WO2011061204A1

WO2011061204A1 - Catalyst and isomerisation process

Info

Publication number: WO2011061204A1
Application number: PCT/EP2010/067629
Authority: WO
Inventors: Ahmad Kalantar Neystanaki
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2009-11-18
Filing date: 2010-11-17
Publication date: 2011-05-26

Abstract

An alkylaromatics isomerisation catalyst, which catalyst comprises at least 50 %wt of an acidic inorganic binder; at least 0.01 %wt of a Group VIII metal; and 1-9 %wt zeolite PSH-3 and/or MCM-22, and a process for the isomerisation of alkylaromatics to provide a reaction mixture, said process comprising contacting a hydrocarbon stream comprising alkylaromatics with such catalyst.

Description

CATALYST AND ISOMERISATION PROCESS

This invention relates to a zeolite-based catalyst for the isomerisation of alkylaromatics , more

specifically xylene, particularly to increase the production of p-xylene from a hydrocarbon fraction containing aromatic hydrocarbons containing 8 carbon atoms .

Following fractionation or distillation of crude petroleum oil, a straight-run naphtha fraction, boiling in the 70°C to 190°C range, is obtained. This fraction may be catalytically converted to an aromatic reformate.

On conversion to reformate, the aromatics content is considerably increased and the resulting hydrocarbon mixture becomes highly desirable as a source of valuable chemical intermediates and as a component for gasoline.

Reformate generally contains aromatic hydrocarbons containing 8 carbons atoms such as ethylbenzene and xylenes. Other components may be present for example their hydrogenated homologues such as naphthenes . Steam cracking is another process by which a fraction, so- called pygas, is obtained which is rich in aromatic hydrocarbons having 8 carbon atoms .

These fractions rich in aromatic hydrocarbons having 8 carbon atoms, hereinafter referred to as C8 aromatics, contain ethylbenzene, ortho-xylene, meta-xylene and para- xylene. Additionally, these fractions can contain small amounts of toluene, aromatic compounds containing 9 carbon atoms or more, and non-aromatic compounds

containing 8 or 9 carbon atoms .

Para-xylene is the most useful commodity of the xylene isomers. Benzene and ortho-xylene also are valued as useful compounds . Separation of C8 aromatics is complex because of their close boiling points. In many commercial processes, para-xylene is separated by adsorption and/or

crystallization. Ortho-xylene is generally separated by sending the C8 aromatics to a splitter of which part of the bottom stream is sent to an ortho-xylene distillation column. The C8 aromatics fraction depleted of para-xylene and/or ortho-xylene is sent to a process for xylene isomerisation and ethylbenzene hydroisomerisation which aims to re-establish the thermodynamic equilibrium between the three xylene isomers by isomerisation of meta- and ortho-xylene to para-xylene, and to

hydroisomerise ethylbenzene to xylene. Ethylbenzene hydroisomerisation also is referred to as reforming.

Xylene isomerisation and ethylbenzene

hydroisomerisation is often accompanied by undesirable side-reactions such as dealkylation, transalkylation, disproportionation, aromatics ring saturation and cracking producing undesired side-products such as compounds having of from 1 to 5 carbon atoms, toluene and/or compounds containing 9 or more carbon atoms.

WO 92/04306 describes an alkylaromatics

isomerisation catalyst comprising MCM-22 zeolite. There is no information on the amount of zeolite to be present in the catalyst. The exemplified catalysts contain either no binder or 35 %wt of binder and 65 %wt of zeolite.

WO 95/31421 discloses a catalyst for

disproportionation of toluene to provide C8 aromatic products enriched in para-xylene. The catalyst comprises crystalline material having a certain X-ray diffraction pattern such as zeolite PSH-3 which can have been composited with porous matrix material such that the crystalline material is present in an amount in the range of 2 to 80 %wt . The catalyst used in the example comprises 65 %wt of MCM-49 or MCM-22 besides 35 %wt of alumina. The crystalline material must have been treated with a selectivating agent for example a silicon- containing compound. The examples show that these catalysts give a substantial amount of undesirable byproducts such as C₅ ^~, ethyltoluene, trimethylbenzene and diethylbenzene .

