Novel Catalytic Reforming Process With A Recycle Of The Reduction Effluent Upstream Of The First Reactor And A Recycle Of The Recycle Gas To The Last Reactor Or Reactors In The Series

CATEGORY: GASOLINE
PATENT
Novel Catalytic Reforming Process With A Recycle Of The Reduction Effluent Upstream Of The First Reactor And A Recycle Of The Recycle Gas To The Last Reactor Or Reactors In The Series
United States Patent Application 20120000822
Inventors:S anchez, Eric (Saint Genis Laval, FR)
Application Number: 13/155560
Publication Date: 01/05/2012
Assignee: IFP ENERGIES NOUVELLES (Rueil-Malmaison Cedex, FR)
Abstract:
The present invention describes a process for regenerative reforming of gasolines, characterized by recycling at least a portion of the effluent from the catalyst reduction zone to the inlet to the feed/effluent exchanger that can pre-heat the feed, the other portion possibly being recycled to the head of the first reactor, and by recycling gas from the recycle compressor to the head of the penultimate reactor of the series. This disposition can significantly improve the production of reformate and the hydrogen balances of the unit.
FIELD OF THE INVENTION
The invention relates to the field of catalytic reforming of gasolines, and more generally to moving bed processes. More specifically, it is applicable to regenerative reforming or to the production of BTX (benzene, toluene, xylenes) with continuous catalyst regeneration.
The process for the catalytic reforming of gasolines employing a reaction zone comprising a series of 3 or 4 reactors in series, operating in moving bed mode, and has a catalyst regeneration zone which itself comprises a certain number of steps, including a step for combustion of coke deposited on the catalyst in the reaction zone, an oxychlorination step, and a final step for reduction of catalyst in hydrogen. After the regeneration zone, the catalyst is re-introduced to the head of the first reactor of the reaction zone.
More precisely, the invention concerns a novel process for catalytic reforming of gasolines comprising a recycle of effluent from the catalyst reduction step upstream of the first reactor of the reaction zone and injection of recycled hydrogen to the last or penultimate reactor in order to maintain a partial pressure of hydrogen which is higher on said last reactors and thus to limit deactivation of the catalyst at the end of the reaction zone.
This novel disposition has a number of advantages:

it reduces or even eliminates the re-introduction of water into the reaction system;
it encourages the reactions of naphthene dehydrogenation and dehydrocyclization of paraffins contained in the feed, i.e. those occurring in the first two reactors due to a reduction in the partial pressure of hydrogen in those two reactors, a reduction which is thermodynamically favourable to the reactions in question;
it also favourably modifies the distribution of hydrogen between the various reactors by increasing the H2/HC ratio on the last or last two reactors which are precisely those in which coke has a preferential tendency to form.
EXAMINATION OF THE PRIOR ART
According to the prior art, the reduction effluent from a catalytic reforming unit is generally sent either to the intake of the re-contacting compressor of the hydrogen purification section or to the “fuel gas” grid of the refinery, i.e. to the grid for the gas used as a fuel in the various units or furnaces of the refinery.
The reduction effluent may also be sent in its entirety or in part to the inlet to the separator drum in order to adjust the quantity of water in the recycle gas.
The flowcharts for the prior art purification zone are not modified by the present invention which essentially concerns the reaction zone.
Patent FR 2 801 604 describes a process for the production of aromatics using a catalyst moving in a moving bed, which process comprises at least two steps characterized by a certain (H2)/(HC) ratio, H2 representing the quantity of hydrogen introduced into said step and HC representing the quantity of feed entering said step.
In the patent cited above, the catalyst reduction step is also characterized by certain values for the ratio H2/HC. The values for the H2/HC ratios for the two reaction steps and that of the catalyst reduction step are linked by an inequality. However, in all cases, the recycled hydrogen is sent to the first reactor of the reaction section and thus does not result in favouring the reactions sought in this process which are essentially the reactions of dehydrogenation of naphthenes or the dehydrocyclization of paraffins greatly favoured by low partial pressures of hydrogen.
Patent FR 2 801 605 describes a process for the production of aromatics using a moving bed catalyst which comprises a step for reduction of said catalyst in the presence of a recycle gas introduced in a quantity such that the quantity of pure hydrogen supplied to the catalyst reduction step is in the range 1 to 10 kg/kg of catalyst.
