USRE20950E

USRE20950E - Process fob polymerizing hydrocar

Info

Publication number: USRE20950E
Authority: US
Publication date: 1938-12-13

Description

Dec. 13, 1938. W..B. PLUMMER- PROCESS FOR POLYMERIZING HYDROCARBON GASES Original Filed Nov, 25, 1951 KRNQ Z7? FLELZZZZZWZFPGV Kiiunmmmmnmmmmmmw Reisaued Dec. 13, 1938 UNITED STATES PATENT OFFICE PROCESS FOR POLYMERIZING HYDROCA R- BON GASES William B. Plummer, Chicago, 111., asaignor to Standard Oil Company, Chicago, 111., a corporation of Indiana 18 Claims.

The present invention relates to an improvement in the art of polyme izing unsaturated gaseous hydrocarbons to low boiling liquid hydrocarbons under high temperatures and pressures,

' whereby the polymerization temperature is more effectively controlled than has previously been possible.

The fact that gaseous unsaturated hydrocarbons can be "polymerized to low boiling liquid a hydrocarbons has been known for many years but this process has never been developed commercially. One of the most serious impediments to such commercial development has been the fact that these polymerization reactions are highly ll exothermic. The reaction must be carried out at temperatures ranging close up to 1000 F., under which conditions spontaneous overheating of the reaction due to its exothermicity leads to the formation of large proportions of undesired prod- U nets, in particular hydrogen, methane, and carbon. It has been proposed to counteract this tendency by carrying out the polymerization reactions in a pipe heater wherein the flow of reacting gases inside the coils is parallel with the ll flow of furnace gases outside the coils. By this means, as the reaction tends to overheat, it may lose heat to the relatively cooler furnace gases surrounding the coils. I have found however, that this expedient is not suihcient in many cases 80 to provide suitable control of the reaction temperature.

I have discovered that if such polymerization reactions be carried out in close thermal relationship (but out of direct contact) with a stream 8 or body of oil which is maintained under such pressure as to be susceptible to cracking at the temperature of polymerization reactions, said reaction temperature can be very readily controlled and prevented from rising to an unde- 40 sirable point due to exothermic development of heat. This is due to the fact that the heat of cracking of the oil is endothermic in character and large in magnitude. The specific heat capacity of the oil would not alone be sufficient to I rbsorb the exothermic heat of the polymerization reactions unless an excessively large amount of oil were present. Furthermore the heat of vaporization of the oil would not be suillcient to absorb the heat evolved by the polymerization,

since under cracking conditions the constituents oi the oil are in general so near their critical state that the heat of vaporization has become relatively small. Since the endothermic heat of cracking is large, and since the temperature coll efficient of the cracking reactions is high in this general temperature range, the temperature of the polymerization reactions cannot rise to an undue extent, since any increase in said temperature produces a corresponding increase in the rate of absorption of heat by the oil due to the rapid increase in the rate of cracking. 1

Any apparatus whereby oil under cracking conditions and unsaturated gases under polymerizing conditions can be maintained out of contact but in close thermal relationship with each other, is suitable for carrying out my process. For example, the polymerization reactions might be carried out in a coil submerged in oil maintained at cracking conditions in a large pressure vessel. This arrangement has the disadvantage that coke from the cracking of the oil may be deposited on the outside of the polymerization coils, the removal of such coke being diflicult. I therefore prefer to carry out my process in apparatus consisting basically of adjacent banks of tubes, preferably alternately containing oil and gas, these tubes being maintained in close thermal contact by the presence of a thermally conducting medium between them.

My invention will be clearly understood from the foregoing brief description and from the following detailed discussion of its operation. In the accompanying drawing, which forms a part of this specification,

Figure 1 is a diagrammatic representation of the apparatus and set-up for carrying out the process,

Figure 2 is a front view of the reactor, and

Figure 3 is a side view thereof.

Referring to Figure 1, unsaturated gases from any convenient source enter the system through line 10, are compressed by compressor ll, preheated by heater 1! and injected into reactor II at a pressure of 1000-3000 pounds/square inch and a temperature of 800-l000 F. Suitable oil charging stock enters the system through pipe II and is pumped by pump 15 through heat interchanger or interchangers l8 and preheater 11. The oil is thus heated to a temperature of 800- 1000" F. corresponding to the temperature of the gases undergoing polymerization. The pressure p on the oil may range from 100-1000 pounds/square inch, depending on the cracking characteristics of the oil. It will be understood that the heat interchanger 16 may be located at any desired point, for example, in heat interchange relation with materials in pipes It or I! leaving the reactor l3, or in the bubble tower 20.

The reactor ll will be further described in connection with Figure 2. Oil and its cracking ll tower, and are, pumped by pump through line 26 whereby such oils are returned to the oil supply pipe ll of the cracking system. Gases and vapors of light products are'removed from the bubble tower through the top oil-take 21 and are passed through cooler 28. In line 29 valve 30 reduces the pressure on the cooled products to 50-100 pounds/square inch. Separator 3| operates at this pressure, all liquid products being removed by valved bottom draw-oil 32 while uncondensed gases are removed through valved top draw-oi! l3.

