FI58266B - KONTINUERLIGT FLUIDISERAT-KATALYTISKT KRACKNINGSFOERFARANDE - Google Patents

Description

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Patent- och reglsterstyrelsen 'Anvöion och utt. * Krifun pubiicurad 30.09. o0 ^ (32) (33) (31) Requested «that! moon— Bugtrd prtorltet 17.07.72

USA (US) 27226U

_ (71) Texaco Development Corporation, 135 East U2nd Street, New York, N.Y. 10017, USA (US) (72) Leonce Francis Castagnos, Jr., Nederland, Texas, William Rogers Menzies, III, Groves, Texas, Roy Earl Pratt, Groves, Texas, USA (US) (7 * 0 Oy Kolster Ab ( 5U) Continuous fluidised catalytic cracking process - Kontinuerligt fluidiserat-katalytiskt krackningsförfarande

The invention relates to a continuous, fluidized-catalytic cracking process comprising a reaction step and a catalyst regeneration step, in which a hydrocarbon feed is continuously contacted with a cracking catalyst in a reaction zone under catalyzed cracking conditions to form cracked hydrocarbons and hydrocarbons. with a molecular oxygen-containing regeneration gas at an elevated temperature for a time sufficient to obtain a regenerated catalyst having a substantially reduced carbonaceous impurity, wherein the catalyst is fluidized by an upward flow of regeneration gas to form a dense phase catalyst bed and a dilute phase catalyst.

The invention is characterized in that the catalyst contaminated with carbon black is regenerated in the regeneration zone using a continuous flow of regeneration gas such that the oxygen content of the regeneration exhaust gas is maintained in the range of about 1-10 vol.

58266

Fluidized-catalytic cracking of hydrocarbons is well known in the art and can be accomplished by a variety of continuous circulation processes using a fluidized solid technique. In such processes, the cracking reaction causes coke to deposit on the surface of the powdered catalyst in the reaction zone. During the process cycle, the coke-contaminated catalyst is transferred from the reaction zone to a regeneration zone where the catalyst is contacted with an oxygen-containing gas under conditions sufficient to burn a substantial amount of coke from the catalyst and restore its catalytic effect to the regenerated catalyst. The regenerated catalyst is then removed from the regeneration zone and returned to the reaction zone to react with the hydrocarbon again. Typically, the coke-contaminated catalysts are passed from the reaction zone to the stripping zone to remove stripping hydrocarbons from the catalyst particles prior to passing the catalyst to the regeneration zone. _

Preferably, the catalyst to be regenerated is kept as a dense phase fluidized bed in the regeneration zone. Oxygen-containing regeneration gas is used to keep the catalysts in a fluid state. In addition, steam or other inert gases may be used to provide additional fluidization vapors as needed. It is known that commonly used cracking catalysts such as amorphous silica-alumina, silica-alumina-zeolite molecular sieves, silica-alumina-zeolite molecular sieves ion-exchanged with their divalent metal ions, etc. are rare. when exposed to excessive temperatures.

At too high temperatures, there is a physical change in the structure of such catalytic cracking catalysts, which is usually observed as a decrease in surface area, resulting in a substantial decrease in catalytic effect. It is highly desirable to keep the catalyst in a fluidized-catalytic cracking process at temperatures below the temperature at which the major physical change in the catalyst occurs. It has been found that silica-alumina cracking catalysts as described above can be exposed to temperatures up to 8-16 ° C with obvious damage to the physical structure of the catalyst.

It has been found that small amounts of residual carbon in the regenerated catalyst, especially molecular sieve catalysts, cause improved conversion of the hydrocarbon feed in the cracking process and also improve the selectivity of the cracked hydrocarbon products to the desired hydrocarbon fraction.

See. for example, U.S. Patent 3,563,911. · Preferably, the regenerated catalyst from the regeneration zone has a carbon content of the order of 0.1 wt% or less. The degree of carbon removal from the catalyst in the regeneration zone is affected by at least three variables. The partial pressure of oxygen in the regeneration zone 3 5 82 6 6 has a direct effect on the amount of carbon burning from the catalyst. The amount of carbon burning from the catalyst is also directly affected by the coke content on the surface of the catalyst. When smaller amounts of residual carbon are obtained on the surface of the regenerated catalyst, the amount of combustible carbon decreases. The third factor that affects the amount of carbon burning from the catalyst is the temperature at which the carbon combustion reaction takes place. The combustion reaction of carbon increases with increasing temperature. Since it is desirable to keep the catalyst below the temperature at which physical damage occurs, and preferably below about 8-16 ° C, the variables of the regeneration process in accordance with this invention can be adjusted to suitably achieve the desired low residual carbon on the regenerated catalyst within preferred temperature ranges.