An object of the present invention is to provide an improved catalyst for the isomerisation of

alkylaromatics , more specifically converting C8 aromatic hydrocarbons into para-xylene by isomerisation of xylene and hydroisomerisation of ethylbenzene to xylenes, with limited or no disproportionation . Disproportionation changes the number of carbon atoms of the feed molecules.

Disproportionation of xylene changes the valuable xylene molecule to less valuable toluene and aromatic hydrocarbons containing 9 carbon atoms. Further, it is advantageous if limited or no transalkylatation and/or aromatics ring saturation takes place. Transalkylation converts valuable xylenes and benzene to less valued toluene while aromatics saturation results in the conversion of aromatic compounds into even less valued naphthenes .

According to a first aspect of the present

invention, there is provided an alkylaromatics

isomerisation catalyst which catalyst comprises

at least 50 %wt of an acidic inorganic binder;

at least 0.01 %wt of a Group VIII metal; and

1-9 %wt zeolite PSH-3 and/or MCM-22.

The amounts mentioned above are based on total amount of catalyst. The expression alkylaromatics isomerisation comprises both xylene isomerisation and ethylbenzene hydroisomerisation. This particular combination of components has been found to be surprisingly beneficial in providing a catalyst for the isomerisation of alkylaromatics without substantial disproportionation and transalkylation, more specifically isomerisation of ortho-xylene and metha- xylene to para-xylene and hydroisomerisation of

ethylbenzene to xylene. The use of this catalyst has been found to reduce side reactions such as xylene

disproportionation, transalkylation and cracking. This makes that the catalyst according to the prevent

invention gives less xylene loss while procuding less undesirable compounds such as light compounds containing of from 1 to 5 carbon atoms, toluene and aromatics containing 9 or more carbon atoms .

The present catalyst has been found to lead to an increase in the final yield of desired product, more specifically as para-xylene.

The increased para-xylene content in the product is not only a desired advantage in its own right, but also reduces the size of the recycle of ortho-xylene and meta- xylene .

The present invention is not limited to treatment of alkylaromatics containing 8 carbon atoms but includes the isomerisation of other alkylaromatics such as

alkylaromatics containing 9 carbon atoms or more, including alkylaromatics containing 9 or 10 carbon atoms, which are known to follow similar reaction paths, and to use the same or similar catalyst formulations. Therefore, the present invention relates to isomerisation of alkylaromatics in general, more specifically

alkylaromatics comprising of from 8 to 10 carbons, more specifically alkylaromatics comprising 8 carbon atoms.

The acidic inorganic binder may be selected from any of the suitable acidic refractory metal oxides known in the art. Furthermore, the binder can be non-acidic when added but be converted into an acidic binder during calcination. For example, pseudo-boehmite converts into acidic gamma-alumina during calcination.

A preferred acidic inorganic binder is for example alumina optionally in combination with other compounds such as silica, alumina, titania, zirconia, ceria and/or gallia. Preferably, the binder consists of alumina with up to 50 %wt of other compounds, more specifically up to 20 %wt, more specifically up to 10 %wt, most specifically up to 5 %wt, based on amount of binder. Preferably, the binder consists of acidic alumina.

Alumina can be prepared in different forms. The alumina grades available differ in parameters such as pore volume, average pore diameter, bulk density, and surface area. Although different alumina manufacturers can provide the same or similar alumina products under different names. Different products classifications can have the same or similar or overlapping criteria and/or properties. For example, "high pore" and "wide pore" aluminas tend to have the same or similar properties.

The present invention extends to the use of alumina as the inorganic binder from any source, and examples of suitable alumina binders include grades of the Pural range from Sasol, such as the KR and SB grades, and other wide pore aluminas such as WPA from Criterion.

In a preferred embodiment of the present invention, the pore volume of the inorganic binder as measured with the help of nitrogen is of from 0.6 to 2.0 ml/g, more specifically of from 1.1 to 1.9 ml/g, more specifically of from 1.1 to 1.7 ml/g.

These ranges of pore volume of the inorganic binder include 'wide pore' alumina, which has a more open structure to allow greater interaction with the

alkylaromatics .

In another embodiment of the present invention, the average pore diameter of the inorganic binder is greater than 80 A, preferably greater than 90 A.

