ES2804200T3 - Procedure for reducing corrosive ions in the aromatic compound extraction solvent - Google Patents

Abstract

A process for the reduction of corrosive ions in an aromatic compound extraction solvent in a circulation system where the aromatic compound extraction solvent circulates, the corrosive ions being at least one type selected from the group consisting of chloride ions, ions of sulfate and sulfite ions, the process comprising: a step of forming a non-volatile salt by adding a corrosive ion scavenger to react the corrosive ions with the corrosive ion scavenger, a step of concentrating the solvent comprising the salt , wherein the concentration is carried out in a regenerator for the aromatic compound extraction solvent and the temperature of the extraction solvent circulation system, including the regenerator, is 180 ° C or lower, and a step of removing the salt , characterized in that the corrosive ion scavenger is a quaternary ammonium compound represented by the formula General (1) given below: ** (See formula) ** wherein R1 to R3 are each independently a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer from 1 to 10.

Description

DESCRIPTION

Procedure for reducing corrosive ions in the aromatic compound extraction solvent

Technical field

The present invention refers to a process for the reduction of corrosive ions such as chloride ions, sulfate ions and sulfite ions in a solvent for the extraction of aromatic compounds, the process being capable of preventing corrosion in a system in which that a solvent for extracting aromatic compounds such as benzene, toluene, and xylene from a hydrocarbon stream circulates in oil refineries, coal chemical plants, and the like.

Previous technique

In petroleum refining and hydrocarbon refining in coal chemical plants, there is a perennial problem in that corrosive ions, such as chloride ions, sulfate ions, and sulfite ions originating from various salts present in raw materials cause corrosion of the equipment.

In this sense, a technique of adding an alkali to sequester the corrosive ions is a possible solution. However, salts produced by the addition of an alkali can stick / precipitate and possibly cause serious problems such as deposit build-up and clogging of equipment.

Patent literature 1 discloses a method for preventing chloride corrosion in a condensation system of a petroleum refining process using a plurality of amines such as monoethanolamine, in combination. Patent Document 2 reveals that metal corrosion is prevented by introducing a quaternary ammonium compound such as choline hydroxide (2-hydroxyethyltrimethylammonium hydroxide) into a fluid that can come into contact with the interior of petroleum refining equipment and the like. to prevent the generation of hydrogen chloride.

US 3466 345 A is directed to a process for the extraction of solvents from aromatic hydrocarbons in which the preferred solvent comprises sulfolane and typical aromatic hydrocarbons to be recovered include benzene, toluene and xylene.

Document US 4 191 615 A describes that to avoid corrosion of the apparatus in extraction and extractive distillation processes in which N-substituted morpholine is used as a selective solvent, an additive consisting of: a) phosphoric acid, b) a salt thereof, c) a vanadium compound, d) a molybdenum compound or e) a mixture of two or more of these compounds, the addition being made in an approximate amount of 0.005 to 0.02% in weight of morpholine solvent.

In G 1134582 it is described that sulfolane-type solvents containing corrosive contaminants are purified by contact with an aqueous solution containing an alkaline compound and with an alkali-resistant liquid, which is poorly soluble in water and dissolves the solvent. sulfolane type more easily than water by separating a solvent phase containing an alkali resistant liquid from the aqueous phase and subsequently recovering the sulfolane type solvent from the solvent phase.

US 2006/043340 A1 describes that a quaternary ammonium compound is used as a metal corrosion inhibitor.

Appointment list

Patent literature

PTL1: JP 7-180073 A

PTL2: JP 2004-211195 A

Summary of the invention

Technical problem

However, with conventional procedures, although chloride ions derived from salts contained in petroleum and the like are reduced, it is difficult to remove them completely. Therefore, it is not uncommon for chlorides, chloride ions, sulfate ions, and sulfite ions to be present in hydrocarbon mixtures such as naphtha obtained by oil refining and the like, and there is still the problem of corrosion by corrosive ions in a system in which said hydrocarbon mixture is used as a raw material.

