US2394849A

US2394849A - Process for treating hydrocarbons

Info

Publication number: US2394849A
Authority: US
Publication date: 1946-02-12
Anticipated expiration: 1963-02-12

Description

T.. F. DQUMANI ry-:TAL PRccssV FOR TREATING HYDRocARBoNs Filed Aug. l1, 1942 ATT Patented ret. 12, 1946 2,394,849l

Thomas F. Doumani and Clyde H. 0. Berg, Long Beach, Calif., assignors to Union Oil Company o' wIt is the object of of California, Los Angeles, Calif., a corporation j of California application August ii, i942, sei-ini 10.454384 a claims; (ci. iss-c7) 'Ihis invention relates to a process for the thermal treatment of hydrocarbons. More specincally the invention relates to the thermal treatment of hydrocarbons in the presence of hot spent combustion gases. p

our invention to provide improvements in the process of thermaltreatment of hydrocarbons in the presence of hot spent combustion gases, whereby we are able to produce to protect the refractory linings ofthe hotv zones: the use of uid catalysts and their regeneration in the combustion zone.; lthe elimination of nii vtragenv in the combustion gas; the use of an excess of oxygen in the combustion mixture; the use of extremely high gas velocities to prevent excessive carbon deposition; and the pre-heating of the hydrocarbon feed to an incipient cracking tempeinture, with or without the presence of dil'uents or recycled materials.

Referring to the ligure, hydrocarbon fuel and air 'are admitted through lines l and 2 to burner I which leads into combustion zone 4. The proportions of hydrocarbon fuel and air may be adlusted by means of valves l and i so that when l the fuel is burned the resulting combustion gases contain a minimum amount of free oxygen. A diluent such as water, steam or spent combustionv gases may be introduced as through line 'i controlled by valve 8, in order to maintain the temperature in combustion zone 4 at the desired value. y

The combustion gases leaving zone 4 pass through line 8 into reactor zone I0. During their passage through line 9 they are mixed with hydrocarbon feed which is introduced 'through pump Il, valve I2. preheater Il, and line I4.

When a fluid catalyst is used, it is introduced i through pump i! either into burner 3 (as through valve I6 and line Il) or into line 9. In the latter instance, it may be introduced either before Junction with line I4 (through valve i8 and line I!) or after junction with line I4 (through valve 2l and line 2l) as desired. The gases leaving ref- 'ugu h ems of oducts, auch as monoi0 actor I0 are then passed through line 12 to sepenns'uydireniis (suchpras for example buarator Zlin which the solid catalyst is Separated tadiene) aromatica and many other valuable hyand drawn 0K thlOllEh line and valve 15 for redrocarbons from charging stock which is largely activation and reuse. -The sas passing through parafllnic or naphthenic-in character and .may ASepdddlwl 23 is the!! Passedihmuh line 2f t0 'be ngrmanv gaseous or liquid, 15 quenching zone 21. When no catalyst is used-in I The process of our invention comprises burn'- y the PIOCCBS #he 855GB 110m reactor l0 .are P65584 ing hydrocarbon fuel to obtain spent fuel gas havthrough line 28a directly to line 28 and qunchini j ing a' temperature above about 2000,F.; mining Zone 2'l.4 l this hot spent Vi'uel gas with the hydrocarbons to lA Spray 0f quenching medium is introduced v be treated and with ilui'd'catalysts, if desired; 201Mo zone 21 throughlinc Il Controlled by Valve passing this mixture-w a reaction zone; sudoe'n- ,29- This quench. may be water. gasoline, or any 1y lowering the temperature of the mixture to n other hydrocarbon fraction. The liquid product point where no further reaction or conversion of gathers in the bottom of zone' 21 and. 18 passed ythe hydrocarbons being treated takes place; and y 121110118111111@ 30 into settling zonevll.` If water panting the desired fraction from the product, 25 is used as a quenching means it will stratify with 'me invention resides in the use 'or reiativeiy .the water condensed from the combustion gases high temperatures, snort' contact times,1ow paro8 a lower liquid layer in zone 3| and may be ual; pressures of hydroarbon, andrapid quench.; 0E thlOugh une n and Valve .3. 'The nqing of hot products; the useof a "blanket" gas so, uid hydrocarbon product may then .be drawn olf through line 34 and valve I5. The pressure on settling zone 3i is equalized with that in zone' Il'by means of vapor line 36.