In a further embodiment of the present invention, the bulk density of the inorganic binder is of from 0.2 to 0.8 g/cm³, more specifically of from 0.25 to 0.4 g/cm³, most specifically of from 0.25 to 0.35 g/cm³.

In a yet further embodiment of the present

invention, the inorganic binder is present in the amount of 98.99-10 %wt, more specifically more than 80 %wt, preferably more than 90 %wt, especially at least 92 %wt, based on total amount of catalyst.

A more open structure of the inorganic binder, based on one or more of parameters such as pore volume, pore diameter and bulk density, provide better diffusion of the reactant(s) reaching the catalytic material in the catalyst, and better diffusion of the product (s) away from the catalytic material. Greater reactant(s) and product (s) diffusion around the catalytic material increases the reaction rate and/or yield and/or purity.

The catalyst includes at least 0.01 %wt of a

Group VIII metal of the Periodic Table of the Elements. The amount is the amount of metal on total weight of catalyst. Reference to "Group VIII" as used herein relates to the current IUPAC version of the Periodic Table. Preferred catalytically active metals are nickel, palladium and/or platinum. The most preferred metal is platinum. Combinations of two or more catalytically active metals are also possible, preferably being platinum metal combinations. The catalytically active metal may also be provided in the form of a compound, optionally requiring activation prior to use. In one embodiment of the present invention, the Group VIII metal is present in the catalyst in an amount of 0.01-1 %wt, more specifically 0.1-0.6 %wt, based on total weight of catalyst.

The metal can be combined with the binder and zeolite in any way known to be suitable to someone skilled in the art. Metal can be deposited onto a mixture of inorganic binder and zeolite prior to shaping, but it is preferred to deposit metal onto a shaped carrier comprising binder and zeolite. Preferably, the metal is deposited on the shaped carrier by a method selected from the group consisting of pore volume impregnation, wet impregnation and ion exchange .

Pore volume impregnation is the preferred method of emplacing metal onto the shaped carrier comprising binder and zeolite. Pore volume impregnation comprises

contacting the shaped carrier with an aqueous solution of one or more metal salts which aqueous solution has a volume which is slightly higher than the pore volume of the shaped carrier. Preferably, the metal salt containing aqueous solution has a pH below 7. The exact pH depends on the amount and kind of metal salts present and the composition of the shaped carrier.

If ion exchange is applied, it is generally

preferred that the pH of the ion-exchange medium is below 10.

Zeolite PSH-3 is a well known zeolite and has been described in US-A-4439409. MCM-22 also is a well known zeolite and has been described in US-A-4954325. The person skilled in the art generally considers these zeolites to be the same compound. Zeolites having a different name but the same or a very similar X-ray diffraction pattern can be used as well in the present invention. Preferably, the zeolite present in the catalyst according to the present invention is PSH-3 and/or MCM-22. Zeolite PSH-3 and MCM-22 generally have an aluminosilicate basis, optionally including one or more other elements.

The catalyst could be provided by admixture of the inorganic binder and zeolite components, following by shaping, and then typically drying and calcining the pre- former product. Optionally, the addition of the Group VIII metal is carried out after drying and/or calcining of the catalyst pre-former, and optionally there is a further calcination thereafter. Preferably, the catalyst is prepared by extrusion. Therefore, the catalyst preferably is an extrudate .

It is known that the crystal morphology of a zeolite influences its activity and stability. In the present invention, it is particularly preferred that the zeolite PSH-3 and/or MCM-22 has a surface area as measured with the help of nitrogen adsorption of from 480 to 600 m²/g, more specifically of from 500 to 580 m²/g, more

specifically of from 520 to 570 m²/g.

The provision of a zeolite having defined parameters such as those described above in relation to zeolite crystal morphology is known to those skilled in the art and is not further described herein.

The amount of zeolite PSH-3 and/or MCM-22 is at least 1 %wt, more specifically at least 1.5 %wt, more specifically at least 2 %wt, more specifically at least 2.5 %wt, most preferably at least 3 %wt . The zeolite PSH- 3 and/or MCM-22 content preferably is at most 8 %wt, more specifically at most 7 %wt, more specifically at most 6

%wt, most preferably at most 5 %wt . All amounts are based on total amount of catalyst. Whilst the catalyst of the present invention may include a minor or very small amount zeolites other than PSH-3 and/or MCM-22, the catalyst preferably comprises only PSH-3 and/or MCM-22 as the zeolite.

