CN107201255A - A kind of desulfurization refining method and device of mixed liquefied oil gas - Google Patents

Abstract

The invention provides a desulfurization and refining method and device for mixed liquefied petroleum gas. The refining method provided by the present invention is to pass the coked liquefied petroleum gas from the coking unit into the riser reactor of the catalytic cracking unit and carry out the cracking reaction together with the catalytic cracking feed, and then distill it from the fractionation system in the catalytic cracking unit to form a mixed Catalyze the mixed liquefied petroleum gas of liquefied petroleum gas, and then send it to hydrogen sulfide extraction device and mercaptan extraction device to remove hydrogen sulfide and mercaptan respectively. A part of the desulfurized mixed liquefied petroleum gas is used as an organic solvent for back-extracting the disulfide in the regenerated alkali liquor, and the liquefied petroleum gas after absorbing the disulfide is returned to the catalytic cracking riser reactor for treatment; the desulfurized liquefied petroleum gas product sulfur The content is not more than 10μg/g. The refined mixed liquefied petroleum gas can be fractionated to produce propylene products that meet the sulfur content requirements, and can be used as raw materials for the production of low-sulfur MTBE.

Description

A method and device for desulfurization and refining of mixed liquefied petroleum gas

technical field

The invention belongs to the refining field of hydrocarbon materials.

Background technique

Liquefied petroleum gas (liquefied petroleum gas, LPG) is an important petroleum refining product. In the refinery, it mainly includes catalytic liquefied petroleum gas from catalytic cracking unit and coking liquefied petroleum gas from coking unit, and is mainly composed of carbon three A mixture of hydrocarbons and C4 hydrocarbons. The use of liquefied petroleum gas includes being used as domestic or vehicle fuel, and as a chemical raw material, such as the raw material for extracting commercial propylene and synthetic gasoline antiknock agent methyl tert-butyl ether (MTBE). Liquefied petroleum gas usually needs to be desulfurized and refined before it can be used as the target product.

Unrefined liquefied petroleum gas contains harmful sulfides, the sulfides are mainly hydrogen sulfide and mercaptans, and the mercaptans are mainly methyl mercaptans, and other small amounts of sulfides include carbonyl sulfide (COS) and sulfur Ether etc. Comparatively speaking, the sulfides in coking LPG are more complex and higher in content than those in catalytic LPG, especially the proportion of non-mercaptan sulfur is large, and coking LPG is easy to carry The coke powder from the coking unit contains more unstable diolefins and relatively heavy hydrocarbon components than catalytic liquefied petroleum gas, so coking liquefied petroleum gas is undergoing the above two steps of desulfurization It is much more difficult to refine than catalytic liquefied petroleum gas.

At present, the desulfurization industrial refining method of liquefied petroleum gas mainly includes the continuous process of hydrogen sulfide extraction for the purpose of removing hydrogen sulfide and mercaptan extraction for the purpose of removing mercaptan. Alcohol amine extraction is mostly used for hydrogen sulfide extraction, and lye extraction is mostly used for mercaptan extraction. The alcohol amine extraction is to contact the liquefied gas with the alcohol amine compound (such as methyldiethanolamine, MDEA) solution, and absorb the hydrogen sulfide in the liquefied gas, and the alcohol amine solution after absorbing the hydrogen sulfide is desorbed Continuous use. The lye extraction is to contact the liquefied gas obtained by extracting and removing hydrogen sulfide with inorganic lye and alcohol amine, and absorb the mercaptan in the liquefied gas, and the lye after absorbing the mercaptan is regenerated and then recycled. The liquefied petroleum gas after hydrogen sulfide and mercaptan removal becomes a refined product.

