RU2361902C1 - Method of refining of light fractions of secondary origin - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention refers to method of refining of light fractions of secondary origin consisting in separation of wide benzene spread into light and heavy fractions, and in hydro-upgrading of heavy fraction at raised temperature and pressure in presence of catalyst with successive mixing of light fraction and hydro-upgraded heavy fraction; as wide benzene spread there is used fraction boiled out within C₃-220°C; light fraction before mixing with hydro-upgraded heavy fraction is subject to sulphur refining by means of extracting with alkali, to successive fractioning and to extracting gas fractions ΣC₃ and ΣC₄ out of it.

EFFECT: upgraded quality of end products due to reduced sulphur contents in gas fractions and in benzene fraction at simultaneous maintaining its octane number.

4 cl, 2 ex

Description

The invention relates to the field of oil refining and petrochemicals, specifically to a method for purification of light fractions of secondary origin, in particular to an unstable gasoline fraction of catalytic cracking, gasoline fractions of visbreaking, coking processes or mixtures thereof.

It is known that, depending on the catalyst used in the catalytic cracking process and the temperature regime of the reactor-regenerator unit, the content of unsaturated hydrocarbons that are carriers of the octane number in catalytic cracking gasoline is from 7 to 40% by weight.

Catalytic cracking gasoline obtained from raw materials (vacuum gas oil) that has not undergone preliminary hydrotreating is characterized by a rather high sulfur content. Depending on the sulfur content of the feedstock in catalytic cracking gasoline, the content varies between 0.15-0.4% by weight. Such gasoline, even when diluted with low-sulfur components (reformates, isomerizates, etc.), in some cases does not allow reaching the required sulfur content in commercial gasoline, which, in accordance with GOST R51105-97, is not more than 0.05% by weight, and in accordance with the requirements of EN 228 of the EEC member states for marketable gasoline of the EURO-4 standard - not more than 0.005% wt.

Analysis of the hydrocarbon composition of catalytic cracking gasoline shows that the main part of high-octane unsaturated hydrocarbons is contained in the head fraction of gasoline, which is characterized by a low content of sulfur compounds, mainly of the mercaptan type. With an increase in the fractional composition, the content of sulfur compounds increases sharply.

(K.Rock. Production of low sulfur gasoline by industrially proven catalytic refining. Moscow conference on oil refining technologies. June 25-26, 2001).

Another valuable catalytic cracking product is ΣС ₃ and ΣC ₄ hydrocarbons, which contain a large amount of unsaturated hydrocarbons, which makes them a valuable raw material for the petrochemical industry. Depending on the sulfur content in the feedstock in fractions ΣС ₃ and ΣС _4, the sulfur content can reach 1.0% wt. and OJ% wt. respectively. The main requirement for the quality of ΣС ₃ and ΣС ₄ fractions for using them as raw materials of petrochemical processes is sulfur content of not more than 0.001% wt.

A known method of purification of a gasoline fraction of catalytic cracking, in which stable gasoline of catalytic cracking is subjected to fractionation into light C ₅ - 120 ° C and heavy 120 ° C - KK fraction, followed by hydrotreating the heavy fraction in the presence of aluminum-nickel-molybdenum catalyst at a pressure of 3.0 MPa, space velocity supply of raw materials 2-3 hours ^-1 and a temperature of 250-290 ° C and obtaining a component of marketable gasoline by mixing a light fraction with a hydrotreated heavy.

(Khavkin V.A., Gulyaeva L.A., Osipov L.N., Kaminsky E.F. Chemistry and technology of fuels and oils, 2001, No. 1, pp. 10-13)

The disadvantages of this method include the need for preliminary stabilization of a wide unstable gasoline fraction of catalytic cracking (extraction of C ₃ -C ₄ hydrocarbons) and the inability to obtain a component of marketable gasoline with a sulfur content of less than 0.05% wt. with a slight, 0.5 points by the motor method, a decrease in the octane number.

A known method of hydrotreating a gasoline fraction of catalytic cracking, in which stable catalytic cracking gasoline is divided into light C ₅ - 130-160 ° C and heavy 130-160 ° C - KK fractions, heavy fraction 130-160 ° C - KK is subjected to hydrotreating in the presence of alumina - or alumina-cobalt-molybdenum catalyst at a temperature of 200-320 ° C, a pressure of 1.0-3.5 MPa, a volumetric feed rate of 1-10 hour ^-1 and then the hydrotreated heavy fraction is mixed with a light fraction.

