US2552573A - Hydrocarbon conversion - Google Patents

Description

May 15, 1951 G. A. MILLS HYDRocARBoN CONVERSION Filed Sept. 26, 1946 Patented May 15, 1951 7 HYDROCARBON CONVERSION George Alexander Mills, Ridley Park, Pa., as`

signor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware Application September 26, 1916, Serial No, 699,383

VThis invention relates to the catalytic conversion of hydrocarbons under cracking conditions using a solid cracking catalyst, and is particularly concerned with the maintenance of the cracking catalyst at an emcient level of catalytic activity.

In the catalytic conversion of hydrocarbons under cracking conditions, hereafter referred to as catalytic cracking, the original hydrocarbons are converted to hydrocarbons of different molecular weight or structure or both by contact with a cracking catalyst, which directs and accelerates the cracking reaction and concomitantly accumulates a deposit of hydrocarbonaceous material commonly referred to as coke. Since the accumulation of such a deposit on the catalyst diminishes its efficiency and since this effect increases as the amount of the deposit increases, it is the common practice in moving catalyst systems to continue the cracking or on-stream period until the catalyst accumulates a deposit of coke which contains carbon to the total amount of about l to 20 grams per liter of catalyst. (Since the carbon content is conveniently determined, the amount of the coke deposit is generally, as it is herein, referred to its carbon content; as herein used, the amount of the coke deposit is `expressed as grams of carbon per liter of contact mass which has been abbreviated to grams per liter.)

When the catalyst is employed as a static bed cooled by indirect heat exchange, the total amount of the coke accumulated is generally somewhat less, usually being of the order of to grams per liter. Thereafter, the catalyst is treated to remove the majority of the deposit on the catalyst by combustion during a regeneration period by contacting the coked catalyst with an oxidizing gas. Due to the difficulty of removing the last portion of the deposit, the catalyst is generally not completely regenerated. After the termination of the regeneration period, the catalyst, in commercial practice, generally has a deposit of less than 1 to 3 grams Aper liter for moving catalyst systems and about the same amount for the above type of static bed operation. Under these conditions, the catalyst is sufficiently restored to an efficient level of activity as to be ready for reuse in the cracking operation.

The cracking catalysts commercially available for use in the cycle of `operations described above have certain properties such that there is only a gradual loss in catalytic activity under the moderate conditions commonly employed in 7 Claims. ,(CL196-52) the various phasesof the cracking process. If.

however, these catalysts are subjected to an atmosphere containing steam, a considerable loss in catalytic activity occurs, the extent of the loss in activity depending, for a given tempera` t'ure and length1 of exposure, on the partial pressure of the steam. Since steam is frequently used to aid in the volatilization of high boiling hydrocarbon fractions and hence is present during the cracking period, and is commonly used to strip or purge volatile hydrocarbons from" the catalyst prior 4to regeneration, most catalysts are slowly deteriorated or aged in use during the cracking and purging periods and must be replaced with fresh catalyst when the activity has dropped to an'ineflicient level.

Aging 'of'cracking catalysts is also causedby the steam formed in the combustion of the hy-` drocarbonaceous deposit or coke which consists essentially of carbon and hydrogen (a typical deposit `contains about 5 to 8 weight per cent of hydrogen with the remainder essentially car,' bon) associated in the form of compounds which are of undetermined composition and which are non-volatile withl steam stripping at tempera` tures of the order of 600 to 1000c F.` Combustion of such a deposit produces ilue gases which contain; particularly in the early stages of the combustion of the Vdeposit when `preferential combustion of thehydrogen of the deposit occurs, an amount of steam sufficient, at the ele-' vated temperatures of combustion, to lower the activity -of the catalyst to economically undesirable levels, this effect being particularly` cracking or purging periods, this effect being particularly noticeable when clay cracking cata` lysts are used. For this reason, it has been the previous'practice to limit the temperatures at which regeneration is conducted to 1100 F. or

be protected against the deleterious effect, ofdefI activating partial pressures of steam at elevated temperatures, such as temperatures above 800 F., by maintaining a substantial amount of cokel Y Present.