Uncondensed gases may be returned to the polymerization step, may be purified to increase their olefin content prior to so returning them, or may be cracked to increase their olefin content prior to recycling. In the event it is desired to increase the olefin content of the gases in line 33, they may be by-passed through valved conduit l0 and introduced into the absorber II .where they are scrubbed with an absorber oil.

The fixed gases will be vented through valved conduit 42. The enriched absorber oil is withdrawn from the bottom of the absorber through 1 in close thermal contact with each other.

line 43 and passed to the stripper H where the dissolved gases are removed from the absorber oil and passed through conduit 45 to line III.'

The stripped absorber oil in stripper I4 is removed through conduit 40 and passed through the cooler 41 and then returned to the absorber ll The polymerizing-cracking reactor it (see Figs. 2 and 3) may consist of an insulated receptacle with closely spaced pipes 34 therein. The oil cracking stock may be introduced by pipe 35 and discharged by pipe 36; the unsaturated gases may be introduced by pipe 31 and the polymerized products discharged by pipe 38. In each case a single conduit is formed by the pipes which are connected by return bends 38, which are removable to facilitate cleaning of the tubes. The

,only fixed requirement on the construction and arrangement of the reactor is that the oil cracking tubes and the gas polymerizing tubes shall be In apparatus designed to operate at or about the maximum contemplated temperature of 1000 it may be sufficient to arrange. the tubes in close juxtaposition toeach other in a simple heat-insulated chamber, since at these temperatures the rate of heat transfer by radiation through gases may be sufficiently rapid tor the present purposes. It may be necessary, especially at lower temperatures, to provide more intimate thermal contact between the tubes; this may be accomplished by surrounding the tubes with a cast billet or a bath of molten alloy. -I prefer to surround the tubes with a metal conductive medium such as cast aluminum, which has a melting point above the I reaction temperatures and which combines the advantages of high conductivity and lightness. If higher melting point metals are used there may be danger of melting the tubes in casting.

Low melting alloys are satisfactory except for structural ditnculties (the cast aluminum would be in the form of a solid billet). It will be possible, if so desired, to construct the reactor by boring or casting closely adjacent holes in a large block of metal and suitably cross-connecting said holes or'conduits with return bends, or by covercontrol in polymerization, but, also promotes economies of heat in the oil cracking operation, as well as further economies which are realized by the joint utilization of apparatus in both systems.

While the foregoing is a full and complete description of my invention it will be understood that I am not limited therein except as defined by the following claims:

I claim:

1. In polymerizing gaseous unsaturated hydrocarbons at pressures of 1000-3000 pounds per square inch, and temperatures of 800-1000 R, the method of controlling the polymerization temperature in an elongated tubular polymerization zone which comprises transferring heat therefrom to a body of oil at about the same temperature but at a diflerent pressure whereby the exothermic heat of polymerization is utilized to supply the endothermic heat of cracking.

2. The process for polymerizing gaseous unsaturated hydrocarbons at 1000-3000 pounds per square inch and 800-1000" F., in a continuous manner which comprises passing said hydrocarbons through an elongated tubular polymerization zone, passing a stream of oil through an elongated tubular cracking zone under cracking conditions 01' temperature and pressure, and transferring heat from one zone to the other whereby the exothermic heat of polymerization is utilized to promote cracking, thereby stabilizing polymerization temperature.

3. The process of obtaining low boiling hydrocarbon oils which comprises compressing unsaturated gases to pressures of 1000-3000 pounds per square inch, heating said compressed gases to a temperature of 800-l000 F., passing said compressed gases through an elongated tubular polymerization zone, heating a hydrocarbonoil heavier than gasoline to about the same temperature at a lower pressure, passing said oil v through a cracking zone, maintaining said polymerization zone and said cracking zone in heat exchange relation with each other, introducing 1 products.

4. The process of claim 3 wherein the lighter products are returned to be recompressed and reheated in the polymerization treatment.

5. In combination, means for compressing unsaturated hydrocarbon gases to 1000-3000 pounds/square inch, means for heating said compressed gases to 800-1000 F., means for heating an oil heavier than gasoline to an equivalent temperature, an elongated gas polymerization reaction system and an elongated oil cracking reaction system adjacent thereto and in close thermal contact therewith, means for passing said heated gases and said heated oil through said reaction systems respectively, a fractionating tower, means for passing products from both said systems into,

ring means.

said iractionating tower, means for withdrawing oils heavier than gasoline from said tower ,and for returning said oils to the oil heating means, means for withdrawing gases and vapors from said tower, 'means for cooling said gases and vapors, and means for separating condensed low boiling hydrocarbons from uncondensed gases.

