GB2280618A

GB2280618A - Activating catalysts

Info

Publication number: GB2280618A
Application number: GB9315640A
Authority: GB
Inventors: Luc Roger Marc Martens; K Boogaerts; Mark Rockwell Welford
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1993-07-28
Filing date: 1993-07-28
Publication date: 1995-02-08
Also published as: GB9315640D0

Abstract

Heat required for activating a catalyst is generated by an exothermic reaction catalysed by the same catalyst, in partially activated form, or by a further catalyst. The invention is particularly useful for reactivating catalysts comprising metallic nickel passivated using oxygen.

Description

CATALYSTS The invention relates to the activation of catalysts, especially to the reactivation of catalysts that have been passivated for ease of handling or for other reasons.

Hydrogenation catalysts comprising metallic nickel are normally supplied by manufacturers in passivated form to shield the nickel during transport: if the catalysts are not passivated, they are pyrophoric and/or become less active when handled or transported. The passivated catalysts must be reactivated before use, reactivation normally involving heating in the presence of hydrogen.

The present inventors have found that in some circumstances problems may arise if it is desired to reactivate a passivated nickel catalyst Ifl situ (that is, in the location where it is to be used in the plant) and, for example, the feed preheater for the plant is not capable of heating the hydrogen to be used in the reactivation method, and any other fluid, typically an inert liquid, mixed with the hydrogen, to a temperature at which reactivation of the passivated catalyst can take place within an acceptable time.

Problems similar to those described above in connection with the reactivation of passivated nickel catalysts may also be encountered when other catalysts, for example non-activated noble metal catalysts, are to be activated by processes involving elevated temperatures, particularly temperatures higher than those that can be achieved using the feed preheater for a plant.

In a first aspect, the present invention provides the use of heat generated by an exothermic reaction catalysed by a partially activated catalyst to promote further activation of the catalyst.

In a second aspect, the invention provides a method of activating a first catalyst, which comprises carrying out an exothermic reaction catalysed by a second catalyst, the reaction being carried out at a temperature at which the first catalyst is not activated, or is not fully activated, and using heat from the reaction to activate, or enhance the activation of, the first catalyst.

US Patent No. 4 530 917 describes the activation of catalysts which have been presulphurized or presulphided ex situ. The catalysts are subjected to a conventional activation step in situ in the presence of hydrogen, whereupon the active metal(s) in the catalyst become sulphurized. It is indicated that the temperature may increase slightly as a result of the reaction that takes place during the activation step, but there is no suggestion that the heat generated be used to promote further activation of the catalyst, or to promote activation of a different catalyst. Indeed, it is indicated that it is desirable to reduce the temperature increase, and in the specific example of an activation process, the initial temperature of the hydrogen stream is higher than the activation temperature so that activation can be effected without raising the temperature of the hydrogen stream.

US Patent No. 4 719 195 describes a two-step process for the activation of a catalyst which has been treated ex situ with a sulphurization agent. In the second part of the second step of the activation process, the catalyst is brought, in situ, to a temperature of at least 275 C, optionally in the presence of hydrogen and a hydrocarbon liquid cut which is preferably a portion of the cut to be treated over the catalyst. It is stated that the second part of the second step is slightly exothermic, but again the suggestion is that the heat generated should be removed: there is no suggestion that heat generated by an exothermic reaction be used to increase the temperature of a treating medium which is initially at too low a temperature for full activation of the catalyst to take place.

The invention also provides a method of activating a catalyst which comprises contacting a partially activated catalyst with at least one substance which, in the presence of the partially activated catalyst, will undergo an exothermic reaction, the substance(s) initially being at a temperature lower than that required for full activation of the catalyst, or a temperature at which activation proceeds relatively slowly, and heat from the exothermic reaction being used to raise the temperature of the substance(s) to a temperature at which further activation of the catalyst can take place, and/or at which activation proceeds at a greater rate.

The invention further provides a method of activating a first catalyst, which comprises contacting the first catalyst and a second catalyst, in either order, with at least one substance which, in the presence of the second catalyst, will undergo an exothermic reaction, the substance(s) initially being at a temperature lower than that required for full activation of the first catalyst, or a temperature at which activation proceeds relatively slowly, and heat from the exothermic reaction being used to raise the temperature of the substance(s) to a temperature at which activation, or further activation, of the first catalyst can take place, and/or at which activation proceeds at a greater rate.

