Catalyst Distribution in the Regenerative Reforming Progress

Abstract

The invention concerns a regenerative reforming process in 3 or 4 reforming reactors, wherein: for 3 reactors, the catalyst distribution between the 3 reactors is such that in the range 30% to 36% by weight of catalyst is present in each of the 3 reactors; for 4 reactors: the catalyst distribution between the 4 reactors is such that in the range 22% to 28% by weight of catalyst is present in each of the 4 reactors.

Description

The gasoline reforming process was developed in the 1950s and since then has witnessed major technological advances, often linked to the appearance of new generations of catalysts in three successive stages:

The appearance of a catalyst based on platinum on alumina in the 1950s. The units operated at pressures of the order of 5 MPa and the catalyst was regenerated approximately every 6 months;

Towards the end of the 1960s, bimetallic catalysts appeared which meant that the operating pressure could be reduced to close to 3 MPa;

Finally, at the start of the 1970s, the appearance of continuous catalyst regeneration meant that operating pressures of the order of just 1 MPa could be employed.

Currently, regenerative reforming units operate at pressures of a few bars (1 bar=0.1 MPa) on highly selective catalysts producing a maximum amount of hydrogen. The general tendency which comes out of this evolution is a continued drop in pressure which has a major impact on reformate yields.

Numerous chemical reactions occur in a reforming process.

The principal reaction is the dehydrogenation of napthenes to aromatics; this is the most sought-after chemical family as it favours high octane numbers.

The dehydrocyclization of paraffins to aromatics and the isomerization of paraffins, in particular paraffins containing 5 or 6 carbon atoms, is also sought after since it is also accompanied by an increase in the octane number.

Unwanted reactions, i.e. those which do not increase the octane number, which may be cited include hydrocracking of paraffins and naphthenes as well as coking.

Thermodynamic data show that the equilibrium of various chemical families is displaced towards the aromatics at low pressure, which explains the technological advance in units towards ever lower operating pressures, while maintaining a certain partial pressure of hydrogen which can limit deactivation of the catalyst by coke. Coke is a compound with a high molecular weight, characterized by a low H/C ratio, generally in the range 0.3 to 1.0, which is deposited on the active sites of the catalyst. While the transformation selectivity of hydrocarbons into coke is very low, the amount of coke accumulated on the catalyst may be very high. Typically, for moving bed units, such amounts are in the range 3% to 10% by weight at the outlet from the last reactor.

Two techniques exist in the field of so-called regenerative units:

• • in the first case the reactors are placed side by side;
  • in the second case the reactors are stacked.

In both cases, the effluents from the reactor are re-heated in a furnace before being introduced to the head of the next reactor, since overall the reactions which are taking place are endothermic and the reactors are operated at inlet iso-temperature.

The catalyst distribution, as a % by weight of catalyst, is augmentary in the various reactors in the reforming process of the prior art. In fact, the first reactors are smaller than the last reactors. Thus, the catalyst distribution is augmentary in prior art reforming units. In particular, the weight of catalyst is greater in the last reactor or in the two last reactors compared with the first or two first reactors.

The table below illustrates the prior art catalyst distributions.

Distribution (percentage by weight of catalyst in the reactors)
Reactor 1	Reactor 2	Reactor 3	Reactor 4	Sum
10	15	30	45	100%
12.5	12.5	25	50	100%
10	15	25	50	100%
20	30	50	—	100%

The present invention concerns a fixed bed or moving bed, preferably moving bed, process for regenerative reforming of a feed comprising paraffinic, naphthenic and aromatic hydrocarbons in which the catalyst distribution between the various reactors is particular. It has been discovered in the context of the present invention that the performance of the reforming process can be improved by a flat distribution of the catalyst.

PRIOR ART

U.S. Pat. No. 5,858,205 describes a reforming process with 3 or 4 reactors. In the case of 3 reactors, the catalyst distribution is augmentary. The three reactors respectively comprise 20%, 30% and 50% of the catalyst. In the case of 4 reactors, the reactors respectively comprise 10%, 15%, 25% and 50% of the catalyst. The catalyst distribution proposed in that patent differs from the flat catalyst distribution of the invention both for 3 reactors and for 4 reactors.