rthereon is regenerated at temperatures above 1200 F., such as temperatures in the range of 1200 to 1350 F., without substantial loss in activity by contacting such a catalyst with an oxidizing gas under combustion conditions, said catalyst having been subjected to prior process conditions such that sucient coke, such as amounts in excess of 15 grams per liter, hasV been deposited on the catalyst as to maintain a protective amount of said coke on said catalyst during those portions of the regeneration period when deactivating partial pressures of steam are Since the deactivating effect of the steam depends, among other variables, on the temperature of the operation and partial pressures of 0.1 pound per square inch or lower can deactivate at temperaturesof 1200 F. and higher, it is preferred to protect the catalyst by a minimum amount of coke which varies according to the temperature of the operation as hereinafter described. Research has indicated that, by operating the cracking operation under conditions such that the total amount of coke present on the catalyst at the start of regeneration is higher than that formerly used, the regeneration may be effected at higher temperatures than previ ously thought desirable. The increase in the temperature of regeneration has many important advantages, among which is a greatly increased rate of combustion as well as a lower evolution of heat and decreased amounts of oxidizing gas needed for the same amount of carbon removed, the latter effect being due to an increase in the ratio of carbon monoxide to carbon dioxide in the flue gas. These advantages may be realized in a preferred embodiment of the present invention, in which the amount of coke on the catalyst at the start of a combustion effected at substantially atmospheric pressure and at temperatures of 12009 F. or higher is 30 grams per liter or higher and the catalyst accordingly protected in the presence of the partial pressures of steam in the initial stages of combustion (about 1.5 to 3.0 or even as much as 4.5 pounds per square inch). As the regeneration proceeds. the amount of cokedeposit, and hence its protective eiect, isv reduced but the concentration of steam in the flue gases decreases relatively more rapidly. Thus, although the concentration of steam in the flue gases (due to combustion of the coke deposit) may be as high as 15 or 20 or occasionally as much as about 30 volume per cent during the first third of a regeneration effected in connection with a stable cyclic operation, it is generally lower than 5 to 8 volume per cent during Ysecond third of the regeneration. However. it has been found that the deactivating effect of gases having concentrations of steam of even 5 volume per cent (about 0.8 pound per square inch partial pressure of steam) is appreciable at 1200 F. if the period of exposure is sufficiently extended and it is therefore preferred to malnduring regenerations at 1200 F. and higher until the partial pressure ofl steam in the ue gas is:

less than about 0.8 pound per square inch.V Since investigation has shownV that 15 to 20 grams per liter of the hydrocarbonaceous deposit protects commercial cracking catalysts against the deactivating effect of steam at 1200 F. at least as much as does 6 to 8 grams per liter at 1050 F., the advantages of a regeneration effected at the higher temperature may be maintained even in the later stages of a regeneration of a catalyst initially having a deposit amounting to at least 3Q grams per liter without sacrificing the activity of the catalyst.

In another embodiment of the invention, the deactivating effect of steam used in the cracking period is minimized by maintaining a protective deposit on the catalyst during this period. This may be accomplished by incompletely regenerating the catalyst and leaving a residual deposit sufficient to protect the catalyst in the subsequent operations, a particularly eifective amount being in excess of about 10 grams per liter. It has been found that, when steam is preesnt in deactivating amounts, the advantages gained by the protective effect of deposits of coke in excess of l0 to l5 grains per liter more than offsets any loss in the cracking activity of catalysts having such deposits. Furthermore, as the amount of coke on a cracking catalyst is increased above about 20 to 25 grams per liter, additional reduction in cracking activity is at .a reduced rate whereas the protective effect of such deposits in regard to the deactivating effect of steam continues to increase. Moreover, the loss in cracking activity due to the deposit of coke on the'icatalyst may be counteracted by increasing the severity of the cracking conditions (increasing the temperature or pres.- sure or decreasing the spacey velocity and the like) or by the use of avery active catalyst such as aV catalyst which,l Without the deposit of coke, would overcrack the charge stock, and produce excessive quantities of gas and coke;

For example, in crackingk operationsr involving the contact of a catalyst with hydrocarbons admixed with deactivating. amounts of steam, such as amounts between 5 to .20 parts by weight of steam to 100v parts of hydrocarbons, at temperatures of 950 to 110,0.o the pressure of the operation being approximately atmospheric (these conditions correspond to about 6.0 to 10.0 pounds per square inch partial pressure of steam for most hydrocarbon charge stocks), it is preferred to, subject the catalyst to prior operating conditions, such as prior contact with hydrocarbons or prior partial regeneration, so that atleast l5 grams per liter of coke is initially on the catalyst when it is contacted with such deactivating amounts of steam.v Larger initial amounts of coke are preferred `for the higher Vconcentrations of steam or higher temperatures of cracking or both. Where lower temperatures, such as 800 to 950 F. are` employed in the cracking operation,

a minimum deposit ofthe order of grams per conium, magnesium, uranium, beryllium and the like. Other synthetic colloidal masses such as phosphates of zirconium, cerium, 'thorium and theli'kel may beused. In any event, the utility of a cracking catalyst may-.bey evaluated by a stand-Y ardized activity test. and it is preferred, in the.

present invention, to use catalysts of moderate or high activity, such as catalysts having activities of greater than 25 and preferably above 30.

