FR2515171A1 - Gasoline component mfd. from cracker butene(s) fraction - by selective oligomerisation of isobutene, with isomerisation and recycle of rest - Google Patents

Abstract

An olefinic 4C fraction from steam- or catalytic-cracking is upgraded as follows. (a) It is reacted over fluorided Al2O3, boron-contg. Al2O3 or SiO2/Al2O3, converting at least 90% of the isobutene, mainly to dimers and trimers, and less than 10% of the n-butenes. (b) The di- and tri-isobutene are removed by distn., at least partly hydrogenated and then used in gasoline. (c) the remaining prod. from (a) (largely 4C) is extractively distilled, to remove paraffins overhead. (d) The other prod. from (c) (at least 99% n-butenes) is isomerised over fluorided Al2O3 or SiO2/Al2O3, giving substantial conversion of n- to iso-butene. (e) The prod. from (d) is distilled to remove 1-3C by-prods., and the rest is recycled to (a). Most (e.g. 98.85%) of the butenes present are converted to an excellent gasoline component.

Description

The present invention relates to a method for recovering cuts
C4 olefins made available to the market through the development of various steam cracking processes and catalytic cracking of naphthas and gas oils.

The olefins, butenes and isobutenes, can be used for petrochemical syntheses of more elaborate products (alcohols, aldehydes, acids, nitriles, etc.), but the tonnages of these C4 cuts are, in general, too large or at least may become too important for this recovery path to be considered on its own.

A second recovery method consists in recycling this C4 cut to the cracking unit (steam cracking) or catalytic cracking, after hydrogenation of the olefins; but, here, the isobutane contained in the hydrogenated cut, and which represents more than 50% by weight of the cut considered, does not give sufficiently interesting ethylene yields and also leads to a significant production of methane which is hardly usable only as fuel.

A third way of upgrading said cut C4 consists, after hydrogenation of this cut, in separating the n-butane from llisobutane by distillation and in recycling only to the steam cracking unit the nbutane, reserving the isobutane for other uses more advantageous, such as for example an alkylation for the production of iso-paraffinic gasoline. Nevertheless, the yields of ethylene and propylene, in a steam cracking thus produced, do not exceed 38 and 20 respectively, by weight, and the production of methane is approximately 25% by weight.

A fourth way of valorizing the C4 cut consists in alkylating
the olefins of this cut with the isobutane it contains, of
in order to maximize the yields of species. However, in the step
of alkylation, the behavior of isobutene is less favorable than
that of butenes for obtaining a gasoline with a high octane number; indeed, the Research (or Clear) octane numbers of normal butene alkylates are higher than those of isobutene alkylates.

 There are still other ways, for example that consisting in converting isobutene, the isobutene of the charge, into di and trimers of isobutene without substantially affecting the butenes of the charge, then isomerizing the butene-1 of the charge into butene. -2 in order to then subject the butenes-2 to an alkylation reaction with isobutane (French patent application No. 80 22204 of October 16, 1980).

Now we have discovered that it could be wise to modify this latter technique in the following way which consists in transforming all of the butenes contained in the initial charge into dimers and trimers of isobutene which are products which constitute an excellent fuel. automobile.

The process which is the subject of the present invention thus consists in first subjecting the charge (olefinic C4 cut), charge generally freed from at least the major part of the butadiene which it may contain, to a polymerization during which the overall conversions of the normal butenes contained in the feed, remain below 10% by weight and during which at least 90% by weight of the isobutene is converted (preferably at least 92% conversion of the isobutene), this hydrocarbon essentially transforming into dimers and trimers of isobutene; then, the product obtained is subjected to fractionation with a view to obtaining, on the one hand, a first fraction, containing the unreacted butenes, (which is sent to a series of operations aimed at processing n-butenes into isobutene which will be polymerized in turn, operations which will be described later) and on the other hand, a second fraction consisting of the dimers and trimers of isobutylene which will be sent to the gasoline pool, after have it (at least in part) subjected to partial or total hydrogenation.

Said first fraction containing the normal butenes which have reacted little or not during the polymerization is sent to an extractive distillation unit in order to obtain on the one hand the C4 paraffinic hydrocarbons present (butane, isobutane etc ... ) which were not affected during the polymerization and which can be sent to the gasoline pool, and on the other hand a fraction containing almost all of the normal butenes.