It will be appreciated that in the above two methods the catalyst is one which is either activated solely by heating or is one which, if the temperature is sufficiently high, will be activated by the substance, or at least one of the substances, or its/their reaction product(s).

The invention has particular applicability to the reactivation of passivated catalysts, but is not limited thereto. By a passivated catalyst is meant a catalyst which has been rendered less active, for example, to render it less active to reactions which could be deleterious to it, and/or to render it less active as a catalyst for the reaction, or one of the reactions, it is capable of catalysing when fully active. The catalyst can be passivated intentionally, using a passivating agent, or may be unintentionally passivated during manufacture or on storage.

For convenience, the invention will be described below with reference to the reactivation of passivated nickel catalysts for hydrogenation reactions, but it will be appreciated that the invention is also applicable to the activation of other catalyst systems, for example, the activation of a non-activated noble metal catalyst, or the reactivation of other catalysts which have been passivated.

Examples of catalytic hydrogenation reactions carried out on a commercial scale are the hydrogenation of aldehydes (to give alcohols), of unsaturated hydrocarbons (to give saturated hydrocarbons), of acetylene-derived chemicals (to give olefinic and saturated materials), of unsaturated fatty acids (to give olefinic or saturated fatty acids), of ketones (to give secondary alcohols), and of esters of unsaturated fatty acids (to give esters of partially or fully hydrogenated fatty acids). The present invention has particular applicability to the hydrogenation of unsaturated hydrocarbons, particularly aromatic hydrocarbons, to give saturated hydrocarbons, but is not limited thereto.

Catalysts typically used for hydrogenation reactions include, for example, nickel, palladium platinum, molybdenum, cobalt, iron, chromium, rhodium, ruthenium and copper catalysts. As indicated above, catalysts comprising metallic nickel are difficult to transport because metallic nickel is pyrophoric, and also has a tendency to become less active when it is exposed to air, and such catalysts are normally supplied in passivated form. Passivating agents typically used by manufacturers of catalysts comprising metallic nickel are gaseous agents, for example, molecular oxygen (usually diluted with an inert gas, for example, nitrogen), carbon dioxide, other oxygen-containing compounds, and inert liquid agents, for example, water, inert hydrocarbons, and alcohols. The protective layers formed by the physical and or chemical interaction of these passivating agents with the metallic nickel must be removed during the reactivation process in order to obtain maximum activity when the catalyst is used. (A separate reactivation step may be unnecessary when the feedstock that will be processed using the catalyst is used as a passivating liquid.) As indicated above, reactivation of catalysts comprising metallic nickel has in the past normally been effected by heating the catalyst in the presence of hydrogen. Typically, hydrogen, optionally mixed with a liquid heat-carrier, for example, an inert hydrocarbon, is preheated and passed over the catalyst until reactivation is complete.In some cases the hydrogen or hydrogen/heat-carrier mixture must be heated to a relatively high temperature (for example, the hydrogen or hydrogen/heat-carrier mixture must normally be heated to a higher temperature when reactivating, for example, an oxygen-passivated nickel catalyst than when reactivating, for example, a carbon dioxide-passivated nickel catalyst), and this may cause problems, for example, where a passivated catalyst is to be reactivated in situ in a plant where the feed gas for the reaction to be carried out in the plant does not need to be heated to the temperatures required for reactivation of the catalyst.

In accordance with the present invention, at least some of the heat required for the reactivation of a passivated catalyst is derived from an exothermic reaction. The exothermic reaction is catalysed, in the first aspect of the invention, by the passivated catalyst itself, in partially activated form. In the second aspect of the invention, the exothermic reaction is catalysed by a second catalyst. The invention is particularly applicable to reactions carried out under adiabatic conditions.

The exothermic reaction used in accordance with the invention is preferably a reaction of the same type as the reaction to be catalysed by the reactivated catalyst.

Thus, where the passivated catalyst, when reactivated, is to be used for catalysing a hydrogenation reaction, the exothermic reaction is preferably also a hydrogenation reaction (in which case the substances heated by the exothermic reaction comprise hydrogen and the compound, or mixture of compounds, hydrogenated). The compound, or mixture of compounds, hydrogenated in the exothermic reaction may, if desired, be the same as the compound or mixture to be hydrogenated after activation of the passivated catalyst, but this is not essential, and in some cases it may be desirable to use a different compound or mixture of compounds when reactivating the catalyst from that used for the reaction to be catalysed by the reactivated catalyst.