The gas fraction leaving the top of zone 21 passes through pump 31 (which may act as a compressor), valve Il and line I! to absorber 40. In the absorber, it contacts an absorption oil introduced through line 4l and valve 42 and gas and steam may be taken overhead through line DI and valve 52, thereafter to be separated into the desired fractions by conventional methods. The absorption oil is drawn olf the bottom of stripper 48 through line 53 and valve and y may be recycled to the absorber.

In order to protect the refractory with which combustion zone 4 is lined, by preventing outward diffusion of combustion gases, it has been found desirable to introduce a blanket gas through pump 55 and line 56 into the steel shell of combustion gether with about ten times this volume of. air,

and about 6 lbs. (120 S. C. F.) per hour of steam. The combustion of this gas maintained a-temperature estimated as about 3500 F. in zone I.

A hydrocarbon feed comprising a 170 F. to 380 F. boiling range gasolinefraction from Los Angeles'Basin crude, and having 'a gravity of about 52 A. P. I. and a sulfur content o'f about 0.05%

by weight, was preheated toabout 1100 F. and

introduced through line I4 at a rate of about 3.4 gallons'f (22 lbs.)` per hour. The hydrocarbon feed and combustion gasesl were mixed in line 9 and passed to reactor I where-they remained at a temperatureof -about 1500 F.4 and a pressure of about 12 lbs. per square inch gage for a period of about 0.2 second. 'Il'he exit gases were immediately quenched with a water spray in zone 2l to a temperature of about 115 F. The hydrocarbon liquid product withdrawn from settling zone-3l through line 3l was emulsifled and the yield of this product was estimatedL at about 7% of the weight of the hydrocarbon feed. About 93% of the'feed stock was converted to gases which were taken off at the top of quenching zone 21, mixed with the combustion gases. The C'. fraction` (containing only thosehydrocarbons having 4 carbon atoms) recovered from this mixture by .absorption and distillation consisted of approximately66%-butadiene, 32% butenes and 2% butanes, and totaled about 8% by weight of the feed. Ethylene and propylene were obtained also, in yields of about 14% and 8% of the feed, respectively.l Hydrocarbons having more than 4 carbon atoms were recovered from the'gas fraction in a yield of about 18% of the feed, making the total yield of product having over 4 carbon atoms about 25% of the feed. This product con. tained appreciable amounts of isoprene and other dioleiins, and consisted principally of olenic and aromatic type hydrocarbons.

In a second example employing the same apparatus, about 80 S. C. F. ofthe same fuel gas was burned per hour with the theoretical quantity of air, adding only about .8 1b. of steam per hour. The same hydrocarbon feed stock was preheated to a temperature of about 920 F.. and introduced into the hot combustion gas stream at a rate of about '7.'I'gallons per hour. 'Ihe reactor temperature was maintained at a temperature 4of v about 1250 Fiand a pressure of about 13 lbs. per

square inch gage, the contact time again being about 0.2 second. The exit gases were again quenched with water to a temperature of aboutv cubic inches. In the latter apparatus. the hydrocarbon feed entering through line Il is injected practically `into the burnerfilame or combusf feed stock. This product contained appreciable amounts of dioleiins. and large amounts of olen and aromatic-type hydrocarbons.

The operating conditions are critical in many respects as indicated by the following description of the apparatus and the limiting operating variables.

The combustion chamber may be operated at temperatures between about 2000 and 5000 F. using a liquid or gaseous fuel.

drocarbon fuel 'and air lines l and 2 may be required. For the lower temperatures, diluent gases such as steam or spent combustion gases are introducedin therequired quantity through line 1.

" The combustion-chamber is designed 4as a steel shell with a high temperature lining such as fire brick Vand carborimdum. This lining. may be protected yby the use of a blanket gas as described earlier.v In the apparatus employed in the above l examples, theV burner was a surface combustion type burner described in Bulletin PR-38 of the Surface Combustion Corporation of Toledo, Ohio. page NL-5. Itwas Tunnel Burner No. 1302. This burner was inserted for a distance of about 9 inches into the combustion chamber-,which had a lengthof about 9 inches (beyond the burner,- tip), and a volume of about 28 cubicinches. In the later` work, smaller combustion zones have been employed, one for example, having a length of only about 3 inchesand a volume of about 9 tion zone.

