separate the products of the oxidation reaction requires a large amount of solvent. Solvent regeneration systems and the extraction process add two additional steps to the process, making it very difficult.

A known method of oxidative desulfurization using alkyl hydroperoxide in the presence of a molybdenum catalyst on alumina. Then follows the decomposition of sulfones using a catalyst such as a molecular sieve based on bilayer hydroxides, as well as inorganic metal oxides (U.S. Patent No. 6,368,495).

The disadvantages of this method include the complexity and instability of the process.

The closest technical solution to the proposed one is the method of oxidation-adsorption desulfurization of liquid hydrocarbon fuels, including the deposition of metal nitrates on silicate or clay minerals of the smectite class, namely montmorillonite, laumonite, bentonite, vermiculite, natural and synthetic molecular sieves, zeolites and active aluminum oxides . The sorbent obtained by mixing and grinding a mixture of metal salts with an adsorbent, mainly montmorillonite for 2-5 minutes, is immediately contacted with sulfur-containing diesel fuel in a stationary reactor at room temperature and atmospheric pressure with active stirring. Then, after the end of the process, the sorbent is quickly separated from the solution (US Patent Application Publication No. 2008/0257785).

However, the technique for preparing such a sorbent, which is a fine powder with a particle size of about 50 μm, makes it difficult to use it for oxidation in a stream where there is no active mixing and the particle sizes of the triturated composite sorbent do not allow for active mass transfer in a column reactor. Moreover, this method and the sorbent do not provide a sufficient cleaning depth, and the process itself is complex and time-consuming, requires highly selective means to separate the finely dispersed sorbent from the fuel.

The technical problem solved by the present invention is to increase the degree of purification of liquid hydrocarbon fuel from sulfur-containing compounds and ensuring the continuity of the process.

The technical problem is solved in that the mixture of sorbent ingredients is granulated to a particle size of 1-5 mm with a specific surface area of the sorbent 50-600 m ² / g, and the processing is carried out by passing a stream of liquid hydrocarbons through a layer of granular sorbent, which may additionally contain a binder with a volumetric velocity not above 100 h ^-1 , and also the fact that the bulk mixture of sorbent ingredients is made of granules with a particle size of 1-5 mm and a specific surface of 50-600 m ² / g with the following composition, wt.%:

- highly porous adsorbent - 40-80;

- nitric acid metal salt - 20-60.

In this case, the highly porous adsorbent is selected from the group: bentonite, montmorillonite, activated carbon or highly porous silica, and the nitric acid metal salt is selected from the group: iron nitrate, nickel nitrate, copper nitrate.

The technical problem is also solved by the fact that the mixture of sorbent ingredients additionally contains a binder to increase the strength of the granules. The mixture of sorbent ingredients is made of granules with a particle size of 1-5 mm and a specific surface area of 50-600 m ² / g with the following composition, wt.%:

- highly porous adsorbent - 30-70;

- nitric acid metal salt - 20-60;

- binder - 10-20.

Silica or alumina in the form of nanofibers is used as a binder.

These distinguishing features are significant. The removal of substituted benzothiophenes and dibenzothiophenes (DBT) is carried out in a flow mode at room temperature and atmospheric pressure by their oxidation to sulfones and sulfoxides, followed by adsorption of the reaction products. In this case, benzothiophenes chemisorbed on the catalyst surface are oxidized by metal salts impregnated on the support and are retained in the adsorbed state, and sulfur is almost completely removed. It has been experimentally established that a high speed and depth of fuel purification are achieved with a simultaneous combination of the indicated granule sizes with a given specific surface and the declared fuel flow rate through the granule layer. Moreover, this mode provides a solution to the technical problem in the conditions of the stated ratio of the ingredients of the sorbent. That is, with this size of granules with the specified specific surface, the combination of minimizing the resistance to flow of the cleaned fuel, maximizing the speed and completeness of its cleaning, is optimized.

The method is as follows.

To implement the method, granules are made from finely dispersed carriers — highly porous adsorbents selected from the group: bentonite, montmorillonite, activated carbon or highly porous silica. The granules can be used binder - alumina in the form of nanofibers or silica. A finely dispersed carrier with a particle size of up to 100 μm is mixed with a nitrate metal salt, which is used as iron nitrate, nickel nitrate or copper nitrate. The resulting composite is pressed at pressures up to 100 atm, and then crushed and divided into fractions with the selection of granules 1-5 mm having a specific surface area of 50-600 m ² / g.

