FI118517B - Catalytic regeneration process - Google Patents

Description

118517

FIELD OF THE INVENTION The present invention relates generally to a process for the regeneration of catalysts to maintain a high and stable catalyst activity. Said catalysts are used for the conversion of olefins or paraffins or aromatic substances in CFB (circulating fluidized bed) reactor systems.

10 Current state of the art

Catalysts are generally regenerated at high temperatures of 500 to 800 ° C with air. The purpose of catalyst regeneration is to burn off the coke formed on the catalyst surface because the coke reduces the activity of the catalyst and the selectivity of the desired reaction is lower. Typically, the purpose is to completely or almost completely burn the coke from the catalyst. There are some reactions, such as hydrocarbon cracking, to which the catalysts regenerated in this way are suitable.

··· Coke is considered to contain a wide variety of polyaromatic compounds, small carbon compounds containing 20 aromatic compounds and non-aromatic compounds.

t · ·· · • · · ««

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

Oxidants such as ozone and nitrous oxide have also been used to remove coke from zeolites. Effects of oxidative treatment on active catalysts. . ·. The sites are often detrimental and the choice of treatment conditions is important in limiting the undesirable effects of water in particular on the active sites of the catalyst at elevated temperatures.

However, in order to maximize the yield of the product, certain reactions 5 require some coke to be present and therefore some pre-treatment is required after regeneration of the catalyst. An example of a pre-reaction pre-treatment is described in US 2002/0 019 307, in which a molecular sieve was pretreated with hydrocarbon at a temperature of 300-550 ° C and 0.1-1 MPa to deposit coke into the pores of the molecular sieve. Pretreatment 10 was performed prior to backbone isomerization of olefinic C4-C20 linear hydrocarbons.

FI 20 002 783 discloses framework isomerization of linear C 4 -C 6 olefins to the corresponding iso-olefins. The reaction is suitably carried out in a circulating fluidized bed reactor system (CFB) comprising a reactor section and a regeneration section, allowing continuous regeneration of the catalyst. In regeneration, all coke formed is typically removed from the zeolite catalyst and further pre-treatment of the catalyst is required.

From the foregoing, it can be seen that there is a need for zeolite catalysts ·· ♦ ·. '· *; 20 improved regeneration process, especially in CFB reactor systems.

: ***: Zeolites are described in more detail below. Ferrierite [ferrierite] is a ··· zeolite with the elemental formula of Na2Mg2 [Al6Si3o072] * 18H20. The ferricite aluminum content and cations may vary, so that the formula can be scaled to the following form: (Me ', Me') x / 3 (A102) X (SiO2) 36.x * 18H2O (x <6). There are two types of intersecting channels in ferrite lines., * · *. The 10-ring channels have pore dimensions of 4.2 x 5.4 Å and the 8-ring channels have 3.5 x 4.8 Å.

• In their X-ray diffraction patterns, ZSM-35 zeolites differ from natural ·· # · ferrites. Natural ferrite produces a significant line at 11.33. 30 Ä, which was not defined as a significant line for ZSM-35 zeolites (weak ·· * line in the range 11.3 - 11.5 Å). Subsequently, the definition was changed and today ZSM- * · 3 118517 35 is considered to be equivalent to its isotypes including ferrierite, ISI-6, NU-23 and Sr-D.

The X-ray diffraction patterns of ferritic crystalline structures or tectometallic silicates having a ferritic structure do not differ significantly from ZSM-35 (d-value 11.3 is weak to moderate). Fermenterite, FU-9, ISI-6, NU-23, ZSM-21, ZSM-35 and ZSM-38 are defined as femerite-structured tectometallic silicates.

Zeolite-based catalysts having pore sizes of at least about 4.5 to 10 Å and characterized by pore structures characterized by shear 10-ring and 8-ring channels are defined as ferrerite, dachiardite, epistilbite, heulandite and stilbite.

