JP3859435B2 - Method for preventing contamination of ethylene production equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing contamination of an ethylene production apparatus. More specifically, the present invention relates to a method for preventing contamination by suppressing the production of a polymer in the separation and purification process of an ethylene production apparatus, and enabling the multi-year continuous operation of the apparatus to be carried out smoothly and reliably.
[0002]
[Prior art]
In general, as shown in FIG. 1, an ethylene production apparatus includes a process in which a pyrolysis process, a quench process, a compression process, and a separation and purification process are continuous.
[0003]
In the separation and purification process, petroleum fractions produced by thermal decomposition of naphtha or the like are sequentially distilled in a number of continuous distillation columns, and are generally separated and purified from those having a small number of carbon atoms. That is, a series of distillation towers consisting of a series of distillation towers such as a demethanizer tower, a deethanizer tower, a depropanizer tower, a debutane tower, a depentane tower, a relan tower, a condensate stripper, and a cracked gasoline stripper, It will be separated and purified sequentially.
[0004]
In the pyrolysis process, naphtha and the like are pyrolyzed, and petroleum olefins produced by this pyrolysis include various olefins such as ethylene, propylene, butenes, acetylenes, butadienes, pentenes, pentadienes, Indenes, styrenes, etc. are included. The contamination in the separation and purification process is that these olefins are subjected to the action of heat, trace amounts of oxygen or peroxides, metal ions, etc., the radical reaction is promoted, and the polymer is deposited in the apparatus. Is attributed. The bottom of the distillation column is the most dirty part, and if dirt accumulates, the efficiency of heat deteriorates, the flow of process fluid deteriorates, and the operating efficiency deteriorates. is there.
[0005]
Further, dienes such as 1,3-butadiene, isoprene, and cyclopentadiene contained in the oil form a popcorn-like polymer called a popcorn polymer. This polymer has a three-dimensional structure with highly advanced crosslinking, is insoluble in a solvent, and does not melt even when heated. Once this popcorn polymer is produced, it becomes a nucleus and continues to grow exponentially, and the inside of the apparatus may be rapidly blocked, resulting in destruction of the apparatus. For this reason, when this polymer is formed, there is no method other than immediately suspending the apparatus and removing it by a physical method such as high-pressure jet cleaning. As described above, the contamination of a small part of the distillation tower hinders the stable operation of the entire ethylene production apparatus, and in some cases, may cause a decrease in production amount or stop of the entire apparatus.
[0006]
In general, large-scale equipment such as ethylene production equipment is periodically shut down to remove dirt and popcorn polymer deposits due to the polymer in the equipment. It is normal. However, since a huge cost is required to stop and restart the apparatus, a long-term continuous operation that is economically advantageous is planned. When trying to carry out long-term continuous operation in the separation and purification process, it is an important issue to maintain a healthy state in which no polymer is deposited in the apparatus of the distillation column group.
[0007]
So far, as a method for suppressing the formation of a polymer, for example, a method using phenols or hydroxylamines [for example, Japanese Patent Laid-Open No. 50-112304, US Pat. No. 4,434,307 (1984)], phenylene Methods using diamines and nitrosophenols (for example, JP-A-5-156233) have been proposed.
[0008]
However, the method of using phenols, phenylenediamines, and hydroxylamines does not have a great effect of suppressing the formation of polymerized products, and must be used in a large amount to obtain a sufficient effect.
[0009]
As these improvement methods, a method using a polymerization inhibitor such as piperidine-1-oxyls (Japanese Patent Publication No. 51-15001), and piperidine-1-oxyls less than 700 ppb with respect to the amount of oil supplied are added. A method for preventing dirt (Japanese Patent Publication No. 4-26639) has been proposed.
[0010]
Piperidine-1-oxyls bind to alkyl radicals that cause radical polymerization reaction of dienes and stop polymerization at the initial stage, and have high reactivity and high polymerization inhibition activity. Yes. However, since piperidine-1-oxyls react with radicals and consume their own radicals, the polymerization proceeds rapidly when the concentration is insufficient, and the situation is the same as when no polymerization inhibitor is added. Become. Therefore, industrially, it was often used more than necessary from the viewpoint of safe driving, and there was an economic problem.
[0011]
The composition of the oil entering the distillation tower varies greatly depending on the distillation tower. For example, the concentration of 1,3-butadiene in the oil is about several percent in the deethanizer, but about several tens of weight percent in the debutanizer. Moreover, the composition of such oil varies greatly from factory to factory, and varies depending on the operating conditions in the same factory. In practice, the concentration of 1,3-butadiene in the debutane tower varies from about 20% to about 50% by weight. Yes. The above method of adding less than 700 ppb of piperidine-1-oxyl to the amount of oil to be supplied without considering fluctuations in operating conditions such as the composition and temperature of the feedstock is a very dangerous method. It is.