The design of the mixer or that portion of line 9 adjacent -to its intersection with line I4 is rather critical. In the apparatus used/in the examples cited, line 9 was a tube made of carborundum and was of approximately 1/2,y in. inside diameter. At the point of junction with line 9,y

line I4 whichwas a stainless steel line, had an internal diameter of approximately V8 in. Under the conditions existing in the first example above, the mass velocities of the gases in the constricted portions of lines I4 and 9, before intersection with line I4, respectively, were approximately 250,000

'The yield of butadiene in--this instance was about 1.5% of thek hydrocarbon feed (45% by weight of the C4 hydrocarbon product) with yields of ethylene, propylene and butylene'of about 2, 3, and 2% by weight of the feed; respectively. 'I'he total of hydrocarbons having more than 4 carbon atoms recovered from both gas and liquid products amounted to about 80% of the weight of the and '15,000 pounds of gas per square foot of cross section per hour, respectively. In an earlier oper ation in which lower mass velocities were used, (about 20,000 pounds per square foot per hour in each of the above lines) there was appreciable carbon deposition in the equipment and'even in the product.` It is desirable in larger plants to employ correspondingly larger equipment, but to maintain a gas mass velocity in the constricted portion of line 9 between 25,000 and 500,000 pounds per square foot per hour-with a corresponding mass velocity in the constricted portion of line I4 at least double that in line 9. Thesehigh mass velocities are effective in preventing excessive carbon deposition and-s, in providing good mixing. The constricted portion of line 9 between line I4V and reactor I0 need only be long enough to ensure thorough mixing (about 6 to 20 diameters) and may be considered as part of the reactor. Y

'The reactor l0 is built in approximately the same manner as combustion zone 4, its size being suilicient to allow contact times of 0.005 to 5 .0 seconds, preferably below 1.0 second when no catalyst is employed. The temperature and pressure to be used in thereactor will depend on the type of product desired. In general, tempera- In order to achieve the higher temperatures, preheaters on the hypheric'to approximately 100 lbs. The lower temperatures are used where high vg tures between 1000* F. and 2000 F. are suitable although temperatures of 1300' F. to 1600 F. are preferred, with pressures ranging from atmosper square inch.

yields of liquid product arev desired, this being essentially a thermal or catalytic reforming voper-- ation, vand the higher temperatures are more suitable for production of highly unsaturated materiais, low boiling materials, and aromatic type i0 hydrocarbons. The latter processes may be called deep cracking, dehydrogenation or aromatization processes. The contactl time is desirably shorter at the higher temperatures and at higher partial pressures of hydrocarbon in the reaction mixture. The pressures indicated above are total pressures, the partial pressure oi' the hydrocarbon gas (calculated as moles of hydrocarbon feed divided by the total moles of hydrocarbon feed plus the combustion gas and dlluent o gas, times the total pressure) being generally much lower, preferably below atmospheric.' The partial pressure of the hydrocarbon may be controlled independently of the reactor'temperature lated with the hydrocarbon feed. Part or an of the liquid hydrocarbon product may also be reactor together with the feed, or introduced into the combustion zone. It is similarly desirable,

particularly when a gaseosffuel is used, to introduce an excess of fuel over that required for combustion. j

It has been found desirable in some instances to use as muchas excess of-air or oxygen in the combustion mixture over that theoretically required for complete combustion. The excess air acts as a diluent to` control the temperature of the combustion zone, and the excess,

. oxygen reacts with a portion of the hydrocarbon by regulating (1) the -amount of diluent gas in- '25 troduced through line 1 (2) the amount of nitrogen introduced with the air or'oxygen entering through line 2, or (3) the degree of preheating of the hydrocarbon feed. l

feed and appears to initiate desirable reactions or accelerate reaction rats.

Normally the hydrocarbon feed is` preheated to va temperature between 500? F. and 1500 F.

Somewhat improved conversions areobtained in some'instances by preheating to a cracking tem- `Preheater Il may lbe replaced or augmented 3o by a feed preheater system located in or 'around the combustion or reaction zones to utilize the heat liberated 1n mese zones. In quenching zone 21 either water or a hydrocarbon oil may be used'. In the mode of operation 35 indicated in the example,.water was used inj`a sumcient amount to reduce the temperature of the eiiluent gas well below 200 F. in order to condense substantially all of the water.' It may/ be advantageous in some instances, however, to n Vquench the exit gases-from reactor il only to a temperature of about 800' F., or a temperature sufilciently low/to prevent further reactioru cooling the product mixture thereafter by heat interration of the gases, hydrocarbon liquids and aque, ous liquid phase as above.` A portion of the liquid hydrocarbon product maybe used as a quench.