The activity test mentioned above is a standardized test for the characterization and control of cracking catalysts and is used by a number of industrial laboratories. It is known as the CAT-A test and is described in Laboratory Method for Determining the Activity of Cracking Catalysts by J. Alexander and H. G. Shimp, page R-537, National Petroleum News, August 2, 1944. In accordance with the method, a standardized light gas oil is subjected to contactwith a static bed of the catalyst to be tested understandard cracking conditions of atmospheric pressure, 800 F. and a rate of oil flow of 1.5 volumes oi liquid oil per volume of catalyst per hour. The cracked products are collected and analyzed to obtain the activity index, or CAT-A activity, which is the volume of motor gasoline produced divided by the volume of charge stock times 100. The Weight per cent of the uncondensed gas and coke (carbonaceous deposit) as well as the specie gravity of the gas are also determined.

The above described test is used to evaluate the effect of severe process or accelerated conditions; thus, the activity of a sample of a catalyst which has been calcined using no steam, at 1050 F. in flowing dry air for two hours A(hereafter designated as a dry calcination), may be compared with the activity of a sample of the same catalyst which has been calcined in the presence of a high partial pressure of steam at elevated temperatures as, for example, at 1350 F. for four hours using about `15 pounds per square inch absolute pressure of steam (hereafter designated as a steam calcination) Evaluations of the effect of process conditions based on the above and similar calcinations have been compared with data on commercial catalysts which have been in commercial use for many months or even years and the comparison shows that these calcinations can be used to measure the relative effect on cracking catalysts of prolonged exposure at temperatures of 700 to 1500 F. to the quantities of steam encountered in commercial cracking operations.

Multicomponent refractory oxide cracking catalysts, such as silica-alumina catalysts, which show less than a 50% reduction in CAT-A activity between samples subjected to the above described dry and steam caloinations based on the rst named sample (i. e., 100 times the activity of the dry calcined sample minus the activity of the steam calcined sample divided by the activity of the dry calcined sample) are considered to be steam resistant and have a satisfactory commercial life when regenerated according to the present invention. As an example of the effect of the coke deposit, a catalyst which showed a reduction of about 25% in activity between dry and steam calcined samples showed a reduction ci only about 13% when the catalyst used for the steam calcination had a deposit of coke, atY the start of the calcination amounting to 16 grams per liter. Similar results have been obtained for different amounts oi coke deposit and for dilerent process conditions.

Many of the advantages of the present invention may be realized in an embodiment thereof in which the catalyst is protected during a portion of the cracking period when deactivating amounts of steam are present by contacting the catalyst prior to such a portion of the cracking period with hydrocarbons under cracking conditions selected to provide a protective amount of cckedeposit. Thus, in the rst portion of the cracking period, the cracking catalyst, which is preferably of moderate or high activity, is contacted in a first cracking zone with a relatively low boiling charge stock, which preferably completely volatilizes substantially at the temperature of cracking without the aid of steam, and a protective amount of coke, such as an amount greater than 15 grams per liter, thereby deposited on the catalyst. The catalyst is thereafter immediately contacted in a second cracking Zone with a relatively high boiling charge stock in the presence of deactivating partial pressures of steam, the steam being used to aid in the volatilization of the charge stock. If the relatively high boiling stock. is sufficiently easily cracked, the cracking conditions in the rst and second cracking zones, which zones may be in the same or different reactors, may be essentially the same. ,Howeven if advantageous, conditions in the second Zone may be made more severe by increasing the temperature as by mixing catalyst from the rst zone with hot partially regenerated catalyst having a protective coke deposit thereon. Other methods, such as increasing the pressure or decreasing the space velocity or increasing the catalyst to oil ratio, may also be employed for increasing the severity of cracking. After passage through the second zone, the catalyst may be regenerated wholly or partially, such as being regenerated until 4 to 6 grams per liter oi deposit; remain, and thereafter reused in the same process. By this process, the useful life of the catalyst is prolonged by the protective effect of the coke deposit during both the cracking and regeneration periods, while a high yield of cracked products are obtained from various fractions of a crude cil, such fractions having different boiling ranges, by cranking each of these fractions under cracking conditions selected to give the optimum yields for such fraction. By this process, the benecial effect of steam in the volatilization of charge stocks may be utilized while minimizing or avoiding the deleterious effect of steam on the catalyst.