In order to obtain olefins that meet the sulfur content requirements (such as propylene, which is used to produce polypropylene, the sulfur content is generally required to be no more than 3mg/m ³ ) and MTBE with low sulfur content (under the National V gasoline standard, the sulfur content of MTBE is usually required content is not more than 10μg/g), and refineries generally require that the sulfur content of refined liquefied petroleum gas is not more than 10μg/g or even lower. As for coking LPG with high sulfur content and containing a large amount of non-mercaptan sulfur, it is not only difficult to meet the requirements of such a low sulfur content after refining, but also to produce civil liquefied petroleum gas that meets the requirements of sulfur content not greater than 343mg/ ^m3 . LPG products are also more difficult. For this reason, refineries generally desulfurize and refine coking liquefied petroleum gas and catalytic liquefied petroleum gas separately, and usually carry out gas fractionation treatment on the refined catalytic liquefied petroleum gas to concentrate propylene and separate the liquefied petroleum gas of carbon five hydrocarbons It is used as a raw material for synthesizing MTBE (extracting isobutene components and etherifying with methanol to generate MTBE), while the refined coking liquefied petroleum gas is only used as blended civil fuel. In this way, the olefins (propylene and isobutylene) in coking LPG cannot be better utilized.

In refineries, coking LPG and catalytic LPG are also combined for the above-mentioned continuous two-step desulfurization and refining, but the outstanding problem in operation is still that the non-mercaptan sulfur existing in coking LPG is difficult to remove , so that the sulfur content of the refined product is still relatively high. As a result, the refined product is likely to be used only as a civil fuel, and its olefin resources are difficult to effectively use, and the alcohol amine consumption of the alcohol amine extraction unit is similar to that of the lye extraction unit The lye consumption is all very serious, and the operating cost appears to be higher.

In the prior art, lye extraction is usually used in the mercaptan extraction process of liquefied petroleum gas, which mainly includes three steps of lye extraction, lye oxidation, and back extraction. The lye extraction step refers to The liquefied petroleum gas is contacted with the lye, so that the mercaptan in the liquefied petroleum gas is transferred to the lye, and the lye oxidation step refers to oxidizing the mercaptan absorbed by the lye into a disulfide under catalytic oxidation conditions, The back-extraction step refers to separating the oxidized lye from the disulfide by means of organic solvent back-extraction, so that the lye can be recycled. Generally, low-sulfur hydrocarbon oils are used as solvents for the back extraction of disulfides, such as hydrogenated naphtha, gasoline, light diesel oil, etc., and the back extraction solvents are treated by hydrogenation after use. This is disadvantageous for refineries with no or insufficient hydrogen sources. Moreover, naphtha, gasoline, light diesel oil, etc. usually contain a certain amount of aromatics, and sometimes even have a high content of aromatics. When used as a back extraction solvent, it is easy to produce a certain emulsification phenomenon with the lye in contact, which is not conducive to the integration of hydrocarbon phase and The separation of alkali phase affects the desulfurization effect of liquefied petroleum gas alkali extraction.

Based on the existing literature, it can be seen that when the hydrocarbon material to be refined contains a high content of sulfides or contains a large proportion of non-mercaptan sulfides (these non-mercaptan sulfides are difficult to be In the case of liquid extraction), it is usually difficult to obtain the effect of deep desulfurization by conventional lye extraction technology.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and to provide a desulfurization refining method comprising mixing coking liquefied petroleum gas and catalytic liquefied petroleum gas, so that the sulfur content of the refined mixed liquefied petroleum gas is not greater than 10 μg/g .

The invention also provides a desulfurization and refining device for mixed liquefied petroleum gas.

The refining method of the present invention comprises the following continuous steps:

(1) Pass the coked liquefied petroleum gas from the coking unit into the catalytic cracking riser reactor of the catalytic cracking unit, and undergo a cracking reaction with the catalytic cracking raw material entering the catalytic cracking riser, and the relative macromolecules in the coking liquefied petroleum gas Hydrocarbon components and sulfides are converted into relatively small molecular hydrocarbons and sulfides;

(2) The coking liquefied petroleum gas produced by the cracking reaction and the catalytic liquefied petroleum gas cracked from the catalytic cracking raw material flow out from the fractionation system of the catalytic cracking unit together, and enter the alcohol amine extraction unit using the alcohol amine solution as the extraction agent. Extraction and removal of hydrogen sulfide, and then flow into the alkali extraction unit with alkali as the extraction agent to extract and remove mercaptans, and the mixed liquefied gas after desulfurization becomes a low-sulfur liquefied petroleum gas product;

(3) The lye that has absorbed mercaptan through the lye extraction unit flows into the lye oxidation unit, and under the action of air and oxidation catalyst, the mercaptide in the lye is oxidized to disulfide, and the lye can be regeneration;

(4) The regenerated lye mixed with the disulfide after releasing the air is mixed with a part of the refined liquefied petroleum gas that flows out of step (2) and enters the back extraction unit for back extraction operation, and the disulfide is back extracted into said part of refined liquefied petroleum gas;

(5) Part of the refined liquefied petroleum gas mixed with disulfide is separated from the regenerated lye and returned to the riser of the catalytic cracking unit for recycling, while the separated regenerated lye is returned to the lye extraction unit for recycling.