Another parameter of zeolite is its silica to alumina molar ratio (SAR) . In the process of the present invention, xylene is isomerised and ethylbenzene is hydroisomerised . Both reactions need some acid sites to occur. However, too many acid sites leads to undesired de-alkylation and/or disproportionation . Therefore, the silica to alumina molar ratio of the zeolite preferably is of from 10 to 50.

Conventionally, it was thought that isomerisation catalysts need a substantial amount of zeolite in order to be sufficiently active. It has now surprisingly been found that a relatively limited amount of zeolite PSH-3 and/or MCM-22 gives a high isomerisation activity without the undesirable side-reactions such as de-alkylation and disproportionation/transalkylation . The skilled person is not directed in the art to considering using a low zeolite content in an isomerisation catalyst.

Thus, although the present invention provides a catalyst having a lower than expected proportion of zeolite, nevertheless the catalyst of the present invention has been found to be particularly beneficial in the isomerisation and hydroisomerisation of C8 aromatics more especially xylenes and ethylbenzene.

The catalyst of the present invention is

particularly suitable for isomerisation of xylenes to equilibrium composition. The catalyst of the present invention is suitable to provide para-xylene from other isomers of xylene while an additional amount of para- xylene can be obtained by hydroisomerisation of

ethylbenzene to xylenes .

It has been found that the catalyst according to the present invention can be modified to further decrease its disproportionation and/or transalkylation activity. For this, the zeolite PSH-3 and/or MCM-22 is treated with a silicon-containing compound such as ammonium

hexafluorosilicate . Suitably, the treatment further comprises drying, preferably at a temperature of from 70 to 170 °C, followed by calcining, preferably at a temperature of from 350 to 600 °C. The treatment can be carried out by treating either the zeolite per se or the combination of binder and zeolite. Preferably, the zeolite is treated with a silicon-containing compound before being mixed with the binder. Therefore, the present invention further relates to a process for making a catalyst according to the invention which comprises optionally treating zeolite PSH-3 and/or MCM-22 with a silicon-containing compound, mixing the zeolite with binder, drying the mixture preferably at a temperature of from 70 to 170 °C, calcining the dried mixture preferably at a temperature of from 350 to 600 °C, impregnating the calcined mixture with a Group VIII metal, drying the impregnated mixture preferably at a temperature of from

70 to 170 °C and calcining the dried impregnated mixture preferably at a temperature of from 350 to 600 °C.

According to a second aspect of the present

invention, there is provided a process for the

isomerisation of alkylaromatics to provide a reaction mixture, which process comprises contacting a hydrocarbon stream comprising alkylaromatics with a catalyst as defined above.

The hydrocarbon stream to be contacted with the catalyst according to the present invention preferably comprises at least 40 %wt of alkylaromatics comprising 8 carbon atoms, more specifically at least 50 %wt, more specifically at least 60 %wt, more specifically at least 70 %wt, more specifically at least 80 %wt . The hydrocarbon stream may comprise any amount of xylenes, such as more than 30 %wt based on total amount of feedstock. The hydrocarbon stream specifically contains at most 60 %wt of ethylbenzene, more specifically at most 50 %wt . The hydrocarbon stream preferably comprises less than 20 %wt of toluene, more specifically less than 10 %wt . Preferably, the hydrocarbon stream comprises at least 35 %wt of xylene, more preferably at least 40 %wt, more preferably at least 45 %wt . The amount of xylene is the total amount of all isomers.

Most preferably, the hydrocarbon stream contacted with the catalyst contains up to 3% by weight (%wt) of toluene, up to 0.5 %wt of aromatic compounds containing 9 carbon atoms and up to 30 %wt of non-aromatic

hydrocarbons such as naphthenes and paraffins. These amounts all are based on total amount of hydrocarbons contacted with the catalyst.

In order to maintain a chemical equilibrium which is advantageous for the ethylbenzene hydroisomerisation, it is advantageous to recycle naphthenes containing 7 or 8 carbon atoms to maintain the naphthenes concentration in the range of from 4 to 15 %wt, based on total amount of hydrocarbon stream. The exact desirable amount of naphthenes depends on circumstances such as process conditions .

