US2258633A - Gasoline manufacture - Google Patents

Description

Oct.' l4, 1941.'

E. W. THIELE GASOLINE MANUFACTURE Filed Feb. 5, 1938 Patented Oct. 14, 1941 GASOLINE MANUFACTURE Ernest W. Thiele, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application February 5, 1938, Serial lNo. 188,844

' (or. 19e-49) 2 Claims.

This invention relates to the manufacture of gasoline and more particularly to the manufacture of gasoline by a combination cracking process.

It is an object of this invention to provide a new and improved method of gasoline manubination cracking process involving both thermal.

and catalytic cracking. Another object of the present invention is to provide a combination cracking process in which cycle stock made from a viscosity breaker operation is utilized as a feed for a catalytic cracking operation. A still further `object of this invention is to provide a combination cracking process involving catalytic cracking, thermal cracking and thermal viscosity lbreaking and in which these operations are combined in such manner as to produce larger yields of improved gasoline and to minimize operating dificulties. Other and still further objects, uses, and advantages of my invention will become apparent as the description thereof proceeds.

The invention will be described in detail in connection with a specific embodiment thereof shown in the accompanying drawing which formsa por.. tion of this specification and is to be read in connection therewith. The drawing is in simplied flow diagram form.

Referring more specifically to the drawing, heated crude oil from a source not shown enters crude flash tower I through line 2. From crude flash tower I light naphtha together with any excess of normally gaseous hydrocarbons passes overhead through line 3 while a heavy naphtha which serves as a reformer stock is removed by means of trap-out plate 4 through line 5, and virgin gas oilis removed by means of trap-out plate `Ii through line 1. Materials heavier than gas oil are removed from the base of tower I as a residuum through valve 8.

.Returning to the light naphtha and gases which pass overhead through line 3, these pass through condenser 9 into reflux drum I0. Uncondensed gases from this reflux drum are taken overhead through valve .II and ultimately enter stabilizer I2. The condensatefrom reflux drum I is removed from the base thereof through pump I3 and a portion is returned to the top of tower I as reflux by means of valve .I4 and line I5. The remainder is taken through valve I6 and line I1 to storage or further treatment and constitutes the straight run gasoline portion of the product.

The heavy naphtha or reformer stock removed by means of trap-out plate 4 may suitably have an initial boiling point between about 150 F. and about'250" F. and a maximum boiling point between about 300 F. and about 450 F. This material passes through valve I8V and lines I9 and 20,

ultimately entering the coils of thermal cracking furnace 2l. As will be seen hereinafter, the feed to this thermal cracking furnace preferably in cludes cycle stocks from the catalytic cracking and thermal cracking operations as well as the virgin reformer stock to which reference has been made above. v

Gas oil which is removed from tower I by means of trap-out plate 6 may suitably have an initial boiling point of, from about 350 F to about 525 F. and a nal boiling point of from about 575 F. to about 800 F. It passes through valve Z2, line 23, and pump 24, and then through'the coils of catalytic cracking furnace 25. As will be seen hereinafter, thejeed to this catalytic cracking furnace preferably includes cycle stock from a thermal viscosity breaker operation imaddition to the virgin gas oil to which reference has just been made. l

Residuum from the base of crude flash tower I passes through valve 8, line 26, and pump 2l to the coils of thermal viscosity breaker yfurnace 23.

Returning to furnace 25 the heated material passes overhead through transfer line 29 into catalyst chamber 30. It will be understood that in actual practice a number of catalyst chambers will usually be employed either in series or in parallel and that means will be provided for the regeneration of the catalyst. Since, however, the present invention does not reside in s uch details, the catalyst portion of the operation has been shown in the simplest diagrammatic fashion. Various catalysts lcan be used in this catalyst chamber. It is preferred` however, to employ a catalyst of the argillaceous type. Clays, acid treated clay, fullers earth, diatomaceous earth,

. bauxite or the like can be used. Various metal oxides and combinations of metal oxides can be employed.l Synthetic clays, for' instance aluminum silicate, are particularly suitable.

It is appropriate at this point to mention the conditions which may suitably prevail in the three cracking zones to which reference has been made. The conditions prevailing in catalyst chamber 30 being cracked, the results which are desired and particularly upon Ithe catalyst employed. Moreover, the optimum temperature will depend to some extent on the pressure employed and both are inter-related with contact time. However, the

catalytic cracking operation can suitably be conducted at about atmospheric pressure or at other pressures ranging from somewhat less than atmospheric to about 100 pounds per square inch.` 5

Temperatures ranging from about 750 F. to about 1050 F. can be used. Preferably, however, temperatures ranging from about 800 F. to about 975 F. are employed. For instance, the conditions in the catalytic chamber can be atmospheric pressure and about 900 F.