[0012]
The operating conditions of the distillation tower vary greatly depending on the distillation tower. Generally, the bottom temperature of the distillation tower is low in the distillation tower located upstream and tends to increase as it goes downstream. For example, it is about 0 ° C. in the deethanizer but about 180 ° C. in the rerun tower. Even in the same distillation column, the operating conditions are not constant and vary from factory to factory. For example, the bottom temperature of the depropanizer tower is in a wide range from about 70 ° C to about 110 ° C. Even in the same factory, when seawater is used for cooling the top of the tower, for example, the bottom temperature of the depropanizer tower is operated at about 20 ° C. higher in the summer than in the winter.
[0013]
As described above, the separation and purification process for ethylene production has a complicated raw material composition to be handled, and the raw material composition and operating conditions to be handled vary greatly depending on factories, making it difficult to solve the contamination problem due to the polymer. . In particular, there is no standard for determining the optimum addition amount of the polymerization inhibitor, and the actual situation is that it is determined based on past experience or from an economic standard.
[0014]
[Problems to be solved by the invention]
Inhibition of polymerization by stable free radical compounds, polymerization proceeds rapidly when the concentration is insufficient, and the situation is the same as when a polymerization inhibitor is not added. The method of maintaining the appropriate concentration has been a major issue.
[0015]
The object of the present invention is to overcome the drawbacks of such a method for preventing polymerization fouling with a stable free radical compound, and to provide a rational method capable of safely and economically achieving long-term continuous operation of an ethylene production apparatus. It is in.
[0016]
[Means for Solving the Problems]
The present inventors have suitable piperidine-1-oxyls as stable free radical compounds for suppressing the formation of polymer in an ethylene production apparatus distillation column, and the optimum addition amount thereof is a specific conjugated diene at the bottom of the column. The present invention has been found out from the relationship between the concentration of the distillation column, the column bottom temperature of the distillation column, and the (relative) residence time of the raw oil at the column bottom.
[0017]
That is, the present invention of claim 1 is a method of adding piperidine-1-oxyls as a stable free radical compound to the amount of oil supplied to the distillation column in the separation and purification process in order to prevent contamination of the ethylene production apparatus. In this case, the addition amount is not less than the [D] value (μ · mol / kg feedstock supply amount) obtained by the following formula, and “[D] value +3.5” (μ · mol / kg feedstock feed) A method for preventing contamination of an ethylene production apparatus, characterized in that the amount is set to fall within the following range .
[D] = {3.5 + 5 [exp (0.07T)] × C × (V / L) × 10 ⁻⁶ } / F
[Wherein [D] is the amount of stable free radical compound added to the amount of oil supplied to the distillation column (μ · mol / kg feedstock feed amount), and F is the functionality in the stable free radical compound. That is, the number of radical sites in one molecule of the stable free radical compound, T is the bottom temperature (° C.) of the distillation tower, and C is the total concentration of 1,3-butadiene, isoprene and cyclopentadiene in the bottom liquid of the distillation tower (wt %), V represents the bottom volume (m ³ ) of the distillation column, and L represents the flow rate (m ³ / min) withdrawn from the bottom of the distillation column. ]
[0018]
In the invention of claim 2, piperidine-1-oxyls which are stable free radical compounds are 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6,6-tetra Methylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl and 4-ethoxy The method for preventing contamination of an ethylene production apparatus according to claim 1, wherein the method is one or more selected from -2,2,6,6-tetramethylpiperidine-1-oxyl.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The ethylene production apparatus according to the present invention is usually a separation and purification step in which petroleum fractions produced by pyrolyzing naphtha are sequentially extracted from the top of each column by distillation from those having a small number of carbon atoms. , Depropanizer tower, debutane tower condensate stripper, cracked gasoline stripper.
[0020]
The stable free radical compound is an N-oxyl radical compound that can be handled stably at room temperature and in the presence of air, and specifically includes piperidine-N-oxyls. Further, a compound in which a plurality of piperidine-N-oxyls molecules are linked with a dibasic acid or the like and a plurality of N-oxyl groups are present in one molecule can also be used.
[0021]
Specific examples of these compounds include piperidine-N-oxyls having one N-oxyl group such as 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2 , 6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-1 -Oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-phenoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-carboxy-2,2 , 6,6-tetramethylpiperidine-1-oxyl.