Meanwhile, a catalyst is used in a process to obtain an aromatic compound such as benzene, toluene or xylene by reforming a mixture of hydrocarbons such as naphtha. The catalyst is used continuously or is continuously recovered from the reaction product composition and regenerated, but the catalytic activity it deteriorates due to its long-term use, so a regeneration treatment of the catalyst is carried out. Chlorine compounds are often used in catalyst regeneration treatment, and therefore the reformed hydrocarbon fed from the aromatics generator to the extractor may contain not only chloride ions derived from the hydrocarbon mixture of matter. raw, but also chloride ions derived from the chlorine compound used in catalyst regeneration.

In addition, an aromatic hydrocarbon oil which is a reformed hydrocarbon and the like are subjected to an aromatic compound extraction treatment with an extraction solvent. In this extraction treatment, the aromatic hydrocarbon oil is dissolved in an extraction solvent, and the aromatic compound is extracted and distilled off. Next, an aromatic hydrocarbon oil is again supplied to the dilute extraction solvent, and the distillation is performed again. Thus, the extraction solvent is recycled in the extractor from the viewpoint of cost reduction, prevention of environmental pollution, and the like.

As a result, the corrosive ions contained in the aromatic hydrocarbon oil of the successively fed feedstock accumulate in the recycled extraction solvent. In conjunction with a small amount of water present in the extraction solvent, a higher concentration of corrosive ions in the extraction solvent causes rapid corrosion of the extractor. Even when an alkali is added to neutralize the acid producing corrosive ions in the extraction solvent, as is known in the art, salts accumulate in the extraction solvent circulation system. Furthermore, to date, there has been no technical concept of sequestering corrosive ions by adding an alkali.

Thus, an increase in the concentration of corrosive ions in the extraction solvent is a problem specific to the extraction solvent of the circulation system, and an approach is required that provides a greater corrosion suppressing effect than in a system in which the solvent is used only once and discarded.

The use of a procedure such as that described in patent literature 1 to address the problem in the circulation system requires that a plurality of amines combine optimally for neutralization and precipitation, and furthermore, it is likely that the amines are discharged from the circulation system as volatile components due to distillation, thus deteriorating the corrosion suppressing effect. Depending on the conditions, commonly used alkanolamines and the like are likely to be discharged from the circulation system as volatile components due to distillation and lack the ability to remove corrosive ions.

The present invention has been made under such circumstances, and an object is to provide a process for reducing corrosive ions in an aromatic extraction solvent, whereby the corrosive ions in the aromatic extraction solvent are conveniently and efficiently reduced. , in order to suppress the corrosion of an extractor caused by corrosive ions contained in a solvent for extracting aromatic compounds from a circulation system.

Problem solution

The present invention is based on the discovery that by sequestering corrosive ions in an aromatics extraction solvent in a circulation system as a non-volatile salt and concentrating the extraction solvent containing this salt in a facility, the salt concentration in the system, and further, by discharging the concentrated salt, the corrosive ions in the circulating extraction solvent can be conveniently and effectively reduced.

That is, the present invention is defined in the claims.

Advantageous effects of the invention

According to the present invention, corrosive ions in an aromatic compound extraction solvent from a circulation system can be conveniently and efficiently reduced.

Accordingly, the corrosion of an extractor caused by corrosive ions contained in an extraction solvent of an aromatic compound from a circulation system can be suppressed, allowing an aromatic compound to be efficiently extracted.

Brief description of the drawing

[Fig. 1] Fig. 1 is a schematic system diagram of an example of an aromatic extractor.

Description of the achievements

The process for reducing corrosive ions in an aromatic compound extraction solvent of the present invention is a process applied to a circulation system in which the aromatic compound extraction solvent circulates and chloride ions, chloride ions are reduced. sulfate and sulfite ions, that is, corrosive ions. The procedure includes the step of forming a non-volatile salt by adding a sequestrant of corrosive ions to react the corrosive ions with the corrosive ion scavenger, and the step of removing the salt by concentrating the solvent containing the salt.

