US 2956093 A
Description (OCR text may contain errors)
Oct. 11, 19.60 L. A. NlCOLAl 2,956,093
OLEFIN AND TOWN GAS PRODUCTION Filed Feb. 25,1958 2 sheetspsheet 1 f ABSORBENT "-38 33 ABSORPTION TOWER I I41- 4 FIGURE I 3 3 a SEPARATOR a D W mong- FININ J? 42 I UNIT 43 I 26 4e I g v n 4e 34 I6? #1 25Z.. J FLUE GAS 271 *LQB 45 28 zsssrsea CHEMICALS v SEPARATOR PRODUCT TgxlsN HEATER I 44 J, UNIT 3| 'llz ii s'rmPPmeL.
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LLOYD A. NECOLAE flnvenior' By Attorney Oct. 11, 1960 A. NICOLAI 2,956,093
OLEFIN AND TOWN GAS PRODUCTION Filed Feb. 25, 1958 2 Sheets-Sheet 2 I1RECOVERY ZONE 1 t/1 l r- F i OLEFIN mow-"m l CHEMICALS lOlz/ H ILREACTOR ii I |21:;------..------- on. FEED C FROM I09 HEATER Ill ' To HEATER FLUIDIZING GAS I07 I06 LLOYD A. NICOLAI Inventor By/4% Attorney Unite OLEFIN AND TOWN GAS PRODUCTION Lloyd Arthur Nicolai, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware v Filed Feb. 25, 1958, Ser. N0. 7 17,373
4 Claims. (Cl. 260683) The present invention is concerned with the production of unsaturates suitable for chemicals raw materials together with product amenable for utilization as town gas. More specifically, it deals with high temperature thermal cracking by means of fluidized solids techniques and recovery of olefin rich and hydrogen rich fractions from the reaction vapors thus formed.
In recent years, there has been considerable desire in the petroleum industry to convert heavy, low valued hydrocarbons into lighter more desirable products. Towards this end of upgrading hydrocarbon fractions into higher valued products such as ethylene, propylene and other light unsaturates, both the steam cracking and transfer line or chemicals coking processes have been developed. Both these systems, in themselves, are well known to those skilled in the art.
Heretofore, it has been standard practice in steam cracking and high temperature transfer line operations to thermally crack the heavy oil feed to a conversion level in the range of approximately 30-45 weight percent of the feed to C and lighter compounds. It was felt that this level of cracking severity was desirable in that it produced large quantities of unsaturated naphtha fractions, a good feed stream for resin manufacture.
However, the prior art processes for high temperature cracking of heavy oil fractions depend heavily for their commercial success upon the market demand for their unsaturated naphtha product. There'is relatively little flexibility in their operations. Thus, even though suitable feeds for thermal cracking may be readily available, utilization of these prior art systems may be made impractical because of limited demand for chemicals raw material. p
The present invention serves to solve these difficulties and setsforth a system of considerably greater flexibility than was heretofore known. In accordance 'with the present invention, hydrocarbon oil feeds are subjected to high severity cracking conditions while utilizing fluid solids techniques. By use of relatively severe thermal conversion, the major portion of the feed constituents is cracked to give a gas'iform reaction productcontaining substantial portions of olefins, hydrogen and methane therein. By means ofa simple and inexpensive light olefins recovery step, the thermal cracking effluent is segregated into an olefin rich stream suitable as a chemicals raw material, and a second stream containing the major portions of product hydrogen and methane. This second stream is either directly utilizable as a'synthesis or town gas, or in a preferred embodiment, is subjected to a mild hydrofining step so as to hydrogenate polymer precursors, such as acetylenes and diolefins, which might tend to plug burners and the like. The nature of the present system enables a relatively rough, olefin recovery step to be entirely satisfactory in segregating the desired unsaturates product. Further, the hydrofining clean up of the two gas product is simply and economically performed since no extraneous hydrogen need be added to the reaction system.
i States Patent nice dense phase fluid bed conditions or under dilute solids High temperature thermal cracking may be doneunder phase conditions characteristically employed in transfer line operation. Solids suitable for the practice of the present invention include, among others, sand, coke particles, ceramic materials, metallic solids, etc. While basically the thermal cracking is done in the presence of inert solids, it may, under certain circumstances, be desirable to use solid materials having limited catalytic characteristics such as spent catalyst, activated carbon or the like.
The present system is applicable to the treatment of a wide range of hydrocarbon oil fractions. Among feeds available to treatment are light naphthas, light hydrocarbon liquids, gas oils, diesel oil, reduced crudes, petroleum residue, asphalt'tar, shale oil and the like.