In one embodiment of the process of the present invention, the hydrocarbon stream is contacted with the catalyst at a temperature in the range of from 300 to 500°C, preferably at least 350°C and preferably at most 450 °C. The temperature is the outlet temperature, i.e. the temperature of the reaction mixture when it leaves the reactor. The hydrogen partial pressure preferably is of from 1 to 20 bar, more specifically of from 4 to 15 bar, and the hydrogen/hydrocarbon molar ratio preferably is of from 1 to 10, more specifically of from 2 to 6.

The catalyst according to the present invention can be applied at a wide range of weight hourly space velocities such as of from 1 to 15 weight amount feed per weight amount catalyst per hour (hr^_1), more specifically of from 2 to 14 hr^_1. A special advantage of the catalyst of the present invention is that it has been found to be especially suitable for use at high space velocity, more specifically at a weight hourly space velocity of from at least 6 hr^_1, more specifically at least 7 hr^_1, more specifically at least 8 hr^_1, more specifically at least 9 hr^_1, most specifically at least 10 hr^_1 to at most 14 hr^_1, more specifically at most 13 hr^_1 and most

specifically at most 12 hr^_1.

In another embodiment, the conversion of the xylenes present in the hydrocarbon stream is such that the para- xylene approach to equilibrium as defined in the examples below as pXate is at least 90%, more specifically at least 92%, more specifically at least 93%, more

specifically at least 94%, more specifically at least 95%. Further, the ethylbenzene in the hydrocarbon stream which is converted in the process preferably is at least 10%, more specifically at least 15%. Generally, the ethylbenzene conversion will be at most 50%.

Furthermore, the alkylaromatics isomerisation catalyst according to the present invention is suitable for use in reducing the extent of disproportionation and transalkylation which tend to occur on the external surface of the catalyst.

Examples of the present invention will now be described by way of example only. Examples

Catalyst Preparation

A PSH-3/alumina catalyst was prepared starting from Zeolite PSH-3 having a silica to alumina molar ratio of 22 in the ammonium form. The zeolite PSH-3 was mixed with pseudo-boehmite alumina, kneaded and then shaped by extrusion into 1.6 mm cylinders to obtain extrudates containing 5 %wt of zeolite and 95 %wt of alumina, based on total amount .

The extrudates were dried at 120°C and subsequently calcined in air at 550°C for 4 hours. The finished extrudates were then subject to a pore volume

impregnation with the help of a platinum containing solution to obtain extrudates comprising 0.3 wt% Pt, based on total weight of catalyst, followed by drying at

150°C for 1 hour and calcination at 450°C for 2 hours. No further treatment was done on the catalyst. The catalyst obtained is referred to as Catalyst 1.

A further catalyst was prepared in the same way as Catalyst 1 with the exception that the zeolite was treated with a solution containing 0.02 mole of ammonium hexafluorosilicate per liter, dried at 150°C for 2 hours and further calcined at 550°C for 2 hours before being mixed with the boehmite alumina. The catalyst obtained is referred to as Catalyst 2.

Catalyst Testing

Catalysts 1 and 2 were tested in the isomerisation of a feed comprising a mixture of C8 aromatic

hydrocarbons as described in Table 1. Table 1 : Feed composition for catalyst testing

The catalytic test was performed in a plug flow reactor unit encompassing a reactor tube with an internal diameter of 15 mm, into which the catalyst was loaded together with SiC as packing material. After loading the catalyst was dried at 400°C for 1.5 hours and then reduced with H₂ at 450°C. The temperature of the reactor was then lowered to 425°C and the catalyst was treated with a mixture of 80 %wt ethylbenzene and 20 %wt meta- xylene for a period of 24 hours at a weight hourly space velocity (WHSV) of 5 g feed/g catalyst/h and a pressure of 12 barg to reach a stable operation regime. Following this, the catalyst was subjected to a temperature of 385°C and contacted with the feed described in Table 1 at a WHSV of 3.5 g feed/g catalyst/h and a

hydrogen/hydrocarbon molar ratio of 4.

