US2197197A - Pyrolysis of hydrocarbon fluids - Google Patents

Description

April 16, 1940. H. c. scHuTT PYROIYSIS HYDRGCARBO-N FLUIDS Filed July 24, V1937 may uw. hw

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U m S me. mn m -f BY Zaw/ /vf- L@ ATTORNEY A Patented Apr. 16, 1940 i Y v Y UNi'rsn STATES PATENT ori-ie PYROLYSIS F HYDROCARBON FLUIDS Hermann c. Schutt, North Tarrytown, N. Y., as-

signor to The Pure Oil Company, Chicago, Ill., a corporation of @lilo Application July 24, 1937, Serial No. 155,517

Claims. (fili. 196-10) This invention relates'to improvements in the to be understood that the invention is not limited thermolytic conversion of hydrocarbon fluids and to treatment of that type of gas but covers treatis more particularly concerned with improvement of hydrocarbon gases in general. y ments in thermal polymerization of oleflnic gases -Referring to the drawing, the numeral I in- 5- to hydrocarbons boiling within the gasoline dicates a line through which gas is charged to 5 rangethe. system. -This gas is preferably a gas from In the conversion of hydrocarbon fluids by the stabilizer of an oil cracking unit and may be strictly pyrolytic processes, it is necessary to use composed chiefly of Ca and C4 hydrocarbons with such high temperatures that conversion will pro- 'a small amount of C2 hydrocarbons. vThe gas lo ceed too far or secondary reactions will occur may be charged under pressure of approximately 1n unless the reaction is suddenly halted. It has 50-200 pounds per Square inch. The gas is cooledA become common practice among renners to emduring passage through cooling coil 3 from which ploy shock chilling -for thatpurpose. A cool oil it .passes intoV feed tank 5. In the tank 5 the fraction is directly contacted with the reaction gases may be in substantially liquid condition or 1g; products immediately upon their emergence from in a condition of mixed rgas and liquid, depending l5' l 'the reaction zone and the temperature of the re. upon the composition of the gas and the condiaction products thereby suddenly reduced to a tions of pressure and temperature maintained. point where reaction ceases. As chilling stock, 'Ihe gas is taken from the feed, tank 5 through it is preferable to use a condensate ratherthan line 1 by means of pump or compressor 9 in residual stock for the reason that the latter dew which the gas is raised to the desired pressure 20 posits carbon at the point of chilling and is, vwhich-maybe from 200-5000 or more pounds per therefore. objectionable. square inch. The compressed gas, which is sub- However, if the temperature of the reaction stantially in the liquid state, is charged through products, during chilling, is lowered only to a heat exchanger II wherein it may pass in inpoint such that the chilled products can be fracdirect. heat exchange with hot condensate and 25 .tionated without further heating, the `chilled may be preheated to a temperature of approducts have a marked tendency to deposit car- Droximately -200-400 F. The preheated gas bon in the transfer line between the chiller and- 'leaves theexchanger through line I3 and passes the iractionator or Separator. into the inlet of heating coil I5 located in fur- The object of this -invention is to provide nace I1. $0 method and apparatus to overcome the clogging In the heating coil the gases are heated, while and coking of the transfer line from the chiller maintained under the afOreSeid pressure. t0 temor arrester to the separator or fractionator. Deratures ranging from 8001200 F., depending It has been found that if the reaction products upon the pressure, the composition of the charge,

from a conversion zone are chilled by means of and `1113011 the Product desired. If high pressures 85 cool condensate toa temperature below that of are employed, th temperature will not be subconversion, for example, approximately 600 F., stantially in eXCeSS of 1050 FJ if 10W Drellres and a stream of het residual ou is injected into of the Order 0f 200 pounds per square inch are the stream of reaction products immediately emplyed, the temperature Will preferably 'De 40 after cooling below conversion temperature, the from 10751200 F. In the latter case the re- 40 residual oil will act as a solvent and carrying sulting liquid product will be predominantly aro` agent for the tarry matter and coke, thereby prematic. Of cours/e, if the charge to the heating -venting deposition thereof in thev transfer line coll is predominantly or entirely'saturated, -it Vand making possible much longer runs. may be desirable to use lower pressures than In order to better understand the invention, those above mentioned and higher temperatures 4r.

