This invention relates to the production of olefins, and more particularly, to the conversion of saturated hydrocarbons to olefins.

Still more particularly, this invention relates to the production of ethylene by cracking and/or dehydrogenation of saturated hydrocarbons.

Olefins may be produced from saturated hydrocarbons by heating the saturated hydrocarbons to elevated temperatures at which the saturated hydrocarbons are converted to olefins. Thus, for example, ethane may be dehydrogenated at elevated temperatures, and short reaction times to produce ethylene. Similarly, naphtha and heavier hydrocarbon feeds have also been pyrolyzed at elevated temperatures to produce olefins, such as ethylene. It is generally known in the art that short residence times favor olefin production. As a result, tubular short residence time heaters have been used for olefin production wherein a feed including at least one saturated hydrocarbon is rapidly heated to temperatures at which the saturated hydrocarbon is converted to olefins, and in particular ethylene.

Thus, in general, saturated hydrocarbons have been thermally pyrolyzed to olefins in tubular

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-2- heaters at short reaction times; for example, times in the order of 0.2 to 0.5 second and at elevated temperatures; in particular, temperatures in. excess of 1,200°F, with the outlet temperature generally being in the order of from about 1,500° to 1,550° F. It has also been proposed to pyrolyze unsaturated hydrocarbons to olefins at elevated temperatures in an upflow reactor by directly contacting a hydrocarbon feed with heated solid particles, which are at a temperature sufficient to bring the feed to pyrolysis temperatures, and to maintain the feed at such pyrolysis temperatures to effect conversion of saturated hydrocarbons to olefins. The present invention is directed to improving the production of olefins from saturated hydrocarbons by directly contacting a pyrolysis feed with such solid particles.

In accordance with one aspect of the present invention, a pyrolysis feed is directly contacted with heated solid particles to heat the pyrolysis feed to temperatures in which the feed is converted to olefins, with the solids and feed moving in plug flow through a hydrocarbon conversion zone having an outlet which is at a level no higher than the inlet to the zone.

Thus, in accordance with an aspect of the present invention, hydrocarbon is pyrolyzed to olefin by direct contact with solid particles which flow through a zone, with the proviso that the flow be either horizontal flow or downward flow.

In accordance with prior art proposals, a hydrocarbon feed and solid particles are moved upwardly through a reaction zone, whereas in accordance with the present invention, the flow is

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-3- either a horizontal flow or a downward flow. In accordance with the preferred embodiment, such flow is a downward flow.

Thus, in accordance with an aspect of the present invention, olefin production is improved by providing for plug flow of solids and hydrocarbon in . a direction which is either horizontal or downward, with the flow preferably being downward. In a preferred embodiment, the solids and hydrocarbon are passed through a vertical reactor having an inlet at the top and an outlet at the bottom.

The solids which are employed in the conversion may be either catalytic or non-catalytic; accordingly, the present invention is directed to both thermal and catalytic pyrolysis of hydrocarbons to produce olefins.

In a preferred embodiment, a hydrocarbon feed to be pyrolyzed to olefins and solids are cocurrently passed through a transfer line or pipeline reactor as a dilute transport phase, with the reactor having an inlet which is no lower than the outlet thereof, with the outlet preferably being lower than the inlet to thereby improve production of olefins.

In a thermal pyrolysis process, the solid particles may be any one of a wide variety of particles. As representative examples of such particles, there may be mentioned coal, coke, etc. In general, the solid particles can have a wide range of particle size with smaller particle sizes increasing the rate of heat transfer; the scope of the invention is not limited to any particular particle size.