The regeneration zones normally used in the art are cylindrical tanks in which the catalyst to be regenerated is kept as a fluidized bed by means of an upwardly directed oxygen-containing regeneration gas. The regeneration tank is dimensioned so that the surface velocity of the upward gas is in the range where the fluidized catalyst forms a dense phase layer. The density of such a dense phase layer is between about Ο, Τ - ^, 2 kp / cm and the density of the dilute phase may be about 0.007-0.07 kp / cm. There is a interface between the dense phase catalyst layer and the dilute catalyst phase.

The regeneration effluent, which normally comprises the combustion gas from the combustion of coke, inert gases such as without nitrogen, and which may contain unreacted oxygen, is removed from the upper end of the regeneration tank. In order to prevent excessive catalyst losses with the exhaust gas, separation devices are usually used in the regeneration tank to separate solids from the gas. Vortex separators are the most commonly used separators.

When regenerating catalytic cracking catalysts, especially highly active molecular sieve type cracking catalysts, it is preferred to burn a substantial amount of catalyst coke so that the amount of residual carbon on the surface of the regenerated catalyst is very low, preferably on the order of about 0.1 wt% or less. One difficulty that arises in regenerating the catalyst to a low residual carbon is that because the coke is burned by Hapel, it tends to form considerable amounts of carbon monoxide, which further causes further oxidation to carbon dioxide. In prior art methods, the use of an amount of oxygen theoretically sufficient to burn the coke in the fluidized catalyst bed to the desired residual coke on a small amount of regenerated catalyst has often had the undesirable effect of developing a combustible mixture of oxygen and carbon monoxide in the dilute catalyst phase.

Such a combustible mixture of oxygen and carbon monoxide may be subject to further oxidation in the dilute phase, commonly referred to as "afterburning."

This "afterburning" causes a substantial rise in the temperature of the thin catalyst phase, which can exceed about 816 ° C and in severe cases can rise to about 982 ° C or higher. Such high temperatures in the dilute catalyst phase can cause catalyst deactivation, which requires supplementing the process with an additional catalyst to maintain the desired catalytic effect in the hydrocarbon reaction zone. In addition, such high temperatures can damage the mechanical parts of the regeneration zone, especially the vortex separators used to separate the catalyst from the flue gas.

In methods previously proposed in the art for overcoming high temperatures of the dilute phase when performing catalyst regeneration to obtain a regenerated catalyst having a low residual carbon content, three general ways are common. According to the first route, a cooling medium, which may be steam, liquid water, non-regenerated catalyst, hydrocarbon oil, fuel gas, etc., is injected to cool the dilute catalyst phase below the temperature that damages the catalyst or regeneration zone. Examples of this first approach are disclosed in U.S. Patents 2,580,827; 2 1 + 5 »+ 373; 2 I + 5I + 1 + 66; 2 37 »+ 660; and 2,393,839- According to another approach, serial regeneration of the catalyst is used, wherein the catalyst to be regenerated is contacted with an oxygen-containing regeneration gas in a plurality of dilute phase regeneration zones. The catalyst flows from zone to zone and in no zone is the temperature allowed to exceed the temperature at which afterburning occurs. Examples of this second path are disclosed in U.S. Patents 3,563,911; 2 1 + 77 3 »+5; 2,788,311; and 3 »+9» + 858. According to the third approach, indirect heat exchange is used, such as steam generation coils in the dense phase layer. When using such prior art methods, the amount of carbon monoxide present in the flue gas can be considerable, generally between 2 and 6 volumes or even greater.

It is known that carbon monoxide is one of the pollutants in the atmosphere. Further treatment is required to remove carbon monoxide from the flue gas. Generally, the exhaust gas is passed to an exhaust steam boiler, where the carbon monoxide is consumed as oxidizing carbon dioxide while producing steam. However, such flue gas boilers are relatively inefficient and are large in size and thus require significant capital investment.

An improved process has now been invented for regenerating a coke-contaminated cracking catalyst, whereby the residual carbon content of the regenerated catalyst is low and the carbon monoxide content of the combustion gas from the regeneration process is substantially reduced.