(Patent of the Russian Federation No. 2242501, С10G 45/08, 2004)

The disadvantages of this method include the need for preliminary stabilization of the wide unstable gasoline fraction of catalytic cracking (extraction of C ₃ -C ₄ hydrocarbons) and the inability to obtain a marketable gasoline component with a sulfur content of less than 0.005% wt. and the impossibility of processing raw materials with a sulfur content of more than 0.2% wt.

There is also known a method for purifying catalytic cracking gasoline, in which a wide gasoline fraction of catalytic cracking NK - 205 ° C is divided into a light fraction NK - 120 - 140 ° C and a heavy fraction 120 ÷ 140 ° C - KK. The unstable heavy fraction is hydrotreated in the presence of an oxide-sulfide catalyst at a pressure of 2.8-4.5 MPa and a temperature of 250-330 ° C, returned to the main fractionation column and then stabilized (by recovering C ₃ -C ₄ hydrocarbons) together with non-hydrotreated light fraction. The sulfur content in a stable wide gasoline fraction when using the described method is 0.1-0.15% wt. with saved or slightly lost octane.

(Patent of the Russian Federation No. 2134287. С10G 55/06. 1999)

The disadvantages of this method include the impossibility, while maintaining or slightly reducing the octane number, of obtaining a component of marketable gasoline with a sulfur content of less than 0.005% by weight, as well as a high sulfur content in the C ₃ -C ₄ gas product.

The closest in technical essence to the proposed one is a method for hydrotreating gasoline fractions of catalytic cracking, according to which the wide gasoline fraction NK - 205-215 ° C is divided into 3 fractions: light NK - 60-70 ° C, average 60-70 ° C - 150- 160 ° С and heavy 150-160 ° С - КК. The heavy fraction is subjected to hydrofining in the presence of an oxide-sulfide catalyst at a pressure of 2.8-4.5 MPa and a space velocity of 3-5 h ^-1 . The resulting hydrogenate is mixed with light and medium non-purified fractions to obtain a stable gasoline fraction with a sulfur content of 0.07-0.09% wt.

(Patent of the Russian Federation No. 2206601, C10G 67/02, 2003)

The known method does not allow to obtain catalytic cracking products: fractions ΣC ₃ , ΣC ₄ and gasoline (component of commercial gasoline) of the required quality.

The objective of the present invention is to develop a method for purification of light fractions of secondary origin, for example catalytic cracking, which would provide the opportunity to improve the quality of the target products by reducing the sulfur content in the gas fractions ΣС ₃ , ΣС ₄ and in the gasoline fraction (commercial gasoline component), provided that octane number.

To solve this problem, a method for cleaning light fractions of secondary origin is proposed, including the separation of a wide gasoline fraction, boiling within C ₃ - 220 ° C, into light and heavy fractions, hydrofining of a heavy fraction at elevated temperature and pressure in the presence of a catalyst, desulfurization of a light fraction by extraction with alkali, fractionation of a sulfur-purified light fraction with extraction of gas fractions ΣС ₃ and ΣС _{4 from it} and subsequent mixing with a hydrotreated heavy fraction.

Moreover, light fraction desulfurization is preferable to be carried out in two stages using an alkaline solution of monoethanolamine in the first stage and a sodium hydroxide solution in the second stage. According to the proposed method, the light fraction boils in the range from C ₃ to 40-95 ° C, mainly to 60-80 ° C, and the heavy fraction boils in the range from 40-95 ° C to 220 ° C, mainly from 60-80 ° C up to 220 ° C, and hydrofining of the heavy fraction is carried out in two stages at a temperature of 220-380 ° C, a pressure of 2.0-4.5 MPa using a catalyst at the first stage containing Mo and Co and / or Ni compounds as active components in the active sulphidic form supported on Al ₂ O _3, and the second stage catalyst containing as active component ENTOV compound of Mo and Co and / or Ni in an active form sulfide supported on a carrier consisting at 1-90% by weight. from zeolite type ZSM-5 or mordenite in hydrogen form and Al ₂ About ₃ - the rest.

A significant difference of the claimed technical solution is that a wide gasoline fraction is boiled off, boiling within C ₃ - 220 ° C, and the light fraction is subjected to desulfurization before mixing with the hydrotreated heavy fraction by extraction with alkali and then fractionation with extraction of gas fractions ΣС ₃ and ΣC ₄ .

