DE1770412A1 - Process for reforming hydrocarbons in the naphtha boiling range - Google Patents

Description

Process for reforming hydrocarbons in the naphtha boiling range The invention relates to a method for reforming naphtha feedstocks and particularly reforming naphtha feeds with platinum catalysts.

Reforming with platinum alumina catalysts forms one of the most important petroleum processing methods for improving the quality of naphthas or heavy gasoline to gasoline products with a higher octane number. Because the hydrogen purity of the reformate recycle gas during processing of relatively large volumes of naphtha must be maintained, there are even slight improvements in yields Reformate products are technically very essential and allow a considerable Cost saving. For example, an increase in the reformate yield by only about 0.5% by volume means an annual improvement in the yield of the refineries of several million marks. Furthermore, any reduction in the required in a reforming catalyst results Amount of platinum results in considerable savings, which can also amount to several millions Mark can amount to, while at the same time drastic protection of the usually limited Platinum reserves. In one aspect, the invention provides an optimal configuration a low pressure reforming process, such that the process, for example continues to belong to the group of non-irritative lieforination processes and this opens up undesirable yellowing of the platinum utilization, the hydrogen purity t1er recycle gases and the reformate product selectivity with respect to the desired Octane quality.

In the prior art there are several publications that are with the influence of moisture on reforming using platinum metal catalysts deal. For example, US Pat. No. 2,772,217 states that reforming catalysts, the oxides or sulfides of metals of groups IV, V, VI, VII and VIII, after regeneration contain approx. 0.2-1.0% by weight of water. The patent recommends the regenerated catalyst to a moisture content in the range of about 0.1-0.8% by weight to be dried in a stripping zone. But it is also known that the moisture content of the fed into a reforming reactor Catalyst is not the only wave of moisture in the reactor.

U.S. Patent 2,842,482 describes a reforming process in which the return gas contains about 0.5% by volume of water. This amount of water alone however, contributes to a water vapor partial pressure of about 10 mm; mercury at one Total reactor pressure of about 3.8 atmospheres (54 psig) and about 44 mm Hg for a total reactor pressure of about 14 atmospheres (200 psig). On the other hand, reforming treatment is considered proportionate considered dry if the moisture content of the effluent from the last reaction zone, expressed as partial pressure of water at 14 atmospheres (200 psig) total pressure, less than 0.4 mm Hg, and preferably about 0.05 to about 0.2 mm Hg.

U.S. Patent 3,110,703, which relates to reforming in the presence of a platinum-alumina catalyst, teaches that the oil content of the catalyst in at least the initial catalytic reaction zone tends to be at an undesirable level which favors hydrocracking, but this unsatisfactory result can be counteracted by the surface area of the catalyst: to values of etwe. 1 to about 300 m2 / g and preferably from et1., # Ta @ is = t7, wa 1z m2 / g limited. It is claimed that with eiic >> en sizes of the halogen receptacles c> betw. die ge. @ t @ - ..;, - zv @ activity of @la; in-A @ .urn.i ..; rmox @ rd-Iatal ° - °, x @ a;: @ Kr = k _'t 1_f ° _ is ringert, and zwnrY ;; rcA Keep and thus excessive hydrocracking of naphthenes in the first reforming zone.

US Pat. No. 2,952,611 describes a regenerative reforming process described with platinum catalyst, in which the expediency of a maintenance of moisture levels below about 100 parts-per-million is illustrated using a combination of feed dryers, return gas dryers, regeneration gas dryers and other measures to achieve and maintain the desired moisture content. However, it should be noted in particular that this patent specification expressly states that at moisture levels below 100 parts-per-million a very rapid and surprising increase in reformate yields is achieved when naphthenic Gulf Coast naphthas in the presence of a platinum catalyst with a platinum content in the range from about 0.3 to about 0.6 weight-p when combined with a halogen in a concentration in the range of about 0.5 to about 1.5 wt. 4o can be processed. The patent also indicates that the super dry mode of operation a halogen stripping during the oil supply operating period eliminated and thereby ensures a substantially constant halogen content.