In the case of thermal cracking furnace 2| the outlet temperature can suitably range from about 875 F. to about 1100 F. but preferably from about 900 F. to about 1020 F., for instance 940` 15 F., and the outlet pressure can suitably rangeY from about 100 poundsper square inch to about 1500 pounds per square inch, for instance 700 pounds per square inch.

The outlet or transfer line temperature in the 20 case of viscosity breaker furnace 28 should in general be substantially lower than the outlet or transfer line temperature in the case of thermal cracking furnace 2|. The outlet temperature in the case of furnace 28 can, for instance, range- 25 frcm about 825 F. to aboutv975 F., for instance 875 F.- The corresponding pressure can suitably range from about A100 pounds per square inch to about 1000 pounds per square inch, for instance v200 pounds per square inch. 30

Returning to catalyst chamber 38, the cracked material from this chamber passes through line 3| into evaporator 32 which is shown integral with bubble tower 33 and separated therefrom by trap-out plate 34. From the base of evapora- 35 tor 32 a tar or heavy fraction may be removed through valved line 35.

All material lighter'than tar passes overhead from evaporator 32 through trap-out plate 34 intobubble tower 33. From the base of bubble tower 33, i. e. from trap-out plate 34, a gas oil cycle lstock is removed by means of valved line 36 and passes through line 20 and pump 31, and thence through the coils of furnace 2|.

It will be noted that furnace 2| voperates both 45 on a cycle stock from the catalytic cracking operation and on a lighter reformer stock of a virgin nature. It will further become apparent as the ldescription proceeds that a gas oil cycle stock from the thermal cracking operation itself is` recycled to the coils of furnace 2|.' It is a general rule that, for a given degree of cracking, stocks which have already been cracked once require higher temperatures than do virgin stocks. Onthe other hand, it is also a rule that light charging stocks require higher temperatures than heavy charging stocks. For this reason it is particularly appropriate to cycle a light virgin reformer stock, such as that removed from trap-out plate 4 of tower I, together with heavier 60 cracked cycle stocks to a single cracking operation, such as that conducted in furnace 2|', since the optimum conditions are approximately the same for the various stocks.

From furnace 2| these cracked materials pass 6 through transfer line 38 and pressure reduction valve 39 into evaporator 40 which is shown integral with bubble tower 4| and separated therefrom by trap-out plate 42. Tar is removed from and line 20, from which it passes through hotl oil 5 pump 31 and is introduced into the coils of fur. nace 2| as previously indicated.

In place of having separate evaporators and bubble towers for the products from catalyst chamber 30 and furnace 2|, products from furnace 2| can be passed from line 38 through shutolf valves 45a and 45h and pressure reduction valve 45e into line 3| and thence into evaporator 32. In this case evaporator 40 and bubble tower 4| with accompanying equipment are not required. The mixed cycle stocks will leave by line 36 and enter furnace 2| together, just as whenseparate towers areprovided.

Returning now to viscosity breaker furnace 28, it will be seen that the cracked material from this operation passes through transfer line 46 into evaporator 41 which is integral'with bubble tower 48 and separated therefrom by trap-out plate 49. From the base of evaporator 41 tar is removed by means of valved line 50 while from trap-out plate W't the base of bubble tower 48 a gas oil cycle stock is removed by means of valve 5| and cycled via lines 52 and 23 and hot oil pump 24 lto the coils of catalytic cracking furnace 25.

From bubble towers 33, 4| and 48 materials lighter than gas oil, which consist generally of gasoline range hydrocarbons and lighter materials, pass overhead through lines 53, 54 and 55, respectively, and thence through condensers 56, 51 and 58, respectively, and lines 59, 60 and 6|. respectively, to reflux drums 62, 63 and 64, respectively. The gases from these various reflux drums are taken overhead through valves 65, 66 and 61 and line 68 to compressors 69 from which they pass to stabilizer l2. Any gases which are already at pressures as high as that of stabilizer I2 can, of course, be luy-passed around compressors 69.