According to the present invention, the dense phase fluidized bed of a coke-contaminated catalyst is contacted at an elevated temperature in the regeneration zone with an amount of oxygen-containing gas such that the amount of coke combustion is sufficient to lower the regenerated catalyst greater "afterburning" in the dilute catalyst phase. According to the invention, an excess of oxygen is used relative to the coke to be burned, i.e. so that free oxygen is present in the combustion gas. The temperature of the dilute catalyst phase is controlled by the rate at which the oxygen-containing Regeneration gas is fed to the regeneration zone. The temperature of the dilute catalyst phase is controlled by adjusting the regeneration gas supply rate to the regeneration zone to control both the excess oxygen and the inert gas, e.g. nitrogen, in the case where air is used as the regeneration gas.

According to the invention, the temperatures of the dilute catalyst phase can be controlled "" below the temperatures at which the catalyst substantially loses its potency, to those temperatures at which the mechanical parts of the regeneration zone are damaged or lose their strength. By following the process of the invention, the regeneration of the catalyst can also be carried out without the use of additional cooling devices, such as indirect heat exchange or cooling rings. In addition, the catalyst can be regenerated in a single dense phase catalyst bed. The carbon monoxide content of the flue gas can be kept within the desired narrow limits without the use of expensive flue gas treatment equipment such as flue gas boilers. Another advantage of the increased amount of coke combustion is that the amount of catalyst in the regeneration zone can be reduced compared to the amounts used in previous methods in the art.

The surface of the catalyst regenerated at the carbon content level has a great effect on the conversion and the obtained product distribution in the fluidized catalyst cracking of hydrocarbon oils such as gas oils, vacuum gas oils, shale oils, straight-run residues, atmospheric waste, etc. The carbon content of the regenerated catalysts is particularly advantageous when a highly active moxecyl screen type cracking catalyst is used and when the cracking reaction is effected in an ascending line where the contact time is short and the catalyst is present in the open phase in the hydrocarbon feed vapor. For example, under constant operating conditions and constant coke production, reducing the amount of carbon by weight in regenerated screen catalysts from 0.35 ~ ii to about 0.1 5? Increases the conversion of hydrocarbons, e.g., by as much as about 2.5% by volume, thereby increasing the conversion. as a result, the production of less valuable heavy fuel oil will decrease. It is also conceivable that reducing the amount of carbon on the surface of the regenerated screen catalyst from about 0.2 wt.% To about 0.05 wt.% May improve the conversion by about 2 vol -> {or more and increase the gasoline yield by about 1.4 vol. -> S, respectively.

It has surprisingly been found that coke-contaminated catalysts can be regenerated to a low residual nickel content of 0.1 wt% or axle in a simple tin phase regeneration zone at temperatures below about 816 ° C and preferably 691-760 ° C. According to the invention, a dense phase 6 58266 fluidized catalyst bed, such as one having a density of about U, 7 ~ h, '<£ 3 ..... .... .... ....

kp / cm, maintained in the regeneration zone using excess oxygen-containing gas relative to the amount of coke to be burned to give the catalyst a sufficiently long residence time to obtain the desired low residual carbon catalyst at a dense phase mattress temperature below about 816 ° C and preferably 691-760 ° C.

The temperature of the dense phase bed is lowered by increasing the amount of regeneration gas excess used.

According to the invention, the temperature in the dilute phase of the regeneration zone is controlled if it rises above the desired temperature by adding a larger amount of regeneration gas.

A further result of the process according to the invention is that a considerable part of the carbon monoxide reacts in the regeneration zone, so that the concentration of carbon monoxide in the flue gas comprising the combustion gases from the regeneration process is substantially reduced. In terms of increased environmental protection requirements, the reduction of carbon monoxide, which is a bad air pollutant, is a desirable result of the catalyst regeneration process. For example, according to the present invention, the carbon monoxide content of the flue gas can be reduced to less than 1%, preferably less than 0.1% by volume of the flue gas without further treatment.

