ITMI940765A1 - PROCEDURE FOR THE JOINT PRODUCTION OF ETHERS AND HIGH-OCTANIC HYDROCARBONS - Google Patents

Description

Description

The present invention relates to a process for the joint production of ethers and high octane hydrocarbons, obtained by reaction of hydrocarbon cuts containing C4 and / or C5 iso-olefins with primary alcohols in stoichiometric defect (molar ratio of primary alcohols / iso-olefin <1) with respect to iso-olefins and / or with terlachyl ethers. The mixture obtained can then be hydrogenated with conventional methods to obtain a product with further improved octane characteristics.

Environmental reasons are in fact helping to reformulate the composition of gasoline; the "Clean Air Act Amendments" (CAAA) in the USA are providing general guidelines that will probably be followed with little variation by other countries in the near future.

In summary, the general trend is towards the production of fuels that burn better and have fewer evaporative emissions. The main measures to achieve this objective are the following (for a more specific discussion see for example: G.H. Unzelman, Fuel Reformulation, 3i (2), (1993), 41 and D. Sanfilippo, F. Ancillotti, M.Marchionna, Chim. & Ind., 76, (1994), 32 and references contained therein):

- oxygenated compounds will play an increasingly important role as components of gasoline; - the content of aromatic compounds will be strongly reduced, especially that of benzene;

- there will be a reduction in the volatility of gasoline to minimize evaporative losses; - the content of photochemically reactive olefins and precursors responsible for the formation of atmospheric ozone will be reduced;

- both the sulfur content and the final boiling point of gasoline will also be reduced.

All these measures therefore entail the need to design new processes capable of positively contributing to the above needs. With regard to the production of oxygenated products (or rather those that have proved to be the most promising in this class) it should be noted that the CAAA have assigned oxygenates a permanent function in future reformulated gasolines both as an increase in the octane number and as an oxygen supply.

Tert-alkyl ethers have established themselves as the oxygenated compounds of choice; among these the most important are MTBE (methyl-tert-butylether), ETBE (ethyl-tert-butylether) and TAME

(tert-amyl-methyl ether). These ethers are generally obtained by reaction in liquid phase of C4-C5 iso-olefins with methanol or ethanol, in a stoichiometric amount or slightly higher than the said iso-olefins, in the presence of an acidic ion exchange macromolecular resin. The production of these ethers, especially MTBE, has been continuously growing in recent years (for a more specific discussion see for example: H.L.Brockwell, P.RSarathy, R-Trotta, Hydrocarbon Proc., Sept. 1991,133 and W.J. Piel , Fuel Reformulation, 2 (6), (1992), 34). In addition to the oxygenated compounds, also purely hydrocarbon products are proving to be particularly attractive as regards the reformulation of gasolines; among these the alkylate definitely stands out since it has a high octane number, a low volatility and is practically free of olefins and aromatics.

The liquid phase alkylation process is a reaction between isoparaffinic hydrocarbons, such as isobutane, and olefins, for example propylene, butenes, pentenes and related mixtures, in the presence of an acid catalyst for the production of C7-C9 hydrocarbons with a high octane number to be used in gasoline (see for example: A.Corma, A.Martinez, Catal.Rev.-Sci.Eng., 35, (1993), 483 and references contained therein).

The main problem of the alkylation process is due to the fact that with the growth of environmental regulations both traditional processes (with hydrofluoric acid and with sulfuric acid) are encountering considerable difficulties, which suggest an uncertain future; that with hydrofluoric acid due to the toxicity of this acid, especially in populated areas, and that with sulfuric acid due to the large production of acid sludge as well as the considerable corrosive power of the catalyst.

Alternative processes with solid acid catalysts are being developed but their commercial applicability has yet to be demonstrated.

On the other hand, a hydrocarbon product of this type is increasingly desired due to its octane characteristics (high both the Research Octane Number (RON) and the Motor Octane Number (MON)) and those relating to the boiling point (low volatility but low final point) that place it in that range of extremely interesting compositions for obtaining gasolines more compatible with today's environmental needs.

