US3067130A - Platforming process - Google Patents

Description

TEMPERATURE REQUIRED TO Dec. 4, 1962 PRODUCE DEBUTANIZED REFORMATE YIELD, %V

I00 F IO OCTANE NUMBER REFORMATE, F

SULFUR ON CATALYST, %W

D. BALDWIN, JR, ETAL 3,067,130

PLATFORMING PROCESS Filed May 9, 1960 1 l l l l 2 3 4 5 6 7 8 9 -IO CATALYST AGE, BBL/LB CATALYST AGE, B BL/LB FIG. 3

| l l 2 3 4 5 6 708 9 IO DESULFURIZED NAPHTHA, BBL/LB THEIR ATTORNEY 3,067,130 PLATFQRMING PRUCESS Douglas Baldwin, Jan, Genoa, and Maxwell Nager, Pasadena, Tex., assignors to Shell Gil Company, New York, N.Y., a corporation of Delaware Filed May 9, 1966, Ser. No. 27,639 1 Claim. (Cl. 2tl$-140) This invention relates to the upgrading of naphthas by Platforming.

Platforming is herein defined as a catalytic reforming process in which a hydrocarbon fraction containing naphthenes and paraffins and boiling in the gasoline boiling range is contacted in the vapor phase and in the presence of a substantial pressure of hydrogen with a catalyst containing platinum on a suitable support such as alumina under dehydrogenating conditions of temperature e.g., 800l000 F., whereby a product of improved octane number is obtained.

In Platforming the main reactions leading to improvement of the octane number are the dehydrogenation and dehydroisomerization of naphthenes and dehydrocyclization of paraflins to aromatic hydrocarbons and the hydrocracking of low octane normal parafiins. Minor reactions which also occur are the isomerization of normal paraflins, and some condensations. During the operation the catalyst gradually loses activity due, at least in part, to the accumulation of tarry carbonaceous deposits.

In the usual practice the conditions of Platforming severity are initially adjusted to give a product having the desired octane number and then the temperature is gradually raised to counteract the decline in the activity of the catalyst until a point is reached where further temperature increase is impractical because of temperature limitations of the equipment or other reasons. At this point the run is stopped.

The severity of the Platforming operation is primarily a function of the temperature, pressure, and space velocity. Generally in commercial practice the severity is controlled by the temperature as explained above. The pressure and space velocity normally are not altered over any appreciable range in a given Platforming plant.

If runs are made with a given feed stock over a range of severities two things are observed. First, as the severity is increased the octane number of the product increases but the yield of product decreases. This then gives a yield vs. octane number curve and it will be apparent that it is desirable to operate at the minimum severity affording the necessary octane number in order to maximize the yield. Secondly, as the severity is increased the rate at which the catalyst loses activity increases. It is customary to express this rate of loss of activity of the catalyst in term of degrees of temperature increase required to maintain the octane number per barrel of feed per pound of catalyst. Thus, for example, a decline rate of F. means that for each barrel of feed passed per pound of catalyst the reaction temperature must be increased 10 F. in order to maintain a constant quality of the product. If the maximum temperature increase in such a case is 100 F. (e.g., 850 to 950 F.) it is seen that the maximum catalyst life under these conditions is 10 barrels per pound of catalyst. The decline rate is not necessarily constant throughout a run but is generally approximately In commercial practice there are three types of Platforming operations herein designated as continuous, semiregenerative and regenerative. As Will be evident from the above, when mild conditions (i.e., low severity) are sufficient to obtain a product of satisfactory octane number the catalyst decline rate is very low and the process may be operated continuously for many months producing dfiblfid Patented Dec. 4, 1962 the maximum quantity of product. In this case when the catalyst is spent it is replaced by a charge of fresh catalyst or catalyst that has been reworked in a separate plant. The cost of the catalyst is of the order of $5.00 per pound.

Under conditions of somewhat greater severity the rate of catalyst decline is such that less than about 20 barrels of feed may be processed per pound of catalyst. To replace a catalyst under these conditions would result in a cost for catalyst alone of at least around 25 cents per barrel. This would be prohibitive. In this case it is the custom to regenerate the catalyst in situ. However, since regenerations are few and infrequent the provision of regular regeneration facilities is not justified. The whole plant is shut down during the regeneration. This type of operation with infrequent regeneration is called semi-regenerative Platforming.

Under still more severe conditions the decline rate becomes so rapid that very frequent regeneration is required. In this case it would be uneconomical to shut down the whole plant at short intervals and to avoid this it is the practice to arrange the reactors with suitable plumbing so that each may be taken separately off stream and regenerated while the process is continued in the other reactors. This last method of operation is designated regenerative Platforming.

The process of the present invention relates to semiregenerative Platforming. It has no application in continuous or regenerative Platforming.

When starting up a non-regenerative Platforming run with a fresh batch of catalyst it has been found desirable in some cases to curtail the high initial activity of the catalyst by including some sulfur in the feed during the first few hours of processing. This prevents so called runaway hydrocracking which is highly exothermic and which is sometimes encountered at the start up. It is well known, however, that in non-regenerative Platforming sulfur in the feed is a poison to the catalyst and consequently it is the practice to pretreat the Platforming feed to desulfurize it. This is normally done by hydrodesulfurizing the feed with a supported cobalt molybdenum catalyst using off-gas from the Platforming operation. Also in regenerative Platforming sulfur in the feed is most undesirable and in fact cannot be tolerated because the catalyst reactor walls, piping, etc. become somewhat sulfurized and upon regeneration oxides of sulfur are formed which ruin the catalyst. Moreover, scale which is formed in the heater, piping, etc. tends to deposit in the catalyst bed and thereby causes plugging which results in excessive pressure drop.