One situation where it may be desirable to use a different compound or mixture of compounds for reactivating the catalyst from that used subsequently is where it is advantageous to produce more heat in the reactivation step than is desirable when carrying out the subsequent reaction. The production and circulation of heat can also be controlled by appropriate choice of the rate at which the compound or mixture of compounds is fed to the reactor, and the proportion of inert carrier liquid, if any, mixed with the reactive compound(s).

As indicated above, it may be possible to carry out the reactivation step using a single catalyst, namely the passivated catalyst which is to be reactivated. In this case, the passivated catalyst is advantageously heated to a temperature at which partial reactivation thereof occurs, and is then used to catalyse an exothermic reaction, the heat from the exothermic reaction being used to effect further reactivation of the catalyst. It may be desirable, in this case, for heat generated by the exothermic reaction to be recirculated, for example, using heat-exchangers, and used to heat the fluid substance(s) for reactivating the catalyst.

Preferably, the invention is carried out using two catalysts, namely the passivated catalyst to be reactivated and a second catalyst. Heat from an exothermic reaction carried out using the second catalyst can then be used to reactivate the passivated catalyst, which is preferably positioned downstream of the second catalyst, although this is not essential if heat from the exothermic reaction is recirculated to heat the fluid substance(s) for the reactivation step. Advantageously, the second catalyst is capable of catalysing the same type of reaction as the catalyst to be reactivated, for example, both the catalysts may be capable of catalysing the reaction of hydrogen with the same types of compounds. In this case, as the passivated catalyst becomes reactivated, it will itself normally catalyse the exothermic reaction, thus contributing to the heat to be recirculated.

Positioning of the passivated catalyst downstream of the second catalyst may also be advantageous when each of the catalysts (when fully activated) is capable of promoting the same reaction, the second catalyst is fully active at a temperature at which the passivated catalyst is not, and the liquid feed (comprising the substance(s) to be hydrogenated) contains a catalyst poison, for example, sulphur. If the feed is supplied to the reactor at a temperature at which the second catalyst is fully active, the poison will tend to be retained by the second catalyst and will not be carried through to the rest of the catalyst. In the absence of the second catalyst, if the passivated catalyst was not fully activated, only a proportion of the sulphur would be retained by the first portion of the catalyst, and the sulphur would quickly be carried further through the catalyst bed.Once a catalyst becomes partially or fully poisoned by sulphur, reactivation can become very difficult, requiring temperatures which are too high to be reached in situ and which, if reached, would cause deterioration of the catalyst.

Where two catalysts are used these could, if desired, be mixed together. This is not, however, at present preferred as the less active catalyst would dilute the more active one, and less heat would be produced by exothermic reaction for a given volume of the catalyst mixture as compared with the same volume of the more active catalyst.

In a particularly advantageous embodiment of the invention, the passivated catalyst is capable, when reactivated, of catalysing a hydrogenation reaction, and the second catalyst, if used, is capable of catalysing the same type of hydrogenation reaction, the hydrogenation reaction preferably comprising, in each case, the hydrogenation of an unsaturated hydrocarbon, particularly an aromatic hydrocarbon. Where a second catalyst is used, this may be a catalyst which is essentially the same as the passivated catalyst after reactivation. If desired, the second catalyst may be the same as the passivated catalyst apart from the use of a different passivating agent, the passivating agent for the second catalyst being at least partially removed to permit the exothermic reaction to take place. In this case the second catalyst is preferably capable of being reactivated at a lower temperature than that required for reactivating the other catalyst.

As indicated above, the passivated catalyst, when reactivated, preferably comprises metallic nickel. The nickel is preferably in finely dispersed form on a carrier. Methods of forming such a catalyst are well known to those skilled in the art, and do not form part of the present invention. Suitable carriers include, for example, alumina, silica, silica/alumina mixtures, and other metal oxides.

The invention is particularly suitable for reactivating nickel hydrogenation catalysts that have been passivated using molecular oxygen, optionally in admixture with an inert gas: thus, for example, air may be used as the passivating agent. Such catalysts require relatively high temperatures and/or relatively long treatment times for reactivation, and are not readily reactivated in situ in a hydrogenation reactor suitable, for example, for hydrogenating aromatic hydrocarbons.