The present invention offers considerable flexibility in that it essentially provides for the production of two product streams, namely, light unsaturated chemicals, and town gas. The relative proportion of each may be controlled by "varying the cracking intensity and thus it is readily adaptable to changes in market conditions for olefins and town gas consumption. Particularly desirable sites for the practice of the present invention are found in those areas, as for example Europe, in relatively short supply of fuel and having limited demand for chemicals products.
By way of clarification, the term town gas is used to denote a combustible gas made and supplied for general fuel use. i
The terms gases and vapors are used-synonymously.
The various aspects and modifications of the present invention will be made more clearly apparent by referring to the following description, drawings and accompanying examples.
Figure I illustrates an integrated combination process for high temperature transfer line cracking coupled with olefin recovery and hydrofining steps.
Figure II depicts means for producing both chemicals and town gas under dense phase, fluid bed conditions.
Turning to Figure I, there is shown a combination system consisting primarily of thermal cracker 10, heater 11, separator 13 together with absorption tower 1-4 and hydrofiner 16. p
As indicated in the drawing, thermal cracker 10 is in the form of an elongated, conduit-like reaction zone, normally referred to as a transfer line reactor. Heat for thermal conversion is supplied by the circulation of hot contact solids, e.g. sand, from heating-zone 11 through the thermal cracker.
Heater 11 is depicted as a fluid bed combustion zone although a transfer line burner or moving bed zone could alternatively be employed. As Will be later further described, carbon coated reactions solids are circulated from separator 13 to heater 11 by means of conduit 30. Oxygen-containing gas, e.g. air, is injected into the fluid bed 17 of carbon containing solids by means of inlet 21, the combustion of the carbonaceous matter serving to heat the solids to a temperature of about 50 to 200* F. above that of the reaction zone. When, as is illustrated, a transfer line reactor is to be employed for thermal cracking, the combustion bed will be at a temperature in the range of about 1350 to 1800 'F., e.g. 1600 F.
.If sufficient fuel is not provided by the carbonaceous.
matter laid down on the solids during the thermal cracking step, aswill usually be the case, extraneous fuel such as low valued heavy ends and/or portions of the town gas product may be added to the combustion bed through inlet 51. A
In order to maintain a constant solids mass inventory in the system, solids may be added or witdrawn from the burner through line 18, or by means of outlets in other parts of their circulation path such as conduit 31. Generally, there is little net production of coke, and fine solids need be added to replace lost fines. Hot flue gases, after having entrained solids removed therefrom in separator 44, are withdrawn overhead through line 45. Their latent heat may be recovered and utilized for various purposes, such as supplying heat for stripping unit and/or heating unit 39. Separated entrained fines are returned to the combustion bed as shown, or may be recovered as such for direct passage to thermal cracker 1%.
A portion of the hot contact solids is withdrawn from heater 11 and passed by means of conduit 19 to transfer line cracking zone 10. Propelling gases such as steam, light hydrocarbons, etc., introduced through taps 20 and 22, serve to convey the hot solids upwardly into and through thermal cracker 10 in the form of a rapidly moving gas-solids suspension. The solids-gas mixture generally passes through the reaction zone as a suspension of approximately 2 to 20 lbs/cu. ft. density and at velocity of about 10 to 60 ft./sec., e.g. ft./sec.
Hydrocarbon oil feed, such as a naphtha suitably preheated to a temperature of about 650 F., is introduced into the rapidly flowing hot contact solids suspension by means of injector 23. If desired, oil injection means may be disposed longitudinally and circumferentially about thermal cracker 10. By means of vertically spaced injectors such as inlets 23 and 24, the effective length of the thermal cracking zone, and hence the reaction period may be readily altered.
The reaction conditions in thermal cracker 10 are maintained to give a greater severity of thermal conversion than would be practiced in standard transfer line chemicals coking units. In accordance with the present invention, the oil feed is cracked to about 95 to 100 wt. percent conversion to C and lighter products on a cokefree basis. If butadiene is also desired, the conversion should be less, say about 70%, and the heavier components, excepting butadiene, recycled to the cracking step. The cracking severity may be readily increased by increasing reaction temperature and residence time. In the embodiment presently described, a reaction temperature of 1500 F. and a residence interval (time of feed-solids contact prior to quenching or other arrestment of the reaction) is about 0.6 second.
Upon contact with the hot solids, the hydrocarbon oil is converted into light gaseous products and carbonaceous residue which is deposited upon the reaction solids. Substantial portions of hydrogen, methane, light olefins such as ethylene and propylene are formed together with other hydrocarbon products. In accordance with the present invention, the thermal cracking gasiform products contain at least vol. percent of light olefins (ethylene and propylene) and at least 15 vol. percent of hydrogen.