Thus, by forming the corrosive ions in the aromatic compound extraction solvent in the circulation system into a non-volatile salt and concentrating the extraction solvent containing the non-volatile salt, the corrosive ions in the solvent that cause corrosion of a extractor can be conveniently and efficiently reduced.

[Circulation system!

The process of the present invention is applied to a circulation system in which the aromatic compound extraction solvent contains at least one type selected from the group consisting of chloride ions, sulfate ions, and sulfite ions that are corrosive ions. An example is a system in which a solvent is recycled in the process of extracting an aromatic compound from an aromatic hydrocarbon oil in the refining of a hydrocarbon oil, such as petroleum.

The aromatic hydrocarbon oil is, for example, an oil containing an aromatic compound obtained by reformation, and specifically containing benzene, toluene or xylene as an aromatic compound, and a mixture of any of them.

[Aromatics extraction solvent!

An aromatics extraction solvent commonly used in hydrocarbon oil refining can be used, examples include sulfolane, diethylene glycol, triethylene glycol, tetraethylene glycol, N-methylpyrrolidone, dimethylsulfoxide, morpholine, N-formylmorpholine, methyl carbamate, diglycolamine, furfural, phenol and the like. One of these solvents can be used alone, or two or more can be used in combination. Among them, sulfolane is used appropriately. Sulfolane may gradually undergo thermal decomposition during use, and may contain sulfuric acid as an impurity and possibly produce sulfate ions and sulfite ions, but sulfolane is not problematic because the process of the present invention is also capable of reducing sulfate ions. and sulphite ions derived from sulfolane.

[Corrosive ion sequestrant!

Corrosive ion scavenger is a compound capable of forming a salt with corrosive ions, and a corrosive ion scavenger is used that does not volatilize in a circulation system to which the corrosive ion scavenger is added. The corrosive ion scavenger is very basic because the salt formed with the corrosive ions is a neutral salt, and the corrosion of an extractor can be further suppressed.

Corrosive ion scavenger is a quaternary ammonium compound represented by the following general formula (1). Due to the concern of higher ash content in the circulating system solvent and from a workability point of view, the inorganic alkali to be added is a quaternary ammonium compound as mentioned above.

In formula (1), R1 to R3 are each independently a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer from 1 to 10. Specific examples of R1 to R3 include alkyl groups linear or branched and the like, such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group.

Specific examples of such quaternary ammonium compounds include hydroxymethyltrimethylammonium hydroxide, hydroxymethyltrimethylammonium hydroxide, choline hydroxide, 2-hydroxyethyltrimethylammonium hydroxide, 3-hydroxypropyltrimethylammonium hydroxide, and the like. One of them can be used alone, or two or more can be used in combination.

Preferably, R1 to R3 are each independently a hydrocarbon group having 1 to 3 carbon atoms, and n is an integer from 1 to 4. When having such a low molecular weight, the quaternary ammonium compound has an excellent soluble in water and exhibits sufficient effect as corrosive ion sequestrants even in a small amount, and therefore the corrosion suppressing effect of the extractor, which is the effect of the present invention, is further enhanced. Among these, choline hydroxide (also called choline), where R1 to R3 are all methyl groups and n is 2, is particularly preferred.

As for handling, such a quaternary ammonium compound is generally preferably used as an aqueous solution. The concentration thereof is not particularly limited, and it is preferably 5 to 50% by mass.

Since ammonia and other amines are weakly basic, the salts formed by these alkalis and corrosive ions are acidic salts, and even a small amount of water, if present, causes corrosion. On the other hand, since the quaternary ammonium compound, as described above, is strongly basic, the salt formed by the corrosive ions is a neutral salt and is unlikely to cause corrosion even in the presence of water.

In addition, the salt formed by the quaternary ammonium compound and the corrosive ions has deliquescent properties and fluidity, so it is unlikely to stick and is free from the risk of accumulation of deposits and clogging within the equipment of the circulation system.