Thus, for example, full reactivation of one particular oxygen-passivated nickel catalyst for the hydrogenation of aromatic hydrocarbons was found to require heating for one hour at 240 C or heating at 8 to 16 hours at 2000 C, even the lower of these temperatures being significantly higher than the maximum temperature obtainable using the standard feed preheater for a typical hydrogenation reactor for aromatic hydrocarbons. Catalysts passivated using other passivating agents, for example, other oxygen-containing passivating agents, may also require relatively high temperatures for reactivation.

In accordance with the invention, a nickel hydrogenation catalyst that has been passivated using oxygen (or other passivating agent) can be reactivated either by preheating the passivated catalyst to, for example, 1500C using a stream of hydrogen and an inert carrier gas and then carrying out an exothermic hydrogenation reaction using the partially reactivated catalyst, or by using a second catalyst. If a second catalyst is used, this is preferably a nickel hydrogenation catalyst that has been passivated using carbon dioxide.This catalyst can then be reactivated at, for example, 150 C using a stream of hydrogen and inert carrier gas, and can then be used to carry out the exothermic hydrogenation of, for example, an aromatic hydrocarbon, the heat produced being used to reactivate the oxygen-passivated catalyst (or other passivated catalyst).

The invention makes it possible to carry out the activation of a catalyst in a reactor at a temperature which could not normally be attained in that reactor.

This may make it possible to use a less expensive catalyst, or one with more advantageous properties, in a particular reactor, compared with the catalyst that would normally be needed for that reactor. Although some reactants will be consumed by the exothermic reaction, the reaction products of the activation step can in many cases be produced with acceptable characteristics for further use. As indicated above, the invention is not limited to the reactivation of passivated catalysts comprising metallic nickel, but is also applicable to the reactivation of other catalysts which have been passivated (for example, the reactivation of passivated cobalt catalysts), and the activation of other catalysts (for example, the activation of non-activated noble metal catalysts).

One form of reactor suitable for carrying out the method of the invention is shown, by way of example only, in the accompanying drawing, which is a diagrammatic longitudinal section through a reactor.

Referring now to the drawing, Fig. 1, a vertical reactor 1 is provided with an inlet 2 at the top and an outlet 3 at the bottom thereof. A heat exchanger 4 is provided for permitting exchange of heat between effluent leaving the reactor via the outlet 3 and feed gas to be fed to the reactor via the inlet 2.

Within the reactor are a first catalyst bed 5 and a second catalyst bed 6, the first bed being positioned above the second. The second bed, and the lower portion 7 of the first bed, comprise an oxygen-passivated nickel hydrogen catalyst, while the upper portion 8 of the first bed comprises a carbon dioxide-passivated nickel hydrogenation catalyst. The reactor can be used in the manner described in the following Example.

The following Example illustrates the invention.

8.7 parts by mass of an oxygen-passivated hydrogenation catalyst comprising finely dispersed nickel on a carrier were loaded into a reactor of the type shown in the accompanying drawing, and 1.0 parts by mass of a carbon dioxide-passivated hydrogenation catalyst, also comprising finely divided nickel on a carrier, were then loaded on top of the oxygen-passivated catalyst. The oxygen-passivated catalyst was supplied under the trade name HTC 400 by Crosfield and the carbon dioxidepassivated catalyst was supplied under the trade name Ni3288 by Harshaw Chemie (now Engelhard Chemie).

The carbon dioxide-passivated catalyst was reactivated by passing through it a hydrogen/saturated hydrocarbon mixture preheated to 150 C. When the said catalyst was reactivated, the feed was switched to an unsaturated hydrocarbon/saturated hydrocarbon/excess hydrogen mixture to cause an exothermic hydrogenation reaction to take place, catalysed by the reactivated catalyst, and to increase the temperature of the gas stream. The unsaturated hydrocarbon was initially supplied at a rate of 4 parts by mass/hour and the saturated hydrocarbon at a rate of 8 parts by mass/hour.

After an hour, the unsaturated hydrocarbon feed rate was increased to 6 parts by mass/hour, and the hydrogen feed rate was increased to compensate for hydrogen used up in the exothermic reaction.