[0022]
Piperidine-N-oxyls having two N-oxyl groups include bis- (2,2,6,6-tetramethylpiperidine-1-oxyl) succinate, bis- (2,2,6, 6-tetramethylpiperidine-1-oxyl) adipate, bis- (2,2,6,6-tetramethylpiperidine-1-oxyl) sebacate, N, N′-bis- (2,2,6,6) -Tetramethylpiperidyl-1-oxyl) 1,6-hexanediamine and the like.
[0023]
Examples of piperidine-N-oxyls having three N-oxyl groups include tris- (2,2,6,6-tetramethylpiperidine-1-oxyl) phosphite.
[0025]
[D] is a minimum addition amount (μ · mol / kg raw material supply amount) of a stable free radical compound to the oil supplied to the distillation column, which is obtained by the above formula.
[0026]
F represents the number of radical sites having the functionality i.e. stable free radical stable free radicals, in the piperidine -N- oxyls corresponding to the number of N- oxyl groups present in one molecule.
[0027]
C is the total concentration (wt%) of 1,3-butadiene, isoprene and cyclopentadiene in the bottom liquid of the distillation tower, and is measured by collecting the bottom liquid from the bottom bottom liquid extraction line. The measurement method is not particularly limited, but it is preferable that the gas chromatograph is simple, the measurement can be performed in a short time, and a measurement device is embedded in the extraction line so that the measurement can always be performed.
[0028]
T represents the bottom temperature (° C.) of the distillation column, and is usually measured by installing a temperature sensor at the bottom of the distillation column.
[0029]
V is a distillation column bottom volume (m ³ ). Specifically, referring to FIG. 2 , in the distillation column, in order to maintain the distillation, a part of the bottom liquid is transported from the lower part of the distillation column to a reboiler (reboiler), heated and returned to the distillation column. However, the bottom volume of the distillation tower in the present invention is the volume of the bottom of the distillation tower filled with the liquid feed oil in the lower part of the distillation tower below the return line from the reboiler, and the bottom of the distillation tower. And the volume of the extraction line 4 connecting the reboiler and the volume of the reboiler filled with the supply oil, the volume of the return line 5 from the reboiler and the volume of the reboiler upper cover 7 are not included. This is a unique value for each distillation column.
[0030]
L is a flow rate (m ³ / min) withdrawn from the bottom of the distillation column, and can usually be measured by a flow meter installed in the distillation column.
[0031]
The amount of addition of piperidine-N-oxyls, which are stable free radical compounds , is an eigenvalue determined by the apparatus, and [D] can be calculated by automatically measuring C, T, and L. The object of the present invention can be achieved more appropriately.
[0032]
The addition place is added to the raw material supply line, distillation tower reflux line and reboiler of the distillation column where contamination due to the formation of the polymer is a problem, or is added in portions from a plurality of locations. Further, when the raw material is supplied via a tank, it may be added to the raw material tank.
[0033]
The amount of the stable free radical compound and piperidine-N- oxyls added to the oil supplied to the distillation column is controlled within the range of [D] value or more and “[D] +3.5” value or less . If the addition of the stable free radical compound is lower than the [D] value, the polymerization is not sufficiently suppressed, and dirt and popcorn polymer may be generated due to the deposition of the polymer, and long-term continuous operation may not be obtained. Further, if it is more than “[D] +3.5”, the effect lasts sufficiently and contributes to the suppression of the fouling of the subsequent distillation column. However, there is no problem from the economical point of view.
[0034]
The added amount of piperidine-N-oxyls, which are stable free radical compounds in the present invention , is not limited to the stable free radical compound added anywhere in the target apparatus, but is added in the previous distillation step. Stable free radical compounds that remain in the distillation column system should also be considered.
[0035]
When there are contamination problems in a plurality of distillation columns, they may be added to each distillation column . In the case where a continuous distillation column is used, if dirt is generated in the downstream distillation column, piperidine-N-oxyls which are stable free radicals are added to the most upstream distillation column, and the downstream distillation column is added. by measuring the stable free radical amount remaining in the in the raw material, adding only shortfall is advantageous fewer said stable free radical amount. Incidentally, the stable free radical weight liquid chromatography, can be measured by gas chromatography, ESR (Electron Spin Resonance) method is most suitable.
[0036]
Other known polymerization inhibitors, antioxidants, dispersants, metal deactivators and the like may be added and used within a range not impairing the object of the present invention, but the present invention is not intended to limit their use. Absent.
[0037]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to the following Example at all.