Condensate from reflux drums 62, 63. and 64- is removed through pumps 10, 1| and 12 respectively, and a portion is returned to the appropriate bubble tower by means of valves 13, 14 and .15, respectively, and lines 16, 11 and 18, respectively. The remainder of this condensate passes through valves 19, and 8|, respectively, and thence through line 82 into stabilizer l2.

Stabilizer l2 is operated at an elevated pressure in the conventional manner. It is equipped with a reboiler which includes the conventional trap-out plate 83 and heater 84. The stabilizer is also provided with reflux and the pressure, reboiling and reflux are controlled to take stabilized gasoline olf the base of the tower through valved line 65 for storage, further treatment or use.

Gases eliminated in producing stabilized gasoline pass overhead from stabilizer I2 through line 86 and condenser 81 and thence to reuxV drum 88. Condenser 81 is operated to condense such portion of the four carbon atom hydrocarbons as cannot be utilized in the finished gasoline together with a considerable amount of three carbon atom hydrocarbons. This condensate is removed from 5 the base of reflux drum 88 by means of pump 88 and a portion of it is returned to stabilizer I2 as reflux through valve 80 and line 8|. The remainder is removed from the system through valved line 92 for storage and use. Light gases gre removed from the system through valved line It will thus be seen that my new combination cracking operation involves the separation of a crude oil or reduced crude oil into fractions comprising a heavy naphtha which is cracked thergas oil charging stock which is once-through basis and from the thermal cracking breaker y manner as to give only a very light cracking, the

gas oil produced is not far removed in characteristics from virgin gas oil and thus constitutes a particularly suitable charging stock for the catalytic cracking operation.

The iiow diagram of my combination cracking process as well as the description of it is highly simplied and various detailsL such for instance as heat exchangers; pressure, temperature-and 4iiow control devices; safety devices; stripping towers for trap-out streams; 4additional valves and pumps;I insulation; to detail these features would add nothing to the knowledge oi those skilled in the art and wouldmerely serve to encumber this specification unnecessarily.

While my invention has been described in connection with aspeciiic embodiment thereof, it is to be understood that this can be modified etc., are omitted since in various ways and that I do not mean to be lim- 3 ited thereby but only to the scope of the appended claims which should beconstrued as broadly as the prior art will permit.

I claim:

l. A combination cracking process comprising separating a crude petroleum oil into fractions including a heavynaphtha fraction, a virgin gas oil fraction and a residuum fraction, subjecting said gas oil fraction to a catalytic cracking operation, separating the products of said cati alytic cracking operation into fractions including a gasoline fraction and a gas oil cycle stock fraction, subjecting said gas oil cycle stock fraction together with said heavy naphtha fraction to a non-catalytic thermal cracking operation, separating the products of said thermal cracking operation into fractions which include a gasoline fraction and another gas oil cycle stock fraction, 'recycling said last mentioned gas oil cycle stock fraction to said thermal cracking operation, subjecting said residuum to a non-catalytic viscosity breaker operation, separating the products of said viscosity breaker operation into fractions includingl a' cleancycle stock fraction, and recycling said clean cycle stock fraction to said ceatalytic cracking operation.

2. The method of increasing the efficiency of a combination thermal and catalytic cracking system for the manufacture of high quality gasoline which method comprises fractionating a hydrocarbon charging stock in the absence of crackedproducts to obtain a gas-oil fraction and a heavier-than-gas-oil fraction, passing the heavier-than-gas-oil fraction to a viscosity breaking system and heating it therein to a temperature of about 825 tov 975 F. at a pressure of about 100 to 1000 pounds per square inch, passing gas-oil from the products of the viscosity' breaking step in admixture with gas-oil from said first fractionating step through a catalytic cracking chamber at a temperature of about 800 F. to 975 F. and a pressure oi about atmospheric to pounds per square inch in the presence of a cracking catalyst, passing gas-oil from the products of catalytic crackingtogether with heavy' naphtha from said irst-named fractionating means to a thermal cracking zone, maintaining a pressure of about 100 to 1500 pounds per square inch and a temperature of about 875 F. to 1100 F., fractionating the products from the thermal cracking zone in the absence of products from the catalytic cracking and viscosity breaking steps, returning gas-oil from the thermal cracking fractionating step Ato said thermal cracking zone and blending the gasoline obtained from said-first fractionating step, said catalytic cracking step, said viscosity breaking step and said thermal cracking fractionating step, respectively.

ERNEST W. THIELE.

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