It has now been found, however, that in semi-regenerative Platforming the inclusion of sizeable amounts of sulfur in the feed is desirable and should be used throughout the run provided that a desulfurized feed is used during the last approximately 2 barrels per pound of the run. Thus, it has been discovered that in semi-regenerative Platforming, particularly to an F10 octane level of around or higher, the yield and catalyst stability are both considerably improved by incorporating sulfur in a concentration of around 300 ppm. in the feed and that such operation is possible provided that a sulfur-free feed is used during the last approximately 2 barrels per pound. It has been found that after using a feed containing sulfur it requires about 2 barrels per pound of sulfur-free feed to desulfurize the catalyst to a point where it can be regenerated. The magnitude of the effects Will be shown by the following examples in which reference will be made to the accompanying drawing.

FIGURE 1 of the drawing is a graph showing the temperature required to provide 100 Fl0 Platformate vs. the catalyst age under semi-regenerative conditions.

FIGURE 2 is a graph showing the debutanized Platformate yield vs. catalyst age in the same semi-regenerative runs. FIGURE 3 is a graph showing the sulfur content of the catalyst after use with a sulfur-containing feed and during subsequent treatment of a desulfurized feed.

In these examples the feeds were heavy naphthas having the properties shown in table 1.

These feeds were Platformed with Universal Oil Products Co. commercial R-8 Platforming catalyst under the conditions shown in Table 2.

TABLE 2 Example 1 2 3 Catalyst UOP, R-8 UOP, R-S UOP, R-B Outlet Pressurc,p.s.i.g 350 350 350 Hz/Oil, Mole Ratio 6 7 6 LHSV 2.0 2.0 2.0

Example 1 In this example the catalyst was not presulfided and the desulfurized feed was Platforms-d under the stated conditions. The temperature was increased with time as shown by curve 1 in FIGURE 1 to maintain the production of platformate having an F-l-O octane number of 100. The yield of debutanized reformate declined as shown by curve 1 in FIGURE 2.

Example 2 In this example the catalyst was presulfided by treatment with H S for 2 hours at 900 F. Thiophene was added to the feed to give 100 p.p.m. sulfur during the entire run. The results are shown in curve 2 of FIG- URES 1 and 2.

Example 3 In this example the catalyst was not presulfided but thiophene equivalent to 300 p.p.m. of sulfur was added to the feed. After processing 5.4 barrels of feed per pound of catalyst a desulfurized feed was substituted for 2 barrels per pound. The results are shown in curve 3 in FIGURES 1 and 2.

It should be noted that under these relatively severe conditions the operation according to the invention (i.e., where a sulfurized feed was used through the run up to 2 barrels per pound of the end) the temperatures required to obtain a 100 F-l-O product were consistently lower and increased at the lowest rate. Also, and more importantly, the rate of yield decline was much lower.

The catalyst in all runs was regenerable at the end of the runs. However, it should be noted that the catalyst in Example 3 would not be regenerable if the run Were stopped at 5.4 barrels per pound. The reason for this will be apparent from FIGURE 3. Here the catalyst was used in the treatment of a feed containing 300 p.p.m. sulfur and then analyzed for sulfur. A desulfurized feed was then treated with the same catalyst and its sulfur content periodically determined. As shown by the curve in FIGURE 3 the sulfur content of the catalyst comes to a new low equilibrium value but it requires about 2 barrels of the desulfurized feed per pound of catalyst to achieve this end. If the catalyst contains more than a few hundredths of a percent of sulfur it cannot be regenerated because during the burning, oxides of sulfur are formed which permanently impair the activity of the catalyst and which are corrosive to the metal walls of the reactor and auxiliary equipment.

In operating according to the invention the amount of sulfur in the feed to the Platforming reaction zone should be at least 200 p.p.m. and preferably 300 p.p.m. based on the feed. This includes any sulfur introduced with the recycled hydrogen. Higher concentration up to 400 p.p.m. or even 500 p.p.m. may be used but are generally not recommended because most plants are not constructed of alloys which are sufiiciently resistant to corrosion. The specified high sulfur concentration is maintained throughout the run except for the last approximately 2 barrels per pound of catalyst in which a desulfurized feed is substituted. Thus, for example, if the run length is to be 15 barrels per pound the sulfur-containing feed is used for about 13 barrels, per pound and the desulfurized feed is used during the period from 13 to 15 barrels per pound. The feed used during the last 2 barrels per pound should be desulfurized to a sulfur level not exceeding about 25 p.p.m. Following the last 2 barrels per pound with desulfurized feed the catalyst is flushed of hydrocarbons, regenerated by burning off the carbonaceous deposits, and reused in a new run.

We claim as our invention:

In the semi-regenerative reforming of a heavy naphtha by contact in the vapor phase with a platinum catalyst on a suitable support in the presence of substantial pressure of hydrogen under dehydrogenating conditions of temperature to an F-l-O octane number of about 100 for a run length between about 5 and 20 barrels per pound References Cited in the file of this patent UNITED STATES PATENTS 2,861,944 Coley et al. Nov. 25, 1958 3,006,841 Haensel Oct. 31, 1961 FOREIGN PATENTS 826,909 Great Britain Jan. 27, 1960

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