Title of Invention	"A COMPOSITION FOR THE INHIBITION OF COKE IN PYROLYSIS FURNACE"
Abstract	The subject invention relates to a composition for the inhibition of coke in the pyrolysis furnace comprising 75-125 ppm potassium, 10-75 ppm antimony oxalate and 20-60 ppm dimethylsulphoxide dissolved in a diluent to form a homogenous solution.

Full Text

The subject invention relates to a composition for the inhibition of coke in the pyrolysis furnace. More specifically, the invention resides in the composition for the inhibition of coke deposition and coke spalling for the pyrolysis of hydrocarbons comprising potassium, antimony, dimethylsulphoxide and mixtures thereof as coke inhibitors and process thereof. The subject composition comprises of potassium oxalate, antimony oxalate, dimethylsulphoxide, in the range of 75 ppm potassium as potassium oxalate, 50 ppm antimony as antimony oxalate and 21.0 ppm dimethylsulphoxide. The object of the subject invention is to achieve the maximum reduction of coke deposition upto 96% in the pyrolysis furnace. The other object of the invention is to eliminate the coke spalling considerably in the pyrolysis furnace and to avoid the discontinuity in production, which occurs because of accumulation of the coke in the pyrolysis furnace. Still, other object of the invention is to increase the life of the coil, which is affected by frequent decoking and to increase the utility costs In the petrochemical industry, pyrolysis of hydrocarbons (ethane and/or propane, naphtha, gas oil) is a very important process for the manufacture of light olefins such as ethylene, propylene and 1,3-butadiene, as well as other valuable by-products. A common problem associated with any pyrolysis process is the formation of coke which deposits on the inner walls of the reactor and downstream heat exchanges. Although several processes and products have been tried to reduce the coke formation during pyrolysis, however, the desired success could not be achieved. The mechanisms which are believed to contribute in the coke formation are heterogeneous catalyst mechanism, heterogeneous noncatalytic mechanism and homogeneous noncatalytic mechanism. Due to the high gas temperatures, coke continuously deposits on the reactor walls as well as in the transfer line heat exchangers. The coke deposit are also sloughed off the tube wall and collect in the U-joints in the furnace, thus hampering the flow causing spalling. Eventually, the coke deposition in the coil and transfer line heat exchangers or spalled coke becomes so large that the reactor and/or the transfer line heat exchangers need to be cleaned. The coke layer deposited on the walls of the reactor gradually builds up and increases the heat transfer resistance between the tube metal and the process gas, and also increases the pressure drop across the reactor. Moreover, the coke build-up in the reactor also reduces the effective volume of the reaction zone, thereby decreasing the product yields. In order to compensate for this, the tube metal temperature as well as the inlet reactor have to be gradually increased. After a few weeks of operation the inlet pressure or the tube metal temperature reaches the maximum allowable level, and the furnace has to be shut down for decoking. Depending upon the coil design of the furnace, feedstock and cracking severity, the run lengths are generally limited from 30 to 70 days. Frequent decokings result in loss of production, affect coil life and increase utility costs. During the process of decoking, the hydrocarbon feed flow is stopped and only dilution steam flow is maintained since steam reacts slowly with the deposited coke. After some time, air is added along with steam and the air rate is slowly increased as the decoking progresses. The oxygen in the air reacts with coke to form carbon oxides and steam. Coil decoking can take from a few hours to 2 days to complete. Cleaning the transfer line heat exchangers, usually takes longer as the furnace has to be cooled and the coke removed by mechanical means. Conventionally, the technique commonly used to passivate the reactor walls is to either presulfide the reactor (Shah et al., 1976; Trimm and Turner, 1981) or to add sulfur compounds to the feed (Bajus et al., 1981, 1983). Although sulfur compounds are well-known to reduce the yield of carbon oxides during pyrolysis, the effect of these compounds on coke formation are quite doubtful, and in some cases sulfur compounds have been reported to increase coke formation (Reyniers and Froment, 1995; Brown et al., 1994). Other passivation techniques which have been claimed to reduce coke formation include depositing on the reactor surface a layer of silica (Brown et al., 1982) or aluminum (Albright and McGill, 1987). Additives such as nitroxides (Ferrell, 1987) and phosphorous compounds (Kisalus, 1989; Ghosh and Kunzru, 1988; Vaish and Kunzru, 1989) have also been found to be effective in passivating the reactor surface and inhibiting coke formation. Use of different types of additives to enhance the coke-steam reaction are available conventionally, where alkali and/or alkaline earth metal salts have been used. Potassium carbonate was shown to be an effective catalyst for coke gasification during pyrolysis (Kohlfeldt and Herbert, 1959; Mandal and Kunzru, 1986). Forester (1989) claimed reduction in coke formation by use of magnesium acetate, magnesium nitrate, calcium nitrate or calcium chloride as an additive. Gandman and Jo (1994) used a mixture of Group IA metal salt, a Group MA metal salt and a boron acid or salt as coke inhibitor and found it to be effective in