JPS6350399B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is suitable for use on cracking tubes in furnaces used for the pyrolysis of gaseous streams containing hydrocarbons, and on any heat exchanger used for cooling the effluent stream from the furnace. by the use of special antifoulants effective to reduce the rate of carbon formation on the walls of such cracking tubes and in such heat exchangers. Concerning how to do so. Cracking furnaces form the heart of many chemical manufacturing processes. Often, the performance of this cracking furnace will carry the major profit potential burden of the entire manufacturing process. Therefore,
It is extremely desirable to maximize the performance of the cracking furnace. In manufacturing processes such as ethylene production, feed gases such as ethane and/or propane and/or naphtha are fed into a cracking furnace. A diluent fluid, such as steam, is typically combined with the feed material being fed to the cracking furnace. Within the furnace, the feed stream that is combined with the diluent fluid is
Mainly hydrogen, methane, ethylene, propylene,
It is converted to a gas mixture containing butadiene and small amounts of heavier gases. At the exit of the furnace, the mixture is cooled, removing most of the relatively heavy gases, and compressed. This compressed mixture is directed to various distillation columns where the individual components, such as ethylene, are purified and separated. The separated product, of which ethylene is the main product, then goes to an ethylene plant where it is used in a number of other steps for the production of a wide variety of secondary products. The primary function of a cracking furnace is to convert the feed stream to ethylene and/or propylene.
Semipure carbon, called coke, is formed as a result of the furnace cracking operation. Coke is also formed in the heat exchanger used to cool the gas mixture flowing from the cracking furnace. Coke formation is generally a homogeneous thermal reaction in the gas phase (thermal coking).
(thermal coking) and a heterogeneous catalytic reaction between hydrocarbons in the gas phase and metals in the walls of cracking tubes or heat exchangers (catalytic coking). . Coke is generally said to form on the metal surfaces of cracking tubes that are in contact with the feed stream and on the metal surfaces of heat exchangers that are in contact with the gaseous effluent from the cracking furnace. However, coke is
It should be recognized that it also forms on connecting conduits and other metal surfaces exposed to hydrocarbons at elevated temperatures. Therefore, the word "Metals"
Hereinafter, reference will be made to all metal surfaces that are exposed to hydrocarbons during the cracking process and that give rise to coke deposition. The normal mode of operation of a cracking furnace is to periodically shut down the furnace to burn-out the deposited coke. This downtime results in substantial production losses. Additionally, coke is an excellent thermal insulator. Therefore, with the adhesion of coke,
Higher furnace temperatures are required to maintain the gas temperature in the cracking zone at the desired level. Such relatively high temperatures will increase fuel consumption and at the same time shorten tube life. Another problem associated with carbon formation is metal erosion, which occurs in two ways. First, it is well known that in catalytic coke formation the metal catalyst particles are removed or shed from the surface and into the coke. This phenomenon results in extremely rapid metal loss,
This ultimately results in the destruction of the metal. The second mode of erosion is caused by carbon particles migrating from the tube wall and into the gas stream. The frictional action of these particles is particularly severe at the return bend in the furnace tube. However, another and more subtle effect of coke formation is that the coke enters the alloy in the furnace tube in the form of a solid solution. This carbon then reacts with the chromium in the alloy to precipitate chromium carbide. This phenomenon, known as carburization, causes the alloy to lose its inherent oxidation resistance and thus become susceptible to chemical attack. The mechanical properties of the tube are also adversely affected.
