JP5660654B2 - Method to prevent soil growth in the gas phase inside an oil quench tower - Google Patents

Description

  The present invention relates to a method for preventing the growth of dirt in a gas phase portion inside an oil quench tower in a process for producing olefins such as ethylene and propylene.

  Production of olefins in the petrochemical industry is usually carried out by thermal decomposition of naphtha. Naphtha is pyrolyzed at 800-850 ° C with dilute steam in a pyrolysis furnace, rapidly cooled to 350-400 ° C at the outlet of the cracking furnace, and then sent to an oil quench tower (also called a gasoline fractionator or gasoline rectification tower). It is done. The feed gas introduced from the bottom of the column is cooled by making countercurrent contact with quench oil, which is a process liquid circulated from the lower, middle, and upper stages of the column, and the components present in the feed gas are Liquefaction and condensation are separated according to the boiling point.

  On the other hand, in the oil quench tower, in order to improve cooling efficiency and separation, a large number of trays (tray) are installed in the tower. The shelves are equipped with shelves with a lot of fine holes for gas to move upward, and caps are attached to the holes so that the gas bubbles when it passes through the condensate for gas-liquid contact. A shelf board (bubble cap tray) or the like that further increases the area is employed. The feed gas contains ethylenically unsaturated compounds such as cyclopentadiene, cyclohexadiene, styrene, methylstyrene, divinylbenzene, and indene. These compounds are thermally polymerized in an oil quench tower to form a polymer. Cause various obstacles. For example, there is a problem that the viscosity of the bottom liquid of the oil quench tower rises due to the formation of the polymer, and the thermal efficiency is lowered in the heat recovery process. In addition, the polymer produced in the tower adheres to the shelf and wall of the equipment in the gas phase section and grows, resulting in resistance to liquid flow. Cause a decline. In addition, as the growth of dirt progresses, the holes in the shelf are completely blocked, the pressure in the tower rises, the amount of feed gas that can be processed is limited, and in the worst case, the operation is temporarily stopped and the inside of the tower is stopped. Needed to be washed.

  In order to solve such problems, as a method of suppressing the increase in the viscosity of the bottom liquid of the oil quench tower, a method of using sulfonic acid or a salt thereof together with a polymerization inhibitor (Patent Document 1), a heat recovery process in the middle stage In a gasoline fractionation column having a heat recovery process liquid (Patent Document 2) for controlling the circulating amount and temperature of the heat recovery process liquid, and further suppressing fouling and viscosity increase in a hydrocarbon stream containing an ethylenically unsaturated monomer Although the methods (Patent Document 3) are disclosed, these methods are effective in suppressing polymerization in the process liquid, but both methods prevent the growth of dirt in the gas phase part to which the present invention is directed. Had no significant effect.

JP 7-166152 A JP 2002-309271 A JP 2006-500399 A

  An object of the present invention is to provide a method for efficiently preventing the growth of dirt in a gas phase portion in an oil quench tower of an olefin production process, and more specifically, a shelf in the gas phase portion in the oil quench tower. Another object of the present invention is to provide a method for efficiently preventing the growth of dirt generated on the tower wall.

  The inventors of the present invention have examined the occurrence of dirt adhering to the plates and tower walls in the gas phase inside the oil quench tower of the olefin production process, and conducted a detailed analysis of the dirt. It is found that diene compounds with low boiling point are contained in the components, and the generation mechanism of dirt is contained in the gas phase at the shelf, especially the gas phase condensing part on the back side of the shelf and the tower wall in the gas phase condensation temperature zone As a result of diligent investigations to prevent the generation of dirt from the assumption that some diene compounds are condensed and polymerization occurs and the polymer (soil) grows from that point, the diene compound is contained. The inventors have found a method for preventing the growth of dirt by efficiently presenting an effective amount of a polymerization inhibitor in the condensate of process vapor, and have completed the present invention.

That is, in the invention according to claim 1, in the gas phase part of the oil quench tower of the olefins production process having a heat recovery process in the middle stage of the tower, the return line of the quench oil which is the heat recovered process liquid is connected to the normal pressure. presence by boiling to inject one or more polymerization inhibitors selected from monoalkyl hydroxylamine and dialkyl hydroxylamine is 100 to 200 ° C., the polymerization inhibitor 1ppm~1000ppm the condensate of process steam in It is a method for preventing soil growth in a gas phase part of an oil quench tower.

  According to the present invention, it is possible to efficiently prevent the growth of dirt in the gas phase part of the oil quench tower, so that the oil quench tower can be continuously operated and contribute to the stable operation of the entire plant.