Patent application FR 09/02802 describes a circuit for recycling effluent from the reduction zone to the last reactor or reactors of the reaction zone. This recycle does not modify the partial pressure of hydrogen in the first reactor, which is precisely the action sought in the present application.
None of those three documents, which may be considered to represent the closest prior art, discloses in a precise manner the re-introduction of effluent derived from the catalyst reduction step to the head of the first reactor and/or the injection of effluent derived from the separator drum of the recycle compressor (RCY), generally known as the recycle gas, to the head of the last or penultimate reactor of the reaction zone of a catalytic gasoline reforming unit. The combination of these two streams results in an improvement in the unit yields, in particular as regards the reformate defined as hydrocarbons containing more than 4 carbon atoms and denoted C4+.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 represents a general view of a catalytic reforming unit comprising 4 reactors in series and a catalyst regeneration zone.
The catalyst circuit is marked in thicker lines.
FIG. 1 shows the recycle of the reduction effluent 4 in part to the head of the first reactor and in part to the inlet to the feed/effluent exchanger as well as the re-introduction of recycle gas 7 from the recycle compressor RCY to the head of the last (R4) and penultimate (R3) reactor.
BRIEF DESCRIPTION OF THE INVENTION
The present invention may be defined as a process for catalytic reforming of a gasoline with a distillation range in the range 60° C. to 250° C. employing a moving bed catalytic reforming unit comprising at least four reactors in series, and a regeneration zone for said catalyst, in which the effluent from the catalyst reduction step forming part of the catalyst regeneration zone is recycled in part to the inlet to the feed/effluent exchanger E1, with the other portion being recycled to the head of the first reactor R1 and in which the gas stream derived from the recycle compressor RCY is sent to the head of the penultimate reactor R3 of the reaction section.
In accordance with a first variation of the present invention, the gaseous effluent from the reduction step is sent in its entirety to the inlet to the feed/effluent exchanger.
In accordance with a second variation of the present invention, the gaseous effluent from the reduction step is sent in its entirety to the head of the first reactor.
In accordance with a third variation of the invention, the gaseous stream derived from the recycle compressor RCY is sent in its entirety to the head of the third reactor.
A variation which combines any one of variations 1 and 2, concerning the gaseous reduction effluent, with variation 3 which concerns the gaseous stream deriving from the recycle compressor RCY, for example variation 1 and variation 3, or variation 2 and variation 3, fall within the scope of the invention.
More precisely, in a first configuration of the process for catalytic reforming of a gasoline in accordance with the present invention, the gaseous reduction effluent 4 is sent in its entirety to the head of the first reactor R1, and the effluent 7 from the recycle compressor RCY is sent in its entirety to the penultimate reactor R3.
In a second configuration of the process for catalytic reforming of a gasoline in accordance with the present invention, the gaseous reduction effluent 4 is sent in its entirety to the inlet to the feed/effluent exchanger E1, and the effluent 7 from the recycle compressor RCY is sent in its entirety to the penultimate reactor R3.
Several technical advantages result from sending a portion of the reduction effluent to the inlet to the feed/effluent exchanger and a portion to the head of the first reactor.
Firstly, the reduction in the partial pressure of hydrogen in the first reactor results in a substantial increase in the production of aromatics and hydrogen with respect to the conventional prior art layout. In fact, the reduction in the H2/HC ratio on reactor R1 can improve the naphthene dehydrogenation reactions in said reactors and reduce cracking of long chain paraffins.
Further, the reduction in the partial pressure of hydrogen on the first reactor R1 results in a reduction in the consumption of the recycle compressor RCY and finally in a reduction in the size of said compressor because of the new discharge pressure thereof and/or in the reduction in the recycle ratio. The discharge pressure of the recycle compressor RCY is in fact substantially reduced compared with the prior art. Said discharge pressure is substantially equal to the inlet pressure of the first reactor in the prior art and equal to the pressure of the last or penultimate reactor for the process of the invention.
Further, recycling the effluent from the recycle compressor RCY arriving at the head of the last (R4) or penultimate (R3) reactor means that the H2/HC ratio in these reactors in which the major portion of the coke is produced can be substantially increased.
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