GB1578896A - Thermal cracking of hydrocarbons - Google Patents

Description

(54) THERMAL CRACKING OF HYDROCARBONS (71) We, GENRIKH LVOVICH STOLYAR, of kvartira 85, korpus 2 Svobodny prospekt, 7, Moscow, NIKOLAI LEONIDOVICH BARABANOV, of kvartira 10, ulitsa Shturvalnaya 2, Moscow, BORIS SAMOILOVICH BOUDEN, of kvartira 109, Slavyansky bulvar, 27, Moscow, TAMARA NIKOLAEVNA MUKHINA, of kvartira 44, korpus 3, ulitsa Festivalnava. 15 Moscow, NADEZHDA PETROVNA SOLOMINA, of kvartira 111, ulitsa Kosmonavtov, 22-a, Tjumenskoi oblasti, Nizhnevartovsk, EKATERINA BORISOVNA FRID, of kvartira 31, ulitsa Polezhaeva, 7, Grozny, and GALINA IVANOVNA ASHIKHMINA, of kvartira 1, ulitsa Kutuzova, 5 Kuibyshevskoi oblasti, Novokuibyshevsk, all Union of Soviet Socialist Republics, all Citizens of the Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to thermal cracking of hydrocarbons, and more particularly to a process for thermal cracking of hydrocarbon feedstocks wherein coke deposition is substantially prevented.

Thermal cracking of hydrocarbon feedstocks includes such processes as thermal decomposition of hydrocarbon feedstocks to olefines, thermal cracking of heavy oil fractions, and slow coking. These processes are accompanied by the formation of coke and its deposition on the internal surfaces of heating elements such as pipes of a cracking furnace.

The deposition of coke in the internal surfaces of heating elements impairs heat transfer, lowers the yield of the finished product, and reduces the production efficiency of a cracking furnace and the service life of its pipes.

Coke deposition on the walls of cracking furnace pipes is a serious handicap to an improved process for thermal cracking of hydrocarbon feedstocks carried out in tubular heaters.

The present invention provides a process for thermal cracking of hydrocarbon feedstocks wherein coke deposition is substantially prevented by carrying out the thermal cracking process in the presence of steam and also in the presence of at least one alkaline-earth metal sulphurcontaining salt as a coke deposition inhibitor.

Thus, in the process according to the invention, use is made of one or more alkaline-earth metal sulphur-containing salts such as sulfates, sulfides and thiosulfates.

It is preferable to add aqueous solutions of the above-mentioned salts. The proportion of salts in aqueous solution is selected having regard to the solubility thereof.

The inhibitor is preferably introduced into the process in an amount of from 5 to 100 parts by weight of the inhibitor per million parts of the feedstock being treated.

The aforesaid lower limit of the inhibitor proportion depends upon the properties of the hydrocarbon feedstock being treated, whereas the upper limit thereof is selected as being sufficient to permit the process to proceed. effectively. The amount of the inhibitor used is more preferably from 30 to 40 parts by weight thereof per million parts of the feedstock being treated.

It will be appreciated that feedstocks other than refined gasoline may be used in the process according to the invention, for example ethane, a kerosene oil-gas fraction, distilled gasoline or a propanebutane fraction could be used.

The present invention makes it possible to prevent coke deposition on the internal surfaces of heating elements. This, in turn, permits the continuous operation of thermal cracking furnaces to be increased and the complicated operation of burning out coke deposits to be eliminated.

Inefficient operation and shutdown of the cracking units is not attributable to the formation of excessive coke deposits on the reaction zone surface.

The present invention makes it possible: 1. To conduct the thermal hydrocarbon feedstock cracking process in more severe conditions in terms of shorter hydrocarbon residence time in the reaction zone and selection of higher temperature therein.

The optimum conditions of the process are determined by the maximum temperature permissible for the material of a tubular heater whose surface is not contaminated in the course of the operating cycle, and as a result, its temperature is decreased.

2. To use a wider varietv of initial hydrocarbon materials such as refined gasolines which are prone to higher rates of coke formation.

3. To reduce the amount of steam injected into the hydrocarbon feedstock being treated.

4. To carry out the process of thermal cracking of hydrocarbon feedstock on a unit of any capacity, e.g. on an ethylene apparatus with a production capacity of 300 to 450 thousand tons of ethylene per annum, without interrupting the operating process as a whole.

The invention will be further described with reference to the following illustrative Examples. The amount of inhibitor is given in the Examples in proportions as calculated for the anhydrous substance and the feedstock being treated.

EXAMPLE 1 Refined gasoline was introduced into a thermal cracking furnace at a rate of 10 t/h, as a feedstock tending to permit a high rate of coke formation and having the following composition, in percent by weight: nparaffins, 28; i-paraffins, 57; naphthenes, 8; aromatic hydrocarbons, 7; the specific weight of gasoline Y:O being equal to 0.685 and the boiling range being from 50 to 157"C. Also introduced into the furnace at a flow rate of 4 t/h was steam and an aqueous solution of CaSO4 in a concentration of 1 g/l, CaSO4 being introduced in an amount of 50--55 p.p.m.

by weight. The temperature of the thermal cracking gas at the furnace outlet was 82830"C. After a run period of 3236 hours the furnace operation was discontinued and the parts of the furnace coil subject to the highest rate of coke deposition under usual conditions were detached for inspection. Coke deposits were not found in the tubes.

EXAMPLE 2 Refined gasoline was introduced into a thermal cracking furnace at a rate of 1.0 t/h.