In order to understand the invention more fully, reference should be had to the drawing which illustrates an embodiment of the present invention, which invention is not, however, limited in scope thereto. Fig. 1 is a schematic flow diagram in which details of conventional auxiliary equipment have been omitted for clarity and which will be described in connection with operations in which a fluent refractory contact mass is cyclically circulated in a system known as the T. C. C. system. Details of this system, as applied to cracking operations, have been described in various published articles (see, for example, The T. C. C. Catalytic Cracking Process for Motor Gasoline Production by R. H. Newton, G. SQ Dunham, and T. P. Simpson, Transactions of the American Institute of Chemical Engineers, volume 4l, page 215, April 25, 1.945, and the articles there cited) and hence will not be repeated here. Although the drawings exemplify one type of moving contact mass operation, the present invention can be embodied in other types of operations which use fluent solid Contact masses or may be embodied in that type of operation known as xed bed operation.

In Fig. 1 a cracking catalyst, such as a lowalkali content silica-alumina gel having a mol ratio of silica to alumina of between about 5 to 1 and 15 to 1, is fed from hopper 5 by catalyst leg 6 to reactor 'l Where the catalyst is contacted with' a light. charge stock, such as a virgin or cracked naphtha or gas oil having a dew point at atmospheric pressure below the temperature of cracking in reactor 1, the light charge stock being introduced to the reactor by line 8r after having been previously vaporized. The catalyst, as introduced to reactor l, is preferably a high activity catalyst, such as a catalyst having a CAT-A activity of greater than 30 and preferably greater than 35, and preferably has a low coke deposit, such as less than 4 to 6 grams per liter, such as 2 to 4 grams per liter. The charge stock is cracked by subjecting it to cracking conditions such that at least 35 and preferably 40 or more volume per cent of gasoline based on the charge stock is produced. Such cracking conditions are generally included in the ranges of 800 to 950 F.; atmospheric and higher pressures up to 100 pounds per square inch; ratios of the liquid volume of charge stock charged per hour to bulk volume of catalyst circulated per hour of 0.1 to and space velocities (ratio of the liquid volume of the charge stock charged to the reactor per hour to bulk voliune of catalyst in cracking zone) of 0.1 to 5.0. Alternatively, the charge stock f may bea virgin or cracked gasoline, which is reformed to yield a high octane gasoline, such as a gasoline of over 70 octane number. In any event, the catalyst accumulates a protective coke deposit by remaining in the reactor for a length of time (which is called the residence time) such that, under the cracking conditions employed in reactor l, the catalyst accumulates a deposit greater than about grams per liter but generally less than grams per liter. The catalyst is then .conveyed by line il to reactor 9 where it is contacted with a relatively high boiling charge stock, such as a hydrocarbon fraction having a dew point of over 800 F. as, for example, a crude residuum from which the tar has been removed. The relatively high boiling charge stock, which is introduced to reactor 9 by line l2 after having been heated to a suitable temperature, is admixed with high temperature steam from line I3 in order that the steam may aid in the Volatilization of the charge stock. The charge stock which is preferably substantially completely in the vaporrphase as it enters reactor 9, passes upward through reactor 9 and is at least partially cracked by contact with the downwardly moving catalyst. The cracked charge stock or synthetic crude is removed from reactor 9 by line I4 and conveyed to a fractionation system for the separation of various products such as gasoline, solv .vent naphtha, fuel oil, recycle gas oil and the like. In a similar fashion, synthetic crude from reactor l' is conveyed to the same or a similar fractionation system by line i5 for similar treatment.

The temperature of the catalyst in reactor 9 may be'increased above thetemperature of the catalyst in line il by mixing the catalyst fromr reactor l with catalyst from line I6, which catalyst has been partially regenerated in regenerator Il and thereby increased in temperature. The amount of catalyst from line l5 used in reactor 9 will depend on the relationship of the temperatures in reactor l, regenerator Il and reactor 9 but it is generally preferred to use an amount of catalyst such that the temperature of reactor 9 is raised so as to produce at least 30 and preferably over Yvolume per cent of gaso- Y line from the charge stock. The temperature rise of the catalyst from reactor l Will generally be of the order of V50" to 150e F. In this manner, heat produced as av result of the regeneration ofthe coked catalyst is utilized in connection with the cracking operation and serves to balance the endothernricr effect of the latter. The catalyst in line I6 has been preferably regenerated so that the coke deposit thereon is about equal tothat on the catalyst in line Il (i. e., about 15 to 25 grams per liter) and isl thereby likewise protected against the steam encountered in reactor 9 in which reactor the steam concentration may range from 5 to 20 parts by weight of steam to 100 parts of oil at 1 to 2 atmospheresY or slightly higher total pressure (i. e., arange of 6 to 20 pounds per square inch partial pressure of steam). By maintaining at least 10 grams per liter of coke on the catalyst and preferably 15 grams per liter or more if the partial pressure of the steam is above 10l pounds per square inch, the deactivating effect of the steam present in the reactor is diminished. Thus,. for example, a catalyst subjected to 15 pounds per square inch partial pressure of steam at 900 F. has 2 or more times the life (for the same reduction in CAT-A activity) when it is protected with 15 grams per liter of coke than it doesV when the amount of coke is maintained at the usual level of 4 to 6- grams per liter..