In the main patent 1 20'7 534 a reformer process is described which is carried out at pressures preferably below about 28.1 atmospheres (400 psig) and in which the surface area of the catalyst is preferably kept above about 200 m2 / g , by regulation the water or moisture content of the catalyst during reforming, regeneration and start-up after regeneration of the catalyst. This patent explains that there are at least three sources of water in contact with the catalyst in the reforming reaction zones. A qu? 11e for water is the naphtha charge, which can contain up to about 10-15 parts-per-million of water. A concentration of 15 parts-per-million water in the feed naphtha t.-contributes, according to the data there, about 0.08 mm Hg to the total partial pressure of water in the reaction zone when a total pressure in the reaction zone of about 14.05 atmospheres (200 psig). However, an undried recycle gas easily builds up this water pressure to 0.5 - 2.0 mm Hg partial pressure. This patent also states that this amount of water in the reaction zone vapors does not adversely affect the activity of a platinum group metal reforming catalyst, but it does lead to a lower volume yield of C5 + reformate from a feed with a boiling range from C5 to an end point of 121 ° C ( 250 ° F) than maintaining a partial pressure of the final effluent of the reforming zone in the range of about 0.05 to about 0.2 mm Hg 0.6% by weight platinum on a suitable alumina support with a content of up to about 0.7% by weight chlorine. Surprisingly, it has now been found that significant advantages can also be achieved with a low pressure reforming treatment (preferably below about 28.1 atmospheres (400 psig) and more preferably in the range from about to about 24.6 atmospheres (100-350 psig)) when the combined moisture content of the reactants, which contributes to the water vapor partial pressure in the inflowing material and is found by Refoi matausfluß, is kept within a relatively narrow range of about 0.1 to about 0.2 mm Rg. It was further found that the hydrogen purity of the reformate recycle gas depends on the moisture content or partial pressure of water determined in the total effluent from the last reactor, so that below a partial pressure of water of about 0.1 mm Hg there is a considerable decrease in the efficiency of the catalyst in terms of maintaining hydrogen purity Reformate recirculation gas is present above a desired lower limit and the reformate product selectivity. It has also been found that in a preferred mode of operation, when the moisture content is above a partial pressure of water of about 2.8 x 10-4 kg / cm 2 (0.004 psi), undesirable reductions in product yields and catalyst activity and stability are also encountered.

According to the invention then, a method is for re- form of hydrocarbons in the naphtha boiling range at a pressure below about 28.1 atm (400 psig), usually between about 7 and 28, 'I atm (100-400 psig) suitable 3 and reforming temperatures, usually . about 454-52700 (850-980oF) I in the presence of a platinum reforming catalyst containing less than about 0.45 wt% and typically about 0.3 to 0.45 96 platinum is provided at the amount of moisture contained in the incoming material is controlled so that the moisture content of the process remains in equilibrium and still a high hydrogen purity is maintained in the recycle stream. The moisture balance of the process is preferably regulated so that the partial pressure of water in the slide material draining off the process is 0.1 to 012 mm Hg. Furthermore, the amount of water to the first reactor in the series of reactors is preferably maintained at a value of 0.08 to 0.16 mm Hg. If necessary, the moisture balance in the circuit can be maintained by adding water to the recycle stream. The feed is normally dried prior to introduction into the first reactor.

The method according to the invention thus represents an improvement or further development of the method according to the main patent in that the moisture content is regulated in a special way in the method of the present invention ; this enables a catalyst with a lower platinum content to be used. Both processes are essentially low pressure reforming processes. A relationship was developed between the water content of the feed in ml / m3 and the water partial pressure of the final reactor effluent in mm Hg for reforming using practically perfect gas dryers. This relationship is: If, on the other hand, the recycle gas separator located downstream of the last reforming reactor is operated under sufficiently elevated temperature conditions so that entrained water is carried overhead in the recycle gas stream withdrawn therefrom, the relationship between the water content of the feed and the overhead product of the separator takes the following form: The following applies to the above equations: PH 20 = partial pressure of water, in mm Hg; = Total pressure, in mm Hg; CH = water content of naphtha, in ml / m3 (= parts-per-2 million); MGN = molecular weight of the naphtha; = Specific weight of the naphtha, in g / cm3; = Molar increase in naphtha on passage through the reactors, moles of product / mole of naphtha (usually 2 to 2.5); G = moles of excess recycle gas per mole of naphtha (usually 1 to 195); R = total recycle ratio, moles of recycle material / mole of naphtha; K = vapor-liquid equilibrium constant for water in the separator.

