SU1728790A1 - Method for determination hydrogen sulfide and mercaptans in oil - Google Patents

Abstract

This invention relates to analytical chemistry, in particular, to methods for determining hydrogen sulfide and mercaptans in petroleum. The goal is to improve the accuracy of the method and its simplification. Equal volumes of the sample of oil and 20% sodium bicarbonate aqueous solution are placed in the reactor and heated to 75-80 ° C until the release of the desorbing gas is stopped, in the stream of which hydrogen sulfide and desorbing mercaptans are determined. After settling and separation of liquids in the reactor, the aqueous phase is separated and non-sorbing mercaptans are determined in it. 1 dw., 2 tab. cl

Description

This invention relates to analytical chemistry, in particular, to methods for determining sulfur components in petroleum and petroleum products.

There is a known method for determining hydrogen sulfide and mercaptans in a gas by successively passing the gas through acidified and alkaline solutions of cadmium chloride and subsequent separate iodometric determination of sulfide and cadmium mercaptide.

The method is inconvenient when the content of hydrogen sulfide is much higher than the content of mercaptans, usually found in natural hydrocarbon fluids.

The known method of potentiometric determination of mercaptans in diesel fuels consists in the titration of mercaptans with a standard solution of silver nitrate with potentiometric registration of the equivalence point.

The disadvantage of this method is the impossibility of determining hydrogen sulfide and the need to clean the sample from it when determining mercaptans.

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There is a known method for determining hydrogen sulfide in petroleum by its desorption with nitrogen before analysis.

The disadvantage of this method is the low degree of desorption of mercaptans.

Closest to the invention is a method for determining gaseous components dissolved in petroleum products by desorbing them to the analyzer with gas formed during the decomposition of the gasifier substance mixed with the sample of the petroleum product. An oily acid amide is used as a blowing agent, which releases nitrogen during decomposition.

The disadvantage of this method is the incomplete extraction of the components dissolved in the oil sample, especially the highly soluble ones.

The aim of the invention is to simplify the method and increase its accuracy while making it possible to determine hydrogen sulfide and mercaptans from a single oil sample.

The goal is achieved in that according to the method, the determination of hydrogen sulphide and mercaptans in oil, including the introduction of a blowing agent into the sample being analyzed, the desorption of components dissolved in oil by the gas formed during the decomposition of the blowing agent, in the desorbing gas flow, sodium bicarbonate solution is used as a gasifier substance, which is heated to 80 ° C and hydrogen sulfide and desorby dissolved in oil are desorbed with carbon dioxide formed The mercury portion of the mercaptans and the non-desorbed mercaptans remaining in the oil are converted into mercaptids by treating the oil sample with an alkaline solution formed during the decomposition of the gas-forming agent, after which the hydrogen sulfide is determined in the desorbing gas in a known manner, and the mercaptans are determined together in the desorbing gas and the alkaline solution solution or separately in them, followed by summing.the results of the definitions.

The desorption of hydrogen sulfide and the desorbing part of the mercaptans from the oil sample and the absorption of the non-desorbing part of the mercaptans by the products of thermal decomposition of sodium bicarbonate makes it possible to simplify the method and improve the accuracy of the analysis by eliminating the loss of the non-desorbing mercaptans and the single determination of mercaptans from

mixtures of mercaptids from desorption gas and alkaline solution.

The drawing shows the scheme of implementation of the method.

Volumes of a 20% sodium bicarbonate aqueous solution and a sample of the test oil are placed in the reactor 1. The reactor is placed in a thermostat 3 and through a reflux condenser 2 is connected to an analyzing

device 4, the reactor is heated to 75-80 ° C. At a temperature not lower than 75 ° С, sodium bicarbonate decomposes with the release of carbon dioxide.

2 No..CNSO3- No. 2CO3 + H20 + C02, (1)

which desorbs hydrogen sulfide and part of mercaptans from petroleum. To raise the temperature above 80 ° C is impractical because it would increase the evaporation of oil and water from an aqueous solution of sodium bicarbonate.

The resulting sodium carbonate as a result of hydrolysis creates an alkaline medium in aqueous solution.

MaOCO3 + H20Ј2Na + 20H + COzt. (2) As the hydrolysis constant increases, and the solubility of carbon dioxide decreases with increasing temperature, the equilibrium of reaction (2) shifts to the right. Formed with alkali reacts with non-desorbing

part of the mercaptans with the formation of mercaptides

RSH + NaOH - RSNa + H20. (3)

Hydrogen sulfide and mercaptans in successively connected bubblers with acidified 5 and alkaline 6 10% solutions of cadmium chloride or absorbed desorption gas are passed through the stripping gas from the stream of the stripping gas (carbon dioxide),

filled with indicators for hydrogen sulfide and mercaptans on a sorbent (indicator powders), to determine the Absorbed components in a linear-coloristic way.