Furthermore, high octane hydrocarbon products such as those generated by the alkylation reaction are also endowed with low sensitivity (difference between RON and MON) and it is known that ethers such as MTBE, ETBE, etc., are favorably affected by the lowering of the sensitivity of gasoline, always increasing moreover their already high octane value.

This means that there are many advantages to coupling a saturated high octane hydrocarbon product (such as alkylate) with ethers such as MTBE.

Furthermore, the joint presence of significant quantities of the two products also allows the content of unwanted components such as aromatics, olefins and sulfur to be significantly reduced by dilution.

In the past, alternative proposals have been made to replace the alkylate with another high octane product.

The joint production of isobutene oligomers with MTBE, obtained by a two-stage process, has in fact been reported (DE-2944457). In the first stage the isobutene was oligomerized with conversions between 50-90% to oligomers and then in a second stage etherified with methanol to produce MTBE. A partial hydrogenation of the overall product was also suggested.

The main problem of this process consists in the fact that in the oligomerization phase, heavy oligomers such as trimers and tetramers of isobutene are produced in excessive percentages (molar selectivity within the fraction of oligomers of 15-30% and 1 -2 %). (The molar selectivity, referred to a particular oligomer j, is defined as the ratio between the mmoles of oligomer j formed and the mmoles of isobutene converted into total oligomers.) The tetramers are completely outside the petrol fraction because they are too high boiling and therefore represent a net loss of gasoline yield; as regards the trimers (or their hydrogenated derivatives) it is desirable to strongly decrease their concentration since they have a boiling point (170-180 ° C) at the limit of future specifications on the final point of reformulated gasolines.

On the other hand, the problem of minimizing the formation of oligomers higher than dimers at percentages lower than 15% (molar selectivity) is a typical problem of the oligomerization of isobutene as also reported in the literature regarding both the processes for obtaining "polymer" gasoline "and for those for petrochemical intermediates (F. Asinger," Mono-olefins: Chemistry and Technology ", Pergamon Press, Oxford, pp. 435-456 and G. Scharfe, Hydrocarbon Proc., Aprii 1973,171).

From the foregoing it is evident that there is great interest in obtaining a new dimerization process of C4-C3 iso-olefins which allows the production of a higher quality product, through the achievement of greater selectivities.

It has now surprisingly been found that by carrying out the oligomerization reaction of the C4-C3 iso-olefins in the presence of substoichiometric quantities of primary alcohols and / or in the presence of teralkyl ethers, the co-production of high octane ethers and a fraction of oligomers is selectively obtained. of isoolefin, particularly rich in dimers (molar selectivity> 85%) and practically free of higher tetramers and oligomers (<1%).

A further positive aspect of the present invention is given by the fact that the overall co-production process of high octane oligomers and ethers is much more easily controllable from a thermal point of view than the oligomerization process alone, thus greatly simplifying the problems of manageability of the process itself.

The reaction product can then be hydrogenated to give a completely saturated final product with a high octane number and low sensitivity.

The hydrogenation can be carried out with conventional methods as for example described in F. Asinger, "Mono-olefins: Chemistry and Technology", Pergamon Press, Oxford, p. 455. By way of example, table I shows the octane numbers of some of the products obtained by the process object of the present invention:

TABLE I

No.

Optionally, the hydrocarbon product (both olefinic and saturated) can also be separated from the ether fraction as it is higher boiling (at least in the case of products deriving from methanol and ethanol) and used separately from the ethers; by operating in this way, however, the advantage deriving from the lowering of the sensitivity of the product, comprising both the oxygenates and the saturated hydrocarbons, mixed with a basic petrol is lost.

Table II shows a typical range of concentrations of the constituents of the mixture obtained by co-production according to the present invention, pointing out however that in particular situations compositions outside this range are also welcome.

TABLE II - Average composition of the mixture

The process, object of the present invention, for the joint production of ethers and high octane hydrocarbons starting from hydrocarbon cuts containing the iso-olefins C4 and / or C5 by means of oligomerization with acid catalysts is characterized by the fact of carrying out the oligomerization reaction in the presence of primary alcohols in quantities such as to have a molar ratio of primary alcohols / iso-olefins C4 + C5 lower than 1

and / or in the presence of teralkyl ethers in a quantity such as to have in the feed a molar ratio of teralkyl ethers / C4 + C5 iso-olefins lower than 1, preferably between 0.2 and 0.8.