BRIEF DESCRIPTION OF THE INVENTION

The invention concerns a regenerative reforming process in 3 or 4 reforming reactors, wherein:

• • for 3 reactors, the catalyst distribution between the 3 reactors is such that in the range 30% to 36% by weight of catalyst is present in each of the 3 reactors;
  • for 4 reactors: the catalyst distribution between the 4 reactors is such that in the range 22% to 28% by weight of catalyst is present in each of the 4 reactors.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a moving bed or fixed bed, preferably moving bed regenerative reforming process. The feed generally comprises paraffinic, naphthenic and aromatic hydrocarbons. In general, 3 or 4 reforming reactors are used to carry out reforming.

The catalyst distribution between the various reactors is said to be flat (as opposed to an augmentary or diminishing catalyst distribution) if the following condition is met:

• • for 3 reactors, the catalyst distribution between the 3 reforming reactors is such that in the range 30% to 36% by weight of catalyst, preferably in the range 32% to 34% by weight of catalyst, more preferably in the range 32.5% to 33.5% by weight of catalyst is present in each of the 3 reactors;
  • for 4 reactors: the catalyst distribution between the 4 reactors is such that in the range 22% to 28% by weight of catalyst, preferably in the range 24% to 26% by weight of catalyst, more preferably in the range 24.5% to 25.5% by weight of catalyst is present in each of the 4 reactors.

The catalyst may either be in a fixed or moving bed. Preferably, the catalyst is in a moving bed.

The feed treated by the process generally comprises paraffinic, naphthenic and aromatic hydrocarbons. Said hydrocarbons generally contain 5 to 12 carbon atoms per molecule.

In the case of a moving bed catalyst, the mean reactor inlet temperature is generally in the range 480° C. to 550° C., preferably in the range 490° C. to 540° C. The mass flow rate of feed treated per unit mass of catalyst is generally in the range 1 to 4 h⁻¹. The operating pressure may be fixed to between 0.2 MPa and 0.9 MPa. A portion of the hydrogen produced is recycled in accordance with a molar recycle ratio in the range 2 to 10, preferably in the range 3 to 6. Said ratio is the molar ratio of the recycled hydrogen to the flow rate of the feed.

Any catalyst for gasoline reforming may be used in the context of the process of the invention.

Catalysts for reforming gasoline are bifunctional catalysts having two essential functions to obtain the correct performances: a hydrodehydrogenating function which ensures dehydrogenation of the naphthenes and hydrogenation of coke precursors, and an acid function which ensures isomerization of naphthenes and paraffins and cyclisation of long-chain paraffins. The hydrodehydrogenating function is provided by platinum. However, platinum also has a hydrogenolyzing activity, to the detriment of the gasoline yield required for gasoline reforming. This hydrogenolyzing activity may be greatly reduced, and thus the selectivity of the catalyst increased, by adding tin.

A halogen is responsible for the acid function of the catalysts which is responsible for isomerization and cyclisation of C₆-C₁₁ paraffins. An optimum halogen content exists for each catalyst.

The catalysts also generally comprise at least one metal M from the platinum group, preferably platinum, at least one promoter X1 selected from the group constituted by tin, germanium and lead, preferably tin or germanium, more preferably tin, at least one halogen and a porous support. It may also comprise at least one promoter X2 selected from the group constituted by gallium, indium, thallium, phosphorus and boron.

The porous support is generally at least one refractory oxide selected from the group constituted by oxides of magnesium, titanium, zirconium, alumina and silica. Preferably, it is silica, alumina or silica-alumina, and highly preferably it is alumina.

According to the invention, said porous support is advantageously in the form of beads, extrudates, pellets or powder. Highly advantageously, said support is in the form of beads or extrudates. The pore volume of the support is preferably in the range 0.1 to 1.5 cm³/g, more preferably in the range 0.4 to 0.8 cm³/g. Further, said porous support has a specific surface area which is advantageously in the range 50 to 600 m²/g, preferably in the range 100 to 400 m²/g, or even in the range 150 to 300 m²/g.

The catalyst of the invention preferably contains 0.01% to 5% by weight of metal M from the platinum group, more preferably 0.01% to 2% by weight of metal M and still more preferably 0.1% to 1% by weight of metal M.

The amount of promoter X1 or X2 is preferably in the range 0.005% to 10% by weight, more preferably in the range 0.01% to 5% by weight and still more preferably in the range 0.05% to 2% by weight.

When the catalyst of the invention contains tin, the tin content is preferably in the range 0.1% to 2% by weight, and highly preferably in the range 0.1% to 0.7% by weight, or even in the range 0.1% to 0.5% by weight.

