GB2131043A

GB2131043A - Selective hydrogenation of dienes in pyrolysis gasoline

Info

Publication number: GB2131043A
Application number: GB08233746A
Authority: GB
Inventors: Willem Groenendaal; Onno Leendert Maaskant; Lambert Schaper
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1982-11-26
Filing date: 1982-11-26
Publication date: 1984-06-13
Also published as: JPS59105083A; FR2536759B1; FR2536759A1; CA1216311A; BE898299A; AU2165383A; IT8323879A0; DE3342521A1; NL8303740A; IT1168974B; AU559246B2; JPH0631331B2; KR840007433A; KR910004883B1; ZA838762B; GB2131043B

Abstract

Dienes in pyrolysis gasoline are selectively hydrogenated in two stages at elevated temperature and pressure with hydrogen in the presence of supported first and second stage catalysts comprising 1-5, respectively from 5-40%w of one or more metals from Group 8, based on total catalyst. The first stage catalyst preferably consists of nickel- containing alumina spheres.

Description

SPECIFICATION Process for selective hydrogenation of dienes in pyrolysis gasoline This invention relates to a process for the selective hydrogenation of dienes in pyrolysis gasoline and to hydrogenated pyrolysis gasolines thus obtained.

As will be known, pyrolysis gasoline is obtained as a by-product in the preparation of ethene and/or propene by means of high-temperature pyrolysis (e.g. cracking in the presence of steam) of gaseous or liquid hydrocarbons, such as naphtha or gas oil.

Pyrolysis gasolines on the one hand are extremely unstable owing to the presence of a relatively high proportion of highly olefinically unsaturated hydrocarbons, and on the other hand contain aromatic compounds and alkenes having a high octane number which are particularly valuable and are in themselves useful as stable motor gasoline components.

In order to obtain a product which can be used for different purposes, e.g. as a stable gasoline with high octane number or as a raw material for the production of aromatic compounds, the highly olefinically unsaturated compounds which mainly consist of dienes, for example those of cyclopentadiene type, have to be removed from a pyrolysis gasoline. This removal may be achieved by partial hydrogenation of the dienes to monoolefins. Because the hydrogenation of monoolefins in general leads to a reduction in octane number, such a hydrogenation is to be avoided as much as possible. Moreover, in doing so the hydrogen consumption is kept to a desired low level.

Dienes present in pyrolysis gasolines can be selectively hydrogenated in two subsequent stages with the aid of catalysts with hydrogenating activity such as supported catalysts comprising a metal of Group 6 and/or Group 8 of the Periodic System of Elements. The length of the period during which such catalysts retain sufficient hydrogenation activity is usually unsatisfactory due to gum formation, polymer deposition on the catalyst and an increased pressure drop, particularly in the part of the first stage catalyst bed nearest to the reactor inlet.

The invention provides a solution for this probiem by carrying out the first stage in the presence of a supported catalyst with low hydrogenative Group 8 metal content; in the second stage a catalyst with a higher Group 8 metal content is used.

Accordingly the invention provides a process for the selective hydrogenation of dienes in pyrolysis gasoline, which comprises contacting pyrolysis gasoline in two subsequent stages at elevated temperature and pressure with hydrogen in the presence of supported catalysts, the first stage catalyst comprising 15 /0 w of one or more metals from Group 8 of the Periodic System of Elements, based on total catalyst, and the second stage catalyst comprising from 5-40 %w of one or more metals from Group 8, based on total catalyst.

Preferably the first and second stage catalysts comprise 1-4, respectively 6-30 %w of one or more metals from Group 8, based on total catalyst. The most preferred first and second stage catalysts both comprise nickel as Group 8 metal.

The support of the first and second stage catalysts suitably consists of refractory oxides, such as alumina, silica or silica-alumina; preferred is alumina, containing 0--6 %w of silica.

The metal(s) may be incorporated by any method known in the art for the preparation of catalysts containing one or more components on a carrier, such as impregnation, ion-exchange or (co-)precipitation. A suitable method preparing such catalysts is impregnation of the carrier material in one or more stages with an aqueous solution containing one or more salts of Group 8 metals followed by drying and calcining.

The first stage catalyst suitably has a surface area of 10-600 m2/g; most preferred is a surface area of 20-500 m2/g.