reference should be had 4to the following dein order to crack the gases to produce olens. scriptiou together with the accompanying draw- From the heating coil I5 the heated gases pass ing of which to reaction coil I8 wherein the products are The single figure is a diagrammatic side ele-- maintained u nder substantially the sameA temvational view of apparatus suitable for carrying perature and pressure existing in the heating 5o out the invention. coll, for a period of time'suilicient to bring about Although the invention will be described in conversion of a substantial portion ofthe gases connection with the polymerization of hydroto liquid hydrocarbons. The reaction coil is l* carbon gas consisting chiefly of C3 and C4 fraopreferably of larger cross-sectional area than the tions. a large 'portion 'of which is olenic, it is heating coil and may take the form of a charn- 55 ber. 'Ihe reaction coil is also preferably enclosed in a suitable housing which will permit controlled passage therethrough of a cooling fluid, such as air or flue gas, in order to prevent undue rise of temperature.

The reaction products upon leaving the reaction coil are immediately and suddenly chilled to a temperature below that at which conversion takes place, by injecting into the stream at the point I9, cool condensate. The temperature is preferably lowered to approximately 600 F. It is not desirable to chill the reaction products to temperatures materially below 600 F. since to do so would necessitate subsequent heatingvof the products before fractionation thereof. At a temperature of about 600 F. the reaction products can be fractionated into the desired cuts without additional heat. The chilled products pass through transfer line 2| to the point 23, a short distance from the point I9, and at the point 23 hot residual oil is injected into the partially cooled stream of reaction products. The residual oil is injected at a temperature not materially below the temperature of the chilled products..

In commercial operation the residual oil may be at a temperature of from 525575 F. The 'residual oil acts as' a solvent or carrying agent for the tarry and coky constituents present in the reaction products and prevents deposition of `these materials in the transfer line. `The combined products then pass through valve 25 into the lower portion of the fractionating tower 21. .at the valve 25, pressure may be reduced so that the pressure in theffractionating tower will be maintained between approximately 175-250 pounds per square inch.

Vaporization and fractionation ofthe products take place in the tower 21. A condensate heavier than gasoline and corresponding substantially to gas oil is collected on the plate 29. The gasoline boiling constituents are condensed in the fractionating tower and .collected on the plate 3l. Uncondensed gases and vapors leave the top of the tower through the line 33 controlled by valve 35, where the pressure is reduced to substantially atmospheric, then pass through cooling and condensing coil 31, into gas and liquid sepa: rator 39. Any condensate in the separator 39 is withdrawntherefrom through line II by means of pump 43 and recycled tothe top of the frac.- tionator as reflux liquid.

The gasoline fraction is withdrawn from the fractionator through line l controlled by valve 41 and passed into stripper I9 which may be provided with suitable fractionating plates in order to separate the gasoline boiling constituents from those constituents lighter than gasoline and thereby stabilize the former. A portion of the liquid from the bottom of the stripper is continuously withdrawn through lin`el5h passed' .through heat exchanger o'r reboiler 53`=where it stabilized endpoint gasoline is continuouslywithdrawn from the stripper through line 51 cont trolled by valve 58, to storage. The ygases and vapors removedv from the distillate in the stripper 49, are taken from the top thereof through line 59 and returned to the upper portion of the y fractionator.

Intermediate condensate or condensate heavier than gasoline is withdrawn-from the fractionator through line G-I by means of pump B3. The stream of condensate may be split into two parts one part passing through line 6I controlled by valve t5 and then through heat exchangerv II wherein itis partially cooled by indirect contact with the cool gas charge. The partially cooled condensate leaves the heat exchanger I I, through line 69, is further cooled in the cooler 51 to a temperature of approximately 80100 1". and injected into the stream of reaction products at the point I9; the other portion of the condensate may be passed through line 59 controlled by valve 1I into exchanger or reboiler 53 where it imparts heat to the condensate from the stripper 49, leaves the reboiler 53 through line 12, passes portion of the condensate in line 55. If desired,

vpart or vall the condensate in line 12 may by-pass exchanger 13 by being passed through valve controlled line It will be understood that all the condensate maybe passed through one or the other of these two lines, or the condensate may be -split in any' proportion between the two.