This has benencial effects on the octane number ample, and hydrocarbons, in our process. The catalysts which may perature which may lvary from about 800 F. to about 1500 F., being higher forthe. lower boiling hydroc bons, in general.

'I'he hydrocarbon feed stock may be gaseous, as stated earlier, and may'contain considerable amounts of oleiinic and (aromatic type hydrocarbons. vHigher boiling aromatic hydrocarbons may be stripped of side chains, for exconverted to lower boiling aromatic are those which retain an active, generally noncrystalline form, at the temperaturesemployed.

Magnesia and vanadium trioxide, for example,

fare suitable for use throughout the above change to the temperature desired for the sepa- 40 l specmed reactor temperature 'mes' Cem silicates and metallic oxides are suitable in the lower part of this temperature range. These catalysts may be introdu'ced in suspension in the hyor gum stability of .the liquid product in many so The separation and purification ci' the desired products need not be carried out as indicated in the figure. As indicated above, where one of thedesired products is butadiene, this material may be recovered either from the liquid hydrocarbon -phase or from the gaseous hydrocarbon phase or both.. The process of recovery of-this or other a nitrogen would be included in the combustion g5 .gases and these gases would then consist almost desired products may be one of the simple distillation or extraction or absorption processes or w combinations of these processes which are known by those skilled in the art.

If desired, oxygen may be used rather than air in the burner. This has the advantage that no exclusively of carbon dioxide and water. These may be separated from the product hydrocarbons by a system of condensation and extraction,

rather-.than the absorption system indicated in 7o the figure.

The liquid hydrocarbon product may be treated to remove aromatic type hydrocarbons or other desired fractions as by Vfractionation, extraction drocarbon fuel when a liquid fuel is used. They may also be injected as dry powders into the hydrocarbon feed line Il or into, any of the lines i1, il or 2| as indicated in the figure. Lower reaction temperatures andlonger contact times I are generally used when catalysts are present. Introduction of the catalysts into the hot ccmbustion gases, as through line i1, has the advantage that regeneration of spent catalysts may be accomplished in this combustion zone in some The catalystl separator 22 may be an electric Cottrell type precipitator or may be one ofthe "Cyclone" or mechanical types. This separator may be placed after the quenching zone if a hih temperature auch as 300 to 600 F. is maintained in this zone and no condensation of liquidl is realized. f

Other minor modincations of the above dey ,scribed process, which are apparent to those skilled in the art may be made, without exceeding the scope of theinvention as claimed. For example, interchangers may be employed to achieve heat economies, a dash drum may be used in the feed line following the preheater, steam or azeotropic distillation and the residue recircuor gas may be added to the feed, the combustion liquid or beusedinthisprocess" ditional 'catalyst is introduced into the hydrocarhaving a' temperature of 2000" to 5000 F.`with a 10 hydrocarbon feed stock preheated to a temperature of 500 to 1500 F.; maintaining this mixture at a .temperature of 1000 to 1800 F. and a pressure of 0 to 100 lbs. per square inch gage for a period of 0.1 to 5.0 seconds; suddenly quenching l5 the reaction products to a temperature below 600, F.; separating the spent catalyst and desired conversion products; and recycling the spent catv alyst to the combustion zone.

2. A process according to claim 1 in which ad- 20 ditional catalyst is injected into a portion of the reaction zone. l 3. A process according'to claim l, in which adbon feed line. I

4. A process according to claim 1, in which the catalyst is introduced by suspension in a liquid fuel.

' produced.

5. A process according to claim 1. in which the reaction products are quenched to a temperature below 600 F. without condensation, before separation of the solid catalyst.

6. A process according to claim 1 in which the l catalyst is a metal oxide.

7. A process for hydrocarbon conversion, which comprises burning a mixture of spent finely divided solid catalyst and hydrocarbon fuel in a combustion zone to obtain a suspension of regenerated catalyst in spent combustion gas; mixing the' said suspension with a preheated hydrocarbon feed stock and thereby heating the feed stock to a reaction temperature between about 1000" F. and 1800 F. for a reaction period less than about five seconds; quenching the reaction products to a temperature suillciently low to prevent further reaction; separating spent catalyst and desired conversion products; and recycling spent catalyst to the combustion zone.

8. A process according to claim 'I in which a gasoline feed stock is employed and butadiene is 'THOMAS F. DOUMANI. V CLYDE H. O. BERG.