RU2230096C1 - Method of removing sulfur compounds from light hydrocarbon fractions - Google Patents

Abstract

FIELD: petroleum processing and petrochemistry. SUBSTANCE: method is implemented using aqueous alkali solutions containing polar organic additives selected from the alcohol series and oxidizing sulfur compounds with oxygen-containing gas (air) at 10 to 80(r) and pressure up to 3.0 MPa in presence of cobalt phthalocyanine as oxidation catalysts. Polar organic additives are added to water-alkali solution in amounts 4.5 to 80%. Water-alkali phthalocyanine is supplemented by mono- and dialkylamines, amides, polyamines, and their combinations in amounts up to 3%. Alcohol additives are selected from water-soluble C1-C3-alcohols, glycols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycols), glycerols, ethanolamine, glucose, and sugars. Aqueous alkali solution contains 3 to 20% hydroxides and up to 10% sodium, potassium, and ammonium thiosulfates and sulfates. EFFECT: enabled simultaneous removal of mercaptans, hydrogen sulfide, carbon oxisulfide, and carbon sulfide and expanded resource of useful polar additives. 5 cl, 1 tbl, 5 ex

Description

The invention relates to the purification of refined petroleum products and gas condensate from sulfur compounds and can be used in the gas and oil refining industries.

Known methods for the purification of hydrocarbons from mercaptans (RSH) by oxidizing them to disulfides with oxygen (air) in the presence of phthalocyanine catalysts in an alkaline environment [1. Agaev G.A., Nastena V.I., Saidov Z.D. Oxidative processes for the purification of sulfur dioxide and hydrocarbon condensates. // M .: Subsoil. 1996. - 301 p.].

The process of absorption of carbon sulfide (COS) and carbon disulfide (CS ₂ ) by an alkaline solution is described [2. Process gas cleaning. Edition 2, ed. Semenova T.A. and Leites I.L. // M .: Chemistry. 1977. - 488 p.]:

These reactions are irreversible, but proceed slowly, therefore, to increase the speed of reactions, processes must be carried out when heated to 60-80 ° C. The hydrolysis rate of CS _{2 is} approximately three orders of magnitude lower than the hydrolysis rate of COS, for the complete extraction of CS ₂ , prolonged contact of the gas with an alkaline solution is required, which is the main disadvantage of alkaline treatment of gases and liquid hydrocarbons from CS ₂ .

A method is described for purifying hydrocarbon feedstocks from mercaptans by oxidation with an oxygen-containing gas in an aqueous alkali solution when heated in the presence of a phthalocyanine catalyst with a polar additive, using metal bromide of variable valency I, VI and VII of the periodic system or its complex with ethanolamine. The process is carried out at 20-90 ° C and pressure from atmospheric to 100 atm [3. A.S. (USSR) No. 513069. Kl. With 10 G 27/06, 1974. The method of purification of hydrocarbons from mercaptans. / Mazgarov A.M., Tukov G.V., Fomin V.A., Akhmadulina A.G. // BI No. 17. 1976].

It is known that CS ₂ reacts with MEA to form N-ethyl ethyl dithiocarbamic acid

When heated, this acid regenerates back to the MEA with a yield of up to 50%, i.e. in this method, absorption of a portion of CS _{2 by} monoethanolamine may take place. However, in the description of the invention (a.s. 513069, 1978), COS and CS _{2 are} not discussed. At temperatures of 80-90 ° С, the rate of reactions (1) - (3) increases sharply, however, with increasing temperature above 70 ° С, the extraction of mercaptans with alkaline solutions sharply decreases due to the reversibility of the reaction RSH + NaOH↔RSNa + Н ₂ О. For extraction mercaptans the optimum temperature is up to 45 ° C. In addition, the disadvantage of this method is the use of deficient bromides and a low degree of purification of raw materials from CS ₂ at temperatures up to 65 ° C.