Among them, the coking liquefied petroleum gas from the coking unit is sprayed into the catalytic cracking reactor through the nozzle.

Wherein, the alcohol amine extraction unit includes an alcohol amine extraction process and an alcohol amine desorption process. Wherein, the refining method of the present invention further includes washing and coalescing the mixed liquefied petroleum gas after desulfurization to become a low-sulfur liquefied petroleum gas product with a sulfur content not greater than 10 μg/g.

In the present invention, if not otherwise specified, the catalytic cracking process, alcohol amine extraction process, alcohol amine desorption process, lye extraction process, lye oxidation process, back extraction process and water washing and coalescence treatment Processes such as all adopt known mode to carry out, and the operating condition of each relevant process remains unchanged.

A desulfurization and refining device for mixed liquefied petroleum gas provided by the present invention includes:

(1) catalytic cracking unit, the coking liquefied petroleum gas from the coking unit is passed into the catalytic cracking riser reactor of the catalytic cracking unit, and cracking reaction occurs together with the catalytic cracking raw material entering the catalytic cracking riser;

(2) Alcohol amine extraction unit, the coking liquefied petroleum gas that undergoes cracking reaction and the catalytic liquefied petroleum gas cracked from catalytic cracking raw materials flow out from the fractionation system of the catalytic cracking unit together, and enter the alcohol amine extraction unit for extraction and removal hydrogen sulfide;

(3) lye extraction unit, the material flowing out of the alcohol amine extraction unit continues to flow into the lye extraction unit to extract and remove mercaptans, and the mixed liquefied gas after desulfurization becomes a low-sulfur liquefied petroleum gas product;

(4) The lye oxidation unit, the lye that has absorbed the mercaptan flowing out of the lye extraction unit flows into the lye oxidation unit, and under the action of air and oxidation catalyst, the mercaptide in the lye is oxidized to disulfide substances, the lye can be regenerated;

(5) Back-extraction unit, after releasing air, the regenerated lye mixed with disulfide and a part of refined liquefied petroleum gas are mixed into the back-extraction unit for back-extraction operation, and the disulfide is back-extracted into the part of the refined liquefied petroleum gas, the part of the refined liquefied petroleum gas mixed with disulfide is separated from the regenerated lye and returned to the catalytic cracking unit for recycling, and the separated regenerated lye is returned to the lye extraction unit for circulation use.

Wherein, the alcohol amine extraction unit includes an alcohol amine extraction device and an alcohol amine desorption device.

In the present invention, the coking liquefied petroleum gas is fed into the catalytic cracking device to carry out the cracking reaction, so that the relatively large molecular hydrocarbon components and sulfides in the coking liquefied petroleum gas are respectively converted into relatively small molecular hydrocarbons and sulfides, and at the same time The non-volatile pollutants carried (such as coke powder) are removed, and then processed by the fractionation system of the catalytic cracking unit, and then flow out together with the catalytic cracking liquefied petroleum gas. Compared with coking liquefied petroleum gas and catalytic liquefied petroleum gas, mixed liquefied petroleum gas The direct mixture of gas has relatively lower sulfur content and proportion of non-mercaptan sulfur, and is relatively easy to remove.

In the present invention, the coking liquefied petroleum gas is processed by a catalytic cracking unit and combined into a catalytic liquefied petroleum gas desulfurization refining device for refining, and by performing gas fractionation on the refined catalytic liquefied petroleum gas to concentrate propylene, the propylene in the refinery can be increased. Yield and MTBE product yield (by providing more isobutene components to produce more MTBE), and simplify the operating process, reducing operating costs.