Carburization can also occur with iron and nickel in the alloy. Based on the present invention, an antifouling agent selected from a combination of tin, tin and antimony, a combination of germanium and antimony, a combination of tin and germanium, and a combination of tin, antimony and germanium is applied to the metal. The antifouling agent is contacted with the metal by either pre-treating it with an agent, adding the antifouling agent to the hydrocarbon feedstock entering the cracking furnace, or both. The use of this antifouling agent substantially reduces the formation of coke on the metal and the negative effects associated with coke formation on the metal are substantially reduced. The present invention describes a cracking furnace used in a process for ethylene production. However, the invention described herein provides that the cracking furnace is used to crack the feed material into certain desired components, and that the cracking tube of the cracking furnace or other It is also widely applicable to other methods where coke is formed on metal surfaces. Any suitable germanium can be used in the germanium and antimony combination antifouling agent, the tin and germanium combination antifouling agent, and the tin, antimony and germanium combination antifouling agent. Elemental germanium, inorganic compounds and organic compounds, as well as mixtures of any two or more of these, are preferred sources of germanium. The term "germanium" refers to any of these sources of germanium. Some inorganic germanium compounds that can be used include halides, nitrides, hydrides, oxides, sulfides, imides, sulfates and phosphates. Among inorganic germanium compounds, those containing no halogen are preferred. Examples of organogermanium compounds that can be used include the formula, (where R ₁ , R ₂ , R ₃ , R ₄ are independently selected from the group consisting of hydrogen, halogen, hydrocarbyl, and oxyhydrocarbyl). Hydrocarbyl and oxyhydrocarbyl groups have 1 to 20 carbon atoms which may be substituted with halogen, nitrogen, phosphorus or sulfur.
Examples of hydrocarbyl groups are alkyl, alkenyl, cycloalkyl, aryl groups and combinations of the above, such as alkylaryl or alkoxychloroalkyl groups. Tetrabutylgermanium, germanium tetraethoxide,
Germanium compounds such as tetraphenylgermanium, germanium tetraphenoxide and diphenyldibromogermanium can be used. Germanium tetraethoxide is currently preferred. Any suitable antimony can be used in the tin and antimony combination antifouling agent, the germanium and antimony combination antifouling agent, or the tin, antimony and germanium combination antifouling agent. Elemental antimony, inorganic and organic antimony compounds, and mixtures of any two or more thereof are suitable sources of antimony. The term "antimony" generally refers to any one of these sources of antimony. Examples of some inorganic antimony compounds that can be used include antimony oxides, such as antimony trioxide, antimony tetroxide, and antimony pentoxide;
Antimony trisulfide, and antimony sulfides such as antimony pentasulfide, antimony sulfates such as antimony trisulfate, antimonic acids such as metaantimonic acid, orthoantimonic acid and pyroantimonic acid, antimony trifluoride, antimony trichloride, Antimony halides such as antimony bromide, antimony triiodide, antimony pentafluoride and antimony pentachloride, antimony halides such as antimony chloride and antimony trichloride are included. Among inorganic antimony compounds, halogen-free compounds are preferred. Examples of some organic antimony compounds that can be used include antimony triformate, antimony trioctoate, antimony triacetate,
Antimony carboxylates, such as antimony tridodecanoate, antimony triotadecanoate, antimony tribenzoate, and antimony tris (cyclohexene carboxylate), antimony tris (thioacetate), antimony tris (dithioacetate) and antimony tris ( antimony thiocarboxylate salts such as dithiopentanoate), antimony thiocarbonates such as antimony tris(o-propyldithiocarbonate), antimony carbonates such as antimony tris(ethyl carbonate), and antimony carbonates such as triphenylantimony trihydrocarbyl antimony compounds such as triphenyl antimony oxide, antimony salts of phenolic compounds such as antimony triphenol oxide, antimony salts of thiophenol compounds such as antimonytris(-thiophenoxide) , antimony sulfonates such as antimony tris (benzenesulfonate) and antimony tris (p-toluene sulfonate), antimony carbamates such as antimony tris (diethyl carbamate), antimony tris (dipropyldithiocarbamate), antimony tris (-phenyl dithio antimony phosphates such as antimony tris (dipropyl) phosphate), antimony thiocarbamates such as antimony tris (butyl thiocarbamate), antimony phosphites such as antimony tris (-diphenyl phosphite), antimony phosphates such as antimony tris (dipropyl) phosphate), antimony phosphates such as antimony tris (dipropyl) phosphate, , o-dipropyl thiophosphate), antimony thiophosphates such as antimony tris (o,o-dipropyldithiophosphate), and the like. Antimony 2-ethylhexanoate is currently preferred. Any suitable form of tin can be used as the tin antifouling agent in the tin and antimony combination antifouling agent, the tin and germanium combination antifouling agent, or the tin, antimony and germanium combination antifouling agent. Elemental tin, inorganic and organic tin compounds, as well as mixtures of two or more of these, are suitable sources of tin. The term tin generally refers to any one of these sources of tin. Examples of inorganic tin compounds that can be used include tin oxides such as stannous and stannic oxides, tin sulfides such as stannous and sulfide,