The gas stream then passed through the oxygenpassivated catalyst, raising the temperature of the catalyst. Excess heat was recycled by heat-exchange between the effluent from the reactor and the feed thereto, and the exothermic reaction and the recycling of heat were continued until the temperature of the oxygen passivated catalyst reached approximately 220 C. This temperature was maintained for six hours, during which the oxygen-passivated catalyst was reactivated and the unsaturated hydrocarbon was converted to saturated hydrocarbon suitable for use without undergoing further chemical reaction.

The unsaturated hydrocarbon used in this Example for reactivating the oxygen-passivated catalyst was a mixture of hydrocarbons containing aromatic and/or olefinic components and having a flash point of approximately 30"C. The saturated hydrocarbon used as diluent was a hydrocarbon mixture produced earlier by hydrogenation of the unsaturated hydrocarbon starting material.

After the reactivation temperature had been maintained for six hours, the unsaturated hydrocarbon feed was replaced by saturated hydrocarbon, and the reactor temperatures were brought down to 100 C. The feed was then switched to a mixture containing unsaturated hydrocarbons for hydrogenation in the reactor.

Claims

1. The use of heat generated by an exothermic reaction catalysed by a partially activated catalyst to promote further activation of the catalyst.

2. A method of activating a first catalyst, which comprises carrying out an exothermic reaction catalysed by a second catalyst, the reaction being carried out at a temperature at which the first catalyst is not activated, or is not fully activated, and using heat from the reaction to activate, or enhance the activation of, the first catalyst.

3. The use or a method as claimed in claim 1 or claim 2, wherein the reaction is a hydrogenation reaction.

4. A method as claimed in claim 2 or claim 3, wherein the first catalyst, when activated, is capable of catalysing a hydrogenation reaction.

5. The use or a method as claimed in claim 3 or claim 4, wherein the hydrogenation reaction comprises hydrogenating an unsaturated hydrocarbon.

6. A method of activating a catalyst which comprises contacting a partially activated catalyst with at least one substance which, in the presence of the partially activated catalyst, will undergo an exothermic reaction, the substance(s) initially being at a temperature lower than that required for full activation of the catalyst, or a temperature at which activation proceeds relatively slowly, and heat from the exothermic reaction being used to raise the temperature of the substance(s) to a temperature at which further activation of the catalyst can take place, and/or at which activation proceeds at a greater rate.

7. A method of activating a first catalyst, which comprises contacting the first catalyst and a second catalyst, in either order, with at least one substance which, in the presence of the second catalyst, will undergo an exothermic reaction, the substance(s) initially being at a temperature lower than.that required for full activation of the first catalyst, or a temperature at which activation proceeds relatively slowly, and heat from the exothermic reaction being used to raise the temperature of the substance(s) to a temperature at which activation, or further activation, of the first catalyst can take place, and/or at which activation proceeds at a greater rate.

8. A method as claimed in claim 6 or claim 7, wherein the reaction is a hydrogenation reaction and the substances comprise hydrogen and at least one compound to be hydrogenated.

9. A method as claimed in claim 7 or claim 8, wherein the first catalyst, when activated, is capable of catalysing a hydrogenation reaction and the substances comprise hydrogen and at least one compound to be hydrogenated.

10. A method as claimed in claim 8 or claim 9, wherein the substances comprise hydrogen and an unsaturated hydrocarbon.

11. The use or a method as claimed in claim 5 or claim 10, wherein the unsaturated hydrocarbon is an aromatic hydrocarbon or an olefinic hydrocarbon.

12. The use or a method as claimed in any one of claims 1 to 11, wherein the catalyst, or the first catalyst, is a passivated catalyst.

13. The use or a method as claimed in claim 12, wherein the passivated catalyst comprises nickel.

14. The use or a method as claimed in claim 13, wherein the passivated catalyst has been passivated using molecular oxygen or an oxygen-containing compound.

15. A method as claimed in claim 13 or claim 14, wherein the second catalyst also comprises nickel.

16. A method as claimed in claim 15, wherein the second catalyst is obtained by at least partial reactivation of a catalyst passivated using carbon dioxide or using an inert liquid which can be removed at a relatively low temperature.

17. A method as claimed in claim 2 or claim 7, wherein the second catalyst is positioned upstream of the first catalyst.

18. The use or a method as claimed in any one of claims 1 to 17, wherein heat from the exothermic reaction is recycled to raise the temperature of the catalyst or the first catalyst.

19. A method as claimed in claim 2, carried out substantially as described in the Example herein.

20. Any novel feature described herein, or any novel combination of herein described features.