This last fraction, very rich in n-butenes (99% at least of n-butenes by weight) is sent to an isomerization unit where the butenes are mainly transformed into isobutene; consequently, under the operating conditions and with the chosen catalysts, a composition very close to that which corresponds to thermodynamic equilibrium is obtained.

The isomerization products are subjected to a distillation with a view to separating at the head the C1, C2 and C3 hydrocarbons produced by the parasitic reactions which have occurred during isomerization and a fraction essentially consisting of n-butenes. and the isobutene produced.

This isobutene-rich cut is recycled at least in part to the polymerization unit.

The process corresponding to the invention is shown diagrammatically in the single figure.

The olefinic C4 cut, which generally at this stage contains isobutane, n-butane, butene-1, butenes2, isobutene and little or no butadiene (in general less than 2% and preferably less than 0.7% by weight of butadiene) is introduced via line 1 into a possible drying zone 2. This drying can be carried out in a conventional manner, for example by passing the section through a molecular sieve, preferably a sieve of type 3 A. The cut thus dried is sent via line 3 to a selective polymerization zone 4 during which the isobutene of said cut is essentially transformed into dimers and trimers of isobutene.

In the polymerization zone, the conditions are such that isobutene reacts up to conversion rates higher than 90 or even 92% by weight and even 96%, while the overall conversions of normal butenes remain below 10% or better at 3% by weight and preferably less than 2%, or even 1%.

The polymerization reactions are generally carried out in the presence of a catalyst arranged for example in the form of a fixed bed at a temperature of approximately 30 to 400 ° C., under a pressure of approximately 0.1 to 20 MPa (1 to 200 bars), preferably the temperature is approximately 100 to 140 "C and the pressure is 3 to 5 MPa with a flow rate of liquid hydrocarbons (space velocity) of approximately 0.05 to 5 volumes per volume of catalyst and per hour, preferably between 0.8 and 2.5.

The catalyst of an acidic nature can be an alumina silica or a boron alumina or boronated alumina. It is also possible to choose a catalyst obtained by treatment of transition alumina by means of an acid derivative of fluorine, with optionally addition of a silicic ester. The catalysts used according to the present invention, for the polymerization reaction, appear to have qualities superior to those of other polymerization catalysts such as phosphoric acid on
Kieselguhr or on silica, or on quartz, or such as catalysts of the "solid phosphoric acid" type, that is to say catalysts consisting of a siliceous material with high absorbency impregnated with a high proportion of phosphoric acid, or also such as mixtures of alumina gel and thorine co-precipitated or not, with optionally additions of chromium oxide, zinc oxide or an equivalent metal.

Preferably, in the present invention, an alumina silica is used, the silica content of which is between 60 and 95% by weight and preferably between 70 and 90%, preferably having as additive between 0.1 and 5% by weight. weight of zinc oxide.

The polymerization effluent is withdrawn through line 5.

After separation, by distillation in column 6 of the dimers and trimers of isobutene obtained which are sent to the gasoline pool via line 16 (after possible hydrogenation), the butenes (essentially n-butenes) not having reacted, are sent via line 7 to an extractive distillation zone 8, in order to remove the paraffins present.

In this zone 8, the section C4 is subjected to an extractive distillation in the presence of a solvent such as dimethylacetamide, acetonitrile, furfural, formylmorpholine, dimethyl formamide,
N-methylpyrrolidone etc ... at a temperature preferably between - 10 "C and 2200C; it is more particularly preferred to operate at temperatures between 500 and 1800.

The pressure to which this distillation zone is subjected is between 0.1 and 1 MPa, and preferably between 0.2 and 0.7 MPa.

A ratio, by weight, of solvent / filler of between 1 and 10, preferably between 2 and 6, is used.

At the top, saturated hydrocarbons are collected and at the bottom a solution of olefins in the extraction solvent. The olefins can be removed by simple distillation, by entrainment (stripping) or by re-extraction by means of an immiscible auxiliary solvent such as a paraffinic hydrocarbon easily separable by distillation of butenes (devices not shown in the figure).