tin sulfates such as stannous sulfate and stannic sulfate; stannous acids such as metastannic acid and thiostannic acid; stannous fluoride; stannous chloride; stannous bromide; stannous iodide; tin halides such as stannic oxide, stannic chloride, stannic bromide, and stannic iodide; tin sulfates such as stannous phosphate; stannous oxychloride and stannic oxychloride. This includes tin oxyhalides such as. Among inorganic tin compounds, those containing no halogen are preferred as the tin source. Examples of organotin compounds that can be used include stannous formate, stannous acetate, stannous lactate, stannous octoate, stannous decanoate, stannous oxalate,
stannous benzoate, and stannous carboxylates such as stannous cyclohexanecarboxylate, stannous thiocarboxylic acids such as stannous thioacetate, stannous dithioacetate, dibutyltin bis(isooctylmercaptoacetate) and dibutyltin bis(isooctylmercaptoacetate); dihydrocarbyl tin, such as propyltin bis(butyl mercaptoacetate), bis(hydrocarbyl mercaptoalkanoate), tin thiocarboxylate, such as stannous O-ethyl dithiocarboxylate, tin carbonate, such as propyl stannous carbonate; Tetrahydrocarbyltin, dipropyltin oxide, such as tetrabutyltin, tetraoctyltin, tetradodecyltin and tetraphenyltin;
Dihydrocarbyltin oxides such as dibutyltin oxide, dioctyltin oxide, diphenyltin oxide, dihydrocarbyltin, bis(hydrocarbylmercaptide) such as dibutyltin bis(dodecylmercaptide),
tin salts of phenolic compounds such as stannous thiophenoxide, stannous benzenesulfonate, p
- stannous sulfonates such as stannous toluenesulfonate, stannous carbamates such as stannous diethylcarbamate, stannous propylthiocarbamate, and stannous diethyldithiocarbamate, diphenyl stannous phosphite; tin phosphite such as, stannous phosphate such as dipropyl stannous phosphate, stannous o,o-dipropylthiophosphate, o,
stannous o-dipropyldithiophosphate and o,o
- tin thiophosphates such as stannic dipropyldithiophosphate, dibutyltin, dihydrocarbyl tins such as bis(o,o-dipropyldithiophosphate), bis(o,o-dihydrocarbyl thiophosphate), etc. included. Currently 2-
Stannous ethylhexanoate is preferred. Any of the above tin sources can be used in conjunction with any of the above antimony and germanium sources to form a tin and germanium combination antifouling agent, a tin and antimony combination antifouling agent, or a tin, antimony and germanium combination antifouling agent. can be formed. Similarly, any germanium source described above and any antimony source described above can be used in combination to form a germanium and antimony combination antifouling agent. In combination antifouling agents of tin and antimony,
Any suitable concentration of antimony can be used. about
Antimony concentrations within the range of 10 mol % to about 75 mol % are presently preferred, as outside this range the effectiveness of the tin and antimony combination antifouling agent is reduced. Similarly, any suitable antimony concentration can be used in a germanium and antimony combination antifouling agent. Approximately 10 mol% to approx.
Antimony concentrations within the range of 75 mole percent are presently preferred, as outside this range the effectiveness of the combination of germanium and antimony is reduced. Any suitable concentration can be used in the combination antifouling agent of tin and germanium. Germanium concentrations within the range of about 10 mol% to about 75 mol% are currently preferred, as it is believed that outside this range the effectiveness of tin and germanium combination antifoulants may be reduced. This is because there is. Any suitable antimony concentration can be used in the combination of tin, antimony and germanium.
Concentrations within the range of about 10 mol% to about 65 mol% are currently preferred. Similarly, germanium concentrations within the range of about 10 mol% to about 65 mol% are currently preferred. In general, the combination antifouling agents of the present invention are effective in reducing coke deposition on any hot steel. Tin antifouling agents are believed to be effective in reducing coke deposition on any high temperature steel other than steels with iron contents of about 98% by weight or higher. Steels commonly used for cracking tubes are Incoloy 800, Inconel 600, HK40, 11/4 chromium-1/2 molybdenum steel and type 304 stainless steel.