The closest to the proposed technical essence and the achieved results is a method of purification of hydrocarbon materials from mercaptans by oxidizing the latter with an oxygen-containing gas in an aqueous alkali solution when heated in the presence of a phthalocyanine catalyst and a polar additive, which is used diethylene glycol (DEG) and triethylene glycol (TEG) or mixtures thereof in an amount of 0.5-4.0% of the volume of an aqueous solution of alkali [4. A.S. (USSR) No. 823418. Kl. With 10 G 27/06, 1978. A method for purifying hydrocarbon materials from mercaptans. / Mazgarov A.M., Fomin V.A., Fakhriev A.M., Neyaglov A.V. // BI No. 15. 1981].

In the presence of DEG and TEG, the oxidation rate of mercaptans increases by 1.2–2 times.

The disadvantage of this method [4] is the low efficiency (low speed) of purification of raw materials from carbon disulphide and carbon sulfide with the simultaneous presence of them in the raw material along with mercaptans and hydrogen sulfide. So, for decomposition of CS ₂ by 60% in a solution in pentane, it is necessary to mix this solution with an alcohol-alkaline solution for ~ 3 hours at 60 ° C.

The objective of the invention is the simultaneous purification of hydrocarbon materials (liquefied gases, petroleum distillates, benzene, etc.) from mercaptans, hydrogen sulfide, carbon sulfide and carbon disulfide, as well as expanding the raw material base of the used polar (alcohol) additives.

According to the invention, the solution of the problem is achieved by treating the hydrocarbon feed with aqueous-alkaline catalyst solutions containing polar organic additives, and oxidizing the mercaptides and sulfides with atmospheric oxygen at 10-80 ° C and atmospheric pressure to 3.0 MPa. As catalysts, cobalt phthalocyanines are used in an amount of up to 0.1% and water-soluble mono- and dialkylamines and amides containing up to 8 carbon atoms in the molecule and polyamines (urotropine, melamine, etc.), in an amount of up to 3%. The aqueous-alkaline solution contains in an amount of 5 to 80% polar organic additives from the class of alcohols.

Technologically, the hydrocarbon feed purification process can be carried out in two versions: using a homogeneous solution of alcohols in aqueous alkali and using polymer alcohols impregnated with aqueous alkali with catalysts, called a heterogeneous catalyst. In a homogeneous embodiment, water-soluble low molecular weight C ₁ -C ₃ alcohols, glycols (ethylene glycol, DEG, TEG and propylene glycol), glycerins, ethanolamines and sugars (glucose, xylitol, sorbitol, sucrose, etc.) are used as alcohol additives, which are introduced in an aqueous alkaline solution of the catalysts in an amount of 4.5-30%. In a heterogeneous embodiment, using water-insoluble polymer alcohols, cellulose and its modified forms, they are impregnated with aqueous-alkaline solutions of the same catalysts. The amount of the alcohol component (the basis of a heterogeneous catalyst) in this embodiment can be 50-80% of the total alcohol-water-alkaline mass. A simultaneous use of a water-soluble alcohol and a polymer alcohol is possible, for example, 4.5-10% alcohol additives are introduced into a water-alkaline catalyst solution, and cellulosic material taken in an amount of 20-50% of the solution is impregnated with this solution.

A distinctive feature of the proposed method is the introduction into the aqueous-alkaline solution of the catalysts 4.5-80% alcohol components (additives): 4.5-30% when using water-soluble alcohols, 50-80% when using water-insoluble polymer alcohols, cellulose and its modified forms and 30-50% when using mixtures of soluble and insoluble alcohols.

An additional distinguishing feature of the proposed method is the introduction into the alcohol-water-alkaline solution of a phthalocyanine catalyst of water-soluble low molecular weight (C ₁ -C ₈ ) mono- and dialkyl amines, polyamides and amides in an amount of up to 3%, i.e. the introduction of an additional amine or amide catalyst. The use of other alcohols besides DEG and TEG, including polyatomic alcohols, makes it possible to expand the raw material base of the reagents used and their costs. So, ethylene glycol and sugar (sucrose) are 2-4 times cheaper than DEG and TEG.