ZSM-22 zeolite belongs to the Theta-1 (TON) molecular sieve. The ZSM-15 22 has one-dimensional 10-ring channels (dimensions 4.4 x 5.5 Å). Its elementary booth is a formula; Nan [AlnSi24.n048] · ~ 4 H2O when n <2. ZSM-22 has a relatively low aluminum content and moderate acidity. ZSM-22 is crystallographic in structure orthorhombic with Cmc2i symmetry. The dimensions of the booth are a = 13.8, ·: · b = 17.4 and c = 5.0 Å. Materials of similar topology are ISI-1, KZ-2 and: Vi 20 NU-10.

• · • 1 · • 1 2 3 · • «• · ...! ZSM-23 zeolite belongs to MTT-type molecular sieves. The ZSM-23 has • 1: 1-dimensional 10-ring channels (4.5 x 5.2 A). Its elementary booth has the formula: ···

Nan [AlnSi24-n048] '- 4 H2O at n <2. ZSM-23 has a crystallographic structure of 25 orthorhombic symmetry with Pmc2i. The dimensions of the booth are a = 21.5, b = 11.1 and c ·· ”= 5.0 Ä. Materials for similar topology are EU-13, ISI-4 and KZ-1.

··· • · 2 • · 3 ···!,! ϊ SAPO-11 belongs to the AEL structural group. It has one-dimensional 10-ring channels ··· o (dimensions 4.0 x 6.5 A). The AEL group elementary cubicle has the formula: [AI20P20O80] · Φ {1 · .. 30 The crystallographic structure is orthorhombic with symmetry of Ibm2. The dimensions of the cubicle are: a = 13,534, b = 18,482 and c = 8,370 Å. Materials of similar topology are A1PO-Ilya Mn APO-11.

The ZSM-5 has an MFI structure. The ZSM-5 has a three-dimensional structure with 10 to 5 ring channels (5.1 x 5.5 Å and 5.3 x 5.6 Å). Its elemental enclosure is of the formula: Nan (H 2 O) i6 [AlnSi96-n0i92] when n <27. The ZSM-5 has a crystallographic structure orthorhombic with Pnma symmetry. The dimensions of the booth are a = 20.07, b = 19.92 and c = 13.42 Å. Materials of similar topology include AMS-1B, AZ-1 and Boralite C.

10

The beta zeolite has a three-dimensional structure with 12-ring channels (6.6 x 6.7 Å and 5.6 x 5.6 Å). Its elemental booth has the formula: Na7 [Al7Sis70i2s]. The beta zeolite has a tetragonal crystallographic structure with Pni22 symmetry. The dimensions of the booth are a = 12,661, b = 12,661 and c = 26,406 Å. Materials for a similar topology include, for example, C1T-6 and Tschemichite.

Y-zeolite belongs to the Faujasite (FAU) group. Its structure is three-dimensional and has 12 ring channels (7.4x7.4 Ä). The formula of the Faujasite elementary booth is: (Ca2 +,,. * · * Mg2 +, Na + 2) 29 (H2O) 240 [Al58Sii34O384]. The Y-zeolite has a crystallographic • »: V 20 structure with a cubic symmetry of Fd-3m. The dimensions of the booth are a = ϊ *, · 24.74, b = 24.74 and c = 24.74 A. Materials of similar topology are ···: ... · example NaX and CSZ-1.

Isomerization is defined as a reaction in which the molecular formula of a substance is unchanged but its structure is altered. The isomerization is divided into several groups and the division can be done according to the molecular group to be isomerized (paraffin isomerization, olefin isomerization. In these reactions, linear paraffins or olefins react ♦ «· V · to branched paraffins or olefins (or vice versa). The division can also be * ... · based on the type of reaction (backbone isomerization, double bond isomerization, etc.).

j * \. The present term "skeletal isomerization" (skeletal isomerization) is used in the reaction where one n-olefin reacts to one iso-olefin (or vice versa).

5, 118517

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

5

Dimerization is defined as the reaction in which two linear or branched olefins react with one another to form a di-iso-olefin. In oligomerization, three or more olefins react with each other to form an oligomer. The oligomerization reaction can be represented by the reaction equation: a C n H 2 -> (C n H 2 n) a, where 10 a = 3 to 100. Dimerization and oligomerization can also be carried out with olefins containing different amounts of carbon atoms. Alkylation is the reaction whereby a branched paraffin or aromatic is alkylated with an olefin to give an alkylate or alkyl aromatics.