Reaction solids, propelling gas along with the vaporous conversion products are withdrawn overhead and passed to solids separation unit 13. A quenching agent such as steam, light hydrocarbons or other liquid media may be introduced before and/or after solids separation by means of quench inlets 46 and 47, respectively. It is desirable to quench the reaction vapors to at least 600 F. to stop all cracking. Lower temperatures are preferable because the following olefin absorption step requires much lower temperatures.
As illustrated, separator unit 13 takes the form of an enclosing chamber having one or more cyclone separators 25 therein. Of course, other conventional solids separation means such as vanes or the like may be employed. Separated solids are passed through dipleg 27 into the lower portion of unit 13 from which they are passed to heater 11. In the embodiment illustrated, a mass 28 of contact solids is formed at the bottom of unit 13. Steam or other inert fluids are introduced into solids mass 28 by line 29 so as to strip occluded hydrocarbons therefrom, and to facilitate flow of separated solids into return conduit 30. Stripped vapors and 'the fluidizing 'a chemical products.
4 media pass through balance line 48 and are withdrawn overhead through line 26 together with the bulk of the reaction products. Solids circulation in conduit 30 is aided by one or more aeration taps 32 placed along the solids passageway. Solids are conveniently added or withdrawn through outlet 31.
After solids separation, the gasiform reaction products are cooled, compressed and sent to an olefin recovery step. Unlike the recovery operations of prior art chemicals coking systems, the separation and recovery of light olefins is done in a cheap, relatively inefiicient manner. Since there are large quantities of olefins in the product stream, only partial or incomplete olefin recovery need be utilized in order to remove the desired quantity of the light olefins and thereby give an olefin rich stream (based on the thermal cracking effiuent), and a second product fraction less rich in olefin and containing a high percenttage of hydrogen and methane therein.
As shown in Figure I, the cheap, relatively inefficient olefin recovery step may take the form of an oil absorption process. After cooling in cooler 42, the product gases are separated from the quench liquid in separator 49, compressed by compressor 50 and sent to absorption tower 14. The quench liquid is withdrawn through line 43 and may be recycled to the quench points. An absorbent oil such as pentane or the like, capable of removing light olefins from a fluid stream, is introduced into the upper portion of tower 14 by inlet 33 at a rate of in the range of 0.5 to 2 moles/mole of inlet gas. Countercurrent flow between the reaction products and the absorbent oil is preferably maintained, the olefin rich stream being removed along with spent oil by outlet 34 and a second, hydrogen rich stream suitable for town gas product withdrawn through outlet 38. The tower operates generally at a pressure of 200-300 p.s.i.g. and ambient or cooling water tempertaure, e.g. -100 F.
Oil absorption processes, per se, are well known to those skilled in the art and thus the operation of tower 14 need not be described in detail. Standard techniques of oil absorption tower construction and operations adaptable for use in the present invention may be found beginning on page 668 of the Chemical Engineers Handbook, Third Edition, 1950, McGraw-Hill.
The olefin rich stream withdrawn from tower 14 may be then subjected to conventional stripping in unit 15 for separation of cracked products i.e. ethylene and propylene. Stripping gas introduced through line 35 vaporizes the desired light unsaturates, the chemicals products being withdrawn overhead by line 36, while an oil phase, depleted in light olefins, is removed by outlet 37. The oil may, if desired, be recirculated back to absorption tower 14.
The olefin rich, chemicals product stream withdrawn by line 36 finds use in the production of resins and other polymeric constituents and represents a relatively high priced product.
While Fig. I illustrates the use of oil absorption for the recovery of light olefins products, other cheap, relatively inefficient means for concentrating olefins into a chemicals product may be employed. For example, char adsorption or the like may be utilized. Similarly, oil absorption tower may operate in conjunction with standard distillation towers for purification of the individual olefins. Numerous other modes of separating reaction effluent into an olefin rich stream and a hydrogen rich stream will be apparent to those skilled in the art, and such methods are to be construed as falling within the teaching of the present invention.
It should be clearly noted that the present invention, and the incomplete olefin recovery step employed therein, offer substantial advantages over those systems relying upon essentially complete recovery of olefins for use as Since in accordance with the present invention, it is generally desired to recover only about 5 to 50% of the total ethylene present in thereac- 5 tion gasiform products, the exact value depending upon relative market demands for unsaturates and town gas, a cheap, rough cut operation is quite suitable. Expensive separation techniques are not required, and the overall process is more easily operated.
