RU2827730C1 - Method of purifying oil from hydrogen sulphide and light mercaptans - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to methods of oxidative purification of oil and can be used in gas and oil industry. Invention relates to a method of purifying oil from hydrogen sulphide and light mercaptans, involving oxidation of hydrogen sulphide and light mercaptans with atmospheric oxygen in the presence of an aqueous ammonia solution of a phthalocyanine catalyst at temperature of 50-60 °C and pressure 0.7±0.1 MPa with subsequent separation of waste air by pressure reduction. Preheated to 50-60 °C oil and 20-30% aqueous ammonia solution with dissolved in it phthalocyanine catalyst in amount of 0.05-5 wt.% are mixed in a mixer with subsequent supply to cascade of mixers, and the catalyst composition is dosed in amount of 0.18-0.9 kg/t of oil.

EFFECT: refusal of hydrocarbon gas stripping, increased efficiency of purification in one stage from high content of hydrogen sulphide and mercaptans, reduction of specific consumption of catalyst composition and air, use of waste air with entrained hydrocarbons for heat generation.

1 cl, 1 tbl, 1 ex

Description

The invention relates to methods of oxidative purification of oil and can be used in the gas and oil producing industry, in particular in oil refineries, gas processing plants, in fields, in booster pump stations and oil treatment units.

Low-molecular mercaptans and hydrogen sulfide are highly volatile, highly toxic, have a sharp unpleasant odor and are corrosive, which creates major environmental problems during storage and transportation of hydrocarbon raw materials. According to GOST R 51858-2002, the content of hydrogen sulfide in light oils of the first type is allowed to be no more than 20 ppm, and mercaptans C ₁ -C ₂ no more than 40 ppm.

A method is known for deodorizing purification of oil and gas condensate from hydrogen sulfide and low-molecular mercaptans (RU Patent No. 2120464, published on 20.10.1998) by oxidizing them with atmospheric oxygen in the presence of an aqueous-alkaline solution of a phthalocyanine catalyst, which includes continuously introducing into the feedstock calculated quantities of an aqueous-alkaline solution of the catalyst (25-45% aqueous alkali solution and 0.15-0.25% solution of phthalocyanine catalyst in water purified from dissolved oxygen or a 0.5-1.5% aqueous alkali solution), then air is introduced into the feedstock flow, the resulting mixture is maintained for 5-180 min at a pressure of 0.5-3.0 MPa and a temperature of 25-65°C, after which part of the reaction mixture containing purified feedstock, dissolved exhaust air and emulsified aqueous-alkaline solution of the catalyst is sent for mixing with the feedstock, which is carried out at a pressure of 0.2-0.5 MPa.

The main disadvantages of the known method are the impossibility of using it to clean heavy oils from high content of hydrogen sulfide and mercaptans due to the formation of a difficult to separate emulsion of oil and an aqueous solution of alkali, as well as the high specific consumption of alkali, which is irretrievably consumed in the reaction with hydrogen sulfide.

A method for preparing hydrogen sulfide-containing oil is known (RU Patent No. 2269566, published 10.02.2006). The method for preparing hydrogen sulfide-containing oil by stepwise separation and stripping with hydrocarbon-containing gas in the final separation stage, followed by oxidation of hydrogen sulfide and light mercaptans with atmospheric oxygen dissolved in the feedstock under pressure up to 2.5 MPa, in the presence of aqueous alkaline or aqueous ammonia solutions of phthalocyanine catalysts at a temperature of 20-70°C and then separation of exhaust air by reducing the pressure, wherein exhaust air containing 40-75% light hydrocarbons is used as the hydrocarbon-containing gas for stripping (selected as the closest analogue).

The disadvantage of the known method is high pressure, the need to use hydrocarbon gas for purging, the possibility of making mistakes in the process of preparing the catalytic composition directly at the hydrogen sulfide and mercaptan purification unit, low speed and efficiency of the purification process due to the process occurring in the pipe and separator. In addition, the introduction of an ammonia solution of the catalytic composition before the raw material pump quickly puts the seals of the centrifugal raw material pump out of working order and leaks of pumped products are formed.