The weight percent composition of these steels is as follows.

[Table] =
304SS 9.0 .08 72
19
The antifouling agent of the present invention may be contacted with the metal by pretreating the metal with the antifouling agent or adding the antifouling agent to the hydrocarbon-containing feedstock, or preferably by both methods. good. When pretreating metals, a preferred pretreatment method is to contact the metal with a solution of an antifouling agent. It is preferable to pour a large amount of antifouling agent into the cracking tube. The surface of the cracking tube is left in contact with the antifouling agent for any suitable period of time. At least one minute is preferred to ensure that all surfaces of the cracking tube are treated. In commercial operations the contact time is typically about 10
It may take a minute or more. However, I believe it is substantially advantageous for the operator to be fully sure that the cracking tube has been treated rather than having a relatively long contact time. Metals other than cracking tubes typically require spraying or brushing, but
If the device is capable of pouring water, a large amount of the antifouling agent solution may be poured. Any suitable solvent can be used to make the antifouling solution. Suitable solvents include water and oxygen-containing organic liquids such as alcohols, ketones and esters and aliphatic, aromatic hydrocarbons and derivatives thereof. Presently preferred solvents are n-hexane, toluene, but in commercial operations kerosene will typically be used. The antifouling solution can be used at any suitable concentration. It is desirable to use a concentration of at least 0.1 molar, and concentrations of 1 molar or higher may be used if the concentration is limited by metallurgical and economic considerations. Presently preferred antifoulant solution concentrations are within the range of about 0.2 to about 0.5 molar. If the surface of the cracking tube is accessible, the antifouling solution can be applied to the surface of the cracking tube by spraying or brushing, but application by this method is less effective in preventing coke buildup than by dipping. It turns out that this is true.
Cracking tubes can also be treated with finely divided antifouling powder, but again this is not considered particularly effective. In addition to pretreating the metal with the antifouling agent or otherwise contacting the metal with the antifouling agent,
Any suitable concentration of antifouling agent may be added to the feed stream flowing through the cracking tube. The concentration of the antifouling agent in the feed stream is at least 10 ppm by weight of metals contained in the antifouling agent based on the weight of the hydrocarbon portion of the feed stream. Currently preferred concentrations of antifoulant metals in the feed stream range from about 20 to about 100 by weight based on the weight of the hydrocarbon portion of the feed stream.
Within ppm range. Higher concentrations of antifouling agent may be added to the feed stream, but this does not substantially increase the effectiveness of the antifouling agent, and economic considerations generally discourage the use of higher concentrations. Not done. Antifouling agents can be added to the feed stream in any suitable manner. Preferably, the antifouling agent is added under conditions such that the antifouling agent is highly dispersed. Preferably, the antifouling agent is injected as a solution through an orifice under pressure such that the solution atomizes. The solvents mentioned above may be used to prepare this solution. The concentration of antifouling agent in the solution should be such that the desired concentration of antifouling agent in the feed stream is obtained. Steam is commonly utilized as a diluent for the hydrocarbon-containing feedstock flowing to the cracking furnace. When using the tin antifouling agent of the present invention, the steam/hydrocarbon molar ratio is 2:1.
