Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Plural hydrogenation stages
Reexamination Certificate
2001-06-28
2004-02-17
Yildirim, Bekir L. (Department: 1764)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Plural hydrogenation stages
C585S258000, C585S271000, C585S273000, C585S275000, C585S259000, C208S144000
Reexamination Certificate
active
06693225
ABSTRACT:
SUBJECT MATTER OF THE INVENTION
The present invention proposes a process for hydrogenating a cut containing hydrocarbons comprising highly unsaturated molecules containing at least two double bonds or at least one triple bond such as hydrocarbon molecules, for example 1,3-butadiene, 1,2-butadiene, vinyl acetylene and hydrocarbon molecules containing 4 or more carbon atoms such as 1-butene, 2-butene, n-butane, isobutane and/or isobutene. More particularly, this process is applicable to hydrogenating cuts containing hydrocarbons, in particular butadiene. The reaction can be controlled to produce a high selectivity for butene in the product without losing isobutene and minimising complete hydrogenation of the butenes to butane. Four particular implementations are proposed for the process of the invention: the first and second have a very good selectivity for butene with a lower butadiene conversion (between 80% and 100%); the third and fourth can achieve a butadiene conversion of close to 100%.
PRIOR ART
International patent WO-A-93/21137, corresponding to U.S. Pat. No. 5,281,753, proposes a process for selective hydrogenation and simultaneous isomerisation of hydrocarbons in a mixture containing unsaturated molecules (in particular di-olefins) and containing 4 or more carbon atoms. Hydrogenation is carried out in the presence of gaseous hydrogen through a catalytic reactor with fixed beds. The hydrogen is introduced into the reactor through at least three successive points, gradually increasing the mole ratio of hydrogen to the fraction of unsaturated molecules. That patent teaches that such a ratio should be increased from a sub-stoichiometric ratio at the first injection point to a stoichiometric ratio at the second point, and finally to a ratio that is in excess with respect to the stoichiometry at the last injection point. One particular application described in that patent concerns hydrogenating butadiene in a hydrocarbon cut also containing butane and butenes. That patent teaches that the catalytic beds are separated from each other by beds of inert materials and hydrogenation is carried out as described, for example, in the flow chart of
FIG. 1
in feed and hydrogen upflow mode. No mention is made of recycling a portion of the hydrogenated product and similarly, the excess of hydrogen introduced in particular to the third bed is not specified.
U.S. Pat. No. 3,764,633 describes a process for isomerising mono-olefins containing a double bond disposed at the end of a molecule containing at least 4 carbon atoms and selective simultaneous hydrogenation of polyunsaturated compounds such as di-olefins or acetylenic compounds contained in the treated hydrocarbon cut. That patent teaches that the process can use a plurality of successive beds. In that case, hydrogen injection is staged between the different beds, but the total proportion of hydrogen injected into the first bed is in the range 75% to 98%. The hydrogen is preferably introduced with the feed after vaporising that feed. The quantity of hydrogen introduced decreases from the first catalyst bed to the last catalyst bed. Each reactor contains, for example, two beds of catalyst separated by a partition, the hydrogen being introduced upstream of each of the beds and into each bed. The effluent containing the hydrocarbons and hydrogen leaving the first bed is not sent directly to the second bed but leaves the reactor and passes into a heat exchanger before being re-introduced into the reactor beneath the partition separating the beds above said second bed. That patent does not teach recycling a fraction of the hydrogenated product and further, when one reactor is operating, the other is in a catalyst regeneration phase.
U.S. Pat. No. 4,260,840 concerns selective hydrogenation of butadiene in a C4 cut. The product contains at least 30% by weight of 1-butene and butadiene in trace amounts. That feed is hydrogenated to minimise 1-butene isomerisation and to minimise hydrogenation of the butenes to butane. No mention is made of staged injection of hydrogen nor of recycling a fraction of the hydrogenated product.
U.S. Pat. No. 4,960,960 describes a process for selective hydrogenation containing two zones that may comprise one bed or two successive beds each possibly being supplied with gaseous feed. That process is not specific to a particular hydrogenation reaction and that patent does not teach the staged introduction of hydrogen upstream of each of the catalyst beds. Finally, that patent teaches that the liquid phase passes into a static distributor contained in the reactor itself, hydrogen arriving via another inlet above that static distributor, and no mention is made of the possibility of using a static mixer to improve mixing of the gaseous hydrogen-containing phase and the liquid hydrocarbon-containing cut.
U.S. Pat. No. 4,469,907, having the same priority as European patent application EP-A-0 087 980, describes a method for hydrogenating a petroleum cut containing unsaturated molecules containing 4 or more carbon atoms using a fixed bed reactor in which hydrogen is injected at 2 or 3 successive points. The authors state that the quantity of hydrogen injected into the 2 or 3 injection point corresponds to a fraction in the range 5% to 100% of the quantity injected at the preceding point. The excess hydrogen over the stoichiometry is in the range 10% to 100%. The conversion or selectivity performance is not specified. That patent does not teach recycling a portion of the hydrogenated product from the first reactor.
EP-A-0 523 482 describes a process for selective hydrogenation of butadiene in the liquid phase alone or in a trickle flow. The treated petroleum feeds contain between 20% and 80% of butadiene. The process comprises two reaction sections: at the outlet from the first zone, the butadiene residue in the product is in the range 0.1% to 20% by weight and at the outlet from the second zone it is in the range 0.005% to 1% by weight. In general, the patent envisages a ratio of 5 between the amount of butadiene at the outlet from the first zone and the amount at the outlet from the second zone. That patent envisages a selectivity for butenes of more than 96%. The operating conditions are: a temperature of 40° C. to 120° C., a pressure of 5 to 50 bars and an hourly space velocity of 0.1 to 30 h
−1
. No mention is made of staged injection of hydrogen into the reactor. That patent teaches recycling a portion of the hydrogenated product and using two separate reactors in series with a quantity of hydrogen supplied to each of the two zones of once to twice the necessary stoichiometric quantity. It does not teach the possibility of recycling a portion of the product leaving the first reactor overhead. The quantity of hydrogenated product that is recycled is not mentioned.
EP-A-0 700 984 describes a process for hydrogenating a hydrocarbon cut containing 2 to 20 carbon atoms containing mono-unsaturated hydrocarbons and at least one polyunsaturated hydrocarbon. The feed to be treated is at least partially in the liquid form and circulates through a reactor containing at least one fixed bed and at least one static mixer located upstream of the outlet section. That patent states that the beds can be staged in the same reactor with the possibility of injecting hydrogen between two beds. Partial recycling of the product can optionally be carried out, but the quantity of recycled product is not defined. Further, that patent does not teach the use of two successive reactors each comprising two catalyst beds, nor in that case recycling a portion of the liquid product from the first reactor obtained after separating out a gas phase and eliminating the aqueous phase it contains.
DESCRIPTION OF THE INVENTION
In its broadest aspect, the present invention concerns a process for hydrogenating a liquid cut containing hydrocarbons and in particular unsaturated molecules containing at least two double bonds or at least one triple bond wherein the unsaturated molecules containing at least two double bonds or at least one triple bond, ar
Boyer Christophe
Coupard Vincent
Debuisschert Quentin
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Yildirim Bekir L.
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