After the release of carbon dioxide from the aqueous solution and bubbling through the oil sample, the reactor and bubblers are disconnected from the reflux condenser. The reactor is plugged, shaken up, and left to separate the liquids. The aqueous solution of the reaction products is quantitatively transferred to a titration flask. The alkaline solution of the mercaptids from the bubbler 6 is also transferred there.

The total content of mercaptans in the oil is determined by a standard iodometric method. The content of hydrogen sulfide from the contents of the bubbler 5 is determined in the same way.

The content of hydrogen sulfide in oil is calculated by the formula

(Vi-V2) N о.о17 1оо 0 / ,,;

CH, S., May. % (four)

The content of mercaptans in oil in terms of mercaptan sulfur is calculated according to the formula 5m (U, -U2) D0.032.100ms s and%

where in expressions (4) and (5): Vi and V2 are the volumes of sodium thiosulfate, respectively, followed by titration of the control sample and sample titration, ml;

N is the normality of sodium thiosulfate solution, mol / l;

0.017 and 0.032 are respectively the amounts of hydrogen sulfide and mercaptan sulfur, equivalent to exactly 1 ml of exactly 1 n. sodium thiosulfate solution, g;

V is the volume of oil samples, ml;

p is the density of oil, g / ml.

When using a linear-coloristic method for determining hydrogen sulfide and mercaptans, indicator tubes filled with sorbents coated with indicators for hydrogen sulfide and mercaptans graded by absolute amounts of these components (milligrams per milliliter) are connected to the outlet of the stripping gas stream from the reactor instead of bubblers.

The indicator tubes are prepared in the following way.

A saturated solution of lead acetic acid is prepared for the preparation of indicator powder for hydrogen sulfide. 90 g of acetic acid lead are added to 100 ml of distilled water in small portions with continuous stirring. Then, without stopping stirring, 12 ml of glacial acetic acid is added dropwise to the solution. The resulting turbid solution is heated to boiling and cooled. A white precipitate forms from the solution. The solution is separated from the precipitate by decantation.

To 100 g of KSK silica gel with a fraction of 0.15-0.50 mm, add 100 ml of a clear solution separated from the precipitate, and mix thoroughly. The mixture is then placed in an oven at 120 + 2 ° C and maintained, stirring occasionally with a glass rod until it is completely free of water (until constant weight).

Glass tubes with an internal diameter of 2.5 mm and a length of 70-120 mm are filled with the dried powder.

Calibrate the indicator powder. To do this, a certain volume of Vr gas with a known content of hydrogen sulfide Cn.-S is passed through the indicator tube, after which the length of the colored layer of indicator powder I is measured. The coefficient of gray intensity of the indicator powder is calculated using the formula for hydrogen sulfide

KH, S -: - mg / mm. (6)

To prepare the indicator powder for mercaptans, silica gel KSS-4 of a 0.25-0.50 mm fraction is placed in a flask, to which hydrochloric acid diluted 1: 1 is added at the rate of 3 ml of acid per 1 g of silica gel and boiled t for 1 h, then vigorously stirred with a glass rod with a rubber tip. The powder is washed by decantation in warm (50-60 ° C) distilled water to a negative reaction to

chlorine ion. The washed powder is dried in a drying cabinet at 120 ° С, and then calcined in a muffle furnace at 850-900 ° С for 2 h. The calcined and cooled powder is moistened with a 4.4% solution

copper acetate at a rate of 90 ml per 100 g of silica gel, stirred and dried at room temperature to a friable state.

Prepare a clarified sulfur solution in

benzene. Sulfur is crushed into powder, placed in a flask with a ground in stopper, poured with benzene and kept for 2 days, periodically shaking the contents of the flask.

The dried powder is moistened with a clarified solution of sulfur in benzene at a rate of 90 ml per 100 g of powder, stirred and air dried at room temperature to a friable state.

Glass tubes with an inner diameter of 2.5 mm and a length of 70-150 mm are filled with the prepared indicator powder.

The sorbent is calibrated in indicator tubes by passing through them a known volume of Vr gas with a known C content based on mercaptan sulfur, and the length of the colored layer I is measured. The gray intensity of the indicator powder is calculated by the mercaptans using the formula

Vr See, -,

Km

I

The analysis using the linear-color method is carried out in the following sequence.

Instead of bubblers 5 and 6, successively indicator tubes are connected to the outlet of the reactor using rubber couplings.

