DE2134609A1 - Process for the production of unsaturated hydrocarbons - Google Patents

Description

Process for the production of unsaturated hydrocarbons

The invention relates to a process for the production of unsaturated hydrocarbons by pyrolysis of a Konelnwasserstoff starting material at high temperature ta a tubular reactor in the presence of water vapor.

Such methods are generally known. They will used in particular in the manufacture of ethylene, all : depending on the raw material used also other unsaturated compounds such as propylene, butylene, Butadiene, aromatic compounds and heavier hydrocarbons can be obtained in greater or lesser yield.

riacri Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd edition, Volume 8, Pages 5o4-5o6 are e.g. under normal and usual ratios at a pyrolysis temperature

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between 7oo and 87o C, at a hydrocarbon partial pressure, • which is not higher than necessary to obtain the desired throughput through the Seaktor, with a steam to hydrocarbon ratio (weight ratio) which is from ο _f 2-o.4 : 1 for ethane and propane to o the way up, 5-1, ο: for kerosene and gas oil and a conversion of 55-65% with ethane as the starting material in addition to ethylene and lighter fractions only 5% of a product obtained which heavier than ethane f while fjaphta gives a fairly large yield of propylene, butylene, butadiene, gasoline, and aromatic compounds. Furthermore, the reaction mixture always contains small proportions of acetylene and methyl acetylene, which are partially hydrogenated before the main product, ethylene, and, if desired, propylene can be won.

As stated in an article in "Hydrocarbon Processing" November 1969, Pages 176-177 describe procedures of this type such as k follows carried out.

The starting material is generally diluted with steam and the mixture in a tubular reactor for a short time The mixture exiting the reactor is then rapidly cooled and this cooled Mixture then fractionated, whereby the heavy parts * such as gasoline and fuel oil, the remaining Gas mixture is then compressed and after a treatment for removing acid gases and drying in different

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P rOdu ": t-7ractions separated.

The separated saturated hydrocarbons, the largest of them Tail Ätfran and propane is put back into the cycle dar pyrolysis reaction or in a separate pyrolysis reactor cracked.

The acetylene and metby1acetylene, pond themselves in small Forming quantities, before the extraction of ethylene and propylene, a partial hydrogenation to ethylene or propylene subject.

It has now been found that in these processes, which are known per se, the Realetionsbedingunjen can be changed so that with a higher degree of conversion of the starting material, which consists of 99% ethane and while maintaining an acceptable yield of ethylene, such amounts of acetylene that this can be obtained as an independent valuable by-product. An additional advantage is that the partial hydrogenation of acetylene to ethylene, which was necessary in the known processes to prevent the ethylene from being contaminated with acetylene, can be avoided can.

Accordingly, the present invention is that a Preheated mixture of a hydrocarbon feedstock with a steam to hydrocarbon ratio

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BATH ORIGINAL

(Weight ratio) of 2-3: 1 at a temperature between 1,000 and 1,100 ° C with a residence time of ik 0.1 sec. Through a tubular reactor with an inner diameter (clear width) of no more than 5 cm (2 inches) is directed.

It is important that the tubular reactor have an inside diameter of no more than 5 cm (2 inches), since with a larger diameter (in previous practice, diameters in the range of 7.5 cm (3 inches) were common) the amount of heat which \ Necessary to reach a temperature of 1,000 and 1,100 ° C, the mixture of steam and hydrocarbon feedstock could not be transferred through the wall of the tube without the tube wall having to be heated to a considerably higher temperature than that Material of the tubular reactor could withstand.

Also the weight ratio of steam to hydrocarbon feedstock in the order of magnitude of 2-3: 1 is necessary. If this ratio is less than 2: 1 for a

If the temperature is 1 coo-1 100 ° C, such a temperature is formed Amount of coke that the reactor tubes, in particular because of their relatively small inner diameter, within a short time Time are clogged and the procedure must be interrupted to disassemble the oven for cleaning.

At a weight ratio of steam to hydrocarbon feedstock, which is greater than 3: 1, the cost will be incurred by adding more steam than usual

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in the known processes arise so high, whereas practically no advantages are achieved with the fact that this cannot be accepted economically.

With a ratio of steam to starting material within the specified limits on the one hand, an acceptable one becomes The course of the pyrolysis reaction is achieved while on the on the other hand, the steam reacts with the carbon that may have formed, forming CO and Hp, which continuously be blown off, creating a major blockage the reactor tubes is prevented.

As stated above, in the method according to the invention the residence time in the tubular reactor ^ a-o, 1 see. Is this residence time larger, a considerable amount of coke can be formed without affecting the yield of the desired compounds Is improved. Preferably, the residence time between o, o3 and 0.08 seconds lie, because then an optimal result is obtained.

In order to obtain this residence time, the mixture of the hydrocarbon starting material is preferably passed through the reactor _{at a pressure between 1 f o and 2, o atm.abs.} A lower pressure is of course possible, but in this case the back pressure at the end of the reactor is less than one atm., Which means that a vacuum pump is necessary. But using this vacuum pump means only one

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Disadvantage because the gas mixture, which after cooling down the from the. Reactor coming mixture and separation of the heavy products from it must be compressed again.