Schematic of a SUS autoclave used in the soil growth prevention test of the present invention

In the method for preventing the growth of dirt of the present invention, an effective amount of a polymerization inhibitor for preventing the growth of dirt is present in the condensate of the process vapor in the gas phase part of the oil quench tower having a heat recovery process in the middle stage of the tower. Ru contamination prevention method der oil quenching tower gas phase, characterized in that to.

  In the gas phase part of the oil quench tower, condensation of process vapor occurs on the tower wall or shelf in the condensation temperature zone, and especially on the back side of the shelf in the condensation temperature zone, a large amount of process vapor that has risen on the back side of the shelf. There is a constant supply of condensate that collides and contains ethylenically unsaturated compounds, and the generation of soil due to the polymerization of the ethylenically unsaturated compounds and the growth of soil are active.

  In order for the polymerization inhibitor to be present in the condensate on the back side of the shelf where the generation of soil and the growth of soil is active in this way, the process liquid existing at the bottom of the shelf behaves similarly to process steam. Maintaining an effective amount of the polymerization inhibitor in the condensate by adding a specific polymerization inhibitor that indicates and supplying the specific polymerization inhibitor into the condensate along with the process vapor evaporating from the process liquid. Can do. This method can be applied not only to the rear side of the shelf but also to prevent the growth of dirt on the tower wall in the process vapor condensation temperature zone.

  Such a specific polymerization inhibitor is preferably one having a boiling point in the range of 100 ° C. to 200 ° C. in consideration of transfer of the polymerization inhibitor to the gas phase side of the oil quench tower. Although a polymerization inhibitor having a boiling point outside this range can also be used, it is added to the process liquid at a position below the site where the contamination is generated because the migration ratio of the polymerization inhibitor to the gas phase side is low. It is necessary to keep the concentration of the polymerization inhibitor high, and the efficiency of the addition amount is inferior compared to the polymerization inhibitor having a boiling point in the range of 100 ° C. to 200 ° C. at normal pressure.

  Examples of the compound having a boiling point of 100 ° C. to 200 ° C. at normal pressure include diethylhydroxylamine, dimethylhydroxylamine, methylethylhydroxylamine, dipropylhydroxylamine, dibutylhydroxylamine, dipentylhydroxylamine, diisopropylhydroxylamine, Examples thereof include monoalkylhydroxylamine such as monoisopropylhydroxylamine and dialkylhydroxylamine, among which dimethylhydroxylamine, diethylhydroxylamine and monoisopropylhydroxylamine are preferable. These polymerization inhibitors are used alone or in combination of two or more. Moreover, you may use together with another polymerization inhibitor in the range which does not impair the effect of this invention.

  The above-mentioned specific polymerization inhibitor injection site is not particularly limited as long as it is a process liquid at a position below the site where the contamination is generated, but it is a problem from the point of arrival efficiency of the polymerization inhibitor. In the process where a part of the process liquid in the middle column of the column is extracted and heat recovered, the polymerization inhibitor is placed in the return pipe of the quench oil that is the heat recovered process liquid. It is preferable to inject.

  In the addition of the specific polymerization inhibitor, it may be a stock solution or may be added in a state dissolved in a solvent, a process solution, or water. When two or more polymerization inhibitors are used in combination, each active ingredient may be added separately, or may be added as a one-part preparation mixed at a predetermined ratio. Also in this case, it may be added in a state dissolved in the above-mentioned solvent, process liquid, or water.

  The effective amount of the polymerization inhibitor in the present invention is 1 ppm to 1000 ppm, preferably 10 ppm to 1000 ppm, with respect to the condensate in the gas phase. In order to maintain the concentration, a polymerization inhibitor is added to the process liquid at a position below the site where dirt is generated. If it is less than 1 ppm with respect to the condensate in the gas phase, it is not possible to expect a sufficient effect, and if it exceeds 1000 ppm, the effect is sufficient, but the effect is not improved for the amount of addition, which is not preferable from an economical viewpoint. .

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

(Polymerization inhibitor used for testing and boiling point at room temperature)
DMHA: Dimethylhydroxylamine (Aldrich reagent) 101 ° C
DEHA: diethylhydroxylamine (Tokyo Chemical Industry Reagent) 133 ° C
IPHA: monoisopropylhydroxylamine (manufactured by ANGUS) 163 ° C.
TBC: 4-t-butylcatechol (Tokyo Chemical Industry Reagent) 285 ° C
BHT: Butylhydroxyl toluene (Tokyo Chemical Industry Reagent) 265 ° C
PDA: N, N′-di-sec-butyl-p-phenylenediamine (manufactured by JGC Universal Co., Ltd .: trade name UOP No. 5) 320 ° C.
QM: 2,6-di-t-butylcyclohexa-2,5-dienone (Ciba Specialty Chemicals: trade name Prostub 6007) 200 ° C. or higher DBSA: dodecylbenzene sulfonic acid (trade name, Takeca Power B) -121) 200 ° C or higher