The salt formed by the corrosive ion scavenger of the present invention and the corrosive ions has a high boiling point and is not volatile in the circulation system. Therefore, in the distillative refining process for aromatic hydrocarbon oil or the like, the salt is unlikely to evaporate and enter the extracted aromatic compound, and the salt can be separated from the extraction solvent by distillative concentration and can be removed. as a distillation residue.

The corrosive ion scavenger is a quaternary ammonium compound as described above. While the corrosive ion sequestration effect can be exerted only by the corrosive ion scavenger, another agent such as ammonia or a neutralizing amine can be used in combination to further increase the corrosive ion scavenging effect.

Examples of neutralizing amines include monoethanolamine, cyclohexylamine, morpholine, diethylethanolamine, monoisopropanolamine, 3-methoxypropylamine, 2-amino-2-methyl-1-propanol, and the like.

Regarding the amount of corrosive ion scavenger to be added, if the concentration of corrosive ions in the extraction solvent in the circulation system can be predicted or measured, the frequency and concentration of the corrosive ion scavenger to be added can be determined depending on the concentration of corrosive ions. The concentration of corrosive ions can be measured with an absorptiometer, an ion chromatograph, a capillary electrophoresis analyzer or the like.

Regarding the concentration of the corrosive ion scavenger, from the point of view of the effect of the addition, preferably the corrosive ion scavenger is added so that they are 0.5 to 2 molar equivalents of the corrosive ion concentration, and from the point of view of obtaining a more stable corrosive ion sequestering effect, more preferably 1 to 2 molar equivalents.

As a means of indirectly detecting the concentration of corrosive ions, the concentration of metal ions in the extraction solvent in the circulation system can be measured. When the corrosion of the extractor progresses with an increase in the concentration of corrosive ions in the circulating extraction solvent, the concentration of metal ions in the circulation system increases. Accordingly, it is also possible to detect an increase in the concentration of corrosive ions by an increase in the concentration of metal ions. The metal ion concentration can be measured with an absorptiometer, an inductively coupled plasma atomic emission spectrometer (ICP-AES), an inductively coupled plasma mass spectrometer (ICP-MS), or the like.

In this case, it is preferable to find in advance a correlation between the measurement target metal ion concentration and the corrosive ion concentration in the circulation system. Thus, the frequency and concentration of the corrosive ion scavenger to be added can be determined as a function of the metal ion concentration in the circulation system.

Specifically, the target metal ion of the measurement is preferably an iron ion that is likely to be bypassed due to equipment corrosion.

By using the method of the present invention described above as a method of reducing corrosive ions in an extraction solvent when extracting an aromatic compound in a circulation system, the corrosion of an extractor caused by the corrosive ions contained in the extractor can be effectively suppressed. extraction solvent from the circulation system, thus allowing efficient extraction to take place.

The equipment and a treatment mechanism to which the method of the present invention is applied will be described below, by way of example. A schematic diagram of the system of an example of an aromatics extractor to which the process of the present invention is applied is shown in Fig. 1.

In the system flow shown in Fig. 1, a raw material aromatic hydrocarbon oil feedstock that is fed continuously or intermittently from a feed 1 is subjected to desalination treatment in a chloride trap 2 , and then mixed with an aromatics extraction solvent in an extraction column 3 to extract aromatic compounds, such as benzene, toluene, and xylene. The solvent insoluble components are removed from the top of the column and washed in a wash column 4, and then a raffinate 9 is separated.

On the other hand, the aromatic compounds extracted in the extraction solvent are extracted from the bottom of the extraction column 3 together with the extraction solvent. Then, the aromatic compounds and the extraction solvent are distilled off in a separation column 5 and a recovery column 6 to obtain the aromatic compounds.

Here, a corrosive ion scavenger is added as an aqueous solution from an injection facility 10 provided elsewhere in the extraction solvent circulation system, as in the system at the top of the separation column 5.