These distinctive features of the proposed method determine its novelty and inventive level in comparison with the prior art. When cleaning hydrocarbon feeds from H ₂ S, RSH, COS, and CS ₂ using atmospheric oxygen for oxidation, the introduction of an alkaline phthalocyanine catalyst of alcohols in an amount of 4.5-80% in the patent and scientific literature is not described. Introduction to the alcohol-water-alkaline solution of phthalocyanine catalysts of additional catalysts (alkyl amines and amides) in an amount of up to 3% is also not known, it is proposed for the first time.

It is known that alcohols react with carbon disulfide in an alkaline environment with the formation of xanthates

However, this reaction in dilute alkaline solutions even with a large excess of ROH proceeds slowly, especially in the presence of an organic hydrocarbon phase in which CS ₂ dissolves incomparably more than in the aqueous phase.

In the presence of amines and amides, reactions occur.

It turned out that the rate of reactions (4) and (5) is much higher than the rate of reactions (1) and (3), and an almost stoichiometric amount of amines is sufficient for the binding of COS and CS ₂ . Therefore, during the purification of liquefied gases and oil distillates from sulfur compounds, the introduction of up to 3% of amines and amides into alcohol-water-alkaline solutions (extractants) ensures the extraction of not only H ₂ S and RSH, but also COS and CS ₂ . In an alcohol-water-alkaline solution with a large excess of alcohol, amines are restored by a slow reversible reaction:

those. amines and amides essentially catalyze reaction (3). Reactions (1-6) are well studied when using KOH as an alkaline agent. The consumption of amines and amides depends on the content of COS and CS ₂ in the feed and on the required degree of purification of the feed from these impurities. The total content of COS and CS ₂ in liquefied gases is 20-200 ppm, sometimes it can reach up to 500 ppm. The volumetric ratio of hydrocarbon feed and alcohol-water-alkaline solution is 100: (10-25). Hence, the content (in moles) of amine or amide in the alkaline solution should be 4-10 times higher than the content of CS ₂ and COS in the hydrocarbon phase (20 ppm or more). Therefore, the minimum concentration of RNH ₂ or R ₂ NH in an alkaline solution can be taken equal to 0.01% (100 ppm). An increase in the concentration of RNH ₂ above 3% is not necessary. The introduction of an amine (amide) catalyst is required when the alcohol content in the alkaline solution is low (4.5-10%) and, if necessary, accelerate the decomposition reaction of CS ₂ . With a large (20-30%) alcohol content and possibly long (up to 1 hour) mixing, the process can be carried out without the introduction of amine (amide) additives. As in the known methods, NaOH, KOH, NH ₄ OH are used as the alkaline agent, solutions with an alkali content of 3-20% are used. As phthalocyanine catalysts, sulfo-, disulfo-, -tetrasulfo, -dichlorodioxio-disulfo-and cobalt polyphthalocyanines are used. Phthalocyanines are introduced into the solution in an amount of 0.01-0.1%.

The temperature limits of the process (10-80 ° C) and a pressure of 0.1-3.0 MPa are taken as in the known methods, are not distinguishing features. In the absence of CS ₂ and COS in the feedstock, the extraction of mercaptans can be carried out at 10–40 ° С, in the presence of COS a temperature of 45–65 ° С is required, and in the presence of large quantities of CS ₂ (more than 20 ppm) a temperature of 55–80 ° С . A high temperature of 70-80 ° C can be applied only with a low concentration of mercaptans and a high concentration of COS and CS ₂ , when demercaptanization is not a primary problem. It is known [1] that with increasing temperature and the concentration of the phthalocyanine catalyst, the rate of oxidation reactions increases (3-4 times for every 10 ° C). An increase in gas pressure over liquids increases the solubility of air oxygen in the liquid phase, which accelerates the oxidation reactions involving oxygen (see reactions 7–9).

