Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By double-bond-shift isomerization
Reexamination Certificate
2000-12-12
2002-12-17
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By double-bond-shift isomerization
C585S670000, C585S671000
Reexamination Certificate
active
06495732
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the selective hydrogenation of diolefins and acetylenic compounds in a olefin rich stream. More particularly the invention relates to a process utilizing a hydrogenation catalyst in a structure to serve as both the catalyst and as a distillation structure for the simultaneous reaction and separation of the reactants and reaction products.
2. Related Art
Mixed refinery streams often contain a broad spectrum of olefinic compounds. This is especially true of products from either catalytic cracking or thermal cracking processes. These unsaturated compounds comprise ethylene, acetylene, propylene, propadiene, methyl acetylene, butenes, butadiene, amylenes, hexenes etc. Many of these compounds are valuable, especially as feed stocks for chemical products. Ethylene, especially is recovered. Additionally, propylene and the butenes are valuable. However, the olefins having more than one double bond and the acetylenic compounds (having a triple bond) have lesser uses and are detrimental to many of the chemical process in which the single double bond compounds are used, for example polymerization. Over the range of hydrocarbons under consideration, the removal of highly unsaturated compounds is of value as a feed pretreatment, since these compounds have frequently been found to be detrimental in most processing, storage and use of the streams.
The C
4
cuts are sources of alkanes and alkenes for paraffin alkylation to produce C
8
gasoline blending components and as feeds for ether production.
The C
5
refinery cut is valuable as a gasoline blending stock or as source of isoamylene to form an ether by reaction with lower alcohols. Tertiary amyl methyl ether (TAME) is rapidly becoming valuable to refiners as a result of the recently passed Clean Air Act which sets some new limits on gasoline composition. Some of these requirements are (1) to include a certain amount of “oxygenates”, such as methyl tertiary butyl ether (MTBE), TAME or ethanol, (2) to reduce the amount of olefins in gasoline, and (3) to reduce the vapor pressure (volatility).
The C
5
's in the feed to a TAME unit are contained in a single “light naphtha” cut which contains everything from C
5
's through C
8
's and higher. This mixture can easily contain 150 to 200 components and thus identification and separation of the products is difficult. Several of the minor components (diolefins) in the feed will react slowly with oxygen during storage to produce “gum” and other undesirable materials. However, these components also react very rapidly in the TAME process to form a yellow, foul smelling gummy material. Thus it is seen to be desirable to remove these components whether the “light naphtha” cut is to be used only for gasoline blending by itself or as feed to a TAME process.
The use of a solid particulate catalyst as part of a distillation structure in a combination distillation column reactor for various reactions is described in U.S. patent Nos.: (etherification) U.S. Pat. Nos. 4,232,177; 4,307,254; 4,336,407; 4,504,687; 4,918,243; and 4,978,807; (dimerization) U.S. Pat. No. 4,242,530; (hydration) U.S. Pat. No. 4,982,022; (dissociation) U.S. Pat. No. 4,447,668; and (aromatic alkylation) U.S. Pat. Nos. 4,950,834 and 5,019,669. Additionally U.S. Pat. Nos. 4,302,356 and 4,443,559 disclose catalyst structures which are useful as distillation structures.
Hydrogenation is the reaction of hydrogen with a carbon-carbon multiple bond to “saturate” the compound. This reaction has long been known and is usually done at super atmospheric pressures and moderate temperatures using a large excess of hydrogen over a metal catalyst. Among the metals known to catalyze the hydrogenation reaction are platinum, rhenium, cobalt, molybdenum, nickel, tungsten and palladium. Generally, commercial forms of catalyst use supported oxides of these metals. The oxide is reduced to the active form either prior to use with a reducing agent or during use by the hydrogen in the feed. These metals also catalyze other reactions, most notably dehydrogenation at elevated temperatures. Additionally they can promote the reaction of olefinic compounds with themselves or other olefins to produce dimers or oligomers as residence time is increased.
Selective hydrogenation of hydrocarbon compounds has been known for quite some time. Peterson, et al in “The Selective Hydrogenation of Pyrolysis Gasoline” presented to the Petroleum Division of the American Chemical Society in September of 1962, discusses the selective hydrogenation of C
4
and higher diolefins. Boitiaux, et al in “Newest Hydrogenation Catalyst”,
Hydrocarbon Processing,
March 1985, presents a general, non enabling overview of various uses of hydrogenation catalysts, including selective hydrogenation of a propylene rich stream and other cuts. Conventional liquid phase hydrogenations as presently practiced required high hydrogen partial pressures, usually in excess of 200 psi and more frequently in a range of up to 400 psi or more. In a liquid phase hydrogenation the hydrogen partial pressure is essentially the system pressure.
U.S. Pat. No. 2,717,202 to Bailey discloses a countercurrent process for the hydrogenation of lard carried out in a plurality of independent vertical chamber using a pumped catalyst under undisclosed pressure conditions. U.S. Pat. No. 4,221,653 to Chervenak et al discloses a concurrent hydrogenation for using an ebullating bed at extremely high pressures. UK Patent Specification 835,689 discloses a high pressure, concurrent trickle bed hydrogenation of C
2
and C
3
fractions to remove acetylenes.
U.S. Pat No. 5,087,780 to Arganbright disclosed a process for the hydroisomerization of butenes using an alumina supported palladium oxide catalyst arranged in a structure for use as both the catalyst and distillation in a catalytic distillation reactor. The hydrogenation of dienes was also observed under high hydrogen partial pressure, in excess of 70 psia, but not at around 10 psia.
It is an advantage of the present process that the diolefins (dienes) and acetylenic compounds contained within the hydrocarbon stream contacted with the catalyst are converted to olefins or alkanes with very little if any formation of oligomers or little if any saturation of the mono-olefins.
SUMMARY OF THE INVENTION
The present invention comprises feeding a hydrocarbon stream containing highly unsaturated compounds which comprise diolefins and acetylenes along with a hydrogen stream at an effectuating hydrogen partial pressure of at least about 0.1 psia to less than 70 psia, preferably less than 50 psia to a distillation column reactor containing a hydrogenation catalyst which is a component of a distillation structure and selectively hydrogenating a portion of the highly unsaturated compounds. Within the hydrogen partial pressures as defined no more hydrogen than necessary to maintain the catalyst (most likely to reduce the catalyst metal oxide and maintain it in the hydride state) and hydrogenate the highly unsaturated compounds is employed, since the excess hydrogen is usually vented. This preferably is a hydrogen partial pressure in the range of about 0.1 to 10 psia and even more preferably no more than 7 psia. Optimal results have been obtained in the range between 0.5 and 5 psig hydrogen partial pressure.
The hydrocarbon stream typically comprises C
2
to C
9
aliphatic compounds, which may be narrow cuts or include a range of carbon content. The invention is the discovery that a hydrogenation carried out in a catalytic distillation column requires only a fraction of the hydrogen partial pressure required in the liquid phase processes which are the form of prior commercial operation for this type of stream, but give the same or better result. Thus the capital investment and operating expense for the present hydrogenation are substantially lower than prior commercial operations.
Without limiting the scope of the invention it is proposed that the mechanism that produces the effectiveness of the prese
Arganbright Robert P.
Gildert Gary R.
Hearn Dennis
Jones, Jr. Edward M.
Smith, Jr. Lawrence A.
Catalytic Distillation Technologies
Griffin Walter D.
Johnson Kenneth H.
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