These differences make it possible to obtain a commercial gasoline component with a sulfur content of less than 0.005% by weight when cleaning light fractions of secondary origin. subject to preservation of its octane number, as well as commodity fractions ΣС ₃ and ΣС ₄ , characterized by the absence of hydrogen sulfide content and containing residual mercaptan sulfur in amounts of not more than 0,0002% wt.

An analysis of the known technical solutions regarding cleaning methods for light fractions of secondary origin shows that the claimed combination of essential features is new and allows us to solve the problem.

The proposed method for cleaning the quality of light fractions of secondary origin is as follows.

Unstable catalytic cracking gasoline C ₃ - 220 ° C on the gas fractionation unit of the catalytic cracking unit is divided into a light fraction C ₃ - 40-95 ° C, mainly C ₃ - 60-80 ° C, and a heavy fraction 40-95-220 ° C, mainly 60-80-220 ° C.

The light fraction is subjected to desulfurization by extraction with alkali, preferably in a two-stage scheme. Sulfur compounds present in the light fraction are hydrogen sulfide and mercaptans. At the first stage, hydrogen sulfide is removed by an amine reagent, for example, an alkaline solution of monoethanolamine. At the second stage, mercaptan sulfur is removed with a sodium hydroxide solution. As a result of the purification, the sulfur content in the light fraction decreases, while its octane characteristics are preserved, and there is no hydrogen sulfide after purification. The sulfur-purified light fraction is sent to a fractionation column, where ΣС ₃ and ΣС ₄ gas fractions are extracted from it.

The heavy fraction is sent to hydrofining. The hydrotreating is preferably carried out according to a two-stage scheme in two successively bound reactors, in the first of which a hydrotreating catalyst is loaded, containing Mo and Co and / or Ni compounds in active sulfide form as active components supported on Al ₂ O ₃ , the catalyst is loaded in the second reactor containing active compounds of Mo and Co and / or Ni in active sulfide form as active components, supported on a carrier consisting of 1-90% by weight, mainly 65-80% by weight, of ZSM-5 type zeolite or mordenite and in hydrogen form and Al ₂ O ₃ - the rest.

In the first stage (in the first reactor), the hydrofining process is carried out at a temperature of 220-350 ° C, mainly 250-330 ° C, a pressure of 2.0-4.5 MPa, mainly 2.2-3.0 MPa, in a stream of circulating hydrogen-containing gas, the flow rate of which provides a volume ratio of 100-1000 l / l of raw materials, mainly 150-250 l / l of raw materials, the hydrogen content in the circulating hydrogen-containing gas in the range of 70-95% vol., mainly 75-85% vol., volumetric feed rate raw materials 1-10 hour ^-1 , mainly 2-5 hour ^-1 . Under these conditions, hydrotreating reactions from sulfur compounds occur.

In the second stage (in the second reactor), the hydrofining process is carried out at a temperature of 250-380 ° C, mainly 280-350 ° C, a pressure of 2.0-4.5 MPa, mainly 2.2-3.0 MPa, in a stream of circulating hydrogen-containing gas, the flow rate of which provides a volume ratio of 100-1000 l / l of raw materials, mainly 150-250 l / l of raw materials, the hydrogen content in the circulating hydrogen-containing gas in the range of 70-95% vol., mainly 75-85% vol., volumetric feed rate raw materials 1-10 hour ^-1 , mainly 1-3 hour ^-1 . This ensures the occurrence of cracking reactions of long-chain paraffin hydrocarbons and isomerization reactions.

As a result of hydrofining of the heavy fraction under the above conditions, the sulfur content in it decreases and there is a slight increase in the octane number.

Subsequently, the purified light fraction and the hydrobleached heavy fraction are mixed to obtain a stable commercial gasoline component.

The proposed method is illustrated by the following examples.

Example 1

Unstable catalytic cracking gasoline C ₃ - 220 ° C on the gas fractionation unit of the catalytic cracking unit is divided into a light fraction C ₃ - 65 ° C, characterized by a total sulfur content of 0.542% wt., Including hydrogen sulfide 0.5% wt. and mercaptan sulfur 0.04% wt., and a heavy fraction of 65-220 ° C, characterized by a total sulfur content of 0.28% wt.

