US2889384A - Production of olefinic gases from hydrocarbon oils - Google Patents

Description

d States PRODUCTION OF OLEFINIC GASES FROM HYDROCON OILS No Drawing. Application October 24, 1955 Serial No. 542,491

Claims priority, application Great Britain November 11, 1954 Claims. (Cl. 260-683) This invention relates to the production of gaseous mixtures containing olefines from hydrocarbon oils, and in particular to such processes in which the oil is relatively heavy and not capable of being completely vaporised at 400 C. at atmospheric pressure.

The continuous thermal cracking of light distillates e.g. boiling between 100 and 350 C. in a single operation is a well known manufacturing process for the production of lower olefines such as C C and C in good yield. Examples of variants of this process are: tube or coil cracking; tube cracking in the presence of an insert material such as water vapour; cracking with superheated steam; cracking by contact with a moving burden of refractory pebbles with or without an inert material such as water vapour present; and cracking in a fluidised bed.

However, we have found, when these processes are applied to the continuous cracking of heavy hydrocarbon oils which cannot be vaporised completely at 400 C. and atmospheric pressure, that they are each unsatisfactory.

Thus in tube cracking a heavy deposit of carbon is soon formed on the interior surface of the tubes or coils and this seriously hinders the high rate of heat transfer necessary, and frequent interruptions to clean out carbon are required. These disadvantages are not fully over come by having water vapour present.

When cracking is conducted is conducted with superheated steam the inability to vaporise the feed completely leads to distribution difliculties in the empty reaction zone, and there is the strong tendency for tarry materials to be produced.

Cracking by contact with a moving burden of refractory pebbles has the disadvantages that: (i) if high temperatures and very short contact times are used, then carbonaceous deposits form, which tend to clog the system and cannot be etficiently burned oif from the pebbles; or (ii) if the temperature is reduced and longer contact times are used so as to secure good operability, then the gaseous products have relatively low contents of olefines and an olefineszparaffins ratio which is uneconomically low if substantially pure olefines are later to be separated. Some increase of the olefine content is obtained by introducing an inert material such as steam, but this acts as a diluent and decreases the output of the plant.

Cracking in a fluidized bed with the object of obtaining olefines as the principal product is unsatisfactory because of the diificulty in maintaining an adequate state of fluidization, since the particles are continuously increasing in size and agglomeration occurs.

Consequently it may be stated as a generalization that the expected advantage in cost arising from the use in the prior art processes of cheaper, heavier hydrocarbons is wiped out. For when the attempt is made to use large units, for exampule units capable of treating, say, 50,000 tons of heavy oil per annum, and to achieve a atet process which is reliable in operation over long periods it is found that the product gas has such a high paraifinszolefines ratio that the process becomes, on account of gas separation costs, economically unattractive as a source of substantially pure olefines.

According to the present invention there is provided a continuous or semi-continuous process for the production of mixtures containing olefines, more particularly lower olefines such as ethylene, propylene, butadiene and butylenes, in relatively high amount which comprises subjecting a heavy petroleum oil or fraction of the sort which cannot be completely vaporised at 400 C. at atmospheric pressure, to a thermal treatment which yields a gas rich in hydrocarbons but not in olefines, and usable carbonaceous material, and which is capable of being operated with little interruption over long periods at moderate temperatures, such as contacting it continuously with a hot moving burden of solid media, e.g. pebbles, balls, or pellets of regular or irregular shape, of a highly refractory material, at temperatures, pressures and space velocities which yield such a gas, and cause a solid carbonaceous product to be laid down upon the pebbles; continuously feeding the hot product with or without prior separation of its heavy constituents, for example those boiling above 250 C., together with an excess of steam heated to a higher temperature than said product, e.g. in excess of 850 C., to an isolated zone within which it is confined without the supply of additional heat for a short period of time; and then continuously quenching the product to a temperature below 500 C. The olefinic constituents may be separated from the product by, for example, fractional distillation conducted in a series of steps, some of which utilise refrigeration.

Heavy petroleum oil 4 Thermal treatment, contact with moving burden l,

Hot product Superheated steam l Isolated zone, no additional heat l Quenching below 500 C.

Isolation of olefin product While the first thermal treatment may be of the semicontinuous sort with a solid fixed heat transfer medium, which is operated intermittently on the thermal treatment and on re-heating by combustion, it is preferred to use a continuous process and the invention will now be described more particularly in relation to this latter type of process.