The ratio of 2:1 should not be exceeded, as the effectiveness of the antifouling agent will be substantially reduced if the ratio exceeds 2:1. A preferred steam/hydrocarbon molar ratio to promote tin antifoulant effectiveness is within the range of about 0.25:1 to about 0.75:1. This vapor/hydrocarbon molar ratio is approximately It is believed that there will be no impact. It is believed that tin antifouling agents are volatile at high vapor/hydrocarbon molar ratios, and in the case of tin alone, this vapor/hydrocarbon molar ratio is important. Concomitant antifouling agents are not expected to exhibit similar volatility. The cracking furnace can be operated at any suitable temperature. In the process of steam cracking into light hydrocarbons and ethylene, the temperature of the fluid flowing through the cracking tube increases during passage through the tube, reaching a maximum temperature of about 850° C. at the exit of the cracking furnace. The wall temperature of the cracking tube will be higher than this and will become substantially hotter with the accumulation of an insulating layer of coke within the tube. Furnace temperatures of about 2000℃ can be used. Typical pressures in the cracking process are generally about 10 to about 20 psig at the outlet of the cracking tube. Before specifically referring to the examples used to further explain the invention, the experimental apparatus will be described with reference to FIG. 1, which shows a 9 mm quartz reactor. Located inside the furnace 12. A metal coupon is supported on a 2 mm quartz rod inside the reactor 11 to minimize resistance to gas flow through the reactor 11. A hydrocarbon feed stream (ethylene) is fed to reactor 11 through a combination of conduit arrangements 16 and 17. Air is supplied to the reactor 11 through this combination of conduit arrangements. Nitrogen flowing through line arrangement 21 is fed to heated saturator 22 and via line arrangement 24 to reactor 11 . Conduit device 28 is used for pressure averaging. Steam is generated by saturating a nitrogen carrier gas that enters saturator 22 . vapor/
The nitrogen ratio can be varied by adjusting the temperature of the electrothermal saturator. The reaction effluent is passed through the conduit arrangement 31 to the reactor 1.
1. Provisions are also made for directing the reaction effluent to a gas chromatograph for analysis if desired. When measuring coke deposition on a metal coupon, the amount of carbon monoxide produced during the cracking process was assumed to be proportional to the amount of coke deposited on the metal coupon. The rationale for this method for evaluating the effectiveness of antifouling agents is based on the assumption that carbon monoxide is produced from deposited coke by a carbon-vapor reaction. There was essentially no free carbon in the metal coupons examined at the end of the cracking experiment, supporting the assumption that the coke was vaporized by the steam. The selectivity of converted ethylene to carbon monoxide was calculated based on Equation 1 using nitrogen as an internal standard. (1) % selectivity (CO) = mol % CO / mol % N ₂ ×
100 Conversion This conversion was calculated based on Equation 2. (2) Conversion = mol% C ₂ H ₄ / mol% N ₂ ) Feedstock −
(mol % C ₂ H ₄ /mol % N ₂ ) sample (mol % C ₂ H ₄ /mol % N ₂ ) The CO level for a complete feed cycle is the weighted average of all analyzes taken during one cycle ( (3) calculated based on formula (3) as weighted average) Percent selectivity is directly proportional to the amount of carbon monoxide in the effluent flowing through the reactor. Example 1 In this example, Incoloy
800 coupons 1" x 1/4" x 1/16" were used. Each Incoloy 800 coupon was thoroughly cleaned with acetone before applying the coating. The coupon was soaked in a minimum of 4ml of antifoulant/solvent solution. Each antifouling agent was applied to the coupon by soaking for 1 minute. A new coupon was used for each antifouling agent. After this coating, the antifouling agent was heated in air at 700°C for 1 minute. decomposes into its oxides,
Then, residual solvent was removed. Blank coupons were used for comparison by washing the coupons in acetone and heating them in air at 700° C. for 1 minute without any coating. The manufacturing methods for various coatings are as follows. 0.5Msb: 2.76g _of Sb( _{C8H15O2 ) 3} mixed with sufficiently pure n-hexane, hereinafter referred to as solution A.
I made 10.0ml. 0.5MGe: 1.26 g of Ge(OC ₂ H ₅ ) ₄ was thoroughly dissolved in absolute ethanol, a solution 10 hereafter referred to as solution B.
I made ml. 0.5MSn: 2.02g _of Sn( _{C8H15O2 ) 2} dissolved in sufficiently pure n-hexane, hereinafter referred to as solution C.