In this way, one obtains on the one hand through line 10, a weight yield of olefins of approximately 99%, (the complement to 100% consisting of paraffins entrained by line 10 with olefins) and on the other hand , via line 9, a weight yield of paraffins of approximately 92%, the remaining 8% being entrained olefins; the paraffinic section of line 9 can be sent to the petrol pool.

The olefinic cut, containing at least 99% of n-butenes is sent, via line 10 to the isonization zone 11 in order to produce isobutene at equilibrium which will be recycled via line 15, ( after separation in zone 13 of the hydrocarbons containing less than 4 carbon atoms per molecule (line 14) produced by the parasitic reactions) towards zone 4 of polymerization (or towards drying zone 2).

The n-butenes, which arrive in the isomerization zone 11, are brought into contact with an isomerizing catalyst, which may for example be a fluorinated alumina (entered 0.2 and 5% by weight of fluorine) or an alumina on which deposited silica (between 0.5 and 10% by weight of Silo2), for example by adding ethyl silicate followed by hydrolysis and an appropriate heat treatment.

In order to facilitate the regeneration of the spent catalyst during the reaction, in particular by combustion of the highly polymerized products and even of the carbon which could have deposited on the surface of the solid during the reaction, it is often advantageous to introduce on the surface of the catalyst an agent capable of facilitating the combustion of these organic products. Couine combustion activating agent, you can use tot metal or oxide or any other derivative of this metal capable of activating oxidation reactions. By way of nonlimiting examples of such agents, mention may be made, for example, of manganese, silver, chromium, palladium, nickel, copper, the oxides of these metals, etc., without this list being limiting.

These agents can be introduced onto the catalyst, for example by impregnation in the form of a salt or of another compound containing them, provided that the product is soluble in water or any other solvent used.

One can for example use palladium nitrate.

The amount of palladium introduced is preferably between 5 to 100 ppn without these contents being limiting. Preferably, 10 to 30 ppm of palladium is used. The other metals or metal compounds mentioned above would be used with concentrations of the same order of magnitude.

Note that the two compounds which can be deposited on alumina, namely silica and a metal or compound of additional metal, can optionally be introduced in a single impregnation, or in two successive impregnations with intermediate drying and calcination if the metal is introduced first (for example palladium) or with hydrolysis followed by drying and calcination if the silica is deposited first.

These catalysts are preferably used in the presence of water vapor in the reaction medium, the water inhibiting undesirable side reactions.

The catalyst can be used in the form of a fixed bed, a fluidized bed or a moving bed.

When a catalyst is used in the form of a moving bed, a particular method consists in using several reactors in series, placed for example side by side or superimposed: the charge circulates successively in each reactor in an axial or radial flow. The fresh catalyst is introduced at the top of the first reactor where the fresh charge is introduced; it then flows progressively from top to bottom of this reactor from where it is gradually withdrawn from below, and by any appropriate means (lift in particular in the case of reactors arranged side by side), it is transported in top of the next reactor in which it gradually flows also from top to bottom, and so on to the last reactor at the bottom of which the catalyst is also gradually withdrawn and then sent to a regeneration zone. At the exit from the regeneration zone, the catalyst is gradually reintroduced into the top of the first reactor, so as to maintain a high and substantially constant activity level at each point of the catalytic zones. The various catalyst withdrawals are carried out as indicated above "progressively", that is to say either periodically or continuously. Continuous withdrawals are preferred to periodic withdrawals.

The operating conditions in the butene isomerization zone are as follows: the temperature is between approximately 300 and 500 OC and preferably between 400 and 500 OC; the pressure in the reactor is between approximately 0.05 and 1 MPa and preferably between 0.08 and 0.4 MPa the volume speed, expressed in volumes of liquid charge per volume of catalyst and per hour, is generally between 0 , 1 and 10, and preferably between 0.5 and 3.

When operating in the presence of water vapor, the water / hydrocarbon molar ratio is between 0.1 and 10 and preferably between 0.5 and 3.

The product obtained, after isomerization of the butenes, is withdrawn through line 12 and directed to a separation zone 13 in order to eliminate the C1, C2 and C3 hydrocarbons produced by the side reactions during isomerization; the C4 olefinic cut, containing an isobutene content very close to that of thermodynamic equilibrium, is recycled at least in part by line 15 to zone 4 of polymerization.