In the known method, DEG and TEG are introduced into an alkaline solution in an amount of 0.5-4.0%. In the proposed method, it is proposed to introduce more than 4.5% alcohol additives. With the introduction of less than 4.5% alcohols, their effect on the degree of extraction of RSH and on the rate of decomposition of CS ₂ becomes subtle. The introduction of 10-30% alcohols allows you to extract from the raw material more heavy mercaptans (C ₄ and above), as well as more COS and CS ₂ . However, with the introduction of more than 20-30% of low molecular weight alcohols, their losses increase (entrainment of alcohols with a hydrocarbon phase), which is not economically advantageous.

The technology of a homogeneous version of the purification of raw materials from sulfur compounds includes the following stages:

1). extraction of H ₂ S and RSH with an alkaline solution with simultaneous decomposition and absorption of COS and CS ₂ according to reactions (1-5);

2). oxidation of the formed Na ₂ S, RSNa and ROC (S) SNa and RNHOS (S) Na in an alcohol-water-alkaline solution containing phthalocyanine catalysts with atmospheric oxygen according to the reactions

3). separation of the resulting disulfides from the alcohol-water-alkaline solution and the return of this solution to the extraction stage. With repeated recirculation (return to the process), thiosulfates and sulfates formed by reaction (7) accumulate in an alkaline solution. Their presence does not interfere with the extraction and oxidation processes; on the contrary, it favors the separation of the alcohol-water-alkaline phase from the organic phase (sulfate salts are demulsifiers). The concentration of thiosulfates and sulfates is permissible up to 10%, i.e. alcohol-water-alkaline solution may contain 3-10% hydroxides and up to 10% thiosulfate and sulfate of alkali metals and ammonium.

The stages of extraction and oxidation can be combined. However, in this embodiment, disulfides remain in the purified feed. In this embodiment, air is fed into a mixture of hydrocarbon feed and an alkaline solution; extraction and oxidation processes occur simultaneously in both phases: organic and inorganic.

Solid catalysts can also be used in the oxidation step in which the phthalocyanines are supported on the surface of the support. Activated carbons and carbon fiber materials are used as such a carrier.

In the heterogeneous embodiment, reactions (1-9) occur on the surface of the catalyst mass, disulfides of the type R'O (S) SSR accumulate on the surface of the catalyst material. Therefore, periodic replacement of this material is required.

The proposed method is tested in laboratory conditions using examples of purification of model mixtures of hydrocarbons with CS ₂ and CS ₂ + RSH.

Methods for the purification of hydrocarbons from H ₂ S and RSH are studied in detail and described in the patent and scientific literature [1-4]. Of the above sulfur compounds, the most difficult to extract and difficult to oxidize is CS ₂ . Therefore, the examples show the results of experiments on the purification of raw materials mainly from CS ₂ . In conditions where a 30-50% purification of raw materials from CS _{2 is} achieved, the remaining sulfur compounds (H ₂ S, RSH and COS) are practically removed (neutralized) and completely oxidized.

EXAMPLE 1

Model solutions of CS ₂ in pentane and hexane with a sulfur concentration of 100-300 ppm are prepared.

In a flat-bottomed flask with a capacity of 200 ml at a temperature of 5-15 ° C, take 10-14 ml of a 5-20% NaOH solution containing 0.01% cobalt dichlorodioxidisulfophthalocyanine. The calculated amount (0.5-5 g) of the alcohol additive and up to 0.4 g of the amine or amide catalyst are also introduced here. 85 ml of the CS ₂ model solution is introduced into the flask, tightly closed with a rubber stopper and, at a certain temperature, the contents are stirred on a magnetic stirrer for 1 hour.

и соли N-алкилдитиокарбаминовой кислоты

титруются как меркаптиды. Результаты опытов приведены в таблице.At certain intervals (5, 10, 30 and 60 minutes) samples are taken from the flask for analysis. The hydrocarbon phase analysis for the content of CS _{2 is} carried out chromatographically, the total sulfur content is determined on a Spectroscan instrument. The content of sulfides (Na ₂ S) and mercaptides (RSNa) in the water-alkaline phase is determined by potentiometric titration according to GOST 17323-71. In this case, xanthates

and salts of N-alkyldithiocarbamic acid

titrated as mercaptids. The results of the experiments are shown in the table.