Oxygen-containing regeneration gases that can be used in the process of this method include gases that contain oxygen molecules mixed with a substantial portion of an inert diluent gas. Air is a particularly suitable regeneration gas. Other useful gases are enriched air and oxygen together with carbon dioxide and / or other inert gases. In addition, if necessary, water vapor can be added to the dense phase bed together with or separately from the Regeneration gas to provide additional inert dilution and / or additional fluidizing gas. In order to obtain a sufficiently fluidized dense phase catalyst bed with good heat transfer throughout the bed and without relatively dead spots where local temperatures may exceed the temperatures at which the catalyst is damaged, the specific vapor velocity of the regeneration gas may preferably be about 0.2-6.6 km /B. Since, according to the present invention, the partial pressure of oxygen in the regeneration zone can be used as a control parameter to achieve good catalyst regeneration and reduce the carbon monoxide content of the combustion gas, other control devices can be provided to keep the specific vapor velocity For example, the tanks used in current catalytic cracking processes are usually relatively large cylindrical tanks with solid / gas separation devices, such as vortex separators suspended near their upper end. Such tanks usually withstand a reasonable pressure of about 3,586,26 0-3 * 5 kp / cm. By using pressures of 0-3 * 5 kp / cm in the regeneration tank, and preferably 1.1-3.2 kp / cm, it is possible to adjust the specific steam rate in the desired range. By adding additional oxygen in the form of an oxygen-containing regeneration gas and also by increasing the pressure, the specific vapor velocity can be maintained within the required vapor velocities to maintain a good solid phase fluidized bed and the oxygen partial pressure in the regeneration zone can be maintained to give the desired catalyst regeneration.

Surprisingly, the dense phase fluidized bed, maintained at the desired temperature range in the presence of excess regeneration gas, provides essentially complete conversion of coke, with the coke burning to carbon dioxide in the dense phase bed. The specific amount of coke pieces in a dense phase mattress between about 0.12 and about 1.0 kg of coke per hour per kg of catalyst provides a sufficient average catalyst residence time in the dense bed for a sufficient amount of coke to return to the desired low residual carbon surface of the regenerated catalyst. The residence time to regenerate the catalyst to the desired level and maintain the desired dense phase temperature is conveniently obtained by adjusting the volume of the catalyst in the dense phase catalyst bed. In a desired range, the amount of coke on the surface of the catalyst is determined by the operating conditions in the hydrocarbon reaction zone.

In a catalytic cracking zone in which most of the hydrocarbon cracking takes place in an ascending line to which the hydrocarbon feed and regenerated catalyst are fed under conditions in which the catalyst is present as a thin phase suspended in hydrocarbon vapors, the amount of coke deposited on the catalyst can be about 2 to about 10 seconds to achieve a conversion of the hydrocarbon feed of about 50-95 ~ 5f to substances boiling below about 221 ° C using reaction temperatures between about 1 + 71-538 ° C. Under conditions using various forms of hydrocarbon cracking, such as reactors using a fully dense phase catalyst reaction or using a combination of riser cracker and dense phase cracking, the cracking reaction can be controlled by methods well known in the art.

Example 1

One pilot plant operated a fluid catalyst cracking process in which a hydrocarbon feed and fresh regenerated catalyst were combined at the bottom of the riser and in which the catalyst and hydrocarbon vapor were discharged from the top of this riser into the reaction tank. In this reaction vessel, the hydrocarbon vapor was different from the cracking catalyst used, and the cracking catalyst was kept as a fluidized bed by means of the reaction vapor. The spent catalyst from the reaction tank was continuously removed to a stripping section, where the strippable hydrocarbon vapors were removed from the catalyst by stripping with water vapor. Stripping of the spent catalyst was continuously transferred to a regeneration tank. The regeneration tank consisted of a vertical cylindrical tank equipped with means for continuously receiving the spent catalyst, means for removing the regenerated catalyst, a nozzle near the bottom for discharging oxygen-containing regeneration gas, e.g. to remove the flue gas from the regeneration tank. In addition, the regeneration tank was equipped with valves, piping, heating elements, pressure gauges, sampling taps, and flow measuring devices needed to obtain the values shown in this example. In this example, spent catalyst was continuously added to the regeneration tank at 510 ° C through the catalyst inlet nozzle. In the regeneration tank, the catalyst was kept as a dense fluidized bed using air. Catalyst regeneration was performed by increasing dense phase temperatures. Orsat analyzes of the flue gas and residual carbon analyzes of the regenerated catalyst were performed under different operating conditions. The operating conditions and test results are shown in Table 1 below.

