Mineral oils: processes and products – Chemical conversion of hydrocarbons – Reforming
Reexamination Certificate
2001-07-02
2003-11-25
Norton, Nadine G. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Reforming
C208S134000, C208S133000, C208S138000, C208S014000, C208S066000, C585S648000, C585S650000, C585S651000, C585S518000, C585S700000, C585S940000
Reexamination Certificate
active
06652737
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for treating naphtha and making light olefins from the treated naphtha. In particular, this invention relates to the use of a naphthene ring opening catalyst to pretreat naphtha feed, then subjecting the ring opened naphtha to a catalytic cracking process to form light olefin product.
BACKGROUND OF THE INVENTION
There is an increasing demand for light (i.e., C
2
to C
4
) olefin products such as ethylene and propylene, which are useful in polymer processes such as polymerization. The demand for light olefins is growing steadily and is expected to continue growing for the foreseeable future. Olefins are formed in a variety of hydrocarbon conversion processes. Steam cracking and catalytic cracking of naphtha feed are examples of processes to obtain light olefin product. For example, U.S. Pat. No. 5,993,642, discloses hydrocarbon conversion processes using zeolite bound zeolite catalysts. One such process involves the catalytic cracking of a naphtha feed to produce light olefins at typical temperatures of from about 500° C. to about 750° C.
U.S. Pat. No. 5,770,042 discloses a process which includes ring opening naphtha feed to convert naphthenes in the feed to paraffins. A non-acidic catalyst is used for ring opening, and the paraffins are subsequently isomerized over an acidic catalyst to an isoparaffin product.
The known procedures are either not concerned with producing light olefin in the main product, or they are limited in the amount of olefin product that can be made. Low conversion to light olefins is believed to result at least in part from the high naphthene and aromatics concentrations present in the naphtha feed since these components do not easily convert into desirable light olefin products. There is, therefore, a need for processes for forming light olefin products from naphthas containing naphthenes and aromatics.
SUMMARY OF THE INVENTION
In one embodiment, the invention relates to a method for treating naphtha, making olefin product from the treated naphtha, and the products associated therewith. The method comprises contacting a naphtha feed containing naphthene ring-containing compounds with a catalytically effective amount of catalyst capable of opening a ring at a teriary bond and containing at least one Group VIII metal. Preferably the group VIII metal is Ir.
In another embodiment, it is preferred that the naphtha feed is contacted with a catalytically effective amount of a polymetallic catalyst, preferably a polymetallic catalyst comprising Ir under catalytic conversion conditions. The polymetallic catalyst more preferably comprises Ir in combination with at least one metal selected from the group consisting of Pt, Rh and Ru, and the conditions are effective to ring open the naphthene rings and form a ring opened product.
In preferred embodiments, the Ir is present in a range of from about 0.3 to about 2.0 wt. %. It is also preferred that the Pt, Rh, or Ru be present in a range of from about 0.001 to about 2.0 wt. %. In a particularly preferred embodiment, the Ir is combined with Pt.
The naphthene ring opening catalyst may be supported on alumina, silica, zirconia, titania, any inorganic refractory oxide, or a combination thereof. Generally, low acidity supports are preferred, and in this regard the support may be modified by the addition of an alkali or alkaline earth metal, preferably Ba.
Ring opening is preferably carried out at a temperature of from about 150° C. to about 400° C.; a total pressure from about 0 to about 3,000 psig, a liquid hourly space velocity from about 0.1 to about 10 V/V/Hr, a hydrogen treat gas rate from about 500 to about 10,000 standard cubic feet per barrel (SCF/B); or various combinations thereof. The liquid hourly space velocity is based on the volume of feed per volume of catalyst per hour, i.e., V/V/Hr.
The preferred naphtha feed to be treated has an initial and final boiling point within the range of about 0° C. to about 230° C. It is preferably provided at a sulfur content of less than 1 ppm.
The ring opened product is particularly effective for use as feed to a catalytic cracking unit. In this regard, the ring opened product is contacted with a catalytically effective amount of a catalytic cracking catalyst under effective cracking conditions to form an olefin product. Preferred cracking catalysts comprise large or medium pore zeolites. The olefin product is particularly high in ethylene and propylene content.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment, the invention relates to a process capable of providing a large quantity of light olefin product from a naphtha feed. The light olefin product is particularly high in ethylene and propylene content. The process involves ring opening the naphthenic rings of naphthenic ring-containing compounds in the naphtha feed to form paraffins.
As used herein, a naphthene or a naphthenic ring-containing composition refers to a cycloalkane or a composition containing at least one cycloalkane ring in its structure. For example, the term can refer to either a C
5
or C
6
ring-membered cycloparaffin. The cycloparaffin can also include various side chains, particularly one or more alkyl side chains of 1-10 carbons. In addition the cycloparaffin can be attached or fused to other ring structures, forming two or three membered ring compounds. The additional ring members can be saturated or unsaturated, as long as at least one ring of the complete structure contains a tertiary carbon. The ring structure containing the tertiary carbon is preferably saturated. Such a structure may be represented by one or more compounds selected from the group of naphthalenes, indenes, fluorenes, phenanthrenes, anthracenes, acenaphthalenes, and biphenylenes, including partially and completely saturated analogs of such compounds, wherein at least one ring of the compound contains a tertiary carbon, and preferably, the tertiary carbon-containing ring is saturated.
Naphtha feedstream for ring opening will typically contain a mix of hydrocarbons having one or more of the naphthene ring-containing compositions, and the naphthene ring-containing compositions preferably contain at least one alkyl substituent. Preferably, the feedstream will comprise at least about 5 vol. % of at least one naphthenic ring-containing compound more preferably at least about 25 wt. %, most preferably at least about 50 wt. %. Typically the feedstream will comprise from about 5 to about 85 vol. % of at least one naphthenic ring-containing compound.
In a more preferred embodiment, the hydrocarbon containing the naphthene ring compositions which are to be opened will include C
5
naphthene ring compounds which do not include additional ring members. Non-limiting examples of these compounds include cyclopentane, methylcyclopentanes, ethylcyclopentanes, propylcyclopentanes, butylcyclopentanes, and pentylcyclopentanes. It is also preferred that the hydrocarbon containing the naphthene ring compositions which are to be opened include C
6
ring compounds which do not include additional ring members. Non-limiting examples of these compounds include cyclohexane, methylcyclohexanes, ethylcyclohexanes, propylcyclohexanes, butylcyclohexanes, and pentylcyclohexanes. The naphtha feeds used in this invention typically further comprise paraffins, naphthenes, and aromatics, and may comprise olefins and numerous other hydrocarbon compounds.
Naphtha feeds may be obtained from any appropriate source. Non-limiting examples of naphthas which may be utilized include straight-run naphthas, particularly light straight run naphtha, natural gasoline, synthetic naphthas, thermal gasoline, catalytically cracked gasoline, partially reformed naphthas or raffinates from extraction of aromatics. The preferred naphtha feed is a light straight run naphtha. The feed is characterized by having an initial and final boiling point within the boiling point range of a full-range naphtha, preferably an initial and final boiling point within the range of from about 0° C. to about 230° C. It is preferred that the fe
Chen Tan-Jen
Ellis Edward S.
Klein Darryl P.
Martens Luc R.
Touvelle Michele S.
ExxonMobil Research and Engineering Company
Hughes Gerard J.
Kliebert Jeremy J.
Norton Nadine G.
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