The obtained granular sorbent is placed in a column through which a stream of liquid hydrocarbon fuel containing sulfur compounds is passed with a space velocity of up to 100 h ^-1 at atmospheric pressure and room temperature. The result is a purified fuel with a residual content of sulfur compounds from 0.1 ppm to complete purification. The amount of sulfur in the fuel is monitored chromatographically (photometric sensor). After a breakthrough, at a concentration of DBT derivatives of about 0.05 ppm, an additional new column is placed at the column outlet and purification continues. In this case, the initial column is worked out to saturation, and then removed. This saves the amount of catalyst. Since the output curve of the dynamic experience has a sharp rise, the onset of the slip is very sharp and it is necessary to carefully monitor the concentration at the output. At the same time, the undoubted advantage of the proposed method from the point of view of maximum column efficiency and the use of an adsorbent is also the possibility of conducting such a cleaning regime in which the dynamic curve has a steep rise and an almost rectangular front.

The graph (see drawing) shows the dependence of the concentration of the solution at the outlet of the column on the amount of missed solution per 1 g of composite adsorbent for C ₀ = 100 ppm. The output curves for the deep desulfurization of a model diesel fuel for carriers - montmorillonite clay K-10 and activated carbon (AC) are shown. A sharp rise in the output curves shows the possibility of the effective use of these systems for the treatment of hard to remove organic sulfur compounds.

The implementation of the method using the proposed sorbent is illustrated by the following examples.

Example 1

A sorbent is prepared by mixing 60 wt.% Finely divided bentonite powder, 40 wt.% Iron (III) nitrate. The resulting mixture is pressed at a pressure of 100 atm and crushed into particles, from which a 2 mm fraction with a specific surface area of 200 m ² / g is isolated by sieving on sieves. The sorbent is placed in a filter column and diesel fuel is passed through it with a total initial content of substituted benzothiophenes and dibenzothiophenes of 100 ppm at an average volumetric flow rate of 30 h ^-1 . After processing, the impurity content of sulfur compounds was 0.01 ppm.

Example 2

The sorbent is prepared from a mixture of 60 wt.% Finely dispersed activated carbon and 40 wt.% Nickel nitrate. After pressing, crushing and sieving on sieves with a maximum hole diameter of 4 mm, granules of the corresponding size with a specific surface area of 600 m ^{2 /} g are obtained. The sorbent is placed in a filter column and diesel fuel with a sulfur content of 100 ppm is passed through it. The flow rate of the cleaned fuel is maintained at 15 h ^-1 . After purification, the impurity content was 0.05 ppm.

Example 3

Mix 80 wt.% Fine powder of montmorillonite and 20 wt.% Copper nitrate. The mixture is pressed at a pressure of 100 atm. The resulting briquettes are crushed into small particles, from which a 3 mm fraction with a specific surface area of 250 m ² / g is sieved. The resulting sorbent is placed in a filter column and diesel fuel is passed through it with a content of sulfur compounds of 150 ppm at an average speed of 10 h ^-1 . As a result of purification, diesel fuel is obtained with a content of sulfur compounds of 0.05 ppm.

Example 4

A sorbent is prepared by mixing 40 wt.% Highly porous silica, 60 wt.% Iron (III) nitrate. The resulting mixture was pressed at a pressure of 100 atm and crushed into particles, from which a 1 mm fraction with a specific surface area of 500 m ² / g was isolated by sieving on sieves. The sorbent is placed in a filter column and diesel fuel is passed through it with a total initial content of substituted benzothiophenes and dibenzothiophenes of 200 ppm at an average volumetric flow rate of 100 h ^-1 . After treatment, the content of sulfur-containing compounds was 0.08 ppm.

Example 5

The sorbent is prepared from a mixture of 40 wt.% Highly porous silica, 40 wt.% Iron nitrate and 20 wt.% Aluminum oxide nanofibers as a binder. The mixture is pressed at 80 atm, and then crushed into small particles, from which granules of 5 mm in size are separated, having a specific surface of 100 m ² / g. The sorbent is loaded into the column and diesel fuel is passed through it with a total content of substituted benzothiophenes and dibenzothiophenes of 100 ppm at a flow rate of 45 h ⁻¹ . Purified fuel contains 0.01 ppm sulfur compounds.

Example 6

A sorbent is prepared from a mixture of 60 wt.% Finely divided bentonite, 20 wt.% Copper nitrate and 20 wt.% Silica as a binder. The mixture is pressed into briquettes at a pressure of 100 atm and crushed into particles, from which granules of 4 mm in size with a specific surface of 50 m ² / g are isolated. The filter column is filled with sorbent granules and diesel fuel is passed through it with a substituted benzothiophene and dibenzothiophene content of 100 ppm at a flow rate of 45 h ⁻¹ . As a result of fuel treatment, the content of sulfur compounds decreases to 0.01 ppm.