table 1

Experiment No. 1 2 3 1+ 5 6 7 8

Air to the regenerator, m3 (VN) / h 1U, 0 13.9 lU, 2 15.1 15.9 17.0 18.2 21.0

Dense phase 6jk 673 678 69b 722 756 770 767, o temperature C Flue gas analysis (Orsat) CO2, vol.-? 11.8 12.0 12.0 13.0 lfc, 8 16, * »12.0 12.0 0, til.-? 0.6 0, U 0.2 0.2 0.8 1, U 5.1+ 6.2 CO, vol .- $ 7.8 7.6 6.1+ 5.6 1.8 0.0 0.6 0.0 58266

On the surface of the carbon regenerated catalyst, weight # 0.32 0.1 + 3 0.3 0.2 0.12 0.12 0.12 0.11

Coke yield (# from fresh feed) - 7.53 7.26 7.70 7.16 7.37 6.19 6.68

As can be seen from the values in Table 1, the carbon monoxide content of the flue gas decreased as the temperature of the dense phase catalyst bed increased. At about 756 ° C (Experiment 6), the carbon monoxide content of the combustion gas showed 0 # when tested by the Orsat analytical method. A significant portion of the carbon monoxide generated by the combustion of coke on the surface of the catalyst was converted to carbon dioxide in the dense phase layer, thus with very little "afterburning" in the dilute phase. The results shown in column 6 of this experiment, in which carbon monoxide is substantially removed from the flue gas, in which the surface of the residual carbon-regenerated catalyst is reduced to about 0.12% by weight, and in which carbon monoxide afterburning in the dilute phase is not excessive, show superiority.

Example II

The process described in Example I was performed to demonstrate that it is necessary to obtain a sufficient temperature in the dense phase regeneration bed to substantially reduce the CO content in the combustion gas and to reduce residual carbon on the surface of the regenerated catalyst. The second experiment was performed keeping the temperature of the regenerator constant, about 610 ° C. An amount of air was added to give a substantial excess of oxygen to the exhaust gas. However, as can be seen from the values shown in Table II below, the CO content of the flue gas was not substantially reduced and the amount of residual carbon on the surface of the regenerated catalyst was not reduced.

Table II

Air to the regenerator, 12 3 ^ 5 6 7 8 m3 (VN) / h 10.3 10.3 11.2 12.0 12.8 13.6 1U, 7 iU, 7

Dense phase temperature, ° C 6θ6 597 602 558 611 603 610 612

Flue gas analysis (Orsat) CO 2, vol.-Jf 11.8 11.0 11.1 * 11.0 8.8 8.0 8.6 9.8 02, vol. # 0.6 0.8 0 .9 1.0 3.2 3.0 1 +, 1 + 5.0 CO, vol. # U, 6 6.2 5.2 6.0 6.0 5.0 6.0 5.0 10 58266

Carbon regenerated catalyst surface weight /? 0.16 0.12 0.1 + 5 0.1 + 5 0.13 0.20 0.23 0.17

Coke yield (% of fresh feed) 1 +, 81 + 5 »07 5> 29 5.79 5» 1 * 1 + 5 »l + 7 6.05 5.99 The results of this experiment show that the temperature of the dense phase catalyst bed in the regeneration tank must be increased above the normally acceptable Lei -catalyst regeneration temperatures to achieve substantially complete CO conversion to CO 2+. In addition, the excess air at relatively low regeneration temperatures is not sufficient to convert substantially all of C0 to COgt in the regeneration zone. -

Claims (3)

11,582 66 A continuous fluidized-catalytic cracking process comprising a reaction step and a catalyst regeneration step, wherein the hydrocarbon feed is continuously contacted with a cracking catalyst in a reaction zone in a regeneration process. in contact with a regenerating gas containing molecular oxygen at an elevated temperature for a sufficient time to preach a regenerated catalyst having substantially reduced carbonaceous impurity continuous flow of regeneration gas a such that the oxygen content of the regeneration exhaust gas is maintained in the range of about 1-10 vol * - # to convert substantially all of the burnt carbon black to carbon dioxide in the dense phase catalyst bed maintained at a temperature of about 691-816 ° C. Process according to Claim 1, characterized in that the temperature of the dilute catalyst phase does not exceed about 816 ° C. Process according to Claim 1 or 2, characterized in that the carbon monoxide content of the regeneration exhaust gas is kept in the range from about 0 to 0.1 vol. h. Process according to one of the preceding claims, characterized in that the conditions are adjusted so that the concentration of residual carbon black in the regenerated catalyst is in the range from about 0 to 0.1% by weight.