[0038]
[Example 1]
In the dediplo tower in the ethylene production equipment, the representative values of the bottom liquid composition were 33 wt% for 1,3-butadiene, 4 wt% for isoprene, 3 wt% for cyclopentadiene, and the total amount of dienes was 42 wt% at maximum. . The column bottom temperature was 95 ° C. at the maximum, the column bottom liquid extraction amount was 0.78 m ³ / min at the minimum, and the column bottom volume was 15 m ³ . [D] value was calculated | required from these data.
[D] = {3.5 + 5 [exp (0.07T)] × C × V / L × 10 ⁻⁶ } / F
= {3.5 + 5 [exp (6.65)] × (42) × (15 / 0.78) × 10 ⁻⁶ } / F
= 6.6 / F
[0039]
From this result, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HTEMPO), which is a stable free radical of F = 1, is 6.6 to 10.1 μmol / kg of oil supply, weight concentration The standard suggested that 1.2 to 1.7 ppm addition was the optimum addition amount. From the raw material supply line (feed line) of the depropanizer tower, HTEMPO was added and operated so as to maintain 1.2 ppm or more with respect to the raw material supply amount. Previously, the reboiler was clogged with dirt, and it was necessary to switch to a spare reboiler in the middle of operation, but after switching to the method of the present invention, no signs of dirt were observed during operation and there was no need for reboiler switching. It was. In addition, in the inspection after 23 months of continuous operation, each part of the distillation apparatus such as the inside of the distillation tower, the reboiler, and the connecting pipe was opened and inspected in detail. However, there was no contamination.
[0040]
[Example 2]
In the debutane tower in the ethylene production apparatus, the typical values of the bottom liquid composition were 9 wt% for isoprene and 8 wt% for cyclopentadiene. These varied slightly, but the total of these dienes was up to 20 wt%. Similarly, the column bottom temperature was 105 ° C. at the maximum, the column bottom liquid extraction amount was 0.15 m ³ / min at the minimum, and the column bottom volume was 5.5 m ³ . [D] value was calculated | required from these data.
[D] = {3.5 + 5 [exp (0.07T)] × C × V / L × 10 ⁻⁶ } / F
= {3.5 + 5 [exp (7.35)] × (20) × (5.5 / 0.15) × 10 ⁻⁶ } / F
= 9.2 / F
[0041]
From these results, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HTEMPO), which is a stable free radical with F = 1, is 9.2 to 12.7 μmol / kg of the raw material supply amount, and the weight concentration According to the standard, it was suggested that the contamination could be prevented by adding 1.6 to 2.2 ppm. From this, HTEMPO was added from the feed line of the debutane tower so as to maintain 1.6 ppm with respect to the raw material supply amount.
[0042]
After 23 months of continuous operation in this manner, in the scheduled periodic inspection, each part of the distillation apparatus such as the inside of the distillation column, reboiler, and connecting piping was inspected in detail, but there was no contamination. In addition, the reboiler has been blocked by dirt and had to be disassembled and cleaned after 12 months. However, after 23 months of operation, there was no dirt and there was no need for cleaning.
[0043]
Example 3
In different debutanizer the implementation example 2, the representative value of the bottom liquid composition isoprene 11.3Wt%, cyclopentadiene was 13.4 wt%. Although these varied slightly, the total of these dienes was up to 28 wt%. Similarly, the column bottom temperature is a maximum of 110 ° C., and the column bottom liquid extraction is the minimum. It was 95 m ³ / min, and the column bottom volume was 25.2 m ³ . A preferable stable free radical supply amount was determined from these data.
[D] = {3.5 + 5 [exp (0.07T)] × C × V / L × 10 ⁻⁶ } / F
= {3.5 + 5 [exp (7.7)] × (28) × (25.2 / 0.95) × 10 ⁻⁶ } / F
= 11.7 / F
[0044]
From this result, the required addition amount of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HTEMPO) is 11.7 to 15.2 μmol per kg of the raw material supply amount, and 2 based on the weight concentration standard. It was suggested that the addition of 0.0 to 2.6 ppm can prevent soiling.
[0045]
Since HTEMPO was continuously added upstream from the debutane tower, the HTEMPO remaining in the oil supplied to the debutane tower was measured periodically by ESR method. From 1.1 to 1.5 ppm. Thus, 1.1 ppm was added to the feed oil from the feed line of the debutane tower to compensate for the shortage.
[0046]
After 23 months of continuous operation in this manner, in the scheduled periodic inspection, each part of the distillation apparatus such as the inside of the distillation column, reboiler, and connecting piping was inspected in detail, but there was no contamination. Further, in the conventional dirt prevention method, the reboiler is blocked with dirt and needs to be disassembled and cleaned after 12 months. However, after 23 months of operation, there is no dirt and there is no need for cleaning.
