Process for reforming petroleum hydrocarbon stocks

Details Process for reforming petroleum hydrocarbon stocks Process for reforming petroleum hydrocarbon stocks

1992-06-30

2004-05-25

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Reforming

C208S134000, C208S135000, C208S137000, C208S063000, C208S064000, C208S065000

Reexamination Certificate

active

06740228

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a process for reforming a petroleum hydrocarbon stream, particulary hydrodesulfurized highly paraffinic naphtha, wherein the naphtha is reformed over at least one catalyst bed comprising a particular catalyst comprising zeolite KL impregnated with platinum, in which the zeolite crystals have a “hockeypuck” or “coin” shape. The catalyst will hereinafter be referred to as a Pt/KL catalyst.
Use of the Pt/KL catalyst as described results in a significant increase in the aromatic content of the product, minimal cracking of the light naphtha and a consequent improvement in the available octane and hydrogen.
FIELD OF THE INVENTION
The reforming of petroleum hydrocarbon streams is one of the most important petroleum refining processes that may be employed to provide high octane hydrocarbon blending components for gasoline. The process is usually practiced on a straight run naphtha fraction which has been hydrodesulfurized. Straight run naphtha is typically highly paraffinic in nature but may contain significant amounts of naphthenes and minor amounts of aromatics and/or olefins. In a typical reforming process, the reactions include dehydrogenation, isomerization and hydrocracking. The dehydrogenation reactions typically will be the dehydroisomerization of alkylcyclopentanes to aromatics, the dehydrogenation of paraffins to olefins, the dehydrogenation of cyclohexanes to aromatics and the dehydrocyclization of acyclic paraffins and acyclic olefins to aromatics. The aromatization of the n-paraffins to aromatics is generally considered to be the most important because of the high octane rating of the resulting aromatic product. The isomerization reactions included isomerization of n-paraffins to isoparaffins, the hydroisomerization of olefins to isoparaffins, and the isomerization of substituted aromatics. The hydrocracking reactions include the hydrocracking of paraffins and hydrodesulfurization of any sulfur compounds remaining in the feed stock. With lighter naphtha streams (i.e. containing C6 or C7 hydrocarbons), it is often desirable to avoid hydrocracking because of the resulting low carbon number of gaseous products which result.
It is well known that several catalysts are capable of reforming petroleum naphthas and hydrocarbons that boil in the gasoline boiling range. Examples of known catalysts useful for reforming include platinum (optionally with the addition of rhenium or iridium) on an alumina support, platinum on zeolites such as type X and Y (provided the reactants and products are sufficiently small to flow through the pores of the zeolites), platinum on intermediate pore size zeolites as described in U.S. Pat. No. 4,347,394 and platinum on cation exchanged type L zeolites.
While zeolite L catalysts, usually in their hydrogen form, have been employed as catalytic dewaxing catalyst and in other applications, they are particularly useful in reforming because they decrease the amount of hydrocracking which occurs during reforming. For example, U.S. Pat. No. 4,104,320 discloses that the use of zeolite L as a catalyst support increases the selection of the reaction for producing aromatic products. However, this improvement is made at the expense of catalyst life. This catalyst must frequently be regenerated, for example, by subjection to hydrogen treatment, oxidation, oxychlorination, calcining, water treatment and reduction with hydrogen. European Patent Publication EP-A-96479 describes a highly crystalline zeolite L material having a cylindrical morphology. This has improved catalyst life for dehydrocyclization reaction over the conventionally prepared zeolite L disclosed in U.S. Pat. No. 3,216.789.
U.S. patent application Ser. No. 426,211 filed Sep. 28, 1982, to A. Cohen entitled “Improved Zeolite L Catalyst for Reforming” now U.S. Pat. No. 4,448,891 discloses treating a zeolite L material with an alkali solution having a pH of at least 11 prior to calcining the formed catalyst to improve the dehydrocyclization activity of the resulting product. Finally, Belgian Patents Nos. 895,778 and 895,779 disclose use of a barium-exchanged zeolite L catalyst for high yields in reforming, dehydrocyclization, dealkylation, and dehydroisomerization.
The typical reforming catalyst is a multi-functional catalyst which contains a metal hydrogenation-dehydrogenation component which is usually dispersed on the surface of a porous inorganic oxide support, notably alumina. Platinum has been widely commercially used in recent years in the production of reforming catalysts, and platinum on alumina catalysts have been commercially employed in refineries for the past four decades. In the last decade, additional metallic components have been added to platinum as promoters to further the activity or selectivity, or both, of the basic platinum catalyst, e.g. iridium, rhenium, tin and the like. Some catalysts possess superior activity, or selectivity, or both, as contrasted with other catalysts. Platinum-rhenium catalyst, by way of example, possess improved life and high selectivity in contrast to platinum catalysts. Selectivity is generally defined as the ability of the catalyst to product yields of C
5
+ liquid products with concurrent low production of normally gaseous hydrocarbons, e.g. methane, and coke.
In a reforming operation, one or a series of reactors, or a series of reaction zones, are employed. Typically a series of reactors are employed, e.g., 3 or 4 reaction vessels, which constitute the heart of the reforming unit. Although there are cases where split feed operations are practised, these will be discussed at length below. The typical reaction scheme involves a set of serial feed reactors.
It is known that the amount of coke produced in an operating run increases progressively from a leading reactor to subsequent rectors as a consequence of the different types of reactions that predominate in the several different reactors. The sum total of reforming reactions occurs as a continuum between the first and last reactor of the series. The reactions which predominate among the several reactors differ principally based upon the nature of the feed and the temperature employed within the individual reactors. In the initial reaction zone, which is maintained at a relatively low temperature, the primary reaction involves dehydrogenation of naphthenes to produce aromatics. The isomerization of naphthenes, particularly C
5
+ and C
6
naphthenes, also occurs to a considerable extent. Most of the other reforming reactions also occur, but only to a lesser extent. There is relatively little hydrocracking, and very little olefin or paraffin dehydrocyclization occurring in the first reactor.
Typically, the temperature within the intermediate reactor zones is maintained at a somewhat higher level than in the first or lead reactor of the series. Primary reactions in these intermediate reactors involve the isomerization of naphthenes and paraffins. Where, for instance, there are two reactors placed between the first and last reactor in series, the principal reaction in these middle two reactors involves isomerization of naphthenes, normal paraffins and isoparaffins. Some dehydrogenation of naphthenes may, and usually does occur, at least within the second of the four reactors. The amount of hydrocracking increases in the second reactor as does the amount of olefin and paraffin dehydrocyclization compared with the amount of such reactions occurring in the first reactor.
The third reactor of the series, or second intermediate reactor, is generally operated at a moderately higher temperature than the second reactor. The naphthene and paraffin isomerization reactions continue as the primary reaction in the reactor, but there is very little naphthene dehydrogenation. There is a further increase in paraffin dehydrocyclization, and more hydrocracking. At this stage, few if any alkylcyclopentanes or alkylcyclohexanes will be detected in the process stream since they will previously have been aromatized or hydrocracked.
In the last reaction zone, which

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