The catalyst, which after passage through reactor 9, has a coke deposit totaling preferably at least 25 and generally about 30 to 40 grams' per liter or higher, is removed from reactor 9 by line I8, and conveyed to elevator I9 which carries` the catalyst to line 2 lv and thence to hopper 22. The catalyst is fed from hopper 22 by line 23 to regenerator l1 which may be a T. C. C. kiln comprisinga plurality of burning and cooling sections or zones (twor of which are shown in regenerator Il). A controlled amount of air from` manifold 24 burns some of the coke deposit in each section of the kiln, the spent flue gases being removed by manifold 25. Excess heat generated by combustion of the coke deposit is removed by indirect heat exchange, using cooling coils 26. The conditions of combustion in regenerator Il and the temperature of the air used therein are selected so that the heat of combustion soon raises the temperature of the catalyst to greater than 1100 F., such as a; temperature in the range of 1200 Vto 1350 F. The safetemperature of combustion is dependent onthe amount of the coke deposit on the catalyst as introduced to the regenerator, and the lower temperatures, such as about 1200 F., are preferred'when the amount of the coke deposit is about 30 grams per liter whereas higher temperatures, such as l300 or higher, may be employed when the coke deposit is in excess of 40 grams per liter.

The catalystaf,ter partial regeneration, may be conveyedy from regenerator 'l by line 2l to regenerator 28, `which'is similar in design to regenerator il, and additional regeneration effected. Alternatively, a single regenerator with'appropriate arrangements for the draw off of cata..

lyst may be used. AsV noted above, the hydrogenV below the temperature of thermal deactivationY for the particular type of catalyst employed.

The temperature of thermal deactivation of a catalyst is the temperature above which rapid deactivation occurs in a non-deleterious atmosanatra 9V phere, such temperatures being, for example, about 1500 F. for clay catalysts and about 1700 F. for synthetic silica-alumina catalysts. In general, the same temperature of regeneration in both regenerators is correlated with the amount protects the catalyst in the subsequent regeneration. The catalyst from the mixed phase operation may be partially regenerated so as to leave a coke deposit of at least 15 grains per liter and thereafter reused in the mixed phase cracking of protective coke deposit and the partial presoperation. sure of steam. It has been found by investsa- After extended periods of use, most catalysts tion that steam resistant catalysts (as defined are unavoidamy aged, 1n this event, the amount above) will have a satisfactory commercial life of the coke deposit maintained during the crackwhen the minimum amounts of coke given in the ing period may be decreased with a consequent table are observed at the stated partial pressures increase in the catalytic activity. Thus, in a comof steam. i mercial process operated continuously, by start- Table Temp Amount of Partial Amount of Partial Amount of Partial Coke Pressure Coke Pressure Coke Pressure grams per Ibla/sq. grams per Iba/sq. grams per Iba/sq.

liter inch liter inch liter inch 1,15o F 1o s. 9 is 4.4 1,2oo F 15 1.5 1s 3.9 23 4.4 1,a0o F 23 1.5 26 3.9 so 4.4 1,35o F en 1.5