Surprisingly, it has been found according to the invention that a reforming catalyst with a relatively low platinum content, generally not more than about half the platinum content of the commonly used reforming catalysts, in the process according to the invention results in an operating mode which is at least equivalent to that which is normally used Reforming catalysts higher platinum content is achievable. In particular, it was found that the hydrogen purity of the recycle gas separated from the reformate product can be kept essentially the same when using a catalyst with 0.35 wt Platinum is achievable. This drastic technical improvement is possible if the moisture or water partial pressure of the reactants introduced into the reforming is kept within the relatively narrow limits specified above . In order to achieve the surprising and unforeseeable advantages described here, appropriate attention must be paid to the specific sources of water that are relevant in the reforming process. The water content can be controlled by feed dryers, recycle gas dryers and, in some cases, regeneration gas dryers for the relatively infrequent regeneration of the catalyst, or some combination of such devices. To achieve the advantages that can be achieved according to the invention, however, the hydrogen-rich recycle gas must be dried down to a very low value below about 5 parts-per-million and preferably below about 2 parts-per-million, before the dried recycle gas is combined with the one to be reformed Naphtha feed. Thereafter, water is then preferably added in sufficient quantities for the controlled adjustment of the moisture content of the reforming within the relatively narrow limits specified above.

In general Naphthabeschickungenfür are reforming in the boiling range from about 0 5 to äohlenwasserstoffen up to a final boiling point of about 138o or 143 ° C (280 or 290 ° F), but the naphtha feedstock may also comprise, `such a high end point such as 204- ° C (400 ° F). According to a special feature of the invention , the adjustment of the moisture content to a value suitable for the process is facilitated by the fact that. the naphtha also dries to a very low moisture content, so that the moisture content of the combined feed of recycle gas and naphtha can then be precisely adjusted by controlled addition of water and a relatively even distribution in the feed to the reforming can be ensured. It should be noted that water is soluble up to about 100 parts-per-millionion in the naphtha feed. This amount of soluble water is therefore considerably higher than the amount required to achieve the advantages according to the invention, which underlines the critical limits according to the invention.

During an operational implementation of the reforming, in which a Naphtha feed in association with a hydrogen-rich one formed in the facility Recycle gas is fed, the separated from the reformate outflow is hydrogen-rich Recycle gas preferably initially to a water content below about 5 parts-per-million and preferably to a water content of no more than about 2 parts-per-million dried before the hydrogen-rich recycle gas stream with the naphtha feed is united. Although it is not important, both the recycle gas and the naphtha to water contents as low as those indicated above dry, it may be convenient to work in this way and thus maintaining the precise regulation of the moisture content required according to the invention to obtain. On the other hand, the drying of the return gas fulfills the double function, at the same time other undesirable components such as chlorine and hydrogen sulfide, from the gas. One can see in the above It is also much more convenient to precisely control the desired moisture content bring about, just by continuously controlled addition of water to the total charge, which is fed to the first of a plurality of reforming zones.