In the present invention, the liquefied petroleum gas after desulfurization is used as the back-extraction solvent in the mercaptan extraction device, because it does not contain aromatic components that are easy to emulsify with alkali liquor, and the The effect is remarkable when disulfide is used, and it is returned to the catalytic cracking tube reactor for treatment after use, so that no material outside the device is used as a stripping solvent, and no additional hydrogenation treatment is required, and the operation is more convenient.

Description of drawings

Figure 1 schematically shows a preferred embodiment of the present invention.

Fig. 2 is a schematic flow chart of the extractive desulfurization refining method in the prior art.

Fig. 1 is only intended to generally represent the flow of a preferred embodiment of the present invention, and is not intended to give details about vessels, heaters, coolers, pumps, compressors, valves, process control equipment, etc., which are well known Essential equipment for those skilled in the art.

The coking raw material in the refinery enters the coking unit 4 through the pipeline 3 for processing, and the obtained coking liquefied petroleum gas is passed into the catalytic cracking unit 2 through the pipeline 5, and undergoes catalytic cracking reaction together with the catalytic cracking raw material entering the catalytic cracking unit 2 through the pipeline 1, thereby Obtain a kind of mixed liquefied petroleum gas, described mixed liquefied petroleum gas enters alcohol amine extraction device 7 to remove hydrogen sulfide (alcohol amine desorption device is not shown) through pipeline 6, and enters conventional lye extraction through pipeline 8 Extraction device, the mercaptan is removed through the lye extraction unit 9 and then discharged through the pipeline 10 to obtain the refined liquefied petroleum gas product. And the lye that has absorbed the mercaptan that flows out through lye extracting unit 9 flows into lye oxidation unit 12 through pipeline 11, and under the effect of air (not shown) and oxidation catalyst, the mercaptide in lye is oxidized For disulfide, the lye can be regenerated. The regenerated lye mixed with disulfides after releasing the air is mixed with a part of the refined liquefied petroleum gas from the pipeline 10 and flowed through the pipeline 14 through the pipeline 13 and mixed into the back-extraction unit 15 for back-extraction operation. The disulfides are back-extracted into the part of the refined liquefied petroleum gas, and part of the refined liquefied petroleum gas mixed with the disulfides is separated from the regenerated lye, discharged through the pipeline 16, and returned to the catalytic cracking unit 2 for recycling. And the separated regenerated lye (not shown) returns to the lye extraction unit 9 for recycling.

Fig. 2 is the prior art process. The difference from the schematic diagram 1 of the present invention is that the coked liquefied petroleum gas from the coking unit 3 is mixed with the catalytically cracked petroleum gas from the catalytic cracking unit 2 in the pipeline 6 through the pipeline 5, and then the hydrogen sulfide and the hydrogen sulfide are removed through conventional alcohol amine extraction. Conventional alkali extraction removes mercaptans to obtain refined liquefied petroleum gas products. Wherein in back-extraction unit 15, usually adopt the material (such as hydrogenated naphtha) outside this flow process as back-extraction solvent (inflow through pipeline 14), and usually send out through pipeline 16 after finishing back-extraction operation It is processed separately in devices outside this process (such as naphtha hydrogenation units).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below in combination with examples. The examples are intended to generally represent the flow of a preferred embodiment of the invention and are not intended to give details about vessels, heaters, coolers, pumps, compressors, valves, control equipment for the process, etc., which would be useful to those skilled in the art. Basic equipment for people in the technical field. The examples given are intended to illustrate the invention without restricting it in any way.

Example 1

A refinery produces coking liquefied petroleum gas from the coking unit, the sulfur content is reduced to about 3000mg/m ³ after alcohol amine extraction treatment, and the sulfur content is reduced to about 200mg/m ³ ~ 300mg/m ³ after lye extraction .

The refinery produces catalytic liquefied petroleum gas from the catalytic cracking unit. The sulfur content is reduced to about 200 mg/m ³ after alcohol amine extraction treatment, and the sulfur content is reduced to 5 mg/m ³ after lye extraction.