It is, however, preferred, according to the invening with an over active catalyst on which suffition, to have the minimum coke about high- 25 cient coke is maintained during both the cracking er than the values given in the table to provide a and regeneration phases so as to decrease the factor of safety and to allow for the reduction of aging effect of steam present during these and the coke deposit during the regeneration. other process periods, the useful life of the cata- 'Ihe catalyst, after being regenerated so as to lyst can be extended, particularly when the leave a predetermined residue of coke deposit .m amount of coke maintained on the catalyst durthereon, is removed from regenerator 28 by line ing the cracking period is reduced as the aging 29, conveyed by elevator 3| to line 32 and thence of the catalyst proceeds. charged to hopper 5 from which it may be re- It is to be understood that where the term, moved for reuse. partial pressure of steam, is used that such an In another embodiment of the invention, a very expression includes those instances Where steam high boiling charge stock, such as a residuum is essentially the only vaporous material presenty having an end boiling point of greater than 1100 and the partial pressure of steam is hence equal F. and a mid boiling point between 800 to 1100" to the total or absolute pressure of the system. F. at atmospheric pressure is charged in a mixed f Obviously many modifications and variations of phase condition to a cracking catalyst having a the invention as hereinbefore set forth may be protective coke deposit, the catalyst being at a made Without departing from the spirit and. scope temperature generally higher than vapor phase thereof and therefore only such limitations operations, such as temperatures in a range of should be imposed as are indicated in the ap- 900 to 1l00 F. Typical charge stocks employed v pended claims. in such mixed phase operations are commonly ad- I claim as my invention: mixed with about 5 to l0 parts by weight of steam 1. In a catalytic cracking system in which to 100 parts of charge stock prior to the heating fluent solid cracking catalysts contacts substanof the charge stock to the temperature of introtially only hydrocarbons in a first stage cracking duction to the cracking zone, generally about operation and contacts hydrocarbons and sub- 700 to 950 F., in order to prevent coking 0f 50 stantial amounts of steam in a second stage the charge stock in the tube stills used for heatcracking operation, the improvement which. coming The deaCtVatng effect 0f the Steam adprises maintaining cracking conditions in said mlXd With the Charge Stock (Which, for the Op' rst stage cracking operation so as to deposit an eratlon described above, amounts to partial presamount of Coke on, substantially Completely re-, Sures of from about 7'0 to 10'0 pounds Per square 65 generated calatyst sufficient to furnish substanmh) at tpe tempratures of the crackmg Oper tial protection to said catalyst against the deactialol (90o go t100 F), I nay be decreased by em' vating effect of steam in said second stageIl consoymg ta fe teb.' actlvTckffg Caalst Sfucl tacting a'm'ixture of catalyst from said first stage l a ca a ys avmg a ac 1V? y o a and partially regenerated catalyst comprising an east 30 and preferably at above 35, which cata- 60 am t f k t 1e t e ual to the coke on Said lyst has a coke deposit amounting to at least 15 Gun o C0 e a s t q .th h d b grams per liter and preferably in the range of catalyst from the rs 5.3%? W1 y Tocar ons m 20 to 30 grams per liter at the start of the crackthe prseme of a' deactwatmg partlal pressutqe. of. ing operation. When a catalyst is used which is steam m Sald Second stage and therby dgosltm. originally so active that, under the cracking cona'ddltlonal a'munts of coke (.m sala nlnxture o ditions employed in the process, overcracking capalyst partlauy regeneratmg Cata ys from would result (i. e., overcracking is the formation Sad Second Stage cmlmg operano S0 as to pro of gas and coke at the expense of gasoline formaduce catalyst comprlsmg an amount of c oke at tion), the coke deposit decreases the activity of least equal to the? amount O f cle produed m sald the activity of the catalyst and thus decreases f'st Stag? Crackng Operatlon mtroducmg a pot overcracking while protecting the catalyst against t1on of said partially regenerated catalyst to sa1d the deactivating effect of steam. The catalyst, Second Stage laking Operation, further Tege11- after use in the mixed phase cracking operation v @rating aIlOtheI DOItOIl 0f Said partially regengenerally has a coke deposit-amounting to 30 to @rated Catalyst S0 aS t0 pIOduCe Substantially 50 grams per liter, which, as discussed above, 75 completely regenerated catalyst and introducing weer substantially completely regeneratedl catalyst .to

said Vrst stagecrackingoperation.

A:Zwin a catalytic .cracking system in rwhich fluent solid crackingfcatalyst contacts substantially only hydrocarbons in a iirststage cracking operation and contacts hydrocarbons and substantial amounts of. steamin aseccnd stage ,cracking operation, the improvement which comprises maintaining cracking conditions in ,said rst stage cracking operation so as to deposit an amount of ook-e on substantially .completely regenerated' catalyst suiiicientA to .furnish substantial protection to said catalyst against the deactivating eiect of steam in said second stage, contacting a mixture of catalyst from said rst stage and partially regenerated catalyst comprising an amount of coke atleast equal to the coke on said catalyst from the first stage with hydrocarbons in the presence of a deactivating partial pressure of steam in said second stage under such conditions as to deposit an amount of coke on said catalyst suflicient to furnish substantial pro- Y, tection to said catalyst during that portion-of 'l the-subsequent regeneration-when said catalyst is contacted with' deactivating partialA pressuresofV steam, partially regenerating catalyst fromV said second -stagecracking operation at temperatures of at least l200 F. under-conditions such` that the coke deposit that remains on said catalyst is at least as much as the coke deposit on the catalyst from said rststage operation', in-Y troducing a portion of the partially regenerated catalyst to said second stage cracking operation,