In the first stage of the process, the term moving burden does not include fluidized beds. Preferably the movement is solely under gravity. In this stage of the process it is preferred to keep the total pressure as low as possible, provided the pressure is suificient to give continuous even flow between the first and second stages and the pressure at the entry to the second stage and at the exit thereof is not subatmospheric. A suitable total pressure is just a little above atmospheric. Steam should be substantially absent from this first treatment, nor should other diluents gaseous at N.T.P. be present, because they would increase the cost of the ultimate gas separation step. The temperature to be used will depend on the feed, but temperatures of the order of 550 to 750 C., for example, are suitable. It may be said that the first stage yields gaseous products suitable for fuel gas but notfor the direct production of substantially pure olefines in good yield. Preferably also .the solid media comprise pebbles or balls of,carbon,,;and more preferably of coke. The superficial layer of carbon which forms on the pebbles may be conveniently removed by combustion or the enlarged coke pebbles passed through a crusher.

In the second or olefine production stage it is most frequently preferred for reasons of thermal economy that the temperature of the hydrocarbon products should, prior to mixing with the hot steam, be of the same order as that at which they leave the first treatment. A suitable range is, for example 600 to 700 C. Other suitable reaction conditions are, for example: the use of steam preheated to 850 to 950 C.; a steam:hydrocarbon ratio of from 1:2 to 4:1, preferably at least 1:1 if ethylene is the principal desired olefine; and a contact time of 0.3 to 3.0 seconds. Indirect quenching vn'th water by steam raising, or direct quenching with oil or water, may be used, but if the characteristics of the condensible constituents of the cracked mixture do not interfere with heat transfer then indirect quenching is preferred because of its thermal economies.

The present invention in its widest form provides the advantages that mixed gases high in olefines and having favourable olefinescparafiins ratios can be produced from heavy oils of the sort defined, that the conditions in the first thermal treatment stage can be adapted primarily to secure reliability of operation in large scale units, and that the products of the process other than gaseous products can be directed into the form or forms, e.g. liquid fuels, aromatic liquids or coke-like solids, having the most economic outlets.

The preferred form of the present invention using pebbles provides the advantages that it can be operated on the large scale continuously over long periods without interruption on heavy oils of the sort defined to give a large yield of gaseous products of high olefines, in particular ethylene, content, and with high olefinetparaffin ratios, together with carbon as a valuable and/ or marketable by-product, and that this is achieved with a very moderate over-all heat requirement. These advantages spring from the flexibility of design, particularly in respect of temperature, contact time, and product composition, permitted in the first stage, coupled with the ability of the second stage to yield gases With high olefine contents and favourable olefine:paraffin ratios from hydrocarbon vapours which may be low in olefines and high in the corresponding parafiins, and may vary widely in composition. It may be said that in principle the process affords on the continuous large scale a much closer approximation than has heretofore been achieved to the ideal of converting these heavy oils into olefines to the maximum extent on the one hand, and to pure carbon in a valuable form on the other.

Example A gas mixture obtained by contacting a heavy oil, which had a specific gravity of 0.85 and was not capable of being vaporized at 400 C. at atmospheric pressure, with a moving burden of refractory media comprising /s to /4 inch diameter hard petroleum coke pebbles, the average temperature of the gaseous phase in the reactor being 670 to 720 C., using a contact time of to 20 seconds and without the addition of steam to reduce the partial pressure, had the following weight composition.

which renders the ma- The high parafiintolefine ratio,

ethylene on account of terial unsuitable as a source of the high cost of gas separation, and the high contents of C and C hydrocarbons, which make it unattractive economically for this purpose, are to be noted.

The gaseous and vaporous product at 675 C. was mixed with 3.05 times its own weight of steam at 925 C., and the combined stream was passed in turbulent flow through a refractory-lined soaking zone in which cracking of the hydrocarbons was effected by the sensible heat, the contact time being approximately 2 seconds. The material issuing from the soaking zone was immediateiy quenched and the hydrocarbons condensible at N.T.P. were separated out. The residual gas comprising predominantly C and the lighter constituents was obtained in 85.6% yield by weight of the feed gas and had the following composition.

Percent CH 31 9 C 11 40.7 C H 9.4 C H 11.9 C H 0.9 0 1-1 C H n 2 9 C H Nil 2.3

The increased ethylene and decreased C and C hydrocarbon contents of the gas are to be noted. Moreover the ethylenezethane ratio has been raised to 4.33, which renders the gas very much more suited for the recovery of substantially pure ethylene and considerably improves the economics of the process in respect of both running and capital cost.