The technical objective of the claimed invention is to create an effective technology for cleaning oil from hydrogen sulfide and light mercaptans.

The technical result is the elimination of hydrocarbon gas purging, an increase in the efficiency of single-stage purification from high hydrogen sulfide and mercaptan content, a decrease in the specific consumption of the catalytic composition and air, and the use of exhaust air with entrained hydrocarbons for heat generation.

The technical result is achieved in that the method for purifying oil from hydrogen sulfide and light mercaptans includes the oxidation of hydrogen sulfide and light mercaptans with atmospheric oxygen in the presence of an aqueous-ammonia solution of a phthalocyanine catalyst at a temperature of 50-60°C and a pressure of 0.7±0.1 MPa, followed by separation of the exhaust air by reducing the pressure, while mixing oil preheated to 50-60°C and a 20-30% aqueous ammonia solution with a phthalocyanine catalyst dissolved in it in an amount of 0.05-5 wt.%, in a mixer with subsequent feeding to a cascade of mixers, and dosing of the catalytic composition was carried out in an amount of 0.18-0.9 kg/t of oil.

Stabilized oil from the oil preparation unit or from the booster pump station, which has undergone preliminary preparation (degassing, desalination, dehydration), is fed into the heater, where it is preheated to 55°C±5°C.

Then the heated oil is fed to the mixer by a pump. Compressed air is fed to the mixer by a compressor and the calculated amount of catalytic composition (CAC) from the storage tank of the reagent dosing unit is fed by a metering pump. An aqueous solution of ammonia and a factory-made phthalocyanine catalyst is used as the catalytic composition. The composition of the catalytic composition: 20-30% aqueous solution of ammonia with a phthalocyanine catalyst dissolved in it in an amount of 0.05-5 wt.%.

The use of a ready-made catalytic composition allows to reduce the metal consumption and cost of equipment, to eliminate the human factor (errors in the preparation of the solution), thereby eliminating the risk of poor purification of petroleum products due to poorly prepared catalyst solution.

Next, the mixture of oil, CTC and dissolved air is fed into the reaction zone of the mixing reactors.

The reactor is a cascade of vertical and horizontal mixers that do not require additional capital foundations. In the reactor, at a pressure of 0.7±0.1 MPa, hydrogen sulfide present in the oil is oxidized by atmospheric oxygen in the presence of CTC to form elemental sulfur according to reactions (1) and (2). Light mercaptans are oxidized to disulfides according to reaction (3):

H ₂ S + 2 NH ₄ OH ↔ NH ₄ HS⋅NH ₄ OH + H ₂ O (1)

NH ₄ HS + 0.5 O ₂ S + NH ₄ OH (2)

2 RSH + 0.5 O2 RSSR + H2O (3)

After mixing, the oil purified from hydrogen sulfide and mercaptans enters a buffer tank, where the exhaust air is separated when the pressure drops to 0.1 MPa. The exhaust air with the entrained hydrocarbons is then sent to a heater to generate heat, and excess air is discharged to a flare, and the oil is pumped out to the consumer.

The basic technological scheme of the installation is shown in Fig. 1.

Oil heating is carried out in a flow heater 1. At the entrance to heater 1, a sampler 2 is provided for measuring the content of hydrogen sulfide and light mercaptans in the original oil.

Oil supply can be carried out both in continuous and periodic mode as raw materials accumulate at the stage of oil preparation in the oil treatment plant or booster pump station in the buffer tank.

Oil heated to 55°C±5°C (the temperature is controlled by means of temperature sensor 3) is pumped by pump 4 into static mixer 5. The oil flow rate is regulated by means of flow regulator 6.

From the container of the reagent dosing unit 7, the KTK is fed by the dosing pump 8 into the mixer 5. Air is also pumped there by the compressor 10. The flow rate of the KTK and air is regulated by means of flow regulators 9 and 11, respectively.