further regenerating a portion of the-partially re-v and substantial amounts of steam in a second stage cracking operation,.the improvement which comprises maintaining cracking conditions in-said rst stage cracking operation so as to deposit coke to the extent of at least 15 grams of carbon per liter of catalyst on substantially completely re,- generated catalyst having a deposit of less than 6 grams of carbon per liter of catalyst, contacting a mixture of catalyst from said rst stage and partially regenerated catalyst comprising Van amount of coke at least equal to the coke on said catalyst from the iirst stage with hydrocarbons in the presence of a deactivating partial pressure of steam in said second stage under such cracking conditions as to deposit an amount of coke on said catalyst suiiicient to provide at least 15 grams of carbon per liter of catalyst on said catalyst during that portion of the subsequent regeneration when said catalyst is contacted with a partial pressure of steam of more than 0.8 pound per square inch, partially regenerating catalyst from said second stage cracking operation at temperatures of at least 1200 F. under conditions such that a deposit of coke of more than 15 grams of carbon per liter of catalyst remains on said catalyst, introducing a portion ofthe partially re- Y generated catalyst to said second stage cracking operation, further regenerating a portion oi the partially regenerated catalyst `at temperatures of at least 1200 F. so as to produce substantially completely regenerated catalyst having a coke deposit of less than 6 grams of carbon per catalyst is employed in a cyclic process comprisliter of catalyst and introducingsubstantially completely regenerated catalyst to said first stage cracking operation.

4. In the catalytic conversion of hydrocarbons using solid hydrocarbon conversion catalyst, which catalyst is employed in a cyclic process comprising a conversion period and a regeneration period, during which conversion period hydrocarbons contact said catalyst to form conversion products and concomitantly deposit coke on said catalyst and during which regeneration period the coked catalyst is regenerated by-contacting it with oxygen containing gas under combustion conditions so as to remove at least a portion of said coke Vwith the consequent presence- Vof steam in the flue gases present during the regeneration, the steps which comprise contacting said catalystvvith hydrocarbons duringsaid conversion period and depositing a protective amount of coke on said catalyst suiicient to` provide a deposit of at least 15 grams of carbon per liter of .catalyst during the subsequent regeneration l period until the partial pressure of steam-in the nue gases is less than about 0.8 pound per square pound per square inch, separating said partially; regenerated catalyst and flue gases, contactingsaid partially regenerated catalystV withl addi-YA tional oxygen containing gas in a second regeneration zone, completing regeneration oiV said partially regenerated catalyst in said secondjregeneration zone at temperatures of at Aleast-1200? F. and under conditions such thatl the partialV pressure of steam in the gases present` is less than 0.8 pound per square inch and thereafter-contacting completely regenerated catalyst with hydrocarbons under conversion conditions. Y

5. In the catalytic cracking of Vhydrocarbonsusing solid hydrocarbon cracking catalyst, which ing a cracking period and a regeneration period, during which cracking period hydrocarbons contact said catalyst to form cracked products and concomitantly deposit coke on said catalyst and I* during which regeneration period the cokedcatalyst is regenerated by contacting it with oxygen containing gas under combustion conditions sok as to remove at least a portion of said'coke With the consequent presence of steam in the flue gases present during the regeneration, the steps Which comprise contacting said catalyst with hydrocarbons during said cracking period and depositing a protective amount of coke on said catalystsuflicient to provide a deposit of at least 30 grams of carbon per liter of catalyst during the subsequent regeneration period until the partial pressure of steam in the gases present is less than about 1.5 pounds per square inch, contacting catalyst comprising said protective amount of Y coke with an oxygen containing gas in a rst tional oxygen containing gas in a second regenff eration zone, completing regeneration of said partially regenerated catalyst at temperatures of at least 1200 F. and under conditions such that the partial pressure of steam in the gases present is less than 1.5 pounds per square inch and thereafter contacting catalyst so regenerated with hydrocarbons under cracking conditions.