Example
It is proposed to treat a charge originating from a steam cracking and from which the major part of the butadiene has been previously extracted.

This charge has the following composition, in% by weight C4 paraffins 7.7% n-butenes 42.4 isobutene 49.6 butadiene
100.0%
This charge is first subjected to drying on a 3A molecular sieve, then it is sent to an isobutene polymerization zone, together with a recycled butene mixture, coming from the butene isomerization zone, as explained further.

The total charge thus introduced into the polymerization zone, comprises 49.65% by weight of cut C4 fresh olefinine having the composition indicated above and 50.35% by weight of recycling butenes having the following composition, in% by weight paraffins in C4 0.89% n-butenes 60.77 isobutene 38.34
100.00
Thus, the total charge entering the polymerization zone has the following composition in% by weight C4 paraffins 4.27% n-butenes 51.65 isobutene 43.93 butadiene 0.15
100.00%
The polymerization reaction takes place in the presence of a catalyst which is a commercial alumina silica of the Durabead Perl Catalysator New type from the company Kalichemie. To this silica-alumina was added 0.2%, by weight, of zinc.

The operating conditions are as follows
Pressure 4 MPa
Temperature 105 to 110 0C
Spatial velocity (VVH) 0.5
The reaction product is subjected to fractionation (zone 6 of the figure).

Is thus collected via line 7, at the top of the column, a C4 fraction having the following composition, in% by weight, relative to the total charge arriving in the polymerization zone 4 C4 paraffins 4.27% n-butenes 51.65 isobutene 0.15
56.07%
At the bottom of the column, via line 16, a gasoline is collected which represents 43.93% by weight relative to the initial charge and which has the following characteristics - density at 15 ° C. 0.755 - octane number
RON clear 100
RON ethyl 0.05% 103.5
. MON 85 N DND 0.05% ethyl 88 - ASTM distillation
.PI 79 OC
. 5% 101
10% 104
20% 110 30% 120
40% 123
50% 136
. 60% 157
. 70% 170
80% 177
. 90% 192
. 95% 204
. 98% 238
. distillate 99.5%
. 0.5% residue loss
Such gasoline can be sent to the gasoline pool without going through another fractionation or purification step.

The cut leaving via line 7 is sent to an extractive distillation zone 8, in order to separate the paraffinic hydrocarbons contained in the olefinic cut.

The extractive distillation column has 60 trays. The solvent used is dimethylformamide, which is sent to the 8-stage column from the top, with a flow rate equal to 4.2 times that of the feed. The overhead vapors are condensed; half of the condensate is recycled to the top of the column as reflux, while the other half of the condensate is discharged from the system.

The product essentially consisting of dimethylformamide and olefins is sent to a solvent regeneration column (not shown in the figure) comprising 40 trays. The bottom effluent from this column constitutes the regenerated dimethylformamide and is recycled to the extractive distillation column.

Two effluents are thus recovered - via line 10, a product is obtained, containing 99% of the butenes contained in the cut, before extraction, this product having the following composition in% by weight relative to the product introduced into the polymerization zone 4 paraffins in C4 0.32% n-butenes 51.13 isobutene 0.15
51.60% - and through line 9, a cut rich in C4 paraffins, which contains 92.5% by weight of the paraffins contained in the olefin cut before extraction of the saturated hydrocarbons.

This section, which represents 4.47% by weight of the total charge before polymerization, has the following composition, in% weight relative to the product entering the polymerization zone 4
C4 paraffins - 3.95% n-butenes 0.52%
4.47%
These paraffins are sent via line 9 to the petrol pool.

The dewaxed section is introduced, via line 10, into an isomerization zone 11 which operates under the following conditions
Temperature . 450 OC
Pressure 0.1 MPa
Liquid C4 charge volume per volume of
catalyst per hour 2
H20 / HC molar ratio of the olefinic cut 1.30
The catalyst used is in the form of alumina beads of 1 to 2 mm in diameter and it has the following characteristics
grain density 1.23
structural density 3.27 3
total pore volume 0.57 cm
specific surface 200 m / g and its composition is as follows
silica 3% by weight
Palladium 20 ppm
This catalyst and the operating conditions used allow the transformation of n-butenes into isobutene, in order to obtain a product with a composition very close to that of thermodynamic equilibrium.