OBJECT OF THE INVENTION

The invention relates to a process for the regeneration of zeolite catalysts in order to maintain high and stable activity of the catalyst.

It is a further object of the invention to provide a highly active and stable • · ί * · *; zeolite catalyst for the conversion of olefins or paraffins or aromatics in CFB reactor systems.

***: The claims disclose the characteristic features of the process according to the invention.

SUMMARY OF THE INVENTION It has been found that by the method of the invention, the state of the art. The problems associated with the methods can be avoided or at least substantially reduced.

*, ···. Using the process of the invention, stable and high yields of the hydrocarbon product can be achieved without pretreatment of the catalyst * · ·· * 6 118517. The process for regeneration of zeolite catalysts is carried out continuously in the regeneration section of a CFB reactor. The regeneration conditions are selected as follows: 1) to keep the amount of coke in the catalyst within the optimum range, and 2) to modify the nature of coke S formed in the reaction.

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

Detailed Description of the Invention 15

According to the invention, the process for the regeneration of zeolite catalysts is carried out either with an inert regeneration gas at a temperature above the reaction temperature, or with an inert regeneration gas containing 1010 mole% oxygen at a reaction temperature above or below 490 ° C, preferably below 470 ° C. particularly preferred at a temperature of 300-450 ° C, or steam at a temperature above the reaction temperature, in a CFB reactor system that performs a hydrocarbon-related reaction that requires high catalyst activity and high selectivity. The hydrocarbon-linked reaction is selected from: isomerization of olefins, isomerization of paraffins, dimerization, oligomerization and alkylation, in particular backbone isomerization of C 4 -C 7 olefinic hydrocarbons, preferably C 4 -C 7 olefinic hydrocarbons. Examples of suitable inert regeneration gases are paraffins such as methane, butane, and the like; mixtures such as natural gas, nitrogen, carbon dioxide and the like.

# 30 Here the zeolite catalyst refers to the catalyst that contains the zeolite as active. as a component and generally a carrier. The zeolite can be converted by various techniques known in the art e · ··· 7 118517, including ion exchange, calcination treatment and dealumination. Zeolite catalysts may contain metals in ionic, oxide or reduced form. The metal may also be present in the body of the zeolite. The carrier is selected from silicon, alumina, clay and some other suitable carriers.

The zeolites of the invention have acid sites. These acid sites may be formed during the removal of matrix embryos, acid treatments, ammonium ion exchange and calcination treatments, cation ion exchange and calcination or metal reduction.

According to the invention, medium and large pores zeolites having a one, two or three dimensional structure and comprising 8-12 rings, preferably 10 rings, or 8 rings and 10 rings are suitable as the zeolite catalysts for the hydrocarbon reactions involved. The catalyst body preferably has an aluminum content of <6% by weight. The pore size of the zeolite is preferably <0.8 nm.

Suitable zeolite catalysts are selected from the group consisting of ferrerite, ZSM-22, ZSM-23, ZSM-5, SAPO-11, Beta and Y zeolites shown in Table 1 * ·· *. ** ·. 20 below, and said zeolite catalysts are generally supported. Said zeolites • · · * · · · can be used in the following reactions selected from: • · olefin and paraffin isomerization reactions, olefin dimerization and ·· j * · *: oligomerization reactions and alkylation reactions.

* ··· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ··· · «· · • · · * # · ··· • · • · * 8 118517

Table 1.