[0047]
[Comparative Example 1]
In the dediplo tower in which Example 1 was performed, p-tert-butylcatechol was added from the feed line of the depropanizer to the feed oil at 3.5 ppm (21.1 μmol per kg of raw material), as in Example 1. And operated continuously for 11 months. When operated continuously for 11 months by this method, a large amount of rubbery polymer and popcorn polymer were generated in each part of the distillation column, particularly in the bottom of the distillation column and in the reboiler, and a large amount of dirt was generated. In addition, the reboiler was clogged with dirt in 6 months and needed to be disassembled and cleaned.
[0048]
[Comparative Example 2]
In the debutane tower in which Example 2 was performed, p-tert-butylcatechol was 3.5 ppm (21.1 μmol / kg of raw material) and N, N-diethylhydroxylamine was 4.0 ppm with respect to the feed oil from the feed line. The operation was continued for 23 months in the same manner as in Example 2 except that (44.9 μmol per kg of raw material) was added. When operated continuously for 23 months by this method, a large amount of rubbery polymer and popcorn polymer were generated in each part of the distillation column, particularly in the bottom of the distillation column and in the reboiler, and a large amount of dirt was generated. Further, the reboiler was clogged with dirt after 12 months and needs to be disassembled and cleaned, and the distillation column bottom liquid extraction line (depentane tower supply line) was clogged with dirt after 12 months and needed to be disassembled and cleaned.
[0049]
[Comparative Example 3]
In the dediplo tower, representative values of the bottom liquid composition were 26 wt% for 1,3-butadiene, 5 wt% for isoprene, and 6 wt% for cyclopentadiene. These varied slightly, but the total of these dienes was up to 39 wt%. Similarly, the column bottom temperature was a maximum of 82 ° C., the column bottom liquid extraction amount was a minimum of 0.72 m ³ / min, and the column bottom volume was 14.5 m ³ . From these data, [D] was 4.7.
[D] = {3.5 + 5 [exp (0.07T)] × C × V / L × 10 ⁻⁶ } / F
= {3.5 + 5 [exp (5.74)] × (39) × (14.5 / 0.72) × 10 ⁻⁶ } / F
= 4.7 / F
[0050]
From this, the preferable addition amount of HTEMPO was 4.7 to 8.2 μmol per 1 kg of feed oil (0.8 to 1.4 ppm based on weight concentration).
[0051]
However, in practice, since the operation was performed with the HTEMPO addition amount from the feed line of the depropanizer tower being 0.3 to 0.5 ppm, the reboiler was clogged with dirt in the sixth month of operation, and it was necessary to disassemble and clean.
[0052]
【The invention's effect】
By the method of the present invention, the optimum addition amount of the polymerization inhibitor for the purpose of solving the contamination problem due to the polymer can be calculated under various conditions of the process without performing on the basis of past experience or economical criteria. Resulted in long-term safe continuous operation.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of an ethylene production apparatus.
FIG. 2 is a view showing an outline of a distillation tower bottom / reboiler (reboiler).
[Explanation of symbols]
1: Feed line 2: Overhead line 3: Bottom line (column bottom liquid extraction line)
4: Extraction line to reboiler 5: Return line from reboiler 6: Reboiler-lower cover 7: Reboiler-upper cover 8: Heating medium line 9: Heating medium line

Claims (2)

In order to prevent contamination of the ethylene production apparatus, in the method of adding piperidine-1-oxyls as a stable free radical compound to the amount of oil supplied to the distillation column in the separation and purification step, the amount added is as follows: determined by the formula [D] value (μ · mol / kg feed oil supply amount) or more, and "[D] value +3.5" (μ · mol / kg feed oil supply amount) to be within the range An antifouling method for an ethylene production apparatus, characterized by comprising :
[D] = {3.5 + 5 [exp (0.07T)] × C × (V / L) × 10 ⁻⁶ } / F
[Wherein [D] is the amount of stable free radical compound added to the amount of oil supplied to the distillation column (μ · mol / kg feedstock feed amount), and F is the functionality in the stable free radical compound. That is, the number of radical sites in one molecule of the stable free radical compound, T is the bottom temperature (° C.) of the distillation column, C is the total concentration of 1,3-butadiene, isoprene and cyclopentadiene in the bottom solution of the distillation column (wt %), V represents the bottom volume (m ³ ) of the distillation column, and L represents the flow rate (m ³ / min) withdrawn from the bottom of the distillation column. ] Piperidine-1-oxyls which are stable free radical compounds are 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl and 4-ethoxy-2,2,6, The method for preventing contamination of an ethylene production apparatus according to claim 1, wherein the method is one or more selected from 6-tetramethylpiperidine-1-oxyl.

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