The light fraction is sent for cleaning to a hydrogen sulfide extractor under the lower plate. A regenerated 15% solution of monoethanolamine (MEA) is fed to the upper plate of the hydrogen sulfide extractor. The extractor is equipped with plates to ensure the contact of two liquid phases, as a result of which the absorption of hydrogen sulfide from the fraction being purified by the MEA solution occurs. The C ₃ - 65 ° C fraction leaving the top of the extraction column is sent to a sump, where the hydrocarbon phase is washed with water (or steam condensate) from the entrained amine and then separated into a purified C ₃ - 65 ° C fraction and diluted amine solution. An MEA-saturated hydrogen sulfide solution from the bottom of the extractor is then sent for regeneration. The hydrogen sulfide content in the purified fraction C ₃ - 65 ° C is 0.0002% wt.

Next, the fraction C ₃ - 65 ° C purified from hydrogen sulfide is sent to the mercaptan extractor under the lower plate. A 15% sodium hydroxide solution is fed to the top plate of the mercaptan extractor. The extractor is equipped with plates to ensure contact of two liquid phases, as a result of which mercaptans are absorbed from the purified fraction C ₃ - 65 ° C.

The purified fraction C ₃ - 65 ° C, leaving the top of the extraction column, is sent to a sump, where the hydrocarbon phase is washed with water (or steam condensate) from the entrained alkali and then separated into a purified fraction C ₃ - 65 ° C and diluted alkaline solution. An alkali solution saturated with mercaptides and sulfides is sent from the bottom of the extractor for regeneration. The total sulfur content in the purified fraction C ₃ - 65 ° C is 0.00225% wt., Including hydrogen sulfide - 0.000025% wt., Mercaptans - 0.0001% wt.

The purified light fraction C ₃ - 65 ° C is then sent to a fractionation column, where it is separated into fractions ΣC ₃ , ΣC ₄ and the fraction of light gasoline C ₅ - 65 ° C. The light gasoline fraction is characterized by a sulfur content of 0.0036% wt. The octane number determined by the motor method is 86.5 points. The sulfur content in the fractions ΣC ₃ and ΣC ₄ is 0.0001 and 0.00008% wt. respectively.

The heavy fraction of 65-220 ° C is directed to hydrofining. The octane number of the heavy gasoline fraction 65-220 ° C, determined by the motor method, is 81 points.

The hydrotreating process is carried out according to a two-stage scheme in two series-connected reactors in the first of which the GO-70 industrial alumina-cobalt-molybdenum hydrotreating catalyst is loaded, temperature 260 ° C, pressure 2.3 MPa, volumetric feed rate 2.5 hours ^-1 , volumetric ratio of hydrogen-containing circulating gas 200 l / l of raw materials, the hydrogen content in the circulating hydrogen-containing gas in 85% vol., the second reactor is loaded with a catalyst containing Ni as active components in the active sul ff form applied to a carrier, consisting of 70% wt. from ZSM-5 type zeolite in hydrogen form and the rest is Al ₂ O ₃ , temperature 300 ° C, pressure 2.25 MPa, hydrogen-containing gas consumption 250 l / l of raw material, hydrogen content in the circulating hydrogen-containing gas 85% vol. and a volumetric feed rate of 2.5 hours ^-1 .

Hydrobleached fraction of heavy gasoline is characterized by a sulfur content of 0.0033% wt. and the octane number determined by the motor method 81.0.

Subsequently, the sulfur-purified fraction of light gasoline C ₅ - 65 ° C and the hydrotreated heavy gasoline fraction 65-220 ° C are mixed to obtain a stable component of marketable C ₅ - 220 ° C gasoline, which is characterized by a sulfur content of 0.00336% wt. and the octane number determined by the motor method 82.1.

The octane number of the initial fraction of catalytic cracking gasoline is determined by the calculation method based on the octane characteristics of the sulfur-purified fraction of light gasoline C ₅ - 65 ° C and heavy gasoline fraction 65-220 ° C before hydrofining and amounted to 82.1 points.

The octane change in the process was 0 points.

Example 2

Unstable catalytic cracking gasoline C ₃ - 220 ° C on the gas fractionation unit of the catalytic cracking unit is divided into a light head fraction C ₃ - 75 ° C, characterized by a total sulfur content of 0.564 wt.%, Including 0.5% wt. Of hydrogen sulfide. and mercaptan sulfur 0.06% wt., and a heavy fraction of 75-220 ° C, characterized by a total sulfur content of 0.34% wt.

The light head fraction C ₃ - 75 ° C is sent to desulfurization carried out in two stages as in Example 1. The total sulfur content in the purified fraction C ₃ - 75 ° C was 0.0041% wt., Including hydrogen sulfide - 0.00002% wt., mercaptans - 0.00008% wt. The sulfur content in the fractions ΣC ₃ and ΣC ₄ is 0.00008 and 0.00005% wt. respectively.