Zeolite Channels Type Material Isotopic name of frame structure

Ferrierite Na2Mg2 [Al6Si309072] ZSM-35, NU-23, FU-9,

(FER) 4.2x5.4 Å 18H2O ISI-6, Sr-D

Δ 3.5x4.8 Å ZSM-22 4.6x5.7 Å Na ^ AlnS Si ^ ^ Theta-1, ISI-1, KZ-2, NU- (TON) (n <2) ZSM-23 4.5x5.2 Ä Na ^ AlAl-nC ^ EU-13, ISI-4, KZ-1 (MTT) (n <2)

ZSM-5 [100] 5.1x5.5 Å Nan [AlnSi96-nOi92i AZA, AMS-1B, ST

(MFI) 5.3x5.6 Ä (n <27) Silicalite SAPO-11 4.0x6.5 A [SixAl2o.xP2o08o] MnAPO-11 (AEL)

~ Ϋ [111] 7.4x7.4 A (Ca, Mg, Na2) USY, CoAlPO

(FAU) [AI58S1134O384] ~ Beta [100] 6.6x6.7 A Na ^ Sis? - ^^, CIT-6 (BEA) 5.6x5.6 Ä (n <7) • · '- - - * - * • · * • * · • • •••••••••

According to the invention, the above zeolite catalysts are particularly suitable for CFB reactors. The CFB reactor system is described in detail in ··· * ··· *, for example in FI20 002 783, which is incorporated herein by reference.

The principle of the CFB reactor system is illustrated in Figure 1 below.

··· «··· • • e • ·

Figure 1 shows a CFB reactor system. Hydrocarbon 20 is fed to the bottom of the reactor. In a particular embodiment, if hydrocarbon is to be supplied for a ··· dilute suspension, pre-fluidization gas 21 (e.g., nitrogen) is separately supplied to the bottom of the reactor 100. The hydrocarbon carries the catalyst: along reactor riser 1, with the hydrocarbon reacting to the desired compound. The hydrocarbon 9118517 catalyst slurry continues to cyclone 2 where the hydrocarbon is separated from the catalyst. The hydrocarbon is discharged through the outlet assembly 3 to the product treatment section and the spent catalyst is transported along the cyclone branch 4 to the return passage 5 and again to the reactor riser 1. The catalyst, together with the regeneration gas, continues along the slope of the regenerator 8, whereby the coke on the surface of the catalyst is at least partially removed or its nature changed. The flue gas catalyst suspension is transferred to cyclone 9 where the flue gas is separated from the catalyst 10. The flue gas is discharged through the exhaust assembly 10, for example to a heat recovery unit. Thereafter, the catalyst is led along the cyclone branch 11 to the return channel 12 of the regenerator 200 and again to the riser 8 of the regenerator.

The process according to the invention has several advantages over the state of the art. Ji1. When an inert substance is used to regenerate the catalyst, the amount of · · * .V 20 coke is reduced and naturally becomes more polyaromatic.

·· · • · · 2 .2 The selectivity of the catalyst is considered to be high in the reaction, e.g., in the framework isomerization, ··· • 1 * ··· 2 and by-products such as naphthenes, aromatics and the heaviest hydrocarbons. , selectivity is low. Body Isomerization Typically Performed · 3 ·

'··· 1 at 25 to 500 ° C. In body isomerization, regeneration below 450 ° C

, Preferably at air temperature.

In regeneration, part of the coke is desorbed from the catalyst. At the same time coke is transformed into a naturally polyaromatic, and its structure ··· • · * ··· 1 is modified. This means that the H / C ratio of the coke is reduced. As a result of this, the catalyst remains continuously in an active state with high activity and 999 coke content, all of which contributes to high yields of the desired product 118517 with low by-product volume and high selectivity. When regenerated with air or diluted air, some of the coke can be burned to carbon oxides and water. The degree of combustion is preferably limited to keep the amount of coke at optimum value. Combustion can be limited either by controlling the amount of oxygen in the regeneration gas or by controlling the temperature of the regenerator.

Thus, a stable catalyst with optimum activity is obtained. The coke fills the inner cavities of the zeolite particles, and the outer surface 10 of the zeolite crystallites of the catalyst is kept clean by inert flow or small amounts of oxygen or water vapor. This results in the process being continuously run in a stable manner. No repeated regeneration is required. Continuous stable production requires only one reactor instead of multiple reactors and processing steps. In addition, due to the stability of the process and the need for control and adjustment steps 15, pre-treatments are not required. There is no need for production interruptions, which usually lead to unwanted emissions and financial losses. Only in the case where a fresh catalyst is used for the first time when it contains no carbonaceous materials, is the coke incorporated into the catalyst by a suitable method known in the art.