When reforming hydrocarbons with platinum group metal reforming catalysts, it is not uncommon to use three or more reactors in a sequential arrangement; the naphtha is passed through this in association with the hydrogen-rich gas under such conditions that the naphtha is reformed to a reformate product having the desired octane number. In this series of reactors, the temperature and pressure conditions are selected and maintained in such a way that dehydrogenation of naphthenes to aromatics and dehydrocyclization of paraffins occur in the most favorable manner in the intended successive reaction zones. If, for example, three reaction zones are connected in series, the dehydrogenation of naphthenes takes place mainly in the first reactor and to a lesser extent in the second and third reactor, while the dehydrocyclization reactions, which are accompanied by a certain hydrocracking and isomerization, mainly in the second and run off the third reaction zone. If, on the other hand, a reforming plant comprises, for example, four reaction zones, the conversion of naphthenes will predominantly take place in the first and second reaction zones, while the remaining reactions of dehydrocyclization, hydrocracking and isomerization will primarily take place in the third and fourth reaction zones. In a preferred mode of operation in accordance with the invention, the reforming conditions are selected so that the operating pressure is usually below about 28.1 atmospheres (400 psig) and generally in the range of about 14.05 to about 24.6 atmospheres (200-350 psig) .

In a reforming of the type described here, a pressure reduction in the direction of flow of the reactants through the sequence of reforming zones is often maintained, which is no more than the normal pressure drop when the reactants pass through the catalyst beds and the associated devices, while at the inlet of each reactor, reforming temperatures in the range of about 427 ° C (800-1000 ° F) and most often not above about 527 ° C (980 ° F) can be maintained. The temperature of the reaction material is usually adjusted between the individual reactors, and suitable ovens are usually provided for this purpose. In general, the pressure drop discussed above is such that the foremost or first reactor in the plant operates at a pressure which is about 1.4 to about 7.02 at (20-100 psi) higher than the pressure of the last reactor in the process . Usually, an hourly space velocity, based on weight and for each reaction stage, in the range of about 0.5 to about 20 is maintained and sufficient hydrogen is supplied with the hydrogen-rich recycle gas that a hydrogen partial pressure in the reforming process in the range of about? .02 to about 21.1 ata (100-300 psia). Often naphthenreiche naphthas are preferred in the reforming of Naphthakohlenwasserstoffen boiling range to up to about 160 ° C (320 ° F) for the production of Reformatprodukten relatively high octane number, since they are easily converted to aromatic components of high octane. One of the more surprising features of the method according to the invention, however, is that also naphtha feeds that are rich in paraffins, can be converted to Reformatprodukten high octane in high yields, namely purities in hydrogen, which are comparable to those as otherwise can only be achieved with catalysts with higher noble metal contents . The values reported below show that catalytic reforming of a naphtha feed in the presence of a platinum group metal reforming catalyst under a total reactor pressure of less than about 28.1 atmospheres (400 psig), and preferably less than about 21.1 atmospheres (300 psig), is a substantial increase the hydrogen purity of the recycle gas and the yield of C5 + 8eformat product can be achieved with a catalyst which does not contain more than about 0.4 % by weight of platinum . The H2 purity of the feed-in stream is preferably kept at a value of more than 60 mol 4a.

In the reforming process of the invention, the naphtha charge can be dried by any of a number of different methods, e.g., by passage through a solid desiccant such as alumina, molecular sieves, or contact with any other solid absorbent, or the naphtha can be effectively dried by distillation, to bring about a water content that is usually less than about 10-15 parts-per-million by weight. The recycle gas recovered from the effluent of the last reactor can be cooled and then by contact with a solid absorbent such as a molecular sieve or other suitable solid absorbent material. to be dried. Preferably, the recycle gas is contacted with the solid absorbent under conditions such that its water content is reduced to no more than about 2 parts-per-million at 14.05 atmospheres (200 psig); this corresponds to a partial pressure of water no more than about 0.02 mm Rg for a total pressure of 14.05 atmospheres (200 psig).

The invention is illustrated below by way of examples further illustrated with the accompanying drawings.

Figure I is a graph showing the influence of the partial pressure of water, expressed as mm Rg in the effluent of the third reactor of a reforming, on the hydrogen content of the recycle gas in a substantially steady state for an operation using a catalyst with a platinum content of 0.35 wt 4 shows. The operating conditions for each operating run shown in the diagram are detailed in Table I below. All the plotted in Figure I 'ferte derived from at Reformierbehandlungen' i7,6 atm (250 psig) under a processing in the range of 0 6 - boiling 143 ° C (290 ° F) paraffinic naphtha to a C5 + product having an octane number (R +3) of 102.0.