In a catalytic pyrolysis process, the solid particles would include materials which are known to catalyze the conversion of saturated hydrocarbon to

olefins, and in particular those that favor ethylene production. Representative examples of such catalysts, are dislosed in European Patent Application 0-211-340 published on February 25, 1987. It is to be understood, however, that the scope of the invention is not limited to such representative catalysts, and the selection of a suitable catalyst is deemed to be within the scope of those skilled in the art from the teachings herein . In a thermal pyrolysis, the pyrolysis is generally effected at a temperature which is at least 1200°F. In general, the temperature does not exceed about 1600°F. In accordance with preferred aspects, the thermal pyrolysis outlet temperature is in the order of from 1450°F to 1600°F. A selection of a suitable pyrolysis temperature is dependent, in part, on the particular feed, which is subjected to the thermal pyrolysis. The selection of an optimum temperature is deemed to be within the scope of those skilled in the art from the teachings herein.

In a preferred aspect of the present invention, such thermal pyrolysis is effected at a residence time which generally does not exceed about 0.5 sec. (Residence time is measured as the amount of time at which the feed is maintained at temperatures which convert the feed to olefins). In general, olefin production is favored by shorter reaction or residence times. Thus, in accordance with a preferred aspect of the present invention, the residence time does not exceed about 0.3 sec. and preferably does not exceed about 0.2 sec. In accordance with a preferred aspect, the residence time is in the order of from .04 to about .10 sec. The thermal pyrolysis may be accomplished at pressures in the order of from 1 to 10 atm.

In a catalytic pyrolysis process, in general, the temperature is at least 900°F, and in most cases does not exceed about 1600°F. Typical temperatures are in the order of from 1000° to about 1500°F. As in a thermal pyrolysis process, olefin production is favored by short residence times. In general, the residence time does not exceed about 0.5 sec, and preferably does not exceed about 0.3 sec. In accordance with preferred aspects, the residence time would be in the order of from about 0.04 to about 0.10 sec.

Catalytic pyrolysis pressures are generally in the order of from 1 to about 10 atm.

The feeds which are subjected to either thermal or catalytic pyrolysis in accordance with the present invention may be any one of a wide variety of feeds. As known in the art, such feeds include at least one saturated hydrocarbon.

The feed may be comprised of one or more hydrocarbons. For example, the feed, may be comprised of ethane alone, propane alone or mixtures of ethane and propane. Similarly, the pyrolysis feed could be a heavier hydrocarbon feed, which includes saturated hydrocarbons, such as gas oils, naphthas, raffinates, etc..

In a representative operation for thermal pyrolysis, a hydrocarbon feed at a temperature in the order of from about ambient to about 500°F would be admixed with finely divided particles, which are at a temperature from about 1500°F to about 1800°F, with such direct contact mixing of the hydrocarbon and solid particles being effected in a quantity such that the mixture is rapidly and immediately brought to a temperature in the order from about 1200°F to about 1600°F. Such mixing may be effected by

atomizing a liquid feed or introducing a gaseous feed into a transport reactor, with simultaneous introduction of the heated solid particles. The mixture is then passed in a dilute transport phase through a pipeline or transport reactor, without external heating, with such flow preferably being a downward flow. As hereinabove indicated, such contact at such elevated temperature is preferably for a contact or residence time which does not exceed about 0.5 second. Such mixture may be quenched to below cracking temperatures, after the noted residence time, by any one of a wide variety of procedures, such as, for example, direct contact with solid particles, which are introduced at a temperature and in an amount to rapidly bring the mixture to below cracking temperatures.

Alternatively, a quench liquid and/or a quench gas can be introduced into the mixture to rapidly bring the mixture to a temperature below cracking temperatures. Such procedures are generally known in the art.

In accordance with a preferred embodiment, the dilute phase transport reactor is vertically positioned with the inlet being at the top of the reactor, and the outlet being at the bottom. As an example of a transport reactor which is suitable for the purposes of the present invention, reference is made to to a pipeline reactor or a reactor of the type disclosed by Berg et al.,

"The Ultra-Rapid Fluidized (URF) Reactor, A Major New Reactor system" Circ. Fluid Bed Technol. Proc. Int. Conf. (Basu Prabir Editor 1986) Pages 377-83.

The present invention is particularly advantageous in that it is possible to increase the

production of olefins, and in particular, production of ethylene in both thermal and catalytic processes.

Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, within the scope of the appended claims, the invention may be practiced otherwise there and as particularly described.