The mixture of oil, CTC and air from mixer 5 is fed to reactor 12, where hydrogen sulfide and light mercaptans are oxidized by atmospheric oxygen for 10-15 minutes under a pressure of 0.5-1 MPa. The temperature and pressure in the reactor are monitored by sensors 13 and 14, respectively. At the outlet of the reactor, an oil sample is taken by sampler 15 to measure the residual content of hydrogen sulfide and light mercaptans. After the reactor, the oil is fed to separator 16, where air and water are separated from the oil. Air is then directed to the heater, and the excess is discharged onto the candle. The pressure and oil level in the separator are monitored by sensors 17 and 18, respectively. At the outlet of the separator, a control sample is taken by sampler 19 to measure the residual content of hydrogen sulfide and light mercaptans.

Example of implementation of the invention

The oil was processed after preliminary treatment at the UPN unit. The oil consumption was 165 tons/day (6.88 tons/hour). Air consumption was 7 ^nm3 /hour. The CTC was dosed in the amount of 0.18-0.9 kg/t of oil. The CTC was a product manufactured in accordance with Russian Patent No. 2774647, published on June 21, 2022 (25% aqueous ammonia solution with a phthalocyanine catalyst dissolved in it in an amount of 0.1 wt.%).

The test results are shown in Table 1.

Table 1 - Results of the operation of the oxidation-catalytic technology for cleaning oil from hydrogen sulfide

Sampling time H2S/C1-C2RSH content in oil, ppm Specific consumption of CTC
kg /t.n. Oil temperature in reactor, °C Reactor pressure,
kgf/ ^cm2 Entrance to the reactor Exit from the reactor 1 2 3 6 7 8 1 day 10.00 598/110 0.9 59 7 10.30 3/20 0.9 59 7 15.45 0/15 0.9 59 6 17.15 0.9 59 8.5 19.30 0.9 59 8.5 Day 2 9.20 573/98 0.8 56 8.3 9.50 20/29 0.8 56 8.3 10.30 0.8 56 8 12.30 0.7 56 8 12.55 11/23 0.7 56 8 16.15 11/22 0.7 55 8.5 Day 3 8.45 596/109 0.7 55 8.6 9.15 3/19 0.7 55 8.6 11.00 8/21 0.5 54 8.5 12.00 7/22 0.4 54 8.5 Day 4 8.20 567/93 0.3 55 7.3 8.50 0/19 0.3 55 7.3 9.45 0/18 0.25 55 7.3 Day 5 10.45 573/100 0.18 55 7.1 11.15 0/15 0.18 55 7.1

The residence time of oil in the reactor is approximately 10-15 minutes depending on the productivity (oil consumption). As can be seen from the table, the proposed processing technology provides purification from hydrogen sulfide from 600 to less than 20 ppm, and from mercaptans from 100 to less than 30 ppm in 10-15 minutes with a specific consumption of CTC and air 2-3 times less than in the analogue.

The dosage of the CTC is carried out after the raw material pump, which allows to increase the service life of the pump, as a result the risk of leaks of petroleum products containing sulfur compounds and the catalytic composition containing ammonia is reduced. Thus, the safety of production is increased.

Heating at the initial stage of purification allows for more efficient dissolution of air and mixing of CTC in heated oil, improving the efficiency of catalytic technology and reducing the specific consumption of CTC and air by 2-3 times.

The use of a cascade of mixers ensures complete and high oxidation speed of hydrogen sulfide and light mercaptans, reduces metal consumption and the cost of the technology, makes it possible to abandon capital foundations and build block mobile installations for cleaning oil from hydrogen sulfide and mercaptans.

Claims (1)

A method for purifying oil from hydrogen sulfide and light mercaptans, including the oxidation of hydrogen sulfide and light mercaptans with atmospheric oxygen in the presence of an aqueous ammonia solution of a phthalocyanine catalyst at a temperature of 50-60°C and a pressure of 0.7±0.1 MPa, followed by separation of the exhaust air by reducing the pressure, characterized in that oil preheated to 50-60°C and a 20-30% aqueous ammonia solution with a phthalocyanine catalyst dissolved in it in an amount of 0.05-5 wt.% are mixed in a mixer, followed by feeding into a cascade of mixers, and the catalytic composition is dosed in an amount of 0.18-0.9 kg/t of oil.