Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – Triple-bond product
Reexamination Certificate
2000-03-31
2001-12-25
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
Triple-bond product
C585S534000, C585S601000, C585S613000
Reexamination Certificate
active
06333443
ABSTRACT:
The invention relates to a process for producing methylacetylene and propadiene by thermal conversion of a feed comprising at least one hydrocarbon containing at least three carbon atoms per molecule.
The synthesis of methylacetylene and propadiene is known to the skilled person. It is usually carried out by pyrolysis of propylene and/or isobutene or from propane, butane, but-1-ene or a mixture of but-2-ene isomers. French patent application FR-A-2 732014 describes a process for thermal conversion of saturated or unsaturated aliphatic hydrocarbons to acetylenic hydrocarbons. Said process is particularly applicable to the production of acetylene or methylacetylene but it does not describe propadiene formation.
U.S. Pat. No. 5,321,191 describes a process for thermal pyrolysis of hydrocarbons containing at least two carbon atoms. The process is intended for the production of light olefins, in particular ethylene and propylene.
European patent application EP-A-0 323 287, and U.S. Pat. Nos. 5,160,501 and 5,365,005 describe a process for thermal conversion of methane to hydrocarbons with a higher molecular weight, and a reactor for carrying out the process.
U.S. Pat. No. 5,554,347 describes an apparatus comprising a reactor for carrying out reactions such as pyrolysis. That reactor comprises heat exchange means which are supplied with a gas or a gas mixture.
The patent applications cited above use a reactor comprising heating means which are surrounded by sheaths of ceramic material. Those means are supplied with either electrical energy, or with gas so as to heat the feed, to carry out the conversion. The reactor is similar to that used in the present application.
One advantage of the invention is that it can be used to carry out thermal conversion of a feed while controlling the temperature during decomposition, which is currently not possible with conventional steam cracking reactors. The process of the invention enables temperature profiles to be defined. It defines a heating zone divided into three portions in which controlled temperature increases are implemented.
The invention provides a process for producing methylacetylene and propadiene in a reaction zone which is elongate in one direction (one axis) comprises a heating zone and a cooling zone following said heating zone, in which a gas mixture comprising at least one hydrocarbon containing at least three carbon atoms and at least one diluent is circulated in the heating zone, at an absolute pressure which is above atmospheric pressure, in a flow direction substantially parallel to the direction (to the axis) of the heating zone, said process being characterized in that the heating zone comprises at least one pre-heating zone in which the temperature of said gas mixture increases by about 50° C. to 120° C. per {fraction (1/10)} of the length of the heating zone, at least one zone for pyrolysis of the feed in which the temperature rises by about 20° C. to 50° C. per {fraction (1/10)} of the length of the heating zone and at least one methylacetylene-propadiene formation zone in which the temperature rises from about 70° C. to 150° C. per {fraction (1/10)} of the length of the heating zone, the products formed at the end of the heating zone being cooled in the cooling zone then recovered at the end of the reaction zone.
In a particular implementation of the process of the invention, the heating zone comprises at least two banks substantially parallel to the axis separated by a non fluid tight partition of refractory material between two successive banks, each bank comprising a plurality of heating means disposed in at least one layer of heating elements and surrounded by sheaths of ceramic material which are substantially parallel to each other and substantially perpendicular to the axis of the heating zone.
The hydrocarbon-containing feeds used in the present invention comprise hydrocarbons containing at least three carbon atoms per molecule. Non limiting examples are saturated aliphatic hydrocarbons such as propane and alkane mixtures (LPG) or unsaturated hydrocarbons such as propylene and butenes, mixtures of alkanes and alkenes such as propane and propylene, C
3
, C
4
and C
5
cuts produced by fluidised bed catalytic cracking, steam cracking, alkane dehydration and by isomerisation of olefins or by dimerisation.
The feed preferably contains essentially propylene and/or propane and originates from steam cracking.
Under normal pressure and temperature conditions, the feeds are gas mixtures which also comprise at least one diluent. Said diluent is normally selected from the group formed by steam and nitrogen. Preferably, steam is used. The weight ratio of the diluent to the hydrocarbon feed is normally about 0.1:1 to 5:1, preferably about 0.5:1 to 2.5:1. Before being introduced into the heating zone, the gas mixture is pre-heated to a temperature in the range about 100° C. to 650° C. It is then introduced parallel to the axis of the heating zone.
The heating zone is formed from at least one pre-heating zone, at least one pyrolysis zone and at least one methylacetylene-propadiene formation zone. It is usually heated by heating means which are surrounded by a sheath, so as to form heating elements.
Said heating elements provide the heat necessary to initiate the pyrolysis reaction. The total number of said elements in the heating zone is fixed by the operator. It essentially depends on the nature of the feed to be converted and on the size of the apparatus.
The characteristics of the heating elements, their number, the distance separating them and their configuration are, for example, described in the patent documents U.S. Pat. No. 5,554,347 and EP-A-0 323 287. The heating elements are supplied with energy by any means known to the skilled person. Usually, they are supplied with electrical or gas heating, preferably gas, either in isolation or in small groups such that they define heating sections along the heating zone. They can thus modulate the quantity of energy provided along this zone. They can thus establish a thermal profile. The heating zone is normally composed of 2 to 20 heating sections, preferably 3 to 12 sections.
Said zone can also comprise means for controlling and modulating the heating such as those described, for example, in patent documents EP-A-0 323 287 and U.S. Pat. No. 5,554,347.
The heating means can be electrical resistors surrounded by sheaths and heated by electrodes, such as those described in patent documents EP-A-0 323 287 and U.S. Pat. No. 5,160,501, or they can be constituted by sheaths containing a gas burner, as described in patent U.S. Pat. No. 5,554,347.
The heating elements form layers which are substantially parallel to the axis of the heating zone. This then defines banks, each comprising at least one layer of heating elements. Each bank is substantially parallel to the axis of the heating zone. The banks are separated by non fluid tight partitions of ceramic material. Said partitions have adapted shapes, which can create zones of turbulence inside the banks, to encourage the pyrolysis reaction and the methylacetylene-propadiene formation.
The sheaths surrounding the heating means are usually of ceramic material. They can be disposed in a superimposed or staggered manner and can form an array with a triangular, square or rectangular pattern in transverse projection. In the case of electrical resistors, patent U.S. Pat. No. 5,160,501 demonstrates that it is not in any way necessary to have a perfect seal in the sheaths, so as to allow at least a portion of a sheath gas G, contained in the space formed by said sheaths and the resistors, to diffuse. The gas G contains hydrogen and/or stream and/or carbon monoxide and/or an inert gas, which can diffuse from the interior to the exterior of the sheaths without disturbing the pyrolysis reaction. It is then diluted in the gas mixture. Said sheaths have also been described in the patent applications cited above.
The total residence time for the feed in the heating zone is normally in the range about 12 to 2000 milliseconds (ms), preferably bet
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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