Returning the the specific embodiment of Fig. I, the hydrogen rich product fraction withdrawn from absorption tower 14 finds use as town gas. The stream withdrawn by line 38 may be directly used for town gas, but it is normally preferred to clean up the gas so as to remove acetylene and diolefins materials therein. These polymer precursor materials tend to polymerize and plug the burners ultimately used for combustion of the town gas.
Acetylene and diolefins are readily removed by a simple, cheap hydrofining step. Since the hydrogen already in the gas stream is greatly in excess of that needed to effect the desired hydrogenation of the diolefins and acetylene (which are in only trace amounts), a low temperature, high throughput hydrofining step operating without addition of extraneous hydrogen is employed.
The town gas fraction is thus advantageously passed through line 38 into hydrofining unit 16 which contains a standard catalytic solid for hydrofining acetylenes or the like, such as .04% palladium or alumina. The catalytic solids are in the form of a fixed bed. The gases leaving tower 14 via line 38 are at the desired pressure for hydrofining but must pass through heater 39 and thence to line 40 in order to maintain a temperature of about 200 to 250 F., e.g. 225 F. in the hydrofiner. The hydrofining unit 16 is operated at a pressure of the order of 200 p.s'.i.g. and volumetric throughputs of from 500-1700 v. gas/v. cat/hr. e.g. 1000 v./v./hr. are employed. Generally, only about 1% or less of the hydrogen in the stream is required for the desired hydrogenation in unit 16.
The hydrofined town gas is removed by line 41 and passed to storage. It may be utilized as a heat source within the process itself or otherwise processed. While the above-described hydrofining step is particularly advantageous in the event that clean up of town gas is desired, other means of removing highly unsaturated molecules from the town gas produced can be used. For example, the gases of line 38 may be passed over activated alumina to effect the polymerization of acetylenes and diolefins, the alumina being periodically regenerated with With reference to Fig. II, depicted therein is a system for carrying out the present invention by the use of a relatively dense, e.g. 40 lbs./ cu. ft., turbulent bed of contact solids. As shown a mass 112 of reaction solids e.g. sand, is maintained in a highly turbulent pseudo-liquid phase commonly referred to as fluid bed conditions by means of aeration gas, such as steam or feed hydrocarbons supplied by inlet 103.
The reaction solids, primarily ranging from 40 to 500 microns, are maintained at a temperature of 1200 F., or any other suitable temperature appreciably above that which would be used in fuels coking or conventional fluid bed coking of the same feed material. Heat for the system is advantageously supplied, as in Figure I, by circulation of carborrcoated reactor solids through line 104 to a burner vessel (not shown), wherein combus tion of the carbon deposits together with any extraneous fuel material serves to heat the particles to sufiicientlyhigh temperatures so that they supply requisite conversion energy upon being reintroduced to the thermal cracking bed by conduit 108. Aeration taps 107 and 109 serve to convey the solids through line 105 and 108, respectively, in their passage between reactor 101 and the heater vessel. Solids may be withdrawn from the system by conduit 106 and/or other outlets, not shown.
A suitably preheated oil feed is introduced by means of multiple injector 111 into the hot solids bed 112. The oil upon contact with the solids is converted into gasiform products having substantial portions of olefins and 61 hydrogens therein, together with carbonaceous residue which is deposited upon the reaction solids. wt. percent of the oil feed exclusive of that converted to coke is converted to C and lighter compounds. After a residence period of 10 seconds, the reaction vapors together with the fluidizing gases pass upwardly into the dilute solids phase above bed 112 and thence into cyclone 113 wherein entrained solids are separated from the gaseous products. Separated solids are returned to the reaction bed by dipleg 114.
The product gases may be then passed directly to olefin recovery zone 102, or first subjected to an intermediate cooling step to arrest further reaction and condense out non-product gases such as fiuidizing steam.
The gasiform products of the high severity, thermal cracking reaction zone undergoes substantially the same treatment as described in regard to Fig. I. The vapors are subjected to a relatively rough, e.g. 30% recovery of ethylene, olefin recovery step such as oil absorption, char adsorption, or the like. An olefin rich fraction is withdrawn from zone 102 through line 117 and may be used directly asa chemicals raw material or further refined, as desired. The hydrogen rich, town gas stream is removed by line 116, and may be used directly or further treated as by hydrofining, etc., to produce a higher grade town gas product.
With particular reference to Figure I, the following compilation of the compositions of the various product streams will serve to make the present invention more clear.