6. In apparatus as defined in claim 5, in addition, means for returning a part of the flnal uncondensed gases to the unsaturated gas compressl. The process of obtaining low boiling hydrocarbon oils which comprises compressing unsaturated gases to pressures of 1000-3000 pounds per square inch, heating said compressed gases to a temperature of the order of 800-1000 F., passing said compressed gases through an elongated tubular polymerization zone, heating a hydrocarbon oil heavier than gasoline to about the same temperature at a lower pressure, passing said oil through a cracking zone, simultaneously introducing the products from each zone into a single fractionating tower, and separating the desired low boiling hydrocarbon oils from lighter and heavier products.

0. The process of obtaining low boiling hydrocarbon oils which comprises heating a flowing stream of unsaturated hydrocarbon gases during its flow through an elongated passageway toa polymerization. temperature of the order of 800- 1000 F. while maintaining it under a high superatmospheric pressure of the order 01' 1000-3000 lbs. per square inch, heating a flowing stream of hydrocarbon oil heavierthan gasoline during its flow through a separate elongated passageway to about the same temperature while maintaining it under a lower super-atmospheric pressure, thereafter simultaneously passing the stream of reaction products from each passageway into the same iractionating zone, and separating the desired low-boiling hydrocarbon oils from lighter and heavier products.

9. The process of obtaining low boiling hydrocarbon oils which comprises heating a flowing stream of unsaturated hydrocarbon gases during its flow through an elongated passageway to a polymerization temperature of the order of 800- 1000" 1". while maintaining it under a high superatmospheric pressure of the order of 1000-3000 lbs. per square inch,'heating a flowing stream of hydrocarbon oil heavier than gasoline during its flow through a separate elongated passageway to about the same temperature while maintaining it \mder a lower super-atmospheric pressure, thereafter simultaneously passing the stream of reaction products from each passageway into the same i'ractionating zone wherein heavy products I are separated in liquid form and lighter products are separated in vapor form, withdrawing the vapors from said fractionating zone and separating therefrom, as separate fractions, low boiling hydrocarbon oils and a mixture of normally gaseous hydrocarbon products.

10. The process of claim 9 wherein the mixture of normally gaseous hydrocarbon products are returned to be recompressed and reheated in the P lymerization treatment.

11. The process oi obtaining low boiling hydrocarbon oils which comprisesipassing unsaturated hydrocarbon gases through a heating zone and heating said gases to an elevated temperaturewhile being maintained under a relatively high .superatmospheric pressure to accomplish polymerization thereof, separately heating hydrocar-- bon oil heavier than gasoline to an elevated temperature to crack the higher boiling oil into lower boiling ones, simultaneously passing the products resulting from the aforementioned polymerization and cracking to a common separating zone, and separating the desired low boiling hydrocarbon oils from lighter and heavier products.

12. The process of obtaining low boiling hydrocarbon oils which comprises passing unsaturated hydrocarbon gases through a heating zone and heating said gases to an elevated temperature while being maintained under a relatively high superatmospheric pressure to accomplish polymerization thereof, separately heating hydrocar superatmospheric pressure to accomplish polymerization thereof, separately heating hydrocarbon oil heavier than gasoline to an elevated temperature while being maintained under superatmospheric pressure to crack the higher boiling oil into lower boiling ones, simultaneously passing the products resulting from the aforementioned polymerization and cracking to a common separating zone, separating said products into a fraction containing the desired low boiling hydrocarbon oil, a fraction lighter than said low boiling oil and a heavier fraction, said lighter fraction comprising normally gaseous hydrocarbons, and returning normally gaseous hydrocarbons to the polymerization heating zone.

14. The process of obtaining low boiling hydrocarbon oils which comprises passing unsaturated hydrocarbon gases through a heating zone and heating said gases to an elevated temperature while being maintained under a relatively high superatr'nospheric pressure to accomplish polymerization thereof, separately heating hydrocarbon oil heavier than gasoline to an elevated temperature while being maintained under superstmospheric pressure to crack the higher boiling oil into-lower boiling ones, simultaneously passing the products resulting from the aforementioned polymerization and cracking to a common separating zone, separating said products into a fraction containing the desired low boiling hydrocarbon oil, a fraction lighter than said low boiling oil and a heavier fraction, and returning at least a part of said heavier fraction to said oil cracking zone.

15. The process of obtaining low boiling hydrocarbon oils which comprises passing unsaturated hydrocarbon gases through a heating zone and heating said gases to an elevated temperature while being maintained under a relatively high superatmospheric pressure to accomplish polymerization thereof, separately heating hydrocarbon oil heavier than "gasoline to an elevated temperature while being maintained under superatmospheric pressure to crackthe higher boiling oil into lower boiling ones, simultaneously passing the products resulting from the aforementioned polymerization and cracking to a common separating zone, separating said products into a fraction containing the desired low boiling hydrocarbon 01], a fraction lighter than said low boiling'oil and a heavier fraction, said lighter fraction comprising normally gaseous hydrocarbons, returning normally gaseous hydrocarbons to the polymerization heating zone, and returning at,

least a pm of said heavier fraction to said oil cracking zone. 16. The process of claim 9 wherein the mixture 01 normally gaseous hydrocarbon products is treated to increase its olefin content and then re- 5 cycled to the polymerization treatment.