In experiments No. 10-17, in addition to an alcohol supplement, amine or amide catalysts were introduced into an alkaline solution.

In parallel, for comparison, experiments are carried out without the addition of alcohol and amines (No. 1) and the experiment by the known method (No. 17) with the addition of 3.5% DEG. After sampling for analysis, the aqueous solution is separated from the hydrocarbon solution and regeneration is carried out: at 75 ± 5 ° C, air is bubbled through the aqueous solution for 15 minutes. In this case, xanthates and thiocarbamates are oxidized to Na ₂ S ₂ O ₃ and disulfides, and amines are regenerated, the regenerated alkaline solution can be used to prepare alkaline solutions for the experiments shown in the table.

EXAMPLE 2

As a feedstock, the NK-120 ° C fraction obtained from gas condensate and containing 320 ppm mercaptan sulfur and 212 ppm sulfur CS _{2 was used} . To absorb RSH and CS ₂ , a 15% NaOH solution containing 5% ethylene glycol was used. 0.02% cobalt disulfophthalocyanine (DSFC) and 0.66% diethylamine (DEA) are additionally added to this solution. 20 ml of this solution are taken into a 200 ml flask and the NK-120 ° C gas condensate fraction cooled to 5-10 ° C is introduced in an amount of 100 ml. The flask was tightly closed with a rubber stopper and the contents were stirred at 45 ° C for 1 hour. After the aqueous layer is separated from the hydrocarbon. The flask with the aqueous extract was filled with oxygen and heated to 55 ° C with stirring and allowed to stand for 10 minutes. In this case, mercaptides, xanthates and thiocarbamates are oxidized to disulfides. After that, a second portion of the NK-120 ° C fraction is introduced into the flask with an alkaline solution, a second experiment (extraction and oxidation) is carried out, etc., i.e. in subsequent experiments, the spent alkaline solution from the previous experiment is used. The results are shown in the table (No. 17).

As can be seen from the table (No. 1 and 18) in the absence of alcohol additives, the content of CS ₂ during extraction is almost unchanged, and when the content of 3.5% DEG by the known method is reduced by only 28%. In the presence of 20-30% alcohols in an alkaline solution, the degree of purification from CS ₂ for 1 hour is 60-80% (No. 3-7). With a content of 5% ethylene glycol (EG) or DEG, the degree of purification does not exceed 60%. In experiments No. 10-17, where in addition to alcohol additives, an amine or amide catalyst is introduced, the degree of purification from CS ₂ can be increased to 90 percent or more.

Experience No. 17 according to example No. 17 shows that when the content in the alkaline solution of ~ 1% amine catalyst, the alkaline solution can be used repeatedly with good results on the purification of raw materials from CS ₂ . In the purified solution, mercaptan was absent in these experiments.

EXAMPLE 3

As a feedstock, the NK-120 ° C fraction obtained from gas condensate and containing 320 ppm mercaptan sulfur and 212 ppm sulfur CS _{2 was used} . Apply an alkaline solution with a content of: NaOH = 4.5%; EG = 5; DSPK = 0.05%; DEA = 1.0%.

5 ml of an alkaline solution, 45 ml of the NK-120 ° C fraction with a temperature of 0-5 ° C are taken into a 100 ml round-bottom flask. The remaining space of the flask is filled with oxygen from the cylinder.

The contents of the flask are heated to 70 ° C and stirred by shaking. In this case, RSH and СS _{2 are} simultaneously extracted from the organic phase into the aqueous phase and the mercaptides, xanthates and carbamates are oxidized. Due to the evaporation of low-boiling hydrocarbons, the pressure in the flask rises to 2-2.2 atm. In this case, part of the oxygen is dissolved in liquids.

After 10 minutes, the contents of the flask were cooled and the hydrocarbon and aqueous phases were analyzed.

