Field of invention The present invention relates generally to a method for the regeneration of zeolite catalysts, in order to maintain a high and stable activity of the catalyst. Said catalysts are used in converting of olefins or paraffins or aromatics in CFB (circulating fluidized bed) reactor systems.

State of the art Catalysts are usually regenerated at high temperatures of 500-800 °C with air.

The purpose of catalyst regeneration is to burn off coke formed on the catalyst surface, because the coke decreases the activity of the catalyst, and the selectivity of the desired reaction is lower. The objective is typically to burn all or most of the coke in the catalyst. There are some reactions where catalysts regenerated in this manner are suitable, such as cracking of hydrocarbons.

Coke is regarded to contain mostly very diverse carbonaceous compounds comprising poly-aromatic compounds, small aromatic compounds and non- aromatic compounds.

Coke can be removed by oxidative treatment. The regeneration of ZSM-22 zeolite is known from Simon, M. et al (J. Catal. 147 (1994) 484), wherein ZSM-22 catalyst was deactivated in skeletal isomerization of butene. The regeneration temperatures were between 500 and 600 °C and the regeneration gas was oxygen with varying amounts of nitrogen (0-94 %).

Oxidizing agents, such as ozone and nitrous oxide, have also been used for the elimination of coke from zeolites. Oxidative treatment often has detrimental effects on the catalyst's active sites and the choice of operating conditions is

important in limiting the undesired effects, which particularly water has on the active sites of the catalyst at high temperatures.

However, certain reactions require some coke to be present in order to obtain a highest possible yield of a product, and therefore, after the regeneration of a catalyst, some pre-treatment is needed. An example of a pre-treatment before a reaction is described in US 2002/0019307 wherein a molecular sieve was pre- treated with hydrocarbon at a temperature of 300-550 °C and under a pressure of 0.1-1 MPa to deposit coke in the pores of the molecular sieve. The pre-treatment was performed prior to skeletal isomerization of linear olefinic C4-C20 hydrocarbons.

FI 20002783 discloses skeletal isomerization of linear C4-C6 olefins to corresponding isoolefins. The reaction is suitably performed in a circulating fluidized bed reactor system (CFB) comprising a reactor part and a regeneration part, which enables continuous regeneration of the catalyst. During the regeneration, typically all coke formed is removed from the zeolite catalyst and additionally a pre-treatment of the catalyst is required.

Based on the above it can be seen that there exists a need for an improved regeneration method for zeolite catalysts, particularly in CFB reactor systems.

In the following zeolites are described in more detail. Ferrierite is a zeolite wherein the unit cell formula is Na2Mg2 [Al6Si3o072] *18H20. The aluminium content and cations of ferrierite can be varied whereupon the formula can be written in following manner: (Me', Me") x/3 (AIOa) x (Si02) 36-x*l8H20 (x<6). Ferrierites have two types of channels, which are intersecting. The pore dimensions of 10-ring channels are 4. 2 x 5. 4 A, and 8-ring channels are 3.5 x 4.8 A. ZSM-35-zeolites differ from natural ferrierites with regard to their X-ray- diffraction patterns. Natural ferrierite exhibits a significant line at 11.33 A, which is not determined to be the significant line for ZSM-35-zeolites (weak line at 11.3

- 11. 5 A). This definition was later changed and now ZSM-35 is considered to be equivalent to its isotypes, which include ferrierite, ISI-6, NU-23 and Sr-D.

Tectometallosilicates with ferrierite crystal structure have X-ray diffraction patterns, which do not differ significantly from ZSM-35 (the d-value 11.3 is weak or medium). Tectometallosilicates having a ferrierite structure are defined to be ferrierite, FU-9, ISI-6, NU-23, ZSM-21, ZSM-35 and ZSM-38.

Zeolite based catalysts having pore sizes of at least about 4.5 A and a pore structure characterised by intersecting 10-ring and 8-ring channels are defined as ferrierite, dachiardite, epistilbite, heulandite, and stilbite.