I made 10.0ml. 0.5MSn-Sb: 0.81 g of Sn (C ₈ H ₁₅ O ₂ ) was dissolved in sufficiently pure n-hexane to make a 4 ml solution. 1.10g _of Sb( _C8H15O2 ) _{3 in} sufficiently pure n
-Dissolved in hexane to make 4 ml of solution. Both solutions are combined and mixed thoroughly and the resulting solution is hereinafter referred to as Solution D. 0.5MGe-Sb: 5g of Ge( _{OC2H5 ) 4} was thoroughly dissolved in absolute ethanol to make 40.0ml. then
1.1 g of Sb(C ₈ H ₁₅ O ₂ ) ₃ was dissolved in sufficiently pure n-hexane to make 4.0 ml. Mix 4.0 ml of each solution together to make a 1:1 Ge-Sb solution, hereinafter referred to as solution E. 0.5MGe-Sn: 1.26g Ge( _{OC2H5 ) 4} was dissolved in absolute ethanol and diluted with alcohol to make exactly 10ml. 2.7 g of Sn(C ₈ H ₁₅ O ₂ ) ₃ was converted into pure n-
Dissolved in hexane and diluted with n-hexane to make exactly 10 ml. Combine both solutions, mix,
This will be referred to as solution F hereinafter. 0.1MSn-Sb: Add 2.0ml aliquot of solution D to graduated cylinder and add toluene to 10.0ml
I made it. The resulting solution will be referred to as solution G hereinafter. 0.1MSn-Sb-Ge: 0.68g Sn( _{C8H15O2 ) 2 ,} 0.92
g _of Sb( _C8H15O2 ) ₃ and _{0.42g of} Ge( _OC2H5 ) ₄
was dissolved in enough toluene to make 10.0 ml. A 2.0 ml aliquot of this solution was added to a graduated cylinder and enough toluene was added to make up to 10.0 ml. The resulting solution will be referred to as solution H hereinafter. The temperature of the quartz reactor is set to 900± at its highest zone.
The temperature was maintained at 5°C. The coupon was placed in the reactor while it was at reaction temperature. A typical experiment consisted of three 20 hour coking cycles (ethylene, nitrogen and steam), a 5 minute nitrogen purge after each cycle, and a 50 minute decoking cycle (nitrogen, steam and air). During the coking cycle, a gas mixture consisting of 73 ml/min ethylene, 145 ml/min nitrogen, and 73 ml/min steam passed through the reactor in a downward flow. Periodically, snap samples of the reactor effluent were analyzed on a gas chromatograph. The steam/hydrocarbon molar ratio was 1:1. Table 1 summarizes the results of cycling experiments (either 2 or 3 cycles) conducted using Incoloy 800 coupons immersed in test solutions A-H as described above.

[Table] The results of experiments 2, 3 and 4 using tin, antimony and germanium separately are:
Under conditions simulating an ethane cracking process, only tin was effective in substantially reducing the rate of carbon deposition on Incoloy 800. However, the dual combination experiments of these elements used in Experiments 5, 6, 7, 8 and 9 showed some surprising effects. Experiment 5 with tin and antimony and experiment 6 with germanium and antimony show that these combinations are unexpectedly much more effective than expected from their use alone. Runs 8 and 9 showed an unexpected improvement in terms of the effectiveness of germanium alone over tin alone. However, the tin and germanium combination antifouling agent did not show the impressive improvement shown by the tin and antimony combination antifouling agent and the germanium and antimony combination antifouling agent. Not preferred among agents. It is unclear why Experiment 7 was less effective than tin alone. However, Experiments 8 and 9 appear to be better examples of the effectiveness of tin and germanium combination antifouling agents, and this antifouling agent appears to be more effective than tin alone. In experiments 10, 11 and 12, a 0.1M solution was used to demonstrate the improvement obtained with the tripartite combination. Concentrations higher than this, such as 0.5M, tend to mask the improvement. A comparison of experiments 10, 11 or 12 shows that the tin, antimony and germanium combination antifouling agent is much more effective than the best dual (Sn-Sb) antifouling agent. Example 2 Using the process conditions of Example 1, multiple three-cycle experiments were conducted with antifouling agents containing different ratios of tin and antimony and antifouling agents containing different ratios of germanium and antimony. I went.