Slightly less beneficial results were obtained using a 1.53:1 ratio by weight of steam:feed gas, and the same reaction conditions. The C and lighter constituents of the mixture were obtained in a yield of 90.2% by weight of feed gas. The product had the composition by weight:

Percent CH 26.5 C l-l 34.8 C l-I 11.2 C 11 16.6 C 11 3.0 C H 1 n gH o 0.2 H 1.6

Moreover, use of this low proportion of steam offered considerable savings in operating cost.

In both of these procedures the solid media and petroleum material flowed co-currently downward through the reactor.

As a preferred feature of the present invention, then, there is provided a continuous process for the production of ethylene as primary product which comprises subjecting a heavy petroleum oil or fraction which cannot be completely vaporised at 400 C. at atmospheric pressure in a first stage to a thermal treatment under conditions of temperature, pressure, and space velocity, which yield a vaporous product which is not rich in olefines, and carbonaceous material of the nature of coke, by contacting it continuously with a hot moving burden of solid media, e.g. pebbles, balls or pellets of coke using co-current downward flow of the petroleum starting material and the moving burden, and in a second stage continuously feeding the hot gaseous product with or Without prior separation of its heavy constituents, that is those boiling at atmospheric pressure above 250 0., together with an excess of steam heated to 850 C., to an isolated zone within which the mixture is confined without the supply of additional heat for a short period of time; and then continuously quenching the resulting mixture to below 500 C.

As a more preferred feature, the invention comprises the process described in the immediately preceding paragraph further characterized by the combination of features that the average temperature of the gaseous phase in the reactor in the first stage is 670 to 720 C.; those constituents of the gaseous product from the first stage boiling above 250 C. are removed before it is fed to the second stage; the steamzhydrocarbon Weight ratio in the second stage is from 3 :2 to 7:2, and the contact time there is from 0.8 to 2 seconds.

As an also preferred feature, the invention comprises the process described in the second last paragraph characterised in that: the whole of the gaseous product from the first stage is passed to the second stage and the total product from the second stage is quenched directly with oil, e.g. gas oil. Because in practice the condensible constituents of the product are most frequently viscous, tarry liquids which interfere with indirect heat transfer, direct quenching with oil is most often used.

As a most preferred feature the invention comprises the process described in the second last paragraph characterised further by the combination of features described in the last paragraph.

The pressure in the process is kept as low as possible in order to increase the olefineszparafiins ratio, but must be above 1 atmosphere in order to afford gaseous flow through the apparatus.

I claim:

1. A continuous process for the production of mixtures containing lower olefines with ethylene as the principal olefin, said process comprising continuously subjecting, in a first stage, a relatively heavy petroleum oil, which cannot be completely vaporized at atmospheric pressure at 400 C., to contact at a temperature in the range of 670 to 720 C. and in co-current downward flow with a hot moving burden of solid media whereby there is obtained a gaseous product low in olefines content and coke laid down upon said media; and in a second stage continuously feeding the gaseous product from the first stage with no separation of its heavy constituents, together with an excess of steam heated to 920 to 950 C., to an isolated zone within which the resulting mixture is confined without the supply of additional heat for a period of from 0.8 to 2 seconds and then continuously quenching the product from the second stage to below 500 C., the steamzhydrocarbon weight ratio in said second stage lying within the range 3 :2 to 7:2.

2. A continuous process for the production of mixtures containing lower olefines with ethylene as the principal olefin, said process comprising continuously subjecting, in a first stage, a relatively heavy petroleum oil, which cannot be completely vaporized at atmospheric pressure at 400 C., to contact at a temperature in the range of 670 to 720 C., and in co-current downward flow with a hot moving burden of solid media whereby there is obtained a gaseous product low in olefines content and coke laid down upon said media; separating heavy constituents boiling at atmospheric pressure above 250 C. from the gaseous product obtained from the first stage; and in a second stage continuously feeding the gaseous product from which said heavy constituents have been separated, together with an excess of steam heated to 920 to 950 C., to an isolated zone within which the resulting mixture is confined without the supply of additional heat for a period of from 0.8 to 2 seconds and then continuously quenching the product from the second stage to below 500 C., the steamzhydrocarbon weight ratio in said second stage lying within the range 3 :2 to 7:2.