ZSM-22 zeolite belongs to Theta-1 group (TON) of molecular sieves. ZSM-22 has one-dimensional 10-ring channels (dimensions 4.4x5. 5 A). Its unit cell has the following formula : Nan [AlnSi24-n04s].-4 HzO with n<2. ZSM-22 has a relative low aluminium content and moderate acidity. ZSM-22 is from crystallographic order orthorhombic with symmetry Cmc21. Cell dimensions are a=13. 8, b=17.4 and c=5.0 A. Materials with the same topology are ISI-1, KZ-2 and NU-10.

ZSM-23 zeolite belongs to MTT type of molecular sieves. ZSM-23 has one- dimensional 10-ring channels (dimensions 4. 5x5. 2 A). Its unit cell has following formula : Nan [AllSi24, 0481.-4 H20 with n<2. ZSM-23 is from crystallographic order orthorhombic with symmetry Pmc2l. Cell dimensions are a=21. 5, b=ll. l and c=5.0 A. Materials with the same topology are EU-13, ISI-4 and KZ-1.

SAPO-11 belongs to AEL structure group. It has one-dimensional 10-ring channels (dimensions 4. 0x6. 5 A). Group AEL unit cell has following formula : [Al20P20080]. The crystallographic order is orthorhombic with symmetry Ibm2. Cell dimensions are a = 13.534, b = 18. 482 and c= 8. 370A. Materials with same topology are AlPO-11 and MnAPO-11.

ZSM-5 has MFI structure. ZSM-5 has a three dimensional structure with 10-ring channels (5. 1x5. 5 A and 5.3x5. 6 A). Its unit cell has following formula: Nan (H2O)16[AlnSi96-nO192] with n<27. ZSM-5 is from crystallographic order orthorhombic with symmetry Pnma. Cell dimensions are a=20. 07, b=19.92 and c=13.42 A. Materials with the same topology are for example AMS-1B, AZ-1 and Boralite C.

Beta-zeolite has a three-dimensional structure with 12-ring channels (6. 6x6. 7 A and 5. 6x5. 6 A). Its unit cell has following formula: Na7 [Al7Sis70i2g]. Beta-zeolite is from crystallographic order tetragonal with symmetry Pn, 22. Cell dimensions are a=12. 661, b=12.661 and c=26.406 A. Materials with the same topology are for example CIT-6 and Tschemichite.

Y-zeolite belongs to the faujasite (FAU) group. It has a three-dimensional structure with 12-ring channels (7.4x. 7.4 A). Faujasite has a unit cell formula: (Ca2+, Mg2+, Na+2)29(H2O)240[Al58Si134O384). Y-zeolite is from crystallographic order cubic with symmetry Fd-3m. Cell dimensions are a=24.74, b=24.74 and c=24. 74 A. Materials with the same topology are for example NaX and CSZ-1.

Isomerization is considered as a reaction wherein the molecular formula of a substance does not change but its structure changes. Isomerization is divided to many groups and the dividing can be made after the group of molecules that are isomerized (paraffin isomerization, olefin isomerization). In these reactions linear paraffins or olefins are reacted to branched paraffins or olefins (or vica verca).

The dividing can also be made after the reaction type (skeletal isomerization, double bond isomerization, etc. ). Here the expression"skeletal isomerization"is used for a reaction wherein one n-olefin reacts to one isoolefin (or vice verca).

However, in the literature, several other expressions have also been used for the same reaction, such as olefin isomerization, hydrocarbon conversion, preparation of branched olefins, conversion of normal olefins to branched olefins and structural isomerization.

Dimerization is considered as a reaction wherein two olefins, either linear or branched, react together to form diisoolefin. In oligomerization, three or more olefins react together to form an oligomer. The oligomerization reaction can be described with the following reaction equation : a CnH2n -> (CnH2n)a, wherein a = 3-100. Dimerization and oligomerization can also be performed for olefins containing different amounts of carbon atoms. Alkylation is considered as a reaction wherein a branched paraffin or an aromatic is alkylated with an olefin to yield an alkylate or alkylaromatics.