The halogen is preferably selected from the group constituted by fluorine, chlorine, bromine and iodine. Preferably, the catalyst contains 0.1% to 15% by weight of halogen, more preferably 0.2% to 8% by weight, still more preferably 0.5% to 5% by weight. Chlorine is the most preferred halogen. In this case, the catalyst of the invention highly preferably contains 0.5% to 2% by weight, or even 0.7% to 1.5% by weight of chlorine.

Examples

Two tests were carried out.

For these two tests, four microreactors were placed in series with traced and lagged lines to reduce thermal losses between the four reactors to a minimum.

The reactors were operated isothermally, the endothermicity linked to the dehydrogenation reactions being compensated for by the heating elements.

In the first test, the catalyst distribution was augmentary while in the second test, it was flat.

The total mass of catalyst was identical in the two tests. In order to ensure suitable filling of the reactors, a complement of silicon carbide was added.

The catalyst employed was a platinum-tin catalyst on a chlorinated alumina support with an initial chlorine content of 1.1% by weight. The catalyst comprised 0.3% by weight of platinum and 0.3% by weight of tin.

Catalyst distribution
(percentage by weight of catalyst in reactors)
Reactor 1	Reactor 2	Reactor 3	Reactor 4	Sum
10	15	25	50	100%
25	25	25	25	100%

The characteristics of the feed were as follows:

	Density at 20° C.	0.753	kg/dm3
	Research octane number	~60
	Naphthenes + aromatics content	63	% by weight

This transformation was carried out in the presence of hydrogen, using the following operating conditions:

	Total pressure	0.30	MPa
	Feed flow rate	2.0	kg per kg of catalyst

Before injecting the feed, the catalysts were activated at high temperature in hydrogen for 2 hours.

The performances obtained after 72 h of operation are shown in the table below. In both cases, the research octane number of the reformate was 104.

Catalyst	Temperature	Reformate yield	Hydrogen yield
distribution	(° C.)	(weight %)	(weight %)
Augmentary	478	91.8	3.5
Flat	474	92.2	3.6

A flat catalyst distribution can increase the activity of the catalyst and reduce the production of coke. This favours the operation of the catalytic reforming unit.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding FR application Ser. No. 08/00.442, filed Jan. 25, 2008, are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Claims

1. A regenerative reforming process in 3 or 4 reforming reactors, wherein the catalyst employed comprises at least one metal M from the platinum group, at least one promoter X1 selected from the group constituted by tin, germanium and lead, at least one halogen and at least one porous support, said process being characterized in that:

for 3 reactors, the catalyst distribution between the 3 reactors is such that in the range 30% to 36% by weight of said catalyst is present in each of the 3 reactors;

for 4 reactors: the catalyst distribution between the 4 reactors is such that in the range 22% to 28% by weight of said catalyst is present in each of the 4 reactors.

2. A regenerative reforming process according to claim 1, in which the catalyst is in a moving bed.

3. A regenerative reforming process according to claim 1, in which the catalyst further comprises at least one promoter X2 selected from the group constituted by gallium, indium, thallium, phosphorus and boron.

4. A regenerative reforming process according to claim 3, in which the porous support comprises at least one refractory oxide selected from the group constituted by oxides of magnesium, titanium, zirconium, alumina and silica.

5. A regenerative reforming process according to claim 3, in which the specific surface area of the porous support is generally in the range 50 to 600 m2/g.

6. A regenerative reforming process according to claim 1, in which the halogen is selected from the group formed by fluorine, chlorine, bromine and iodine.

7. A regenerative reforming process according to claim 1, in which the mean reactor inlet temperature is in the range 480° C. to 550° C., the mass flow rate of feed treated per unit mass of catalyst is generally in the range 1 to 4 h−1, the operating pressure may be fixed at between 0.2 MPa and 0.9 MPa, and a portion of the hydrogen produced is recycled with a molar recycle ratio in the range 2 to 10.

8. A regenerative reforming process according to claim 1, in which for 3 reactors, the catalyst distribution between the 3 reactors is such that between 32% and 34% by weight of catalyst is present in each of the 3 reactors.

9. A regenerative reforming process according to claim 1, in which for 4 reactors, the catalyst distribution between the 4 reactors is such that between 24% and 26% by weight of catalyst is present in each of the 4 reactors.