Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By contact with solid sorbent
Reexamination Certificate
1999-02-04
2002-03-05
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By contact with solid sorbent
C585S803000, C585S820000, C585S822000, C585S826000, C585S737000, C585S738000, C208S351000, C208S31000R, C208S31000R
Reexamination Certificate
active
06353144
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a chromatographic separation process for producing three effluents which are respectively rich in straight chain paraffins, in mono-branched paraffins, and in di-branched and tri-branched paraffins possibly with naphthenic and/or aromatic compounds, from C5-C8 cuts or intermediate cuts (C5-C7, C6-C8, C7-C8, C6-C7, C7 or C8), comprising paraffinic and possibly naphthenic and/or aromatic hydrocarbons and in some cases olefinic hydrocarbons.
The separation process of the invention uses a separation zone operating by adsorption. The process is suitable for liquid or gas phase operation. The separation zone of the invention contains at least one adsorbent which operates by preferentially adsorbing straight chain paraffins, mono-branched paraffins to a lesser extent and finally, multi-branched paraffins and naphthenic and/or aromatic compounds which may be present, to a minor extent. The separation process of the invention is particularly suitable when coupled with the hydro-isomerization process described in the patent application entitled “High octane number gasolines and their production using a process associating hydro-isomerization and separation”, filed Nov. 25, 1997 by the present Assignee, since it enables straight chain and mono-branched paraffins to be selectively recycled, necessary for paraffins containing at least 7 carbon atoms.
When the feed for the process comprises a C5 cut, isopentane from that cut can either be separated using the process of the invention with the mono-branched paraffins or the multi-branched paraffins depending on the implementation selected, or it can be extracted from the streams traversing the process using at least one deisopentanizer located upstream and/or downstream of the separation unit. In the latter case, the isopentane can act as an eluent in the chromatographic separation step.
BACKGROUND OF THE INVENTION
Increasing environmental constraints have resulted in the removal of lead compounds from gasoline, effectively in the United States and Japan and becoming general in Europe. Aromatic compounds, the main constituents of reformed gasolines, and isoparaffins produced by aliphatic alkylation or isomerization of light gasoline, initially compensated for the octane number loss resulting from removing lead from gasoline. Subsequently, oxygen-containing compounds such as methyl tert.-butyl ether (MTBE) or ethyl tert.-butyl ether (ETBE) were introduced into the fuels. More recently, the known toxicity of compounds such as aromatic compounds, in particular benzene, olefins and sulphur-containing compounds, as well as the desire to reduce the vapour pressure of the gasolines, led the United States to produce reformulated gasolines. As an example, the maximum amounts of olefins, aromatic compounds and benzene in gasoline distributed in California in 1996 were respectively 6% by volume, 25% by volume, and 1% by volume. Regulations are less severe in Europe, but nevertheless there is a distinct tendency, to reduce to a similar level the maximum benzene, aromatic compound and olefin amounts in gasoline which is produced and sold.
Gasoline pools contain a plurality of components. The major components are reformed gasoline, which normally comprises between 60% and 80% by volume of aromatic compounds, and catalytic cracking (FCC) gasoline which typically contains 35% by volume of aromatic compounds but provides the majority of olefinic and sulphur-containing compounds present in the gasoline. The other components can be alkylates, with neither aromatic compounds nor olefinic compounds, light gasolines which may or may not be isomerized, which contain no unsaturated compounds, oxygen-containing compounds such as MTBE, and butanes. Since the aromatic compound content is not reduced below 30% or 40% by volume, the contribution of reformates to gasoline pools will remain high, typically 40% by volume. Increased severity as regards the maximum admissible amount of aromatic compounds to 20-25% by volume will result in a reduction in the use of reforming, and as a result the need to upgrade C7-C10 straight run cuts by routes other than reforming. Upgrading by hydro-isomerization is one possible route, as described in the patent application entitled “High octane number gasolines, and their production using a process associating hydro-isomerization and separation”, filed Nov. 25, 1997 by the present Assignee. The hydro-isomerization process leads to the formation of multi-branched compounds from low octane number compounds. It can only be used to recycle straight chain and mono-branched C7-C10 paraffins, since the hydro-isomerization reaction is equilibrated and low octane number paraffins cannot be sent to the gasoline pool. Further, different hydro-isomerization conditions must be employed for those isomeric paraffins to avoid cracking the most highly branched paraffins. These two points justify research for separation processes which can produce three distinct effluents, respectively an effluent which is rich in straight chain paraffins, an effluent which is rich in mono-branched paraffins and an effluent which is rich in multi-branched paraffins and possibly in naphthenic and/or aromatic compounds.
The use of adsorption separation processes to separate straight chain, mono-branched and multi-branched paraffins has already been the subject of a number of patents (for example U.S. Pat. Nos. 4,717,784, 4,956,521 and 5,233,120, BE-A-891 522, French patent FR-A-2 688 213, U.S. Pat. Nos. 5,055,633, 4,367,364 and 4,517,402). However, those patents only concern a light C5-C6 fraction, and, further, only concern the separation of those distillation cuts into two effluents, one with a low octane number and the other with a high octane number.
Thus, U.S. Pat. Nos. 4,210,771 and 4,709,116 describe separating straight chain paraffins from a C5-C6 naphtha cut using an adsorbent known as calcium 5A zeolite. Further, U.S. Pat. No. 4,367,364 describes this same separation carried out using silicalite (U.S. Pat. No. 4,061,724). Similarly, French patent application FR-A-2 496 486 describes a chromatographic type process which enables the same separation to be carried out using a type A, X, Y or ZSM-5 zeolite. The process considered enables any gaseous feed composed of more than two groups of analogous constituents to be treated and leads to the production of two effluents. That process is characterized in that during the first step, the gas mixture to be treated is injected until the adsorbent is saturated then, after stopping continuous injection of the gas mixture, a vector gas which may be nitrogen, helium or hydrogen or a mixture of one of those non adsorbable inert gases is injected in a second step with a maximum of 40% of the gas injected in the first step. That process enables an enriched fraction containing the purified adsorbed group of constituents and a fraction containing the other groups of constituents of the mixture to be successively recovered from the column outlet. Such a process is particularly suitable for fractionating a C5-C6 cut into two fractions as shown in the examples of patent application FR-A-2 496 486. In that case, the process produces two gaseous streams, the first being rich in straight chain paraffins, and the second being rich in branched paraffins (mono-branched and multi-branched), the two effluents being diluted in an effluent selected from the following three non adsorbable inert gases: nitrogen, helium and hydrogen.
The separation processes described in those various patents are often coupled with a process for isomerizing straight chain paraffins since they have a low octane number.
Similarly, some patents (such as U.S. Pat. Nos. 4,717,784 and 5,055,633) describe processes for separating straight chain paraffins and mono-branched paraffins from a C5-C6 cut. Such straight chain and mono-branched paraffins constitute the low octane number pool, while multi-branched paraffins constitute the high octane number pool. Those patents underline the importance of using adsorbents such as ferri
Bailly Michel
Clause Olivier
Jullian Sophie
Ragil Karine
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Nguyen Tam M.
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