Also introduced into the furnace at a flow rate of 0.35 t/h was steam and an aqueous solution of MgSO4 in a concentration of 0.7 g/l, MgSO4 being introduced in an amount of 35 37 p.p.m. by weight. The temperature of the thermal cracking gas at the furnace outlet was 890--900"C. After a run period of 1009 hours the furnace operation was discontinued and a hot-air blasting test was carried out. No coke was found in the furnace.

The addition of the inhibitors within the ranges specified in the above Examples did not reduce the yield of end products (ethylene, propylene, butylene, etc.).

WHAT WE CLAIM IS: 1. A process for thermal cracking of hydrocarbon feedstocks wherein coke deposition is substantially prevented by carrying out the thermal cracking process in the presence of steam and also in the presence of at least one alkaline-earth metal sulphur-containing salt as a coke deposition inhibitor.

2. A process as claimed in Claim 1, wherein the said sulphur-containing salt is a sulfate.

3. A process as claimed in Claim 1, wherein the said sulphur-containing salt is a sulfide.

4. A process as claimed in Claim 1, wherein the said sulphur-containing salt is a thiosulphate.

5. A process as claimed in any of Claims I to 4, wherein the said coke deposition inhibitor is used in an amount of from 5 to 100 parts by weight thereof per million parts of the hydrocarbon feedstock being treated.

6. A process as claimed in Claim 5, wherein the said inhibitor is used in an amount of from 30 to 40 parts by weight thereof per million parts of the hydrocarbon feedstock being treated.

7. A process as claimed in any of Claims I to 6, wherein the said inhibitor is added in aqueous solution.

8. A process according to Claim 1 for thermal cracking of hydrocarbon feedstocks substantially as herein described in either of the foregoing Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. and the complicated operation of burning out coke deposits to be eliminated. Inefficient operation and shutdown of the cracking units is not attributable to the formation of excessive coke deposits on the reaction zone surface. The present invention makes it possible: 1. To conduct the thermal hydrocarbon feedstock cracking process in more severe conditions in terms of shorter hydrocarbon residence time in the reaction zone and selection of higher temperature therein. The optimum conditions of the process are determined by the maximum temperature permissible for the material of a tubular heater whose surface is not contaminated in the course of the operating cycle, and as a result, its temperature is decreased. 2. To use a wider varietv of initial hydrocarbon materials such as refined gasolines which are prone to higher rates of coke formation. 3. To reduce the amount of steam injected into the hydrocarbon feedstock being treated. 4. To carry out the process of thermal cracking of hydrocarbon feedstock on a unit of any capacity, e.g. on an ethylene apparatus with a production capacity of 300 to 450 thousand tons of ethylene per annum, without interrupting the operating process as a whole. The invention will be further described with reference to the following illustrative Examples. The amount of inhibitor is given in the Examples in proportions as calculated for the anhydrous substance and the feedstock being treated. EXAMPLE 1 Refined gasoline was introduced into a thermal cracking furnace at a rate of 10 t/h, as a feedstock tending to permit a high rate of coke formation and having the following composition, in percent by weight: nparaffins, 28; i-paraffins, 57; naphthenes, 8; aromatic hydrocarbons, 7; the specific weight of gasoline Y:O being equal to 0.685 and the boiling range being from 50 to 157"C. Also introduced into the furnace at a flow rate of 4 t/h was steam and an aqueous solution of CaSO4 in a concentration of 1 g/l, CaSO4 being introduced in an amount of 50--55 p.p.m. by weight. The temperature of the thermal cracking gas at the furnace outlet was 82830"C. After a run period of 3236 hours the furnace operation was discontinued and the parts of the furnace coil subject to the highest rate of coke deposition under usual conditions were detached for inspection. Coke deposits were not found in the tubes. EXAMPLE 2 Refined gasoline was introduced into a thermal cracking furnace at a rate of 1.0 t/h. Also introduced into the furnace at a flow rate of 0.35 t/h was steam and an aqueous solution of MgSO4 in a concentration of 0.7 g/l, MgSO4 being introduced in an amount of 35 37 p.p.m. by weight. The temperature of the thermal cracking gas at the furnace outlet was 890--900"C. After a run period of 1009 hours the furnace operation was discontinued and a hot-air blasting test was carried out. No coke was found in the furnace. The addition of the inhibitors within the ranges specified in the above Examples did not reduce the yield of end products (ethylene, propylene, butylene, etc.). WHAT WE CLAIM IS:

1. A process for thermal cracking of hydrocarbon feedstocks wherein coke deposition is substantially prevented by carrying out the thermal cracking process in the presence of steam and also in the presence of at least one alkaline-earth metal sulphur-containing salt as a coke deposition inhibitor.

2. A process as claimed in Claim 1, wherein the said sulphur-containing salt is a sulfate.

3. A process as claimed in Claim 1, wherein the said sulphur-containing salt is a sulfide.

4. A process as claimed in Claim 1, wherein the said sulphur-containing salt is a thiosulphate.

5. A process as claimed in any of Claims I to 4, wherein the said coke deposition inhibitor is used in an amount of from 5 to 100 parts by weight thereof per million parts of the hydrocarbon feedstock being treated.

6. A process as claimed in Claim 5, wherein the said inhibitor is used in an amount of from 30 to 40 parts by weight thereof per million parts of the hydrocarbon feedstock being treated.

7. A process as claimed in any of Claims I to 6, wherein the said inhibitor is added in aqueous solution.

8. A process according to Claim 1 for thermal cracking of hydrocarbon feedstocks substantially as herein described in either of the foregoing Examples.