The finished first and second stage catalysts are usually treated with hydrogen or a hydrogencontaining gas at a temperature between 300 and 5000C for 1-48 hours and subsequently at least partly sulphided. Sulphiding may be carried out by any method known in the art, for example by contacting the catalyst with a mixture of hydrogen and hydrogen sulphide, or with hydrogen and a sulphur-containing hydrocarbon oil, such as a sulphur-containing gas oil or naphtha or a naphtha spiked with a sulphur compound such as CS2 or dimethyldisulphide (DMDS) at a temperature between 60 and 3000C prior to its use.

The process according to the invention may in both stages take place in the liquid phase or partly in the vapour-, partly in the liquid phase.

Application of a fixed catalyst bed is preferred in both stages in the present process, but it is also possible to apply the catalyst in a fluidized or expanded bed. A very suitable embodiment is that in which the pyrolysis gasoline to be converted, which is entirely or substantially in the liquid phase, is trickled downward co-currently with the hydrogen-containing gas through the fixed catalyst beds.

Often these beds are covered at their inlet by materials which are inert to the reaction, in order to facilitate even distribution of the feedstock, that is, to prevent or reduce channelling through the catalyst bed(s). Because the inerts will occupy a substantial portion of the reaction zone, e.g. up to 1 5 to 20% or more of the reaction zone volume, their use adds to the capital expense of a hydrogenation process both for the reactor(s) and for the costs of the inerts which do not contribute in any significant manner to desired hydrogenation of the feedstock.

The use of layers of inert material can be avoided in the first stage of the present process when the first stage catalyst takes over the function of distributing the feedstock over the catalyst bed(s). In order to perform this function the first stage catalyst preferably comprises particles in the form of pellets, spheres, rings or other three-dimensional objects of which the smallest dimension is greater than 2 mm.

Generally, beds of catalyst particles with a dimension of less than 2 mm tend to plug more readily and are less effective in distributing feed across the initial contact layer of catalyst, whereas the use of particles having dimensions above 30 mm results in catalysts having significantly lower activity.

A particularly preferred first stage catalyst comprises spherical particles having a diameter of 3-25 mm. The use of spherical particles, which have a high abrasion strength, results in improved flow distribution of feedstock and also a reduced pressure drop over the catalyst bed(s), compared with the use of catalyst particles of a different shape. The term "spherical" herein refers to particles having both a true rounded shape and those generally spheroidal particles which do not pass perfectly rounded configurations. Procedures for preparing these particles are known in the art.

When the first stage catalyst bed has a substantial height (which may be 1 5 m or more in an upright reactor) or when a second layer of catalyst particles is placed upon this catalyst bed, it is of advantage that the first stage catalyst particles are resistant to crushing. Preferably the first stage catalyst has a bulk crush strength of 1-4 MPa, most preferably of 1.5-3 MPa.

The second stage catalyst preferably comprises extrudates with a diameter of 1-5 mm and a bulk crush strength of 0.6-3 MPa.

The hydrogen to be employed in both stages of the catalytic hydrogenation may be pure or in the form of a hydrogen-containing gas. The gases employed should preferably contain more than 50% by volume of hydrogen. Very suitable are, for example, the hydrogen-containing gases obtained in the catalytic reforming or steam-reforming of gasoline fractions, and mixtures of hydrogen and light hydrocarbons. Any excess of hydrogencontaining gas is advantageously recycled to one or both stages, possibly after the previous removal of undesired components therefrom.

The catalytic hydrogenations are very suitably carried out at the following conditions which may be the same or different in both stages: a temperature in the range from 50-300 C, preferably 50-1 500C; a total pressure in the range from 10-100 bar abs, preferably 20-80 bar abs; a hydrogen partial pressure in the range from 5-80 bar abs, preferably 10-60 bar abs; a hydrogen feed rate in the range from 50-1000 N1 hydrogen per kg gasoline feed, preferably from 100--1000 N1 per keg feed; a space velocity in the range from 0.1-10 kg gasoline feed per 1 catalyst per hour, preferably 0.5-3 kg gasoline feed per 1 catalyst per hour.A reaction temperature exceeding 1 500C is less desirable in order to avoid enhanced polymerization of the olefinic compounds in the feed. The hydrogenation of dienes to mono-olefins is a strongly exothermic reaction, In order to keep the reactor temperature within the preferred range, liquid product is preferably recirculated and mixed with the pyrolysis gasoline feed. The weight ratio of the liquid product recirculated to the first stage and the pyrolysis gasoline feed thereto suitably is from 0.5-20, in particular from 1-10.