• · · · * ·· 20 Relatively low temperatures between 300 ° C and 500 ° C can be used for regeneration and less harmful temperatures for catalysts. Suitable catalysts, sensitive to high temperatures and water vapor, may also be used in the process provided that the ·· ·: V catalyst and the gases are compatible.

• · · * ♦ • · ·· * 25 Hydrocarbon feed loss is low. When the coke is formed on the catalyst and the catalyst is regenerated in accordance with the invention, a significant amount of coke is left on the catalyst. Thus, the coke does not completely burn into COx gas in each φ · · V · regeneration period. This will lead to a significant reduction in CCV emissions.

The process according to the invention is also particularly suitable for processes in which the hydrocarbon feed contains miscellaneous impurities such as sulfur or nitrogen compounds.

φ · 11 118517

During contact in the reaction part, some of the impurities in the feed remain on the catalyst. Continuous regeneration can be used to adjust 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 intended to limit the scope of the invention.

EXAMPLES Example 1 (Comparative) A hydrocarbon feed containing mainly C5 and Ce paraffins and olefins, as described in Table 2 below, was charged to the CFB unit. As the zeolite, commercial ferrerite was used in the catalyst.

15

Table 2. Composition of the hydrocarbon feed

Paraffins 46% by weight ♦ .. * · * n-Olefins 14% by weight • · ·. ·. · I-Olefins 25% by weight ··· '' * Change 15% by weight · · · · · · · The hydrocarbon feed at 4 kg / h was allowed to react in the CFB unit shown in Figure 1.

The reaction conditions were: temperature 300 ° C and pressure 1 bar (abs). Simultaneously, the catalyst was regenerated continuously with air at 500 ° C. After a flow of 55 hours, the conversion of the n-olefins was 44% and the selectivity to the i-olefins was only 59%.

Example 1 demonstrates that if a conventional regeneration method is used for the C5 and C6 paraffins and olefins, the product will yield a · · *. ..: lower selectivity and lower yield.

12 118517

Example 2.

The feed used in Example 1 was tested under the same conditions in the same 5 reactors. However, nitrogen at 450 ° C was used to regenerate the catalyst. After 55 hours of flow, the conversion of n-olefins was 41% and selectivity to i-olefin was 86%.

Example 2 shows that if an inert gas is used to regenerate the catalyst, the activity and selectivity of the catalyst to the i-olefin remain high.

Example 3.

The feed used in Example 1 was tested in the same reactor at 290 ° C and 1 bar at a hydrocarbon flow rate of 6 kg / h.

Nitrogen at 490 ° C was used for regeneration. After a flow of 40 hours, the conversion of the n-olefins was 33% and the selectivity to the i-olefin was 93%. After 45 hours of flow, 3 mol% of oxygen was added to the regeneration stream. After a flow of 90 ··· hours, the conversion of n-olefins was 34% and selectivity to i- · * ·· 20 olefins was 86%.

· ·· · • · · • ♦ • *

Example 3 shows that regeneration can be controlled by the oxygen content of the regeneration gas. High and stable activity and selectivity are obtained. :> it · 'Regeneration can also be carried out only with air, but in order to obtain a high selectivity in regeneration, it is preferable to use lower temperatures (300-450 ° C).

··· · »* (((: (: Example 4. (Comparative) · · · · · · · · · 30 30 30 30 30 30 30 30 30 30 30 30 30 · · dim · · · · · · · · 30 · 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30

···; 1. The catalyst contained a ferritic zeolite. It had a Si / Al ratio of 29, a BET · 13118517 surface area of 330 m2 / g and a crystallinity of BO%. The reaction was carried out at 150 ° C, 20 bar and WHSV 4. The feed was a commercial butene-containing feed. Petrol selectivities were 83-94%.

Example 5.

The dimerization of n-butene was carried out with a coking zeolite catalyst regenerated according to the invention of Example 4 in a microreactor. The reaction was carried out at 150 ° C, 20 bar pressure and WHSV 4. The feed was 10 commercial butene-containing feeds. The selectivities for gasoline (94-100%) were higher than those obtained with fresh catalyst.