(Dirt growth prevention test)
A test solution is prepared by mixing 10 g of pyrolysis oil obtained from an ethylene plant, 10 g of styrene monomer, and 10 g of isoprene in a 100 ml SUS autoclave shown in FIG. 1 and adding a predetermined amount of a polymerization inhibitor shown in Table 1. , Charged to the bottom of the autoclave. After that, a stainless steel wire netting was installed in the gas phase part at a fixed position from the bottom of the autoclave. Similarly, the polymer obtained from the ethylene plant was washed with xylene and dried at 105 ° C. for 1 hour. 50 mg was weighed and placed in a basket. The autoclave was installed in an oil bath set at 135 ° C. and left for 24 hours. After standing, the autoclave was cooled to room temperature, the polymer on the wire mesh was washed with xylene, dried at 105 ° C. for 1 hour, and the weight was measured. The polymer growth multiple was determined from the weight change before and after the test. This indicates that the smaller the polymer growth multiple, the greater the effect of preventing the growth of dirt in the gas phase. On the other hand, the concentration of the polymerization inhibitor in the condensate was determined by placing a shallow tray (dish) in place of the wire mesh jar in the above test and placing the polymer in it, and testing under the same conditions as above. In parallel, after the test, the condensate collected in the tray was collected, and the hydroxylamines were extracted with water, followed by a colorimetric method, and other polymerization inhibitors were measured by gas chromatography. The results are shown in Table 1.

As shown in Examples 1 to 11 of Table 1, it is clear that the presence of a polymerization inhibitor concentration in the condensate of the process vapor of 1 ppm or more can prevent the growth of dirt in the gas phase, and in particular, condensation examples 1 to 5 a polymerization inhibitor concentration in the liquid is present above 10 ppm, examples 7-9, not more than 1.4 times the polymerization product growth multiples in example 11, contamination growth in gas phase It can be seen that the prevention effect is high. Furthermore, when the results of Reference Example 2 and Reference Example 3 having a boiling point of 200 ° C. or more are compared with Example 5 and Example 11 having a boiling point of 100 to 200 ° C. at normal temperature, Example 5 and Example 11 were compared. In Example 11, the addition of 100 ppm concentration of the polymerization inhibitor in the test solution gives a polymerization inhibitor concentration of 12 to 15 ppm in the condensate, whereas in Reference Example 2 and Reference Example 3 , the same concentration in the condensate is obtained. In order to obtain the polymerization inhibitor concentration, a polymerization inhibitor concentration of 2000 to 4000 ppm is required in the test solution, and it is more efficient to use a polymerization inhibitor having a boiling point of 100 to 200 ° C. at room temperature in the method of the present invention. I understand that.

  As shown in Comparative Examples 1 to 8 in Table 1, when the concentration of the polymerization inhibitor in the condensate of process vapor is 1 ppm or less, the growth of dirt in the gas phase cannot be prevented. From the results of Comparative Examples 1 to 3, even when a polymerization inhibitor having a boiling point of 100 to 200 ° C. at room temperature is used in the method of the present invention, if the polymerization inhibitor concentration in the condensate of process vapor is 1 ppm or less, The effect of preventing the growth of dirt at the phase part is very small, and the growth factor of the polymer is not much different from that of no addition. Even in Comparative Examples 4 to 8 having a boiling point of 200 ° C. or higher at normal temperature, when the concentration of the polymerization inhibitor in the condensate is 1 ppm or less, there is almost no effect of preventing the growth of dirt in the gas phase.

As described above, the presence of an effective amount of a polymerization inhibitor for preventing the growth of dirt in the condensate of the process vapor in the gas phase part of the oil quench tower of the olefin production process, The above-mentioned effective amount is preferably 1 ppm or more, particularly preferably 10 ppm or more, and a polymerization inhibitor having a boiling point of 100 to 200 ° C. at room temperature is a process liquid below the site where the stain is generated. It has become clear that an effective amount of a polymerization inhibitor can be effectively present in the condensate by adding it into the condensate. The polymerization inhibitor particularly suitable for the method of the present invention is at least one selected from monoalkylhydroxylamines and dialkylhydroxylamines having a boiling point of 100 to 200 ° C. at normal pressure.

Claims (1)

In the gas phase part of the oil quench tower of the olefin production process, which has a heat recovery process in the middle of the tower , the boiling point at normal pressure is 100 to 200 ° C. in the return pipe of the quench oil that is the heat recovered process liquid by injecting one or more polymerization inhibitors selected from monoalkyl hydroxylamine and dialkyl hydroxylamines, oil quenching tower gas for causing the condensate of process steam is present the polymerization inhibitor 1ppm~1000ppm A method for preventing the growth of dirt at the phase.

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