JPS6147792A - Method of preventing caulking of cracking furnace for ethylene - Google Patents

Abstract

PURPOSE:To prevent caulking in cracking tube of cracking furnace for ethylene and the following heat exchanger for cooling, by feeding a specific caulking inhibitor to the cracking furnace for ethylene. CONSTITUTION:A caulking inhibitor comprising a compound shown by the formula I and/or formula II (R1-R8 are H, 1-30C alkyl, cycloalkyl, aryl, alkanoyl, aralkyl, or alkenyl; x is 1-6) as an active ingredient is fed to a cracking furnace for ethylene. Preferably, the inhibitor is predissolved in an organic solvent and 10-5,000ppm inhibitor is added to a petroleum raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for preventing coking in a cracking tube of an ethylene cracking furnace and/or a cooling heat exchanger (TLE) at the outlet of the cracking furnace, and more specifically, a method for preventing coking in a cracking tube of an ethylene cracking furnace and/or a cooling heat exchanger (TLE) at the exit of the cracking furnace. By supplying an anti-coking agent to an ethylene cracking furnace for producing ethylene,
Alternatively, the present invention relates to a method for preventing coking in a subsequent cooling heat exchanger. In ethylene production equipment, gaseous hydrocarbons such as ethane and propane, or liquid hydrocarbons such as naphtha and light oil are used as feed oil, and this is fed into a pyrolysis furnace heated to nearly 1000°C to be thermally decomposed to produce ethyl ethylene. . Manufactures propylene. One of the problems with this pyrolysis furnace is the adhesion and deposition of coke generated in the cracking tube and/or subsequent TLE. If coke reaction (accumulation) occurs in these locations, heat conduction will be poor and energy will be lost, and the pressure inside the tube will increase, making it impossible to continue operation and causing danger. To cope with this problem, operators stop operation at regular intervals or in an emergency, and remove adhesion and deposits (decoking) mechanically or by introducing steam or air.

The cause of this undesirable coking is essentially the partial polymerization of the feed oil or of the cracked oil and the subsequent dehydrogenation reaction. Factors related to the rate of coking reaction include the type (composition) of feed oil, the structure of the cracking furnace, and operating conditions. However, attempts to suppress coking by changing these factors from an economic standpoint or operational necessity have their own limits. Therefore, in order to remove these coke deposits, the method of increasing the frequency of forced decoking is exclusively used. On the other hand, there are attempts to chemically suppress coking, such as hydrogen sulfide,
There are examples of sulfur compounds such as dimethyl disulfide (DMDS) being used. There is also a report that phosphorus compounds such as phosphoric acid and phosphorous acid derivatives are effective in suppressing coking (Japanese Patent Application Laid-Open No. 108808/1983).

However, hydrogen sulfide and DMDS are extremely troublesome to handle and are not economically satisfactory. On the other hand, according to research conducted by the present inventors, phosphorus compounds may actually promote coking, so their actual use is quite limited. Furthermore, many of the sulfur compounds and phosphorus compounds are insoluble in hydrocarbons, making them difficult to actually apply. In any case, no drug has yet been found that is fully satisfactory in terms of handling and effectiveness. The present inventors have developed such an ethylene cracking furnace cracking tube and a TL
As a result of analyzing the coking phenomenon in E and examining various chemicals that have a coking inhibiting effect, we discovered that the sulfur compounds represented by the following general formulas (■) and (■) are extremely advantageous in terms of their effects and handling. This has led to the present invention.

SS5(I)
(If) Here R1, R2, R
3, R4, R5, R6, R7, R8 are each independently a hydrogen atom or an alkyl group having 1 to 30 carbon atoms, a cycloalkyl group, an aryl group, an alkanol group, an aralkyl group, or an alkenyl group, and may be different types, and X is an integer from 1 to 6.

Practical examples of compounds represented by formula (1) or formula (2) described in the present invention include NN-diethylthiourea, N,N-dibutylthiourea, N,N-dilaurylthiourea, tetramethylthiuram monosulfide, and tetrabutylthiuram. Examples include monosulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide.

According to the present invention, a compound of formula I or formula (III) is added to an ethylene cracking furnace feed oil at a concentration of 10 to 5000 pI)
.

By preferably adding 50 to 100 ppm, there is an advantage that coke formation in the ethylene cracking furnace cracking tube and/or TLE can be suppressed.

In the present invention, the compound represented by formula I or
000ppm is added, but this is because a sufficient effect cannot be expected with a very small amount, and 5000ppm is added.
The above is based on the judgment that although the effects are sufficient, there are limits from an economic standpoint. Moreover, in the present invention, formula I or ■
Although it is proposed to use at least one kind of compound shown in the following, the use of a mixture of two or more of these compounds
Alternatively, there is no problem in using hydrogen sulfide DMDS in combination with a sulfur compound or a phosphorus compound already known to have an anti-coking effect, and there is no limitation thereto. Furthermore, synergistic effects can be expected depending on the combination of the above.

In order to carry out the present invention industrially, the compound represented by Formula 1 or Ship (2) is dissolved in a general organic solvent such as a hydrocarbon solvent, an oxygen-containing solvent such as alcohol, or a sulfur-containing solvent such as dimethyl sulfoxide. The most common method is to inject it into the feed oil. When injecting, it is desirable to add the chemical continuously and smoothly to avoid pulse injection. In addition, in order to mix the chemicals into the feed oil as uniformly as possible after the chemicals are added to the feed oil until it reaches the cracking furnace, a valve is installed in the middle of the piping or a static mixer is installed. In order to be successful, it is necessary to take measures such as bending or providing bends in the piping. From this meaning,
It is most ideal to add the chemicals described in this invention to the feed oil in advance, but if this is not possible, place the injection point as far as possible upstream of the feed oil from the first port of the cracking furnace. It is desirable to place

Next, the present method will be explained in detail by way of examples. However, the present invention is not limited to the following examples.

[Example test tube heated to 50°C or 850°C (Material: SOS 316. Inner diameter 2.2mm, length 400mm)
) was fed with fixed amounts of naphtha and water. After the specified time has elapsed, remove the test tube and
The amount of attached coke was calculated from the weight ratio before and after the test.

A predetermined amount of a chemical for suppressing coking was dissolved in naphtha, and this was used in the experiment. The test lasted 10 hours,
If there was heavy caulking, the tube would become blocked midway through, so in that case, the test was stopped at that point and the amount of caulking deposited was measured.

Claims (1)

[Scope of Patent Claims] 1. The following general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [ I ] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼[II] (Here, R_1, R_2, R_3, R_4, R_5,
R_6, R_7, and R_8 are each independently a hydrogen atom or an alkyl group having 1 to 30 carbon atoms, a cycloalkyl group, an aryl group, an alkanol group, an aralkyl group, or an alkenyl group, and may be the same or different, Further, the cracking tube of the ethylene cracking furnace is characterized in that it supplies an anti-coking agent containing as an active ingredient at least one compound selected from the group consisting of the compounds represented by (X is an integer from 1 to 6) and/or Or a method of suppressing coke formation in a subsequent cooling heat exchanger. 2. The method according to claim 1, wherein the anti-coking agent is mixed and added to the petroleum-based raw material in advance. 3. The method according to claim 1, wherein the anti-coking agent is dissolved in an organic solvent in advance and then injected into the petroleum-based raw material. 4. Add the above anti-coking agent to petroleum-based raw materials from 10 to
The method according to claims 2 to 3, wherein the additive is added in an amount corresponding to a range of 5000 ppm.