Object of the invention An object of the invention is a method for the regeneration of zeolite catalysts in order to maintain a high and stable activity of the catalyst.

A further object of the invention is to provide a zeolite catalyst with high activity and stability, for converting of olefins or paraffins or aromatics in CFB reactor systems.

Characteristic features of the method according to the invention are provided in the claims.

Summary of the invention It has now been found that the problems related to the methods according to the state of the art can be avoided or at least substantially decreased with the method according to the invention. When the method according to the invention is used, a stable and high yield of a hydrocarbon product can be obtained without any pre- treatment of the catalyst. The method for the regeneration of zeolite catalysts is performed continuously in a regeneration part of a CFB reactor. The regeneration conditions are chosen as follows : 1) to maintain the amount of coke in the catalyst

in an optimal range, and 2) to modify the nature of coke formed during the reaction.

This can be achieved in a CFB reactor system : 1) With an inert regeneration gas, or 2) With an inert regeneration gas containing a low amount of oxygen, or 3) With air at a low temperature, or 4) With water vapour.

Detailed description of the invention According to the invention, the method for the regeneration of zeolite catalysts is performed either with an inert regeneration gas at a temperature higher than the reaction temperature, or with an inert regeneration gas containing equal or less than 10 mol-% of oxygen at a temperature higher than the reaction temperature, or with air at a temperature below 490 °C, preferably below 470 °C, and particularly preferably at a temperature of 300-450 °C, or with water vapour at a temperature higher than the reaction temperature, in a CFB reactor system, wherein a reaction involving hydrocarbons and requiring activity and high selectivity of the catalyst, is performed. The reaction involving hydrocarbons is selected from isomerization of olefins, isomerization of paraffins, dimerization, oligomerization and alkylation, particularly skeletal isomerization of olefinic C4-Clo hydrocarbons, preferably of olefinic C4-c7 hydrocarbons. Examples of suitable inert regeneration gases are paraffins, such as methane, butane and mixtures thereof like natural gas, nitrogen, carbon dioxide and the like.

Here a zeolite catalyst means a catalyst containing a zeolite as an active component and usually a carrier. The zeolite can be modified with different means including ion exchange, calcination treatment and dealumination known from the state of the art. Zeolite catalysts may have metals in ionic, oxide or in reduced

form. The metal can also be in the framework of the zeolite. The carrier is selected from silica, alumina, clay and any other suitable carriers.

Zeolites according to invention have acid sites. Those acid sites can be formed in the removal of templates, acid treatments, ammonium ion exchange and calcination treatments, ion exchange of cations and calcinations or in the reduction of metals.

According to the invention, medium and large pore zeolites having a one, two or three-dimensional structure and containing 8-12 rings, preferably 10-rings, or 8- rings and 10-rings, are suitable zeolite catalysts for the hydrocarbon reactions referred to herein. The framework aluminium content of the catalyst is preferably equal or less than 6 wt-%. Preferably the pore size of the zeolite is equal or less than 0.8 nm.

Suitable zeolite catalyst are selected from the group consisting of ferrierite, ZSM- 22, ZSM-23, ZSM-5, SAPO-11, Beta-and Y-zeolites, and they are presented in following Table 1 and said zeolite catalysts are usually on a carrier. Said zeolites may be used in reactions selected from olefin and paraffin isomerization reactions, olefin dimerization and oligomerization reactions and alkylation reactions.

Table 1. Name of Channels Type species tsotopic framework structure zeolite Ferrierite [001) 10 4. 2x5. 4 A Na2Mg2 [Al6Si3o072] x ZSM-35, NU-23, FU-9, (FER) [010] 8 3. 5x4. 8 A 18H20 ISI-6, Sr-D ZSM-22 [001] 4. 6x5. 7 ANaAlnSi24-n04s], Theta-l, ISI-l, KZ-2, NU-10 (TON) (n<2) ZSM-23 [001] 4. 5x5. 2 A [AlnSi24-n048], EU-13JSI-4, KZ-1 (MTT) (n<2) l ZSM-5 [100] 5. 1x5. 5 A [ASi96-nOi92], AZ-1, AMS-1B, Fe-silicalite (MFI) [010] 5. 3x5. 6A (n<27) I SAPO-11 [001j4. 0x6. 5A [SixAl2o-xP2o08o] MnAPO-11 (AEL) Y [111] 7. 4x7. 4A (Ca, Mg, Na2) USY, CoAlPO (FAU) [Al5sSii340384] Beta [100] 6. 6x6. 7 ANan [AlnSi57-nOi2s], CIT-6 (BEA) [001] 5. 6x5. 6 A (n<7)