Fresh Incoloy 800 coupons, previously cleaned and treated as described in Example 1, were used for each experiment. Antifouling solutions were prepared as in Example 1, but the ratio of elements was varied. The results are shown in FIGS. 2 and 3. Referring to FIG. 2, the combination of tin and antimony was particularly effective at antimony concentrations ranging from about 10 mole percent to about 75 mole percent. Outside this range, the effectiveness of the tin and antimony combination decreases especially in the second and third cycles. Referring now to FIG. 3, it can be seen that in this case as well, the combination of germanium and antimony is effective when the antimony concentration is in the range of about 10 mol % to about 75 mol %. Again, the effectiveness of the combination of germanium and antimony is reduced outside this range. It can also be seen that the effectiveness of the germanium and antimony combination is further reduced with each cycle than was seen with the tin and antimony combination. It is believed that tin and germanium combination antifoulants are essentially the same as tin and antimony combination antifoulants in terms of effectiveness as a function of concentration;
Therefore, the concentration of germanium in the combination tin and germanium antifouling agent is preferably from about 10 mol% to about 75 mol%. Example 3 Commercial ethylene cracker transfer line heat exchanger
Coupons of 11/4 chromium-1/2 molybdenum steel alloy, an alloy commonly used in the industry, were cleaned by the method described in Example 1. Separate coupons were then mixed with solutions A, C and D of Example 1.
Processed with. Each coupon, including the control coupon, was then cycled under the conditions described in Example 1. The results are summarized in Table 1.
Due to the experimental difficulties involved in analyzing effluent gases, we believe that the reported observations, although at different times, provide a comparison of the effectiveness of the antifouling agent.

【table】

Table: Treatment of 11/4 chromium-1/2 molybdenum steel alloys with separate solutions of tin or antimony did not appear to be effective in reducing carbon deposition rates under the conditions of these experiments. . but,
When both tin and antimony are present,
The carbon deposition rate under the same conditions was substantially reduced. Example 4 Type 304 stainless steel coupon Example 1
Cleaned using the method. One coupon was then treated with Solution C of Example 1. The treated and control coupons were then cycled under the conditions set forth in Example 1. The results are summarized in Table 1.

[Table] The table shows types with iron content of approximately 72% by weight.
Tin has proven to be an effective antifouling agent for 304 stainless steel. In contrast, in Example 3, tin proved to be an ineffective antifouling agent for 11/4 chromium-1/2 molybdenum steel alloy with an iron content of about 98% by weight. There is.
Therefore, although tin is an effective antifouling agent for steels with relatively high iron contents, it appears that its use on steels with iron contents of about 98% by weight or greater should be avoided. Example 5 A tin antifouling agent of the present invention was tested in a commercial ethylene cracking furnace. The feedstock to this cracking furnace was ethane, except for a few relatively short periods when propane was used. The cracking tube was separate from the downflow transfer line heat exchanger and a solution containing stannous octoate was pumped into the cracking tube until it filled. The treatment solution was prepared by diluting stannous octoate, Catalyst T-9 from M&T Chemical Company, with 10 volumes of kerosene. The manufacturer reports that the undiluted compound typically contains 28% tin by weight. After about 10 minutes, the stannous octoate solution was removed from the cracking tube. In addition to treating the tubes, this stannous octoate solution was also applied to the transfer line heat exchanger by spraying. The cracking furnace was shut down when the inlet pressure of the cooling tube exceeded a predetermined limit. In the cracking furnaces tested, the tubes had been operated for 10 to 31 days without antifouling agents and had undergone an oxidative combustion treatment to remove coke. Operation was maintained for 40, 49 and 47 days in three separate tests with antifoulant treatment as described above.
This was a substantial improvement over the maximum of 31 days seen without antifoulant treatment. In one experiment, in addition to treating the cracking furnace tube and transfer line exchanger as described above, a stannous octoate solution was injected into the ethane before it entered the cracking furnace. The tin concentration in the ethane was 23 ppm. The antifoulant solution was forced into the ethane through an orifice at elevated pressure with a stream of ethane moving at a linear velocity of about 1000 feet/second. This antifoulant injection continued for 10 of the first 11 days of operation and then stopped. In this experiment, the cracking tube was used for 60 days until excess inlet pressure led to its shutdown. All operations in commercial cracking furnaces are steam/
The ethane weight ratio was 0.35:1 and the cracking tube outlet temperature was about 843°C. Example 6 Using the method of Example 1 and Solution C of Example 1, three separate experiments were carried out at steam/hydrocarbon molar ratios of 1:1, 2:1 and 2.5:1, respectively. The results are shown in FIG. Referring to FIG. 4, it can be seen that the tin antifouling agent performs well at a steam/hydrocarbon molar ratio of 1.0. However, its effectiveness decreased as the steam/hydrocarbon molar ratio increased above this.