According to the present invention, the coked liquefied petroleum gas produced in the coking unit is connected to the riser reactor of the catalytic cracking unit through a pipeline, and injected through a nozzle, and the coked liquefied petroleum gas and the catalytic cracking raw material are cracked together in the riser. Subsequently, the mixed liquefied petroleum gas is distilled from the fractionation system of the catalytic cracking unit, and the mixed liquefied petroleum gas includes the cracked coked liquefied petroleum gas and the catalytic liquefied petroleum gas produced by cracking the catalytic cracking feedstock. The sulfur content of the mixed liquefied petroleum gas is about 250 mg/m ³ after being extracted with alcohol amine, and the sulfur content is reduced to 10 mg/m ³ after being extracted with lye.

Among them, in the back-extraction link of the mercaptan extraction unit, the liquefied petroleum gas after desulfurization is used as the solvent for the back-extraction of disulfides. About 6000μg/g～10000μg/g is discharged to the catalytic cracking reactor for treatment.

It can be seen that if the coking liquefied petroleum gas is not treated by catalytic cracking, the sulfur content can only be reduced to about 200mg/m ³ ~ 300mg/m ³ after alcohol amine extraction and lye extraction. After pretreatment, the sulfur content can be reduced to below 10 mg/ ^m3 after the same alcohol amine extraction and lye extraction, which shows the good effect of the present invention.

Example 2

This example is used to illustrate the effect of using liquefied petroleum gas after alkali extraction and desulfurization as a back extraction solvent for removing disulfides in alkali liquor.

In this embodiment, sodium hydroxide solution is used as the lye of the liquefied petroleum gas alkali extraction unit, and its mass fraction is 20%, and 200 μg/g～500 μg/g of sulfonated cobalt phthalocyanine (commercially available) is dissolved in the lye Sold product), as an oxidation catalyst to oxidize and regenerate the lye that has absorbed mercaptan.

The operation steps of extraction and desulfurization refining are as follows:

The lye is contacted with the liquefied petroleum gas after hydrogen sulfide removal by alcohol amine solution (40% MDEA solution) in the extraction system, the mercaptan in the liquefied petroleum gas is transferred into the lye, and the liquefied petroleum gas after desulfurization becomes the product Send it to the tank farm, where the volume ratio of lye to liquefied petroleum gas is 2:8, the temperature is 40°C, and the pressure is 1.4MPa; the lye that has absorbed the mercaptan is separated from the liquefied petroleum gas and then enters the oxidation system for treatment, among which, as the oxidant The air is injected into the oxidation system according to twice the theoretical amount of the oxidized mercaptide. The pressure of the oxidation system is 0.35MPa and the temperature is 55°C. The mercaptan sodium salt in the lye is oxidized to disulfide so that the lye Regeneration; the oxidized lye is mixed with excess air and disulfide, and after releasing the air tail gas, it enters the back extraction system to contact with the back extraction solvent, wherein the desulfurized liquefied petroleum gas is used as the back extraction solvent, and the alkali The volume ratio of the solution is 3:7, and the back-extraction solvent is recycled. The pressure of the back-extraction system is 1.4MPa, and the temperature is 40°C; the lye after back-extraction is returned to the extraction system for recycling.

As a comparison, refinery refined gasoline products (sulfur content not greater than 50 μg/g, distillation range 33°C to 200°C) were used as the stripping solvent, and other process parameters were the same, except that the pressure of the stripping system was reduced to 0.35MPa .

Table 1 has provided the measurement data of residual disulfide sulfur content in the regenerated lye after back extraction, and the mensuration of its sulfur content is as follows: adopt 90 ℃-120 ℃ petroleum ether (sulfur-free) and lye after back extraction Equal mass is fully mixed, so that the disulfide remaining in the lye after back extraction is transferred into petroleum ether, and then the sulfur content in petroleum ether is measured after standing and separated. This sulfur content value is the residual disulfide in the lye after back extraction. Disulfide sulfur content.

Table 1

As can be seen from the data in Table 1, when the liquefied petroleum gas after desulfurization is used as the back extraction solvent, the disulfide sulfur content in the lye after the back extraction is much smaller than that when refined gasoline is used as the back extraction solvent. The situation shows that the effect of using desulfurized liquefied petroleum gas as back extraction solvent is better. During the operation, it was also found that when refined gasoline was used as the back-extraction solvent, there were sometimes quite a lot of disulfides remaining in the lye after back-extraction, which might be due to the emulsification with the lye.