· «· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·„ · „· · · · · · · · To • · • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·–– IM 1 · · ···

Claims (16)

A process for regenerating zeolite catalysts, characterized in that the regeneration is carried out in a reactor system in which a reaction comprising hydrocarbons is carried out, either with an inert regeneration gas at a temperature higher than the reaction temperature, or with an inert regeneration gas containing equal to or less than 10 mol% of oxygen at a temperature higher than the reaction temperature, or with lute at a temperature below 490 ° C, advantageously below 470 ° C, or with water vapor at a temperature higher than the reaction temperature. Process according to Claim 1, characterized in that the reaction comprising hydrocarbons is chosen from isomerization of olefins, isomerization of paraffins, dimerization, oligomerization and alkylation of hydrocarbons. 15 3. A process according to claim 1 or 2, characterized in that the reaction comprising hydrocarbons is skeletal isomerization of olefinic C4-C10 hydrocarbons, advantageously olefinic C4-C7 hydrocarbons. A process according to any of claims 1-3, characterized in that the inert: * · *: regenerating gas is selected from paraffins and mixtures thereof, nitrogen and:: carbon dioxide. * · · · · · · · · · Process according to any one of claims 1-4, characterized in that the zeolite catalyst is selected from medium and large pore zeolites having a single, two or three dimensional structure containing 8-12 rings and having a ·· · * · .. * catalyst alumina contents of catalyst equal to or less than 6% by weight. ··· ···· ··· • · · · ··· • «· · · · · • · ··· ♦ · • ♦« ·· 118517 Process according to Claim 4, characterized in that the zeolite catalyst contains 10-rings, or 8-rings and 10-rings. Process according to any of claims 1-6, characterized in that the pore size of the zeolite is equal to or less than 0.8 nm. Process according to any of claims 1-7, characterized in that the zeolite catalyst is selected from the group consisting of ferrierite, ZSM-22, ZSM-23, SAPO-11, ZSM-5, Beta-zeolite and Y-zeolite. 10 Process for isomerization of olefins, isomerization of paraffins, dimerization, oligomerization or alkylation of hydrocarbons, in a CFB reactor system, characterized in that regeneration of a zeolite catalyst is carried out either with an inert regeneration gas at a temperature higher than the reaction temperature, or with an inert regeneration gas containing equal to or less than 10 mole% of oxygen at a temperature higher than the reaction temperature, or with lute at a temperature below 490 ° C, advantageously below 470 ° C, or with water vapor at a temperature higher than ··· reaction temperature. Method according to claim 9, characterized in that the inert φ · · ί ((<: the regenerating gas is selected from paraffins and mixtures thereof, nitrogen and 11. A process according to claim 9 or 10, characterized in that the * i ·: zeolite catalyst is selected from medium and large pore zeolites with a single, two or ··· • t * ··· 1 three-dimensional structure, containing 8-12 rings and having a t <; j · base aluminum content of the catalyst equal to or less than 6% by weight. «1 · • · • · • · · · •« i • · · • · • · · · · · · · · · · 118517 Method according to claim 11, characterized in that the zeolite catalyst contains 10-rings, or 8-rings and 10-rings, 13. A process according to any of claims 9-12, characterized in that the pore size of the zeolite is equal to or less than 0.8 nm. Process according to any of claims 9-13, characterized in that the zeolite catalyst is selected from the group consisting of ferrierite, ZSM-22, ZSM-23, 10. APO-11, ZSM-5, Beta zeolite and Y zeolite. 15. A process according to any one of claims 9-14, characterized in that the isomerization is the skeletal isomerization of C4-C10 olefins carried out at a temperature of 25-500 ° C. 15 Process according to any of claims 9-15, characterized in that the isomerization is the skeletal isomerization of C4-C7 olefins. • * · * ♦ ♦♦♦ e · • · * ♦ · * · · · · · · · · · · · ··· · · · · ··· ·· · · · · · · · · · · · • · • · ··· ♦ · · · · · · · · · ··· ♦ · · · ·· «# ·· * ··« · • • t • · ♦ * • t · • ♦ • · · • · · • · ···