In hydrocarbon: RSH - exc.,

CS ₂ - 12 ppm,

  disulfide sulfur: RSSR - 312 ppm,

In the aqueous phase: RSNa - 18 ppm,

CS ₂ - traces

sulfide sulfur (Na ₂ S) - 158 ppm.

The alkaline aqueous phase is separated from the hydrocarbon phase and used for the second experiment.

EXAMPLE 4

A 200 ml glass column equipped with a heating coil is filled with cotton wool (cellulose). A solution is prepared with a NaOH content of 10%, urotropine 2.5%, cobalt dichlorodioxidisulfophthalocyanine 0.05%.

A column of cotton wool is filled with this solution and incubated for 2 hours at 40-45 ° C. After the alkaline solution is drained, the column is purged with nitrogen. The remaining cellulose pulp impregnated with an alkaline solution in the column consists of 77% cellulosic material (cotton wool) and 23% aqueous alkaline catalyst solution.

At a temperature of 55-60 ° C, a model solution of CS ₂ in hexane is passed through the column at an average rate of 0.03 min ^-1 .

Analyze the content of CS ₂ (total sulfur) in the inlet and outlet of the column solutions on the instrument “Spectroscan-S”.

Results: at S _inlet = 132 ppm for 15 hours at the outlet of the column, the sulfur content of S _output does not exceed 20 ppm.

EXAMPLE 5

As a raw material, a wide fraction of light hydrocarbons is used with a content of: mercaptan sulfur - 300 ppm, COS sulfur - 62 ppm, CS ₂ sulfur - 120 ppm. An alkaline solution is prepared with a content,%: NaOH - 18.0; monoethanolamine - 5.0; urea - 2.0; cobalt sulfophthalocyanine - 0.08; glycerin - 8.0.

A 200 ml glass column equipped with a heating coil is filled into 2/3 of the volume with cotton wool (cellulose). The column is filled with an alkaline solution. Withstand 1 hour at 25 ° C, after the solution is drained.

The pulp impregnated with the alkaline solution remaining in the column consists of 46% cellulose and 54% alkaline solution. Through the column from bottom to top pass with a speed of 0.02 min ^-1 NGL and air with the same speed at a temperature of 65 ± 5 ° C. Volume ratio of BFLH: air 1: 1.

In purified BFLH, mercaptans and COS are absent, the content of CS ₂ does not exceed 10 ppm.

Claims (5)

1. The method of purification of light hydrocarbon fractions from sulfur compounds - mercaptans (RSH), hydrogen sulfide (H ₂ S), carbon sulfide (COS) and carbon disulfide (CS ₂ ) by treatment with aqueous alkali solutions containing organic polar additives from the class of alcohols, and oxidation sulfur compounds with an oxygen-containing gas (air) at a temperature of 10-80 ° C and pressure up to 3.0 MPa in the presence of oxidation catalysts - cobalt phthalocyanines, characterized in that the polar organic additives are introduced into the aqueous alkaline solution in an amount of 4.5-80% . 2. The method according to claim 1, characterized in that mono- and dialkylamines, amides, polyamines, mixtures thereof in an amount of up to 3% are additionally introduced into the aqueous-alkaline solution of the phthalocyanine catalyst containing alcohol additives. 3. The method according to claims 1 and 2, characterized in that water-soluble low molecular weight C ₁ -C ₃ alcohols, glycols (ethylene glycol, diethylene glycol, triethylene glycol and propylene glycols), glycerins, ethanol are used as an alcohol additive to an aqueous solution of alkali and cobalt phthalocyanine glucose and sugar. 4. The method according to claims 1 and 2, characterized in that they use high molecular weight polymer alcohols, cellulose and its modified forms, which are impregnated with an aqueous-alkaline solution of cobalt phthalocyanines and amine-amide catalysts. 5. The method according to claim 1, characterized in that the aqueous alkali solution containing polar organic additives contains 3-20% hydroxides and up to 10% thiosulfates and sulfates of sodium, potassium and ammonium.