controlling coke formation in ethane as well as naphtha pyrolysis. Porter and Reed (1987a) reported that compounds of antimony and tin combined with gallium compounds were effective coke gasification catalyst during pyrolysis. In another patent (Porter and Reed, 1987b), additives of indium-tin and indium-antimony were claimed to be effective in reducing the formation of coke in ethane cracking. Combination of tin, antimony and silicon compounds were also found to reduce coke formation (Porter and Reed, 1987c). Though in U.S. Patent Number 5,358,626, several potassium compounds such as acetate, metaborate, metasilicate, carbonate, silicotungstate, nitrate have been claimed as coke inhibitors, but the results of the same in decoking are found to be not so encouraging. In the conventional process of decoking, a mixture of steam and feed hydrocarbon are passed through long heated tubes. Pyrolysis operation is conducted at high temperatures ranging from 750° C to 900° C. Steam is an inert and is used to reduce the partial pressure of hydrocarbons, resulting in higher yield of light olefins such as ethylene and lower coke deposition. The hydrocarbon feedstock is preheated and steam is mixed into it. The mixture so obtained is then passed through heated coils kept in a furnace. The reaction effluent containing steam, reaction products and the unreacted hydrocarbon is rapidly cooled in transfer line heat exchangers. This rapid cooling minimizes the secondary reactions. The cooled gas is compressed and passed through several distillation columns, where the individual components are separated. Since coking is a common problem during hydrocarbon pyrolysis, different methods have been tried to reduce coke formation. Several studies have been reported in which additives are added either to the hydrocarbon or water feed streams. However, these additives reduce coke deposition either by passivating the reactor walls or by catalyzing the coke-steam gasification reaction. Despite the prior efforts, there is still a need for an inexpensive method to reduce coke deposition on the reactor walls as well as coke spelling during pyrolysis of gases or liquids to produce light olefins. In all the above mentioned processes it has been found that they do reduce the formation and deposition of the coke but reactors need to be decoked very frequently, which results in the loss of production, affects coil life and increases utility cost. To overcome the above referenced problems of frequent de-coking, a novel composition has been invented, which is not only inexpensive but delays the procedure of de-coking, which is otherwise required after 30-70 days in the pyrolysis furnace. The subject composition comprises potassium, antimony oxalate, dimethylsulphoxide and mixtures thereof as coke inhibitors in the pyrolysis of Hydrocarbons. Preferably, the subject composition comprises of potassium oxalate, antimony oxalate, dimethylsulphoxide and their mixtures, in the range of 75-125ppm Potassium as potassium oxalate, 10-75 ppm Sb as antimony oxalate and 20-60 ppm dimethylsulphoxide to achieve the maximum reduction of coke deposition upto 96%. In an embodiment, the potassium oxalate and antimony oxalate either used alone or as mixtures in the ratio of 3:1 has found to be significantly reducing carbon deposition during hydrocarbon pyrolysis preferably in ethane pyrolysis. Moreover, antimony oxalate and potassium oxalate either alone or mixture thereof has found to be significantly reducing coke spalling, whereas the dimethyl sulphoxide reduces the yield of carbon oxides considerably. The concentration of potassium oxalate or antimony oxalate in the feed varies from 10 to 100 parts per million parts of Hydrocarbon. For the runs, with mixtures of potassium oxalate and antimony oxalate, the total metal (K+Sb) concentration varies from 75 to 175 parts per million of Hydrocarbon. Accordingly, the subject invention relates to a composition for the inhibition of coke in the pyrolysis furnace comprising 75-125 ppm potassium, 10-75 ppm antimony oxalate and 20-60 ppm dimethylsulphoxide dissolved in a diluent to form a homogenous solution. According to the present invention, a process for the inhibition of coke in the pyrolysis furnace using the composition, comprises :- mixing the composition of 75 ppm potassium oxalate, 5 ppm antimony oxalate and 21 ppm dimethylsulphoxide in water to obtain a homogenous solution, heating the said homogenous solution to form vapors introducing the said vapors in the inlet of the furnace along with the effluent cooling the preheated effluents along with vapors in a condenser passing the said cooled effluent from the said condenser to a collector after routing out the noncondensable gases from the said collector through a pair of gas sampling valves arranged parallelly. In the subject composition the said potassium used is preferably Potassium Oxalate and the diluent used is preferably water. Like any conventional process, in the subject invention also, the pyrolysis of hydrocarbons is conducted in an annular tubular reactor, where the flow of Hydrocarbon having 99.0% purity is metered and preheated upto 740-750 K. The subject composition of present invention comprising potassium, antimony oxalate, dimethylsulphoxide and mixtures thereof are mixed in water which is used as a diluent. The water along with the subject composition is heated till it vaporizes. The said vapors enters just before the reactor inlet. The reactor is heated in a three-zone furnace as done conventionally. To quench the reaction, the reactor effluent is rapidly cooled in a condenser using ice-cold