The second stage of the two stage process according to the invention may be carried out in a reaction zone which is separated from the reaction zone in which the first stage is carried out; preferably both first and second stage catalysts are placed one after the other in a single reaction zone.

The invention is illustrated by the following Example.

EXAMPLE A vertical tubular reactor is filled with 294 cm3 of second stage catalyst in the form of 2.5 mm extrudates comprising 10 %w of nickel calculated as NiO (based on total catalyst) on alumina as carrier, on top of which fixed bed a layer is placed of 5 cm height (98 cm3) of first stage catalyst spheres with an average diameter of 4 mm, a surface area of 230 m2/g and a bulk crush strength of over 1.7 MPa, comprising 2.5 %w of nickel calculated as NiO (based on total catalyst), on alumina as carrier. The catalysts are first treated with hydrogen for 24 hours at 3750C, followed by pre-sulphiding in the presence of hydrogen with straight run naphtha spiked with DMDS (500 ppmw sulphur in the naphtha) for 4 hours at 1000C.

The pyrolysis gasoline feed which has a boiling range of 30--1 500C is mixed with liquid product from the reactor in a weight ratio of 1:5. The mixture containing 2.5 %w dienes and 24 %w mono-olefins is preheated, entering the reactor at a temperature of 800C and a H2 partial pressure of 40 bar abs. The feed is led in downward direction over the catalyst beds at a space velocity of 6 kg feed mixture first and second stage catalyst combined/hour co-currently with 300 N1 hydrogen/kg feed mixture. No pressure drop increase in the reactor system is observed during this experiment. After the process has been operating for 10, respectively 60 days, the liquid product contains 0.15 %w dienes and 22.5 %w mono-olefins in both cases, which shows that selective hydrogenation of dienes can be carried out in stable operation without needing to replace first and/or second stage catalyst frequently.

COMPARATIVE EXAMPLE For purpose of comparison the above procedure is repeated except that the first stage catalyst is replaced by the alumina spheres not containing nickel. The pressure drop over the reactor system increases considerably during this experiment.

After the same operating periods as in the above Example (10, respectively 60 days) the liquid product from the reactor contains 0.1 6, respectively 0.21 %w dienes and 22.6, respectively 22.9 %w mono-olefins. These results are unsatisfactory in comparison with those shown in the Example according to the invention.

Claims

1. Process for the selective hydrogenation of dienes in pyrolysis gasoline, which comprises contacting pyrolysis gasoline in two subsequent stages at elevated temperature and pressure with hydrogen in the presence of supported catalysts, the first stage catalyst comprising 1-5 %w of one or more metals from Group 8 of the Periodic System of Elements, based on total catalyst, and the second stage catalyst comprising from 5-40 %w of one or more metals from Group 8, based on total catalyst.

2. Process as claimed in claim 1, in which the first stage catalyst comprises 1-4 %w of one or more metals from Group 8, based on total catalyst.

3. Process as claimed in claim 1 or 2, in which the first and the second stage catalysts both comprise nickel as Group 8 metal.

4. Process as claimed in any one of the preceding claims, in which the first and second stage catalysts both comprise alumina, containing 0--6 %w of silica, as a support.

5. Process as claimed in any one of the preceding claims, in which the first stage catalyst has a bulk crush strength of 1-4 MPa.

6. Process as claimed in claim 5, in which the said catalyst has a bulk crush strength of 1.5-3 MPa.

7. Process as claimed in any one of the preceding claims, in which the first stage catalyst comprises particles of which the smallest dimension is from 2-30 mm.

8. Process as claimed in claim 7, in which the said particles are spherical.

9. Process as claimed in claim 8, in which the spherical particles have a diameter of 3-25 mm.

10. Process as claimed in any one of the preceding claims in which both first and second stage catalysts are placed one after the other in a single reaction zone.

11. Process as claimed in any one of the preceding claims, in which in both stages the temperature is in the range from 50-3000C, the total pressure is in the range from 10-100 bar abs, the hydrogen partial pressure is in the range from 5-80 bar abs, the hydrogen feed rate is in the range from 501000 N1 per kg feed and the space velocity is in the range from 0.1-10 kg feed per 1 catalyst per hour.

12. Process as claimed in claim 1, substantially as described with special reference to the Example.

1 3. Hydrogenated pyrolysis gasolines obtained by the process as claimed in any one of the preceding claims.