Residual oil may be withdrawn from the fractionating tower at a point a short distance above the bottom thereof through line 15, by means of pump 11, and injected into the line 2l at the point 23. The remainder of the residual oil, with its content of tarry material and suspended carbon, may be withdrawn from the fractionator through line 'I9 and float controlled valve 8l, and passed to storage.

Uncondensed gases from the gas-liquid separator 39 are withdrawn therefrom through line 93 by means of compressor 85 wherein the gases are compressed to a pressure between 150-1000 pounds per square inch, and then pass into the lintermediate portion of fractionating tower 91.

' to insure that the liquid collected in the bottom .of the fractionator is free from methane and hydrogen. The Uncondensed gases leave the top of the fractionator and pass into an after-cooler 93 which is cooled by means of brine coil 95 ory other refrigerating means in order to condense C3 and C4 hydrocarbons together with a portion of C2 hydrocarbons. 'I'he temperature in the f after-cooler 93 isregulated in accordance with thev pressure maintained so that hydrogenyand methane are not condensed. 'I'he latter gases, together with a portion of the C: hydrocarbons, leave the after-cooler through line 91 controlled by valve 99 and are eliminated from the system. The Ca` and C4 hydrocarbons, together with a portion of the Cz hydrocarbons in liquefied condition, are withdrawn from the bottom of the fractionator through line IUI controlled by valve |03 and fed to the feed tank 5 where they are mixed with the fresh gas for recycle to the process.

It will be seen, therefore, that by fractionating the reaction products into a condensateheavier than gasoline and residual oil, the heavy condensate can be cooled down low enough to suddenly chill the reaction products to fractionating tem- .perature and the'residual oil can immediately thereafterwbe injected into the transfer line without substantially lowering the temperature of ISO f:

1. In a process for converting hydrocarbon gases to hydrocarbons boiling within the gasoline range, at high temperatures, the steps of suddenly chilling the reaction products from such conversion process to a temperature not substantially in excess of 600 F. but not below a temperature at which the products are fractionated to obtain residual oil, heavy condensate and gasoline, by contacting the hot reaction products with cool condensate, adding residual oil of the type above fractionated to the partially cooled reactiorr productsA immediately following said chilling step to prevent deposition of tar and carbon, said residual oil being at a temperature which will not .cause material change in temperature of thepartially cooled products, and fractionating the mixture. i

2. The steps in accordance with claim 1 in which the intermediate condensate and residual oil are produced in the process. l

3. The steps in accordance with claim 1 in which the reaction products are chilled to ap.-l proximately 600 F. and residual oil at a temperature of 525-575 F. is added to the partially cooled products.

4. The process of polymerizing olefinic gases which comprises passing said-gases through a reaction zone wherein they are subjected to temperatures between 800 and 1200 F. and pres-` sures between 200 and v5000 pounds per square inch for a period of time suilicient to convert a.

substantial portion thereof to gasoline boiling range constituents, contacting the reaction products immediately upon emergence from the reaction zone withcool condensate' subsequently separated from the reaction products in order to quench to a temperature not substantially in excess of 600 F. but not below a temperature at which separation of gasoline boiling constituents from heavier constituents can be effected. passing the quenched products through a conduit to a fractionating zone, separating the reaction products in said fractionating zone into residual oil, condensate heavier than gasoline and a gasov line boiling range fraction, and contacting said residual oil without cooling with the quenched reaction vproducts during passage through said conduit and before release of pressure.

5. In a process for converting hydrocarbon gas to hydrocarbons boiling within the gasoline range, at high temperatures, the steps of suddenly chilling the reaction products from such conversion process to a temperature not substantially in excess of 600 F. but not below a fractionating temperature by contacting the hot reaction products with cool condensate, passing themchilled products through a, conduit to a fractionating zone in order to separate the products into residual oil, condensate heavier than gasoline, gasoline distillate and gases lighter than gasoline, stabilizingv the gasoline distillate in a separate zone, passing the condensate heavier than gasoline in indirect contact with said withdrawn gasoline distillate in order to heat said distillate sufficiently to sta- 'bilize it and to partially cool said condensate,

using said cooled condensate as the condensate for chilling the reaction products, and contacting said ,residual oil, without substantially cooling, with the chilled reaction products in said conduit'.` immediately after cooling with said condensate.

HERMANN C. SCHU'IT.

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