Figure II shows values that with a catalyst with 0.6 wt.% Obtained platinum; it shows the influence of the partial pressure of water in accordance with FIG on the hydrogen content of the recycle gas. It is particularly important to note that the slope of the lines delimiting the measured values in FIG. II is much lower than in Figure I; this shows that the catalyst with 0.6 wt .-% platinum compared is much less sensitive to the partial pressure of water than the 0.35 catalyst Wt% platinum.

Figure III shows the course of meters as a function of the time w: closer and shows how the in Figu-. I and II plotted points were obtained. In detail, Figure III shows the hydrogen purity and the Activity measured by the required inlet temperature for a product with an octane number of 102, depending on the operating time in an investigation of aging in platinum reforming. In the figure III are the water contents in the outflow of the third reactor during operating times at where the hydrogen purity was essentially in a steady state, cited. For example, it can be seen that the HZ purity from the 4th to the 11th day of the recycle gas remained essentially constant at a value of about 72% when the mean partial pressure of water. was about 0.7 mm Hg. On the other hand totaled the hydrogen purity from the 12th to about the 20th day to about 70.5% when the partial pressure of water averaged about 0.29 mm Hg. Changed from the 20th to the 30th day of the operating period however, the hydrogen content and the water content change rapidly, indicating that the Reformer did not work in a steady state. The values of the figure III provided the points which are marked in FIG. II by a circle. The remaining points in Figure II and Figure I were assigned values accordingly of Figure III for various operational runs in a test facility obtain.

FIG. IV shows the decisive effect of a controlled addition of water within the limits provided according to the invention on the activity, represented by the temperature change for the production of a product with an octane number of 102, and the hydrogen purity; the results come from the operating run "F", which is identified in more detail in Table I below, in an experimental plant. It was observed that during the first 20 days of operation the working plant increasingly dried out and that in the operating period of about 20 to 30 days the water vapor pressure in the plant remained essentially constant at less than about 0.01 mm Hg. During this period of operation, the naphtha feed had a water content of approximately zero. Start ::? on the 27th day, water was added to the naphtha in e @. At a rate of 36 parts by weight per Hillion (200 mole parts per million) injected, corresponding to about 26.05 ml of water per m3 of naphtha charge (4.14 cm3 / barrel (bbl)). This water supply was maintained until the 62nd day, it resulted in a water partial pressure in the outflow from the third reactor of the reformer of 0.192 mm Rg The temperature of the separator was about 270C (801F). It can be seen from the values in FIG. IV that a drastic change in the hydrogen purity of the recycle gas occurred after the above-mentioned water injection and that the hydrogen purity remained essentially constant during the period of continuous water supply after the 30-day period.

Figure Y shows a similar effect on catalyst activity and the hydrogen purity of the recycle gas in a technical operation in a refinery, referred to here as Run N. The operating conditions are given in Table I. Farther became the water content in the feed for the reforming treatment during the first 48 days of operation to about 4.4 ml / m3 (0.7 cm3 / bbl) (6 parts by weight per million r, - 33.3 mole parts per million) set. During this period of operation it was found that the effluent from the third reactor has a water content of 2-3 parts per million (0.02-0.03 mm Hg). At around the 49th day of operation, water was added to the feed in a rate of 25.8 ml / m3 (4.1 cm3 / bbl) (36 parts-per-million by weight --e 200 mole parts per million), which soon afterwards resulted in an outflow from the third reactor which resulted in a water concentration of 12-15 moles-per-million, or 0.13 - 0.16 mm Hg, with a pressure at the outlet of the third reactor of 13.4 atmospheres ('t90 psig), led. From the figure it can be seen that several days, here up to about 4 days. were required until the full effect of the addition of water occurred was evident from the dramatic increase in the hydrogen purity of the recycle gas stream from about 54 5b to about a mean of 73%.