The preheated mixture of a hydrocarbon feedstock and steam having a steam to hydrocarbon weight ratio of 2-3; 1 is preferably prepared by allowing the hydrocarbon feedstock is a portion of the steam which w, preferably at a temperature between 6oo and 75o C, heated, and separately the rest of the steam is preferably at a temperature between 9oo and 1 ooo C preheats and then mixes the two parts just before or just as they come into the reactor.

The hydrocarbon feedstock should preferably be mixed with some of the steam when it is preheated, otherwise it will be during the preheating the hydrocarbons are cracked to form carbon will.

On the other hand, it should be the hydrocarbon feedstock not be mixed with all the steam first and then this mixture is heated, because in this case a sufficiently high temperature cannot be reached quickly enough (residence time to lsÜfef) and it can be undesirable during preheating under the formation

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By-products come to decomposition.

Any starting material can be used in the process according to the invention be used, which in itself as a starting material known for the production of unsaturated hydrocarbons Is.Jedoch is preferably used as the starting material, because this gives the best yield of ethylene and Acetylene, with the smallest proportions of undesirable by-products.

When talking about another hydrocarbon feedstock, e.g. naphtha, the preferred procedure is as follows. The naphtha undergoes pyrolysis in the usual way and under subject to normal circumstances and the ethane formed as a by-product is stored in a separate reactor subjected to the following conditions of pyrolysis The result of this second pyrolysis is then mixed with that from the first cracking reactor and this mixture becomes then worked up together. In this way, an integrated Process obtained which gives an optimal yield of ethylene and acetylene.

The reaction tubes should of course be made of an alloy which is stable under the reaction conditions In general, these are high-alloy steels.

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The reactor tubes are preferably made of a steel based on chromium-nickel, which contains about 30 % Cr and about 30 % Ni, because such steels can be cast into tubes with an inner diameter of 5 cm or smaller and the crystal structure of such steels is the same are best suited for carrying out such pyrolysis reactions of the type according to the invention.

The life of the pipes made from such a steel are poured, is generally longer than the life of pipes, which are made by turning or rolling a high-alloy Stahls were obtained.

example

Ethane is mixed with steam at a weight ratio of steam to ether of 1/2: 1 and this mixture becomes in one Heat exchanger heated to 700 ° C.

In a second heat exchanger saturated steam is preheated to a temperature of 950 ⁰ C.

The preheated steam is then combined with the preheated mixture of ethane and steam in a ratio from 2.5 parts by weight of preheated steam to 1.5 parts by weight preheated mixture of ethane and steam mixed. This way you get a mixture of ethane and steam with one Weight ratio of 1: 3 and a temperature of about 900 ° C.

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The mixture of ethane and steam is now at a pressure of 1.7 atm abs. Through a tubular reactor with a length of 25 meters with an inner diameter of 3.2 cm. The reactor is heated to a temperature of 1025 ° C The residence time of the mixture in the reactor is o, o7 see.

The chemical composition of the reaction product coming out of the reactor is as follows after drying:

Hydrogen 8.17 Gev%

Carbon monoxide 13.86 "

Carbon dioxide 3.61 »

Methane. lo.75 "

Acetylene 13.51 "

Ethylene 44.08 "

Ethane o.44 "

Benzene 4, oo "

Butadiene 1.23 "

Diacetylene ο, 35 "

Total I00.00 wt%

This result gives an ethane conversion of about 99.5%. The ethylene yield corresponds approximately to the yield in the known processes, while 13.51 % acetylene is also obtained.

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Claims (1)

PA TENTANSP YOU Ξ ^Γ .)) Process for the production of unsaturated hydrocarbons by pyrolysis of a hydrocarbon starting material at high temperature in a tubular reactor in the presence of water vapor, characterized in that a preheated mixture of a hydrocarbon feedstock and steam with a steam to hydrocarbon ratio (weight ratio) 2-3: 1 at a temperature between 1,000 and 1,100 ° C with a residence time of: - 0.1 seconds through a tube reactor with an inside diameter (clear width) of no more than 5 cm (2 inches). 2.) Method according to claim 1, characterized in that the residence time in the reactor is between o, o3 and o, o8 see. lies. P 3.) Method according to claim 1 or 2, characterized in that the mixture of hydrocarbon feedstock and steam is passed through the reactor at a pressure between 1 _f o and 2, o atm abs. 4.) Method according to one of the preceding claims. . characterized in that the steam becomes hydrocarbon Ratio within the limits of 2-3: 1 is chosen so that the deposition of carbon is largely is avoided. 109883/1849 -11- 5.) Method according to one of the preceding claims, characterized in that the preheated mixture
from hydrocarbon starting material and steam by preheating on the one hand the hydrocarbon starting material, mixed with a portion of the steam, and on the other hand by separate preheating of the remaining portion of the steam and
subsequent mixing of the two preheated portions is made. 6.) Method according to claim 5, characterized in that the mixture of hydrocarbon feedstock and some of the steam is preheated to 600-750 ° C and the steam to 900-1,000 ° C. 7.) Method according to claim 1 to 6, characterized in that as the hydrocarbon feedstock Xthane is used. 8.) Method according to one of the preceding claims, characterized in that the reactor tubes from a
Chrome-nickel steel are cast, which is about 30 % Cr and
contains about 30 % Ni. 9.) Procedure »ie in the description and / or the example
described. 109883/1849 INSPECT «