The extraction solvent is distilled again for a regeneration treatment in recovery column 6, subjected to a dehydration treatment in a process water extractor 8, returned to extraction column 3 and recycled.

The extraction solvent recovered from the recovery column 6 contains a non-volatile salt produced by the reaction between the corrosive ion scavenger and the corrosive ions in the extraction solvent. The recovered extraction solvent containing said salt is concentrated by distillation in a bypass regenerator 7. By separating and removing a concentration residue and returning a volatilized fraction to the recovery column 6, a regenerated solvent with reduced corrosive ions is fed into the circulation system.

The corrosive ion scavenger can be added in another part of the circulation system. For example, in the aforementioned apparatus, the corrosive ion scavenger can be added from the injection facility 10 provided in the system at the top of the separation column 5, which is a subsequent stage relative to the aromatics extraction column. 3.

The temperature of the extraction solvent circulation system, including regenerator 7, is 180 ° C or lower from the point of view of preventing volatilization of the corrosive ion scavenger and promoting the effect of the latter on the regenerator 7.

As described above, the salt formed by the corrosive ion scavenger and the corrosive ions is a salt that is not volatile in the circulation system and therefore is not discharged on the extract side, for example by the distillation performed to extract aromatic compounds, and can be separated as a distillation residue from the solvent concentration at a specific place such as the regenerator 7 provided in the circulation system for the regeneration of the solvent. Furthermore, the salt can be removed from the circulation system by providing a means to discharge the remaining salt-containing waste.

Examples

The present invention will be described in more detail below, but the present invention is not limited to the following examples.

Laboratory confirmatory test

(Test 1-1)

First, 100 mL of xylene, 96 mL of sulfolane and 4 mL of pure water were introduced into a 500 mL round bottom flask. Hydrochloric acid and an aqueous solution of choline hydroxide (choline) were added to prepare a sample solution with a chloride ion concentration of 100 mg / L and a choline concentration of 340 mg / L.

This sample solution was distilled to remove water. The residual liquid (sulfolane and xylene) remaining in the round bottom flask was extracted twice with 200 mL of pure water.

(Test 1-2)

A sample solution was prepared which had the same concentration of chloride and choline ions as the sample solution from Test 1-1 and to which monoethanolamine (MEA) was added to obtain a concentration of 172 mg / L, and thus the rest, distillation and extraction were performed in the same manner as in Test 1-1.

(Test 1-3, comparative)

A sample solution was prepared with the same chloride ion concentration as the sample solution from Test 1-1 to which no choline hydroxide (choline) was added, and otherwise distillation and extraction were performed. in the same way as in test 1-1.

(Test 1-4, comparative)

A sample solution was prepared with the same concentration of chloride ions and MEA as the sample solution from Test 1-2 to which no choline hydroxide (choline) was added and otherwise distillation and extraction were performed in the same way as in Test 1-2.

Regarding the extracts from the first and second extraction in the above tests, the concentrations of chloride ion, choline hydroxide and MEA were measured with a capillary electrophoresis analyzer. The results of the measurements are shown in Table 1.

Table 1

As is clear from the results shown in Table 1, when choline hydroxide was added (test 1-1), the concentration of chloride ions in the extract was 20 times or higher than when choline hydroxide was not added (test 1-3), which confirms a better removal effect of corrosive ions in the aromatic compound extraction solvent.

When choline hydroxide was added (Test 1-1), the chloride ion concentration in the extract was at least 15 times higher than when only MEA was added (Test 1-4), confirming that the removal effect of Corrosive ions in the aromatic compound extraction solvent was higher.

Furthermore, when choline and MEA were added (Test 1-2), the chloride ion concentration in the extract was high, and it can be said that the effect of removing corrosive ions in the aromatic compound extraction solvent is improves even more.

[Test 2] Real team level test

The following test was performed on the equipment shown in Fig. 1 in a condition in which an aromatic hydrocarbon oil was circulating containing benzene, toluene, and xylene and sulfolane (with a chloride ion concentration of 70 mg / L).