The results can be seen in Table 2, which shows the %wt of ethylbenzene converted (EBC), the final %wt of para-xylene and ortho-xylene found in the xylene mixture (pX in Xyl, and oX in Xyl), the amount of aromatic hydrocarbons containing 9 or more carbon atoms (C9+Aroms), the amount of hydrocarbons containing 1 to 5 carbon atoms (Cl-5) and the %wt of the starting aromatic compounds having 8 carbon atoms being converted into products having a different number of carbon atoms ("C8 aromatics ring loss"). Further, the performance

characteristics were evaluated as follows (wherein EB is ethylbenzene ; pX is para-xylene and oX is ortho-xylene ) :

EBate = %wt EB in C8 aromatics in feed - %wt EB in C8 aromatics in product x 100% %wt EB in C8 aromatics in feed - %wt EB in C8 aromatics at equilibrium pXate = %wt pX in xylenes in product - %wt pX in xylenes in feed x 1 00%

%wt pX in xylenes at equilibrium- %wt pX in xylenes in feed oXate = %wt oX in xylenes in product - %wt oX in xylenes in feed x 1 00%

%wt oX in xylenes at equilibrium- %wt oX in xylenes in feed

The pXate is a measure of para-xylene approach to equilibrium .

Table 2 : Catalyst performance at WHSV 3.5

Subsequently, the WHSV was increased to 4.5 h^-1 and thereafter to 6.0 h^-1. The performance observed is shown in Tables 3 and 4.

Table 3: Catalyst performance at WHSV 4.5 h

Catalyst 1 Catalyst 2

EBC (%) 20 12

EBate (%) 25 13

pXate (%) 98 99

oXate (%) 94 82

C8 aromatics ring 4.1 3.6

loss (%wt)

pX in Xyl (%wt) 24 24

oX in Xyl (%wt) 23 23

Benzene (%wt) 0.88 0.77

Toluene (%wt) 0.79 0.37

C9+Aroms (%wt) 0.96 0.36

Cl-5 (%wt) 2.14 1.82 Table 4 : Catalyst performance at WHSV 6 h

Comparing catalysts 1 and 2 shows that the treatment of the zeolite with a silicon containing compound such as ammonium hexafluorosilicate is effective in lowering the transalkylation and disproportionation activity of the catalyst .

Further, the catalyst testing results show that the catalysts according to the present invention exhibit good xylene isomerisation activity and good p-xylene

selectivity even at very high space velocities. This makes these catalysts suitable for application at high space velocities.

Claims

C L A I M S

1. An alkylaromatics isomerisation catalyst, which catalyst comprises :

at least 50 %wt of an acidic inorganic binder;

at least 0.01 %wt of a Group VIII metal; and

1-9 %wt zeolite PSH-3 and/or MCM-22.

2. A catalyst as claimed in claim 1, wherein the catalyst is an extrudate.

3. A catalyst as claimed in either preceding claim, wherein the pore volume of the inorganic binder is of from 0.6 to 2.0 ml/g.

4. A catalyst as claimed in any preceding claim, wherein the bulk density of the inorganic binder is of from 0.2 to 0.8 g/cm³.

5. A catalyst as claimed in any preceding claim, wherein the SAR is in the range of from 10 to 50.

6. A catalyst as claimed in any preceding claim, which catalyst comprises of from 1 to 7 %wt zeolite PSH-3.

7. A catalyst as claimed in any preceding claim, wherein the zeolite PSH-3 and/or MCM-22 has been treated with a silicon-containing compound.

8. A process for the isomerisation of alkylaromatics to provide a reaction mixture which process comprises contacting a hydrocarbon stream comprising alkylaromatics with a catalyst as claimed in any of the preceding claims .

9. A process as claimed in claim 8 wherein the

hydrocarbon stream comprises at least 50 %wt of aromatic hydrocarbons containing 8 carbon atoms .

10. A process as claimed in claim 8 or 9 wherein the temperature is of from 350 to 450 °C and the hydrogen partial pressure is of from 4 to 15 bar.

11. A process as claimed in any one of claims 8 to 10 wherein the weight hourly space velocity is at least

6 hr^_1.

12. A process as claimed in any one of claims 8 to 11 wherein the hydrogen to hydrocarbon molar ratio is of from 2 to 6.