CH ,, S

respectively on hydrogen sulfide and mercaptans. Desorption from hydrogen sulfide oil and desorbing mercaptans is carried out, and staining of adsorbents in tracer tubes is observed. The length of the colored layer of adsorbents in the corresponding indicator tubes calculate the concentration of hydrogen sulfide in the oil and mercaptans in the desorption gas, wt.%:

.KH2SI. (8)

10pVW

Mr. KM Ifn

See 1 7- {9)

The non-sorbed mercaptans in the oil are determined from the aqueous phase. For this purpose, the determination of hydrogen sulphide and desorbed mercaptans in the desorption gas to the bottom valve of the reactor 1 is sealed with a rubber stopper a test tube with two lateral branches in the upper part with a capacity of 20-25 ml, which is preliminarily placed 5-7 ml of hydrochloric acid, diluted 1: 1. One of the branches is connected to an inert gas source (nitrogen, gels, etc.), to the other, an indicator tube for mercaptans, by which their content in the desorption gas or the unused indicator tube for mercaptans is determined. In the first case, the result is the content of mercaptans in the oil, in the second, if necessary, the content of non-desorbable mercaptans in the oil.

After separation of the liquids, the aqueous phase from the reactor is carefully added dropwise to the tube, ensuring that no liquid is transferred from the tube to the test tube during the reaction.

After the aqueous phase is completely drained into the tube and the reaction is terminated, the reactor valve is closed, and 5-10 times the volume of inert gas is passed through the tube and indicator tube at a rate of 5-10 ml / min. The indicator tube is disconnected from the tube and the content of the corresponding mercaptans in the oil is calculated along the length of the colored layer using formula (9).

Example 1. In reactor 1, 5 ml of 20% sodium bicarbonate solution and 5 ml of oil are placed. In the bubbler 5 is placed 50 ml of a 10% aqueous solution of cadmium chloride and 7.5 ml of 0.1 n. hydrochloric acid solution (pH of the mixture is 1.7). In the bubbler 6 placed 50 ml of a 10% aqueous solution of cadmium chloride and 7.5 ml of 0.1 n. sodium hydroxide solution (pH of the mixture is 12.3). Assemble the instrument. The reactor is placed in a thermostat 3, the temperature in which is maintained automatically at 80 ° C.

The carbon dioxide released by the thermal decomposition of sodium bicarbonate, by bubbling through oil, desorbs hydrogen sulfide and a desorbable part of mercaptans into bubblers 5 and 6 from it, in the first of which hydrogen sulfide is precipitated in the form of cadmium sulfide, and in the second - mercaptans in cadmium mercaptide form.

At the end of the carbon dioxide release in the reactor, the bubblers and the reactor are disconnected from the reflux condenser 2. The reactor is closed with a stopper, shaken to extract the non-sorbed mercaptans with an aqueous alkaline solution and leave for separation of liquids.

The lower (aqueous) phase in the reactor is separated from the oil and combined with the contents of the bubbler 6, draining it through the bottom valve into the specified bubbler.

To the contents of the bubbler 5 add 10 ml of 0.01 n. the iodine solution is agitated and transferred to a titration flask. The remaining solution in the bubbler 5 is washed with distilled water in the same flask.

The contents of the flask are titrated with 0.01 n. Sodium thiosulfate solution until light straw color is added; 2-3 drops of 0.5% starch solution are added and the titration is continued until the solution becomes colorless. In parallel, a series of control titration of the absorption solution (50 ml of a 10% cadmium chloride solution and 7.5 ml of a 0.1 N hydrochloric acid solution) was carried out. When the results of the two titrations coincide, the obtained result is used; if the results do not coincide with 0.1 ml, they conduct three-titration and take an arithmetic average of three definitions.

During the titration of the sample spent 4.25 ml 0.1 n. sodium thiosulfate solution, with the control titration - 10 ml of the same solution.

The concentration of hydrogen sulfide in the oil is calculated by the formula (4) CH ,, S 0,0246 wt.%.

10 ml of 0.1 N is added to the contents of the bubbler 6. iodine solution, shaken and left in the dark for 20-30 minutes to allow the mercaptans to react with iodine. Then 10 ml of concentrated hydrochloric acid diluted 1: 1 with water is added to the bubbler, shaken to dissolve the precipitate and transferred to a titration flask. The remaining solution in the bubbler is washed with distilled water in the same flask.

The contents of the flask are titrated with 0.01 n. sodium thiosulfate solution for starch as well as in the determination of hydrogen sulfide. Simultaneously, a control titration of the absorption solution (50 ml of a 10% cadmium chloride solution and 7.5 ml of a 0.1 N sodium hydroxide solution) was carried out.