The product leaving this isomerization zone, via line 12, has the following composition, in% by weight, relative to the total charge subjected to the polymerization
C1, C2 and C3 hydrocarbons 1.15%
C4 paraffinic hydrocarbons 0.45
n-butenes 30.60
isobutene 19.40
51.60%
After separation, in the distillation zone 13, of hydrocarbons lower than C4 (C1, C2 and C3), the C4 olefinic cut containing all the butenes and of composition close to that of thermodynamic equilibrium (under the operating conditions used) is sent , via line 15, to the polymerization zone 4.

This way of proceeding here makes it possible to transform 98.85% by weight of the olefins, contained in a C4 olefinic cut into automobile fuel of excellent quality.

Claims (9)

1 / Valorization process of an olefinic cut containing essential  hydrocarbons with four carbon atoms per molecule,  from a cracking unit or a cracking unit at the  steam, the process being characterized in that  a) the olefinic cut is sent to a polymerization zone (4)  catalytic in the presence of a catalyst chosen from the group  consisting of fluorinated aluminas, boronated aluminas and  silica-aluminas on the one hand, to be converted at least 90%  of the isobutene that the said olefinic cut contains, in major  part in dimers and trimers of isobutene, and on the other hand,  so that the overall conversions of normal butenes that  contains the said starting olefinic cut remain below  10% by weight, butane and isobutane contained in said  olefinic cuts not being substantially converted;  b) the effluent from the polymerization zone is sent to a zone  fractionation (6) from which one draws on the one hand a mixture of  dimers and trimers of isobutene and on the other hand a mixture  essentially containing paraffins having four atoms of  carbon per molecule and normal butenes;  c) the mixture of dimers and trimers of isobutene undergoes at least  partly partial or total hydrogenation and is collected  as gasoline  d) the mixture of paraffins and butenes is sent to a zone (9)  solvent extractive distillation, in order to eliminate  paraffins.  e) the effluent from the extractive distillation zone, which contains  at least 99% by weight of normal butenes, is subjected to a reaction  isomerization in a zone (12) during which 1a  most of these so-called butenes are transformed into isobutene;  f) the isomerization effluent is sent to a separation zone (14)  in order to eliminate hydrocarbons containing 1, 2 and 3 atoms of  carbon per molecule and in order to recover a fraction containing  isobutene and normal butenes  g) this last fraction thus recovered is, at least in part,  recycled to the polymerization zone of step a). 2 / A method according to claim 1 wherein, for step d), we  operates under a pressure of 0.1 l to 1 MPa at a temperature included  between -10 and 2200C with a solvent weight ratio between  charge  1 and 10. 3 / A method according to claim 2 wherein the pressure is  between 0.2 and 0.7 MPa, the temperature between 50 and 1800C and  solvent  the weight ratio between 2 and 6.  filler 4 / A method according to claim 1 in which the distillate solvent  the extractive lation is chosen from the group constituted by acetoni-  trile, ine-thvlformamide and rnthy1 - pyrrolidone.  5f The method of claim 1, wherein the reaction isom-  rization of step e) is carried out in the presence of an alumina  fluorine containing 0.2 to 5%, by weight, of fluorine or alumina  containing 0.5 to 10% by weight of silica SiO2. 6 / A method according to claim 5 wherein one operates, in addition, in  presence of water vapor, with a water molar ratio  Hydrocarbons  between 0.1 and 10. 7 / A method according to claim 6 wherein said molar ratio  is between 0.5 and 3. 8 / A method according to claim 5 wherein the catalyst contains  in addition a metal or metal compound, said metal being chosen from  the group consisting of chromium, palladium, nickel, copper  manganese and silver. 9 / A method according to claim 8 wherein the concentration expri  mée in the said metal, is between 5 and 100 ppm. 10 / A method according to claim 8 wherein said concentration  is between 10 and 30 ppm. 11 / A method according to claim 9 wherein said metal is  palladium.