According to the invention, the zeolite catalysts presented above are particularly suitable in CFB reactor systems. The CFB reactor system is described for example in FI 20002783 in detail, which is incorporated herein by reference. The principle of the CFB reactor system is illustrated in the enclosed Figure 1.

In Figure 1, a CFB reactor system is presented. Hydrocarbon 20 is fed to the bottom part of the reactor 100. In a special embodiment, if hydrocarbon is desired to feed for diluted suspension, pre-fluidization gas 21 (ex. nitrogen) is fed separately to the bottom part of the reactor 100. Hydrocarbon transports catalyst along the reactor riser 1, hydrocarbon reacting for desired compound. The hydrocarbon-catalyst suspension continues further to the cyclone 2, where

hydrocarbon is separated from the catalyst. Hydrocarbon exits through the exit- assembly 3 to a treatment part of product and the used catalyst is transferred along the cyclone leg 4 to return channel 5 and again to the reactor liser 1. Part of the used catalyst is transferred along the transit tube 7, by adjusting with the valve 6, to the bottom part of the regenerator 200, where the catalyst is fluidized with regeneration gas 23 introduced to the bottom part of the regenerator 200. The catalyst continues together with the regeneration gas along the regenerator riser 8, when the coke on catalyst surface is at least partly removed or its nature is modified. Combustion gas-catalyst suspension is transferred to the cyclone 9, wherein the combustion gas is separated from the catalyst. The combustion gas is removed through the exit-assembly 10, for example to a heat recovery unit. Then the catalyst is led along the cyclone leg 11 to the return channel 12 of the regenerator 200 and again to the regenerator riser 8. The valve 13 is used for the adjustment of equal amounts of regenerated catalyst and catalyst coming from the reactor 100 to the regenerator 200 along the channel 14. The degree of regeneration of the coked catalyst can be adjusted with catalyst exchange.

The method according to the invention has several advantages when compared to the methods according to the state of the art. When an inert substance is used for the regeneration of a catalyst, the amount of coke is decreased and it becomes more polyaromatic in nature. The selectivity of the catalyst is maintained high during the reaction, such as skeletal isomerization, and the selectivity to side products such as naphthenes, aromatics and heavier hydrocarbons is low. Skeletal isomerization is typically performed at a temperature of 25-500 °C. In skeletal isomerization the regeneration temperature below 450 °C is preferable in air.

During the regeneration, part of the coke is desorbed from the catalyst. At the same time coke is transformed to become more polyaromatic in nature and its structure is modified. This means that the H/C ratio of the coke is reduced. As a result the catalyst keeps continuously in an active state, the activity is high and the

amount of coke keeps low, which all in turn achieve high yields of the desired product, the amount of side-products being low and the selectivity being high.

When the regeneration is performed with air or diluted air, part of the coke can be burned to carbon oxides and water. The degree of burning is preferably limited in order to keep the amount of coke at an optimal value. The burning can be limited either by adjusting the amount of oxygen in the regeneration gas or by adjusting the regeneration temperature.

Accordingly, a stable catalyst with optimal activity is achieved. Coke fills the inner cavities of the zeolite particles and the outer surface of the zeolite crystallites in the catalyst is kept clean with an inert stream or with minor amounts of oxygen or water vapour. This results in that the process can be run continuously in a stable manner. No repeated regenerations are needed. Only one reactor is required for continuous stable production instead of several reactors and processing steps. Further, no pre-treatments are required because of the stability of the process and because the need for control and adjusting steps is minimal. No interruptions in the production are needed, which usually cause undesirable emissions and economical losses. Only in the case a fresh catalyst is used for the first time and it contains no carbonaceous substances, coke is incorporated in the catalyst using any suitable method known in the art.