It can be deduced that when the desulfurized liquefied petroleum gas is used as the back extraction solvent, the effective utilization rate of the lye will be higher, and the lye discharge will be less.

Claims (7)

1. A method for desulfurization and refining of mixed liquefied petroleum gas, comprising the following steps: (1) Pass the coked liquefied petroleum gas from the coking unit into the catalytic cracking riser reactor of the catalytic cracking unit, and undergo a cracking reaction with the catalytic cracking raw material entering the catalytic cracking riser, and the relative macromolecules in the coking liquefied petroleum gas Hydrocarbon components and sulfides are converted into relatively small molecular hydrocarbons and sulfides; (2) The coking liquefied petroleum gas produced by the cracking reaction and the catalytic liquefied petroleum gas cracked from the catalytic cracking raw material flow out from the fractionation system of the catalytic cracking unit together, and enter the alcohol amine extraction unit using the alcohol amine solution as the extraction agent. Extraction and removal of hydrogen sulfide, and then flow into the alkali extraction unit with alkali as the extraction agent to extract and remove mercaptans, and the mixed liquefied gas after desulfurization becomes a low-sulfur liquefied petroleum gas product; (3) The lye that has absorbed mercaptan through the lye extraction unit flows into the lye oxidation unit, and under the action of air and oxidation catalyst, the mercaptide in the lye is oxidized to disulfide, and the lye can be regeneration; (4) The regenerated lye mixed with the disulfide after releasing the air is mixed with a part of the refined liquefied petroleum gas that flows out of step (2) and enters the back extraction unit for back extraction operation, and the disulfide is back extracted into said part of refined liquefied petroleum gas; (5) Part of the refined liquefied petroleum gas mixed with disulfide is separated from the regenerated lye and returned to the riser of the catalytic cracking unit for recycling, while the separated regenerated lye is returned to the lye extraction unit for recycling. 2. The method according to claim 1, characterized in that the coking liquefied petroleum gas is sprayed into the catalytic cracking riser reactor of the catalytic cracking unit through a nozzle. 3. The method of claim 1, wherein the alcohol amine extraction unit comprises an alcohol amine extraction process and an alcohol amine desorption process. 4. The method of claim 1, characterized in that the desulfurized mixed liquefied petroleum gas is subjected to water washing and coalescence treatment, and then becomes a product. 5. The method according to claim 1, characterized in that the sulfur content of the mixed liquefied petroleum gas after desulfurization is not greater than 10 μg/g. 6. A desulfurization and refining device for mixed liquefied petroleum gas, comprising the following units: (1) catalytic cracking unit, the coking liquefied petroleum gas from the coking unit is passed into the catalytic cracking riser reactor of the catalytic cracking unit, and cracking reaction occurs together with the catalytic cracking raw material entering the catalytic cracking riser; (2) Alcohol amine extraction unit, the coking liquefied petroleum gas that undergoes cracking reaction and the catalytic liquefied petroleum gas cracked from catalytic cracking raw materials flow out from the fractionation system of the catalytic cracking unit together, and enter the alcohol amine extraction unit for extraction and removal hydrogen sulfide; (3) lye extraction unit, the material flowing out of the alcohol amine extraction unit continues to flow into the lye extraction unit to extract and remove mercaptans, and the mixed liquefied gas after desulfurization becomes a low-sulfur liquefied petroleum gas product; (4) The lye oxidation unit, the lye that has absorbed the mercaptan flowing out of the lye extraction unit flows into the lye oxidation unit, and under the action of air and oxidation catalyst, the mercaptide in the lye is oxidized to disulfide substances, the lye can be regenerated; (5) Back-extraction unit, the regenerated lye mixed with disulfide after releasing the air is mixed with a part of refined liquefied petroleum gas and enters the back-extraction unit, and the disulfide is back-extracted into the part of refined In the liquefied petroleum gas, a part of the refined liquefied petroleum gas mixed with disulfide is separated from the regenerated lye and returned to the riser of the catalytic cracking unit for recycling, and the separated regenerated lye is returned to the lye extraction unit for recycling. 7. The device according to claim 6, wherein, the alcohol amine extraction unit comprises an alcohol amine extraction device and an alcohol amine desorption device.