Example 7

The sorbent is prepared from a mixture of 50 wt.% Finely dispersed activated carbon, 40 wt.% Nickel nitrate and 10 wt.% Nanofibres of aluminum oxide. After pressing, crushing and sieving on sieves with a maximum hole diameter of 2.5 mm, granules of the corresponding size with a specific surface of 600 m ² / g are obtained. The sorbent is placed in a filter column and diesel fuel with a sulfur content of impurities of 100 ppm is passed through it. The flow rate of the cleaned fuel is maintained at 25 h ^-1 . After purification, the impurity content was 0.07 ppm.

Example 8

60 wt.% Finely divided montmorillonite powder and 25 wt.% Copper nitrate and 15 wt.% Aluminum oxide nanofibers are mixed. The mixture is pressed at a pressure of 100 atm. The resulting briquettes are crushed into small particles, from which a 1 mm fraction with a specific surface area of 150 m ² / g is sieved. The resulting sorbent is placed in a filter column and diesel fuel with a content of sulfur compounds of 150 ppm is passed through it at an average volumetric rate of 90 h ⁻¹ . As a result of purification, diesel fuel with a content of sulfur compounds of 0.01 ppm is obtained.

Table 1 shows a comparison of the desulfurization data of the fuel according to the technology of the prototype and according to this invention.

Table 1 C ₀ ppm 4.6-dimethyl dibenzothiophene Contact time, hour Specific flow rate h ^-1 The amount of ml of purified solution per 1 g of composite Capacity * columns for sulfur S mg / g of composite to the point of breakthrough The amount of sulfur at full saturation S mg / g of the composite according to the invention Comparison with prototype (5.1 mg S / g) KK-10 fifty 21 53 78.52 4.81 - 0.94 one hundred 10 58 40.67 3.75 - 0.73 150 four 63 17.38 2.56 - 0.50 150 6 69 29.26 4.39 0.86 one hundred** fifty 19 64.32 6.43 9.00 1.26 300 6 thirty 12.92 3.87 0.75 FROM one hundred** 142 fifteen 167.25 16.73 21.75 4.32 - * the maximum amount of sulfur removed from the solution during purification to 0.01 ppm (to the point of breakthrough). ** full output curve

The proposed technology greatly simplifies the process of oxidative desulfurization through the use of a continuous mode of purification in the fuel stream.

The use of metal nitrates, and in particular a cheap composition based on iron nitrate and the natural adsorbent montmorillonite, opens up possibilities for wide industrial use.

Claims (5)

1. A method for the deep oxidation-adsorption desulfurization of liquid hydrocarbon fuels, comprising preparing a bulk sorbent by mixing highly porous adsorbents with a metal nitrate salt and subsequent processing of liquid hydrocarbons with the specified sorbent, characterized in that the sorbent may additionally contain a binder, while the highly porous adsorbent is selected from the group: bentonite, montmorillonite, activated carbon or highly porous silica, and the nitric acid metal salt is selected from the group: iron nitrate, nor rat nickel, copper nitrate, prior to processing the mixture of liquid hydrocarbons ingredients sorbent is granulated to particle sizes of 1-5 mm with a specific surface area sorbent 50-600 m ² / g, wherein the treatment is carried out by passing the liquid hydrocarbon stream through a bed of granular adsorbent at a flow rate not above 100 h ^-1 . 2. The sorbent for implementing the method according to claim 1, which is a bulk mixture of highly porous adsorbents and nitric metal salts, characterized in that the bulk mixture is made in the form of granules with a particle size of 1-5 mm and a specific surface of 50-600 m ² / g at the following composition, wt.%:
highly porous adsorbent 40-80 metal nitrate 20-60 3. The sorbent according to claim 2, characterized in that the highly porous adsorbent is selected from the group: bentonite, montmorillonite, activated carbon or highly porous silica, and the nitric acid metal salt is selected from the group: iron nitrate, nickel nitrate, copper nitrate. 4. The sorbent for implementing the method according to claim 1, which is a bulk mixture of highly porous adsorbents and nitric metal salts, characterized in that it further comprises a binder, which is used as silica or alumina in the form of nanofibers, while the bulk mixture is made in the form of granules with a particle size of 1-5 mm and a specific surface of 50-600 m ² / g in the following composition, wt.%:
highly porous adsorbent 30-70 metal nitrate 20-60 binder 10-20 5. The sorbent according to claim 4, characterized in that the highly porous adsorbent is selected from the group: bentonite, montmorillonite, activated carbon or highly porous silica, and the nitric acid metal salt is selected from the group: iron nitrate, nickel nitrate, copper nitrate.

Images