Figure YI, on the other hand, shows the rate of decrease in hydrogen purity, shown in percent per day, in operations in which the hydrogen content of the recycle gas is higher than in equilibrium (e.g. immediately after reducing the moisture content), as a function of the water partial pressure. The following should be pointed out in this regard: If a reforming treatment results, for example, in a hydrogen purity of 75 96 at a water partial pressure of 0.1 mm Hg, the hydrogen content is not considered to be in equilibrium, since according to FIG % H2, ie about 60 i6 hydrogen, should be. From Figure VI it can be seen, however, that the hydrogen decrease from about 75 % to about 60% at a rate of about 0.14 to about 0.56% per day, ie with an average of about 0.4% per day, he follows. Thus, at this rate of hydrogen decrease, it would take about 37.5 days for the hydrogen content to reach its 60% equilibrium state after removal of water from the feed. The broad curve path in FIG. VI is indicative of the values obtained with a reforming catalyst of 0.35% by weight of platinum when the hydrogen content is greater than the equilibrium content. Catalysts with a different platinum content will give a different rate of decrease.

From the investigations explained it can be seen that if the Hydrogen content is less than the equilibrium state (i.e. the Moisture content has been increased), the hydrogen content of the gas the Equilibrium reached very quickly. Indeed, it has been observed that when water under these conditions "in, the feed to the reformer is introduced, the hydrogen content of the recycle gas very quickly and before water in the effluent of the third reactor is detected increases. Probably the reason for this seen in that the higher partial pressure of water in the first reactor is the reforming reactions influenced, before all catalyst in the second and third reactors to its new moisture level has been hydrated.

Figure VII gives further relevant observations according to the invention and shows a comparison of the effects of a relatively sharp reduction in the water concentration on the hydrogen content of the recycle gas on the one hand when reforming a naphthenic naphtha over a reforming catalyst with 0.35% by weight of platinum and on the other hand Processing of a paraffinic naphtha at essentially the same humidity conditions derived from the data presented in Figures I and VI. In this test, the partial pressure of water was approximately 0.24 mm Hg during the first 95 days of operation and then the water content was reduced to approximately 0.08 mm Hg. The measured values provided with circles indicate the hydrogen contents that were obtained when reforming a naphthenic naphtha charge with a content of 48% paraffins to give a reformate product with an octane number of 100.0. The dashed line drawn for comparison shows the hydrogen contents obtained from FIGS. I and VI when reforming a paraffinic naphtha with a content of 70 paraffins to give a reformate product with an octane number of 100.0. This comparison makes it clear that a very substantial and different effect on the hydrogen purity of the recycle gas stream at processing of the two different Naphthabeschickungen from the time at which the water content is reduced in the above manner, occurs.

Claims (6)

Claims 1. A method for reforming hydrocarbons in the naphtha boiling range at a pressure below about 28.1 atmospheres (400 psig) and suitable temperature conditions in the presence of a platinum reforming catalyst using a recycle stream combined with the hydrocarbons to be reformed, according to Patent 1 20? 534, characterized in that a platinum reforming catalyst containing less than about 0.45 wt.% Platinum is used and the amount of moisture in the incoming material is controlled so that the moisture level of the process is kept in equilibrium and a high hydrogen purity of the return flow can be maintained. 2. The method according to claim 1, characterized in that the Amount of combined moisture in the inflowing material so that the Water partial pressure of the effluent from the process in the range 0.1-0.2 mm Hg lies. 3. The method according to claim 1 or 2, characterized in that the Amount of water dispersed in the recycle stream fed to the process is, at a value corresponding to a water partial pressure of 0.08 to 0.166 mm Hg 'holds. 4. The method according to any one of claims 1-3, characterized in that the amount of water is regulated so that the hydrogen purity of the recycle stream is at least comparable to that obtained with a reforming catalyst containing at least 0.6 % by weight of platinum can. 5. The method according to any one of claims 1-4, characterized in that the recycle stream recovered from effluent prior to merging with feed for the process to a moisture content below 5 parts-per-million and preferably does not dry more than 2 parts-per-million water. 6. The method according to any one of claims 1-5, characterized in that water is introduced into the recycle stream in order to maintain the desired amount of water in the process.