6. In the catalytic cracking of hydrocarbons using solid cracking catalyst, which catalyst is employed in a process comprising a cracking period and a regeneration period, during which cracking period hydrocarbons contact said catalyst to form cracked products and concomitantly deposit coke on said catalyst, during which regeneration period an oxidizing gas contacts said catalyst under combustion conditions so as to remove at least a portion of said coke, the steps which comprise contacting substantially completely regenerated catalyst having a depositx of less than 6 grams of carbon per liter of catalyst with substantially only relatively light hydrocarbons having a dew point below the temperature of cracking in a first cracking operation and depositing coke on said catalyst such that the total amount of coke on the catalyst after said rst cracking operation totals at least 15 grams of carbon per liter of catalyst, and thereafter contacting said catalyst comprising at least 15 grams of carbon per liter of catalyst with a gaseous mixture of relatively heavy hydrocarbons having a dew point of over 800 F. and steam, said steam having a partial pressure of at least 6 pounds per square inch, in a second cracking operation.

7. In a process for the catalytic cracking of hydrocarbons using solid cracking catalyst, the steps which comprise contacting substantially completely regenerated catalyst having a deposit of less than 6 grams of carbon per liter of catalyst with substantially only relatively light hydrocarbons having a dew point below the temperature of cracking in a first cracking operation and depositing coke on said catalyst such 14 that the total amount of coke on the catalyst after said rst cracking operation totals at least 15 grams of carbon per liter of catalyst, contacting said catalyst comprising at least 15 grams of carbon per liter of catalyst with a mixture of relative heavy hydrocarbons having a dew point of over 800 F. and steam, said steam having a partial pressure of at least 6 pounds per square inch, in a second cracking operaticn, contacting catalyst from said second cracking operation with oxygen containing gas in a rst regeneration zone, eiecting an initial partial regeneration of said catalyst in said rst regeneration zone at temperatures of at least 1200 F. and generating flue gases having a partial pressure of steam of greater than 0.8 pound per square inch, separating said partially regenerated catalyst and flue gases, contacting said partially regenerated catalyst with additional oxygen containing gas in a second regeneration zone and completing regeneration of said partially regenerated catalyst in said second regeneration zone at temperatures of at least 1200 F. and under conditions such that the partial pressure of steam in the gases present is less than 0.8 pound per square inch.

GEORGE ALEXANDER MILLS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,253,486 Belchetz Aug. 19, 1941 2,290,580 Degnen et al July 121, 1942 2,327,489 Becker Aug. 24, 1943 2,348,646 Reeves May 9, 1944 2,356,697 Rial Aug. :22, 1944 2,372,018 Ruthruff Mar. 20, 1945 2,385,326 Bailey, Jr. Sept. 25, 1945 2,407,914 Bailey. Jr., et al. Sept. 17, 1946

Claims (1)

1. 6. IN THE CATALYTIC CRACKING OF HYDROCARBONS USING SOLID CRACKING CATALYST, WHICH CATALYST IS EMPLOYED IN A PROCESS COMPRISING A CRACKING PERIOD AND A REGENERATION PERIOD, DURING WHICH CRACKING PERIOD HYDROCARBONS CONTACT SAID CATALYST TO FORM CRACKED PRODUCTS AND CONCOMITANTLY DEPOSIT COKE ON SAID CATALYST, DURING WHICH REGENERATION PERIOD AN OXIDIZING GAS CONTACTS SAID CATALYST UNDER COMBUSTION CONDITIONS SO AS TO REMOVE AT LEAST A PORTION OF SAID COKE, THE STEPS WHICH COMPRISE CONTACTING SUBSTANTIALLY COMPLETELY REGENERATED CATALYST HAVING A DEPOSIT OF LESS THAN 6 GRAMS OF CARBON PER LITER OF CATALYST WITH SUBSTANTIALLY ONLY RELATIVELY LIGHT HYDROCARBONS HAVING A DEW POINT BELOW THE TEMPERATURE OF CRACKING IN A FIRST CRACKING OPERATION AND DEPOSITING COKE ON SAID CATALYST SUCH THAT THE TOTAL AMOUNT OF COKE ON THE CATALYST AFTER SAID FIRST CRACKING OPERATION TOTALS AT LEAST 15 GRAMS OF CARBON PER LITER OF CATALYST, AND THEREAFTER CONTACTING SAID CATALYST COMPRISING AT LEAST 15 GRAMS OF CARBON PER LITER OF CATALYST WITH A GASEOUS MIXTURE OF RELATIVELY HEAVY HYDROCARBONS HAVING A DEW POINT OF OVER 800* F. AND STEAM, SAID STEAM HAVING A PARTIAL PRESSURE OF AT LEAST 6 POUNDS PER SQUARE INCH, IN A SECOND CRACKING OPERATION.

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