An aqueous solution of choline hydroxide (choline) was added once a week in a place close to the outlet of the separation column. The amount of choline hydroxide added was equimolar to the chloride ions in the sulfolane. The chloride ion concentration was measured by performing extraction with 50 ml of pure water twice, followed by ion chromatography.

After the equipment ran for a predetermined number of days, 1 L of sulfolane was recovered from the bottom of recovery column 6, and the concentration of chloride ions in this sulfolane was measured. The measurement results are shown in Table 2.

Table 2

As can be seen from the results in Table 2, it was confirmed that the concentration of chloride ions in the sulfolane recovered from the bottom of the recovery column 6 decreased as the cumulative choline hydroxide concentration increased. It was also confirmed that the choline remained in the recovered sulfolane. The accumulation rate of chloride ions in the bottom of regenerator 7 was 60 mg / (L-day), that is, it increased about 3 times when adding choline hydroxide in relation to the 23 mg / (L-day) achieved. when no choline hydroxide was added.

Accordingly, it can be said that a favorable effect of removing corrosive ions due to choline hydroxide can be obtained in the actual equipment as well.

List of reference signs

1 Food

2 Chloride trap

3 Extraction column

4 Wash column

5 Separation column

6 Recovery column

7 Regenerative

8 Process water sequestrant

9 Refined

10 Injection facility (Place where corrosive ion scavenger is added)

Claims (9)

1. A procedure for reducing corrosive ions in an aromatic compound extraction solvent in a circulation system where the aromatic compound extraction solvent circulates, the corrosive ions being at least one type selected from the group consisting of chloride ions , sulfate ions and sulfite ions, the process comprising: a step of forming a non-volatile salt by adding a corrosive ion scavenger to react the corrosive ions with the corrosive ion scavenger, a step of concentration of the solvent comprising the salt, in which the concentration is carried out in a regenerator for the extraction solvent of the aromatic compound and the temperature of the circulation system of the extraction solvent, including the regenerator, is 180 ° C or lower, and one step of removing the salt, characterized in that the corrosive ion scavenger is a quaternary ammonium compound represented by the general formula (1) given below:

wherein R1 through R3 are each independently a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer from 1 to 10. The method of reducing corrosive ions in an aromatic compound extraction solvent according to claim 1, wherein the aromatic compound extraction solvent is one or more selected from the group comprising sulfolane, diethylene glycol, triethylene glycol, tetraethylene glycol, N -methylpyrrolidone, dimethylsulfoxide, morpholine, N-formylmorpholine, methyl carbamate, diglycolamine, furfural and phenol. The process for reducing corrosive ions in an aromatic compound extraction solvent according to claim 1 or 2, wherein one or more selected from the group comprising ammonia and neutralizing amines are also used in the circulation system. The method of reducing corrosive ions in an aromatic compound extraction solvent according to any one of claims 1 to 3, wherein the corrosive ion scavenger is added at a frequency and a concentration determined based on a concentration of Corrosive ions in the circulating aromatics extraction solvent. 5. The process for reducing corrosive ions in an aromatic extraction solvent according to claim 4, wherein the corrosive ion scavenger is added so as to be 0.5 to 2 molar equivalents relative to the concentration of corrosive ions. The method for reducing corrosive ions in an aromatic compound extraction solvent according to any one of claims 1 to 3, wherein the corrosive ion scavenger is added at a frequency and a concentration determined as a function of a concentration of metal ions in the circulating aromatics extraction solvent. The method of reducing corrosive ions in an aromatics extraction solvent according to claim 6, wherein the metal ion is an iron ion. The process for reducing corrosive ions in an aromatic compound extraction solvent according to any one of claims 1 to 7, wherein the aromatic compound contains one or more selected from the group consisting of benzene, toluene and xylene. 9. Use of the method for reducing corrosive ions in an extraction solvent for an aromatic compound according to any one of claims 1 to 8 in an extraction process for an aromatic compound.