3. A continuous process for the production of ethylene in high amount from heavy petroleum oils which comprises continuously subjecting, as sole feed, a heavy petroleum fraction, which is incompletely vaporized at atmospheric pressure at 400 C., to contact in co-current downward flow with a hot burden of solid media moving solely under the effect of gravity in a first isolated zone at an average temperature therein of 670 -720" C. whereby there is obtained a gaseous hydrocarbon product comprising a moderate amount of ethylene, and coke in valuable form is laid down on the said solid media, and enriching the olefinic content of said gaseous hydrocarbon product by continuously feeding the said gaseous hydrocarbon product directly with steam at 850 to 950 C., in a weight ratio to hydrocarbon within the range of from 3:2 to 7:2, to a second isolated zone Within which the mixture is confined without the supply of additional heat for a short period of time, and thereafter continuously quenching the product from the second zone to below 500 C., whereby a gas having a greatly increased content of ethylene is obtained, and recovering ethylene and propylene from the said gas.

4. A process, as claimed in claim 3, in which in the second stage the steam:hydrocarbon weight ratio is at least 1:1 and a contact time of from 0.3 to 3.0 secs. is employed.

5. A semi-continuous process for the production of mixtures containing lower olefines with ethylene as the principal olefin, said process comprising semi-continuously subjecting, in a first stage, a relatively heavy petroleum oil, which cannot be completely vaporized at atmospheric pressure at 400 C., to contact at a temperature in the range of 670 C. to 720 C. with a solid fixed heat transfer medium whereby there is obtained a gaseous product low in olefines content and coke laid down upon said media, and intermittently reheating by combustion said solid fixed heat transfer medium while it is not used in the thermal treatment of said first stage, and in a second stage continuously feeding the gaseous product from the first stage with no separation of its heavy constituents, together with an excess of steam heated to 920 to 950 C., to an isolated zone within which the resulting mixture is confined without the supply of additional heat for a period of from 0.8 to 2 seconds and then continuously quenching the product from the second stage to below 500 C., the steamzhydrocarbon weight ratio in said second stage lying within the range 3:2 to 7:2.

References Cited in the file of this patent UNITED STATES PATENTS 1,962,502 Grebe et a1. June 12, 1934 2,111,900 Nagel Mar. 22, 1938 2,363,903 Smith Nov. 28, 1944 2,561,334 Bowles et al. July 24, 1951 2,572,664 Robinson Oct. 23, 1951 2,621,216 White Dec. 9, 1952 2,731,508 Jahnig et al Ian. 17, 1956 2,736,685 Wilson et al. Feb. 28, 1956 2,789,084 Schutte Apr. 16, 1957

Claims (1)

1. A CONTINUOUS FOR THE PRODUCTION OF MIXTURES CONTAINING LOWER OLEFINES WITH ETHYLENE AS THE PRINCIPAL OLEFIN, SAID PROCESS COMPRISING CONTINUOULSY SUBJECTING, IN A FIRST STATE, RELATIVELY HEAVY PETROLEUM OIL, WHICH CANNOT BE COMPLETELY VAPORIZED AT ATMOSPHERIC PRESSURE AT 400*C., TO CONTACT AT A TEMPERATURE IN THE RANGE OF 670* TO 720*C. AND I CO-CURRENT DOWNWARD FLOW WITH A HOT MOVING BURDEN OF SOLID MEDIA WHEREBY THERE IS OBTAINED A GASEOUS PRODUCT LOW IN OLEFINES CONTANT AND COKE LAID DOWN UPON SAID MEDIA; AND IN A SECOND STAGE CONTINUOUSLY FEEDING THE GASEOUS PRODUCT FROM THE FIRST STAGE WITH NO SEPARATION OF ITS HEAVY CONSTITUENTS, TOGETHER WITH AN EXCESS OF STEAM HEATED TO 920* TO 950*C., TO AN ISOLATED ZONE WITHIN WHICH THE RESULTING MIXTURE IS CONFINED WITHOUT THE SUPPLY OF ADDITIONAL HEAT FOR A PERIOD OF FROM 0.8 TO 2 SECONDS AND THEN CONTINUOUSLY QUENCHING THE PRODUCT FROM THE SECOND STAGE TO BELOW 500*C., THE STEAM:HYDROCARBON WEIGHT RATIO IN SAID SECOND STAGE LYING WITHIN THE RANGE 3:2 TO 7:2.