The feed stock comprises a naphtha having the followmg inspection:
I.P.B. F 300 Gravity API 50 The oil is introduced into the reaction zone and thermally cracked at a temperature of 1500 for a period of 0.6 second to give essentially a gasiform product having the following composition:
The total gasiform product is then subjected to an oil absorption olefins recovery step so as to recover about 25% of the ethylene and give two product streams having the following approximate compositions.
TABLE II Olefin rich stream Vol. percent H 1 CH 6 C H 40 C H 7 C H 42 C H 4 C plus Trace Acetylenes and diolefins 'lrace Effluent fan town gas Vol. percent H 23 CH; 41 C H 30 C H 4 0 H; 2 C H Trace Acetylenes and diolefins Trace About 99 The material to be used as town gas is then subjected to hydrofining at 225 F; to hydrogenate acetylenes and diolefins, less than 0.2% ofpthe contained hydrogen being depleted for this purpose. i
The town gas product has a heating, value in the range of 1000 to 1100 B.t.u./ std. ft.
The following tabular presentation sets forth pertinent conditions for several of the. processing steps of Figures I and H, as was heretofore described.
TABLE HI Thermal Cracking Step Broad Preferred Range Range Fluid Bed Unit:
Size Range of Solids, microns -800 40-500 Bed Density, Lbs/cu. ft 30-70 40-50 Reaction Temperature, 1, 100-1, 400 1, 150-1, 300
Reaction Time, seeonds. -20 10-15 Pressure, p.s.i.g 0-50 10-20 Transfer Line Unit:
Size Range of Solids, microns 0-1, 000 40-500 Density of Solids-Gas Suspension,
Lbs/cu. ft 1-30 5-20 Reaction Temperature, F- 1, 300-1, 800 1, 350-1, 600 Reaction Time, seconds.. 0. 0.5-1 Pressure, p.s.i.g 0-50 -20 Hydrofming Step:
Temperature, F 150-300 200-250 Pressure, p.s.i.g 100-300 150-250 Throughput, v. gas/v. cat/hr 300-2, 000 500-1, 700
Numerous modifications apparent to those skilled in the art may be made without departing from the basic concepts of the present invention. For example, a system employing a combination of fluid bed and transfer line thermal cracking or other means of high severity thermal cracking by the use of fluid solids techniques is to be construed as falling within the. scope of this invention. Since the present olefin recovery step need not be exceedingly eflicient, various techniques for accomplishing olefin concentration will be suggested to those skilled in the art.
summarily, in accordance with the present invention, a highly flexible reaction system for the conversion of oil feeds into chemicals products and town gas is realized. Relatively expensive separation and purification of light olefins characteristic of the prior art system, are not required. The town gas product is readily upgraded by an extremely simple hydrofining step and the overall system may be easily adapted tochanges in market demand.
What is claimed is:
1. A process for producing a light, unsaturated hydrocarbon fraction rich in olefins and a town gas fraction poor in olefins, which comprises the steps of introducing hydrocarbon oil feed into a reaction zone containing hot, inert solids maintained at a temperature of at least 1100 P. so as to convert said hydrocarbon oil feed at a coke-free conversion level of at least wt. percent to C and lighter hydrocarbon compounds into a gaseous product stream containing substantial proportions of olcfins and hydrogen, separating said gaseous product stream from said solids, passing said gaseous product stream to a rough separation stage wherein olefins are at least in part recovered to give an olefin rich fraction and an olefin poor fraction, removing said olefin rich fraction containing a major proportion of C and C unsaturated hydrocarbons for use as a chemicals product and withdrawing said olefin poor fraction containing a substantial proportion of hydrogen and a minor proportion of ethylene for use as town gas.
2. The process of claim 1 which further comprises passing said hydrogen containing olefin poor stream to a hydrofining zone, said stream being therein contacted with a hydrofining catalyst maintained at a temperature of ZOO-250 P. so as to hydrogenate acetylenes and diolefins contained in said stream, and recovering from said hydrofining zone, as product, hydrogen-containing material suitable for use as town gas.
3. The process of claim 1 wherein said reaction zone is a transfer line reactor, said hydrocarbon oil being therein contacted for a period of about 0.25 to 1.0 second with a relatively dilute, rapidly moving suspension of hot inert solids at a temperature in the range of 1300- 1600 F.
, 4. The process of claim 1 wherein said hydrocarbon oil feed is selected from the group consisting of light naphthas, reduced crudes, gas oil and asphalt tar.
References Cited in the file of this patent UNITED STATES PATENTS 2,154,676 Haeuber Apr. 18, 1939 2,734,809 Pettyjohn Feb. 14, 1956 2,750,420 Hepp June 12, 1956 2,768,127 Kimberlin Oct. 23, 1956 2,814,653 Hogan Nov. 26, 1957