During the titration of the sample consumed 7.35 ml 0.01 n. sodium thiosulfate solution, with control titration - 9.85; 10.05; 10.0 ml (average 9.97 ml) of sodium thiosulfate solution.

The content of mercaptans in oil in terms of mercaptan sulfur is calculated by the formula (5) 5 m 0.0211 wt.%.

PRI mme R 2. The content of mercaptans in the desorption gas and in the aqueous phase is determined separately.

All desorption of hydrogen sulfide and mercaptans is carried out as in Example 1, but the aqueous phase is drained into a separate titration flask. Barbathers

5 and 6, the same reagents were added as in Example 1. Reagents were also added to the flask with the aqueous phase to determine the mercaptans and titrated.

The results of the determinations are given in table.1.

EXAMPLE 3 A linear colorimetric method is used to determine hydrogen sulfide and mercaptans. For this purpose, indicator tubes for hydrogen sulfide and mercaptans are prepared and calibrated.

Through the indicator tube for hydrogen sulfide pass 1.5 liters of gas with a hydrogen sulfide content of 2.3 mg / l. The length of the colored layer, L, is 34 mm. According to the formula (6), the sulfur content of the adsorbent is determined by hydrogen sulfide Kniz 0.1018 mg / mm. A 1 liter of gas with a mercaptan content of 0.14 mg / l is passed through the indicator tube to the mercaptans. The length of the colored layer is 29 mm. The sulfur capacity of the adsorbent for mercaptans, calculated by the formula (7), is Km 0.0083 mg / mm. All operations for desorption of hydrogen sulfide and mercaptans from petroleum are carried out as in Example 1 with the difference that instead of bubblers 5 and

6 to the outlet of the reactor, indicator tubes are connected in series, respectively, to hydrogen sulfide and mercaptans. Using the formulas (8) and (9), the content of hydrogen sulfide and mercaptans desorbed from petroleum is calculated along the length of the colored layer: Ch s 0.0246 wt.%; 5m 0,0075 wt.%. four

A tube with two lateral branches in its upper part and with a capacity of 20-25 ml is connected to the lower valve of the reactor 1. The connection is made using

rubber stoppers. 5 ml of concentrated 1: 1 dilute hydrochloric acid are placed in the tube.

One of the tap tubes is connected to a nitrogen source, the other is connected to an indicator tube for mercaptans, by means of which their content in the gas of desorption of oil is determined.

The aqueous phase from the reactor 1 is dropwise

0 is added to the tube, ensuring that during the reaction there is no transfer of fluid from the tube to the indicator tube. After that, as the aqueous phase was completely drained from the reactor into a test tube and

5, the reaction in it was stopped, 250 ml of nitrogen were passed through the tube at a flow rate of 10 ml / min. The indicator tube is disconnected from the tube and the total length of the colored slurry, which is 0.10 mm, is measured. By the formula (9), the content of mercaptans in oil is calculated, which is 0.0211% by weight.

In order to compile a metrological examination of the method, the determination of hydrogen and mercaptans in model mixtures is carried out. Dean is used as a model of oil, and ethyl and butylmercaptan are used as mercaptans.

For the preparation of model mixtures

0 a known volume of gas with a known content of hydrogen sulfide is passed through a bubbler with a dean. Based on the difference in concentrations at the inlet and outlet of the bubbler and the volume of the leaked gas, the amount is calculated

5 hydrogen sulphide dissolved in decane.

Solutions of ethyl and butyl mercaptan in decane are prepared by dissolving each mercaptan sample in separate portions of decane. Solutions of mercaptans and sulfur doros in decane are mixed in the calculated volume ratios to obtain given concentrations in the total volume. The determination of hydrogen sulfide and mercaptans in decane is carried out according to the proposed and known methods using the iodometric method, which is arbitration.

The results of the metrological examination of this method are presented in table. 2

0 According to the results of testing the method, the arithmetic mean relative errors of determining hydrogen sulfide and mercaptans according to the proposed method are respectively

5 2.0 and 3.3%, and according to a known method, the error in the determination of mercaptans reaches 12.3% relative. Thus, the proposed method has a high convergence of results than the known methods. However, it does not require complex

equipment is simple to perform and can be used both in laboratory and in industrial conditions.

Claims (1)

Invention Formula The method for determining hydrogen sulfide and mercaptans in oil by introducing a gaseous substance into the sample to be analyzed, desorbing hydrogen sulfide and mercapot gas produced by its decomposition In order to simplify the process and increase its accuracy, an aqueous solution of sodium bicarbonate is used as a gas exponencer, desorption is carried out at 75-80 ° C, after desorption and settling water is separated. phase with the subsequent determination of non-desorbed mercaptans in it. Table 1 table 2 J |