The sulfur-purified light head fraction C ₃ - 75 ° C is then sent to a fractionation column, where it is separated into fractions ΣC ₃ , ΣC ₄ and the light gasoline fraction C ₅ - 75 ° C. The light gasoline fraction is characterized by a sulfur content of 0.0065% wt. The octane number determined by the motor method is 86.4 points.

The heavy fraction of 75-220 ° C is directed to hydrofining. The octane number of the heavy gasoline fraction 75-220 ° C, determined by the motor method, is 80.8 points.

The hydrotreating process is carried out according to a two-stage scheme in two series-connected reactors, the first of which is loaded with GO-86 industrial alumina-cobalt-molybdenum hydrotreating catalyst, temperature 270 ° С, pressure 2.4 MPa, feed volumetric flow rate 2.0 hour ^-1 , circulating volumetric ratio hydrogen-containing gas 200 l / l of raw materials, the hydrogen content in the circulating hydrogen-containing gas within 90% vol., in the second reactor loaded catalyst containing Ni and Mo as active components in active sulfide form, deposited on a carrier consisting of 75% wt. from ZSM-5 type zeolite in hydrogen form and the rest is Al ₂ O ₃ , temperature 320 ° C, pressure 2.35 MPa, the consumption of hydrogen-containing gas provides a volumetric ratio of 200 l / l of raw materials, the hydrogen content in the circulating hydrogen-containing gas is 90% ., the volumetric feed rate of 2.0 hour ^-1 .

The hydrobleached fraction of heavy gasoline is characterized by a sulfur content of 0.0030% by weight. and the octane number determined by the motor method, 80.9.

Subsequently, the sulfur-purified fraction of light gasoline C ₅ - 75 ° C and the hydrotreated heavy gasoline fraction 75-220 ° C are mixed to obtain a stable component of marketable C ₅ - 220 ° C gasoline, which is characterized by a sulfur content of 0.0042% wt. and the octane number determined by the motor method, 83.25.

The octane number of the initial catalytic cracking gasoline fraction is determined by the calculation method based on the octane characteristics of the sulfur-purified light gasoline fraction C ₅ - 75 ° C and heavy gasoline fraction 75-220 ° C before hydrofining and amounted to 82.2 points.

The octane change in the process was plus 1.05 points. From the above examples it is seen that the proposed method for cleaning light fractions of secondary origin allows to obtain a stable component of marketable gasoline with a sulfur content of not more than 0.005% wt. while maintaining or with a slight increase in the octane number of gasoline. Moreover, the sulfur content in the fractions ΣC ₃ and ΣC ₄ does not exceed 0,0002% wt.

Claims (4)

1. The method of purification of light fractions of secondary origin, including the separation of a wide gasoline fraction into light and heavy fractions, hydrofining of the heavy fraction at elevated temperature and pressure in the presence of a catalyst, followed by mixing of the light fraction and hydrofined heavy fraction, characterized in that as a wide gasoline fraction use fraction boiling in the range C ₃ - 220 ° C and a light fraction gidrooblagorozhennoy prior to mixing with the heavy fraction is subjected to desulphurization by extra tion with alkali and subsequently fractionated removing gas fractions therefrom ΣS ₃ and ₄ ΣC. 2. The method according to claim 1, characterized in that the desulphurization of the light fraction is carried out in two stages using an alkaline solution of monoethanolamine and a second solution of sodium hydroxide in the first stage. 3. The method according to claim 1, characterized in that the light fraction boils in the range from C ₃ to 40-95 ° C, mainly from C ₃ to 60-80 ° C, and the heavy fraction boils in the range from 40-95 ° C up to 220 ° C, mainly from 60-80 ° C to 220 ° C. 4. The method according to any one of claims 1 to 3, characterized in that the hydrofining of the heavy fraction is carried out in two stages at a temperature of 220-380 ° C, a pressure of 2.0-4.5 MPa, using a catalyst containing as active components of the compounds Mo and Co and / or Ni in active sulfide form supported on Al ₂ O ₃ and in the second stage of the catalyst containing as active components of the compounds Mo and Co and / or Ni in active sulfide form supported on a carrier consisting of 1-90 wt.% from zeolite type ZSM-5 or mordenite in hydrogen one form and Al ₂ O _{3 the} rest.