Relatively low regeneration temperatures of 300-500 °C can be used, which are less detrimental to the catalysts. Also suitable catalysts, which are sensitive to high temperatures and water vapour, can be used in the method, with the provision that the catalyst and gases are compatible with each other.

The waste of the hydrocarbon feed is low. After the coke is formed on the catalyst and the catalyst is regenerated according to the invention, a significant amount of coke remains on the catalyst. The coke is thus not burned entirely to COx in every regeneration cycle. This results in a significant reduction in COx emissions.

The method according to the invention is also particularly suitable for processes where the hydrocarbon feed contains impurities such as sulphur or nitrogen compounds. During the contact in the reaction part, part of impurities from the feed, remain on the catalyst. Continuous regeneration can be used for adjusting the activity of the catalyst according to the amount of impurities in the feed.

The invention is illustrated in more detail in the following examples, which however are not meant to limit the scope of the invention.

Examples Example 1. (Comparative) Hydrocarbon feed containing mainly C5 and C6 paraffins and olefins, as described in the following Table 2, was charged to a CFB unit. Commercial ferrierite was used as the zeolite in the catalyst.

Table 2. The composition of the hydrocarbon feed Paraffins 46 wt-% n-Olefins 14 wt-% i-Olefins 25 wt-% Others 15 wt-% The hydrocarbon feed of 4 kg/h was allowed to react in the CFB unit depicted in Figure 1. The reaction conditions were: Temperature 300 °C and pressure 1 bar (abs). At the same time the catalyst was regenerated continuously with air at a temperature of 500 °C. After 55 hours on stream, the conversion of n-olefins was 44 % and selectivity to i-olefins only 59 %.

Example 1 shows that if the conventional way of regeneration is used in skeletal isomerization of C5 and C6 paraffins and olefins, lower selectivity and lower yield of the product are obtained.

Example 2.

The feed used in Example 1 was tested under the same conditions in the same reactor. However, nitrogen was used for the regeneration of the catalyst at 450 °C.

After 55 hours on stream, the conversion of n-olefins was 41 % and selectivity to i-olefins 86 %.

Example 2 shows that if an inert gas is used for the regeneration of the catalyst, the activity of the catalyst and the selectivity to i-olefins stay at a high level.

Example 3.

The feed used in example 1 was tested in the same reactor at 290 °C and under a pressure of 1 bar with a hydrocarbon flow of 6 kg/h. Nitrogen was used for regeneration at 490 °C. After 40 hours on stream, the conversion of n-olefins was 33 % and selectivity to i-olefins 93 %. After 45 hours on stream, 3 mol-% of oxygen was added to the regeneration stream. After 90 hours on stream, the conversion of n-olefins was 34 % and selectivity to i-olefins 86 %.

Example 3 shows that the regeneration can be controlled with the amount of oxygen in the regeneration gas. A high and stable activity and selectivity is obtained. The regeneration can also be carried out with air only, but in this case it is preferable to use lower temperatures (300-450 °C) in the regeneration to obtain a high selectivity.

Example 4. (Comparative) Dimerization of n-butene with a fresh zeolite catalyst was performed in a microreactor. The catalyst contained a zeolite with ferrierite structure. Its Si/Al- ratio was 29, BET-surface area was 330 m2/g and crystallinity was 80 %. The reaction was carried out at a temperature of 150 °C, under a pressure of 20 bar and with a WHSV of 4. The feed was a commercial, butene containing feed. The selectivities to gasoline were 83-94 %.

Example 5.

Dimerization of n-butene with a coked zeolite catalyst from example 4, which was regenerated according to the invention, was performed in a microreactor. The reaction was carried out at a temperature of 150 °C, at a pressure of 20 bar and with a WHSV of 4. The feed was a commercial, butene containing feed. The selectivities to gasoline (94-100 %) were higher than obtained with a fresh catalyst.