[Brief explanation of the drawing]

FIG. 1 shows a diagram of the test apparatus used for testing the antifouling agent of the present invention. FIG. 2 is a graph showing the combined effect of tin and antimony. FIG. 3 is a graph showing the combined effect of germanium and antimony. FIG. 4 is a graph showing the effect of steam on tin antifouling agents.

Claims (1)

Claims: 1. A method for reducing the formation of coke on metals in contact with a hydrocarbon-containing gas stream in a pyrolysis process, wherein said metals are combined with a combination of tin and antimony, a combination of germanium and antimony. , a combination of tin and germanium and a combination of tin, antimony and germanium. 2. The method of claim 1, wherein said contact with said antifouling agent comprises contacting said metal with said antifouling agent at a time when said metal is not in contact with said gas stream. the method of. 3. Said metal is mixed with said solution at least about 1
3. The method of claim 2, wherein the contact is carried out for a minute and the concentration of the antifouling agent in the solution is at least about 0.1 molar. 4. According to paragraph 2 or 3 above, wherein the solvent used to form the solution of the antifouling agent is water, an oxygen-containing organic liquid, or an aliphatic or aromatic hydrocarbon. Method described. 5. characterized in that said contact with said antifouling agent consists of adding a suitable amount of said antifouling agent to said gaseous stream before said metal comes into contact with said gaseous stream. The method according to any one of the first to fourth items. 6. Clause 5, wherein the weight concentration of said antifouling agent in said gas stream is at least 10 ppm by weight of antifouling agent metal based on the weight of hydrocarbons in said gas stream. The method described in. 7. Adding said antifouling agent to said gas stream by injecting said antifouling agent solution under pressure such that said solution is atomized. The method described in Section 6. 8. The concentration of antimony in said combination of tin and antimony and said combination of germanium and antimony is within the range of about 10 to 75 mole percent, and the concentration of germanium in said combination of tin and germanium is from about 10 to about 75 mole percent. 8. The method according to any one of items 1 to 7 above, wherein the amount is within the range of mol %. 9. A method for reducing the formation of coke on a metal in contact with a gas stream containing hydrocarbons and water vapor in a pyrolysis process, in which said metal is brought into contact with a tin antifouling agent, wherein said metal is The method of claim 1, wherein the iron content is about 98% by weight or less, and the molar ratio of water vapor to hydrocarbons in the gas stream is less than about 2:1. 10 The molar ratio of steam to hydrocarbon is about
10. The method of claim 9, wherein the ratio is within the range of 0.25:1 to about 0.75:1. 11, wherein said contact with said tin antifouling agent comprises contacting with a solution of said tin antifouling agent when said metal is not in contact with said gas stream. The method described in section. 12. The method of claim 11, wherein the metal is contacted with the solution for at least about 1 minute and the concentration of the antifouling agent in the solution is at least about 0.1 molar. 13. Item 11 or 12 above, characterized in that the solvent used to form the solution of the tin antifouling agent is water, an oxygen-containing organic liquid, or an aliphatic or aromatic hydrocarbon. The method described in. 14. wherein said contacting with said tin antifouling agent comprises adding a suitable amount of said tin antifouling agent to said gas stream before said metal contacts said gas stream. The method according to any one of items 9 to 13 above. 15. The method of claim 14, wherein the weight concentration of the antifouling agent in the gaseous stream is at least 10 ppm by weight of tin based on the weight of hydrocarbons in the gaseous stream. Method. 16 under pressure such that said solution is atomized,
Any one of the fourteenth and fifteenth items, characterized in that said tin antifouling agent is added to said gas stream by injecting a solution of said tin antifouling agent.
The method described in section. 17. A method according to paragraph 11 or 12, characterized in that said solution of said tin antifouling agent is stannous octoate in kerosene.