water. The cooled effluent from the condenser entered a collector. The noncondensable gases from the collector are routed and vented through two gas sampling valves arranged parallelly and through a gas flow meter. To measure the coke deposited on the reactor walls, a bypass line may be provided between the reactor outlet and the condenser inlet. This line is kept closed during the pyrolysis run. The spalled coke may be measured by providing a cup at the reactor exit, which could be opened after each run. Like all other conventional processes available for the pyrolysis of hydrocarbons, on the completion of each run, the system is flushed with nitrogen and allowed to cool. After cooling, the spalled coke on the reactor walls is oxidized by using preheated air. During decoking the bypass line is opened and the main line is closed. The effluent gases, consisting of carbon monoxide, carbon dioxide, nitrogen and water vapor, are passed through a bed of cupric oxide converter maintained at about 620-623 K. In this converter, the carbon monoxide is converted to carbon dioxide as checked by sampling the gas at the exit of the converter. After the converter, the gases are passed through a series of U-tubes. The first pair of tubes contains silica gel which adsorbs the moisture. The next pair of U-tubes are containing a pair of separate portions of Carbosorb and silica gel. Carbon dioxide is adsorbed on silica gel. For all the runs, the hydrocarbon flow rate is 0.32-0.35 gm/min. and the dilution ratio is 0.32-0.36 kg steam/kg hydrocarbon. For most of the runs, the run lengths are 2-4 hours. EXAMPLES EXAMPLE 1: In the composition comprising potassium oxalate and dimethylsulphoxide, having potassium concentration of 100 ppm with respect to ethane feed , the reduction in the amount of coke deposition after three hour run is reduced by 90% The variation in the amount of deposited coke and spalled coke after 3 hour run at different concentration of potassium having sulfur (dimethyl sulphoxide) content of 21 ppm, is shown in table number 1 as : (Table Removed) EXAMPLE 2 In the composition comprising antimony oxalate and dimethylsulphoxide, having antimony oxalate concentration of 100 ppm with respect to hydrocarbon feed , the reduction in the amount of coke deposition after three hour run is reduced by 63%. The variation in the amount of deposited coke and spaded coke after 3 hour run at different concentration of antimony having sulfur (dimethyl sulphoxide) content of 20ppm is shown in table number 2 as : (Table Removed) EXAMPLE 3 In the composition comprising antimony oxalate and dimethylsulphoxide, having potassium concentration of 75 ppm and antimony oxalate concentration of 50 ppm with respect to hydrocarbon feed , the reduction in the amount of coke deposition after three hour run is reduced by 96%. The variation in the amount of deposited coke and spalled coke after 3 hour run at different concentration of antimony and potassium having sulfur (dimethyl sulphoxide) content of 60ppm, is shown in table number 3 as : (Table Removed) The subject composition comprising a ternary mixture of potassium preferably Potassium oxalate, antimony oxalate and dimethylsulphoxide has been found to be more advantageous as compared to alternative additives available conventionally, as both coke deposited on the inner walls of the reactor as well as the spalled coke is drastically reduced upto 96% , such high reductions in coke deposition upto 96% have not been achieved by the use of any alternative additives. Moreover, the effect of alternative additives available conventionally on spalling has not been mentioned, whereas, the ternary mixture of the subject invention comprising potassium oxalate, antimony oxalate and dimethyl sulphoxide has significantly eliminated the coke spalling. The subject application is a statement of invention, and should not in any way construed to restrict the broad scope of the invention. WE CLAIM: 1 A composition for the inhibition of coke in the pyrolysis furnace comprising 75-125 ppm potassium, 10-75 ppm antimony oxalate and 20-60 ppm dimethylsulphoxide dissolved in a diluent to form a homogenous solution. 2 The composition as claimed in claim 1, wherein the said potassium is Potassium Oxalate. 3. The composition as claimed in claim 1, wherein the said diluent is water. 4. The composition as claimed in claim 1, wherein the said potassium oxalate and said antimony oxalate are in the ratio of 3:1 5. A process for the inhibition of coke in the pyrolysis furnace using the composition as claimed in claim 1, comprises :- mixing the composition of 75 ppm potassium oxalate, 5 ppm antimony oxalate and 21 ppm dimethylsulphoxide in water to obtain a homogenous solution, heating the said homogenous solution to form vapors introducing the said vapors in the inlet of the furnace along with the effluent cooling the preheated effluents along with vapors in a condenser passing the said cooled effluent from the said condenser to a collector after routing out the noncondensable gases from the said collector through a pair of gas sampling valves arranged parallelly. 6 A composition for the inhibition of coke in the pyrolysis furnace substantially as herein before described with reference to the accompanying examples.

Documents:

1038-del-1999-abstract.pdf

1038-del-1999-claims.pdf

1038-del-1999-correspondence-others.pdf

1038-del-1999-correspondence-po.pdf

1038-del-1999-description (complete).pdf

1038-del-1999-form-1.pdf

1038-del-1999-form-19.pdf

1038-del-1999-form-2.pdf

1038-del-1999-form-3.pdf

1038-del-1999-gpa.pdf

1038-del-1999-petition-138.pdf