Since the primary alcohol is rapidly converted under the reaction conditions to teralkyl ether, it has also been observed that the addition of teralkyl ether alone may also be useful for the effects of our process (i.e. the selective production of dimers of the C4-C5 isolefins) ; however, it must be borne in mind that this option is less advantageous than the addition of the corresponding alcohols since a certain part of the teralkyl ethers will tend to decompose to isobutene and primary alcohol according to the particular reaction conditions.

Finally, it should be noted that in the case of C4-C5 iso-olefins contained within C4-C5 hydrocarbon streams also including linear olefins it has been observed that at least a part of the linear olefins can be converted into hydrocarbon product without affecting its octane value. However, an enrichment treatment, by means of pre-isomerization, of the internal olefins (2-butenes, 2-pentenes) within the fraction of linear olefins is preferable, since the overall octane number of the mixture is favored.

The object of the present invention can be applied to streams comprising C3-C7 olefins, although the main attention will be directed to streams containing C4-C3 iso-olefins. When the joint process to produce tert-alkyl ethers and high octane hydrocarbons involves the latter olefins, the relative streams will typically contain, within the C4 fraction, isobutane, isobutene, n-butane and n-butenes and, within the C5 fraction , isopentane, 3, methyl-1-butene, n-pentenes, 2, methylbutenes, n-pentane.

Although a considerable variety of sources are available to supply these streams, the most common are those deriving from affine iso-par dehydrogenation processes, FCC units and streams from steam crackers. Finally, in the event that these streams contain diolefins in addition to the desired mono-olefins it will be necessary to eliminate them by means of typical removal treatments (for example washing or selective hydrogenations).

The primary alcohol used can preferably be selected from C1-C3 primary alcohols (containing a number of carbon atoms from 1 to 5); methanol and ethanol are the typical alcohols of choice.

If only teralkyl ether is used, the recommended ethers are MTBE, ETBE, TAME, TAEE (teramyl-ethyl ether).

The iso-olefin together with the hydrocarbon stream in which it is contained is sent with the alcohol (and / or with the ether) in contact with the acid catalyst to produce the ethers and higher oligomers of the iso-olefin. A large variety of acid catalysts can be used for this process: among these, purely by way of example, mineral acids such as sulfuric acid, BF3, supported phosphoric acid, suitably modified zeolites, heteropolyacids and sulfonated polymeric resins, for example Amberlyst 15, are mentioned. and Amberlyst 35, etc.

Among these catalysts, the use of macroreticular sulfonated resins, generally copolymers of styrene and benzene, is preferred; the characteristics of these resins are widely described in the literature (see for example A.Mitschker, R. Wagner, P.M.Lange, "Heterogeneous Catalysis and Fine Chemicals", M.Guisnet ed., Elsevier, Amsterdam, (1988), 61.

A wide range of operating conditions can be employed to jointly produce ethers and high octane hydrocarbons from primary alcohols and iso-olefins in the selectivities desired by the object of the present invention. It is possible to operate in the vapor phase or in the liquid-vapor phase but the operating conditions in the liquid phase are the preferred ones.

The process object of the present invention can operate both in discontinuous and continuous conditions, bearing in mind however that the latter are much more advantageous in industrial practice. The reactor configuration chosen can optionally be chosen between a fixed bed, tubular fixed bed, adiabatic, agitated bed reactor and finally the reactor-column which also allows the separation of the products (a description of the different reactor configurations generally used in industrial practice for the process of etherification is for example reported in: P.R. Sarathy, G.S.Sufiridge, Hydrocaibon Proc., Febr. 1993,45). The range of process conditions, operating in the liquid phase, includes a large variety of operating conditions which will be described below.

The pressure will preferably be above atmospheric to keep the reactants in the liquid phase, generally below 5 MPa.

The reaction temperature is preferably between 30 and 100 ° C. The molar ratio between the fed alcohol and the iso-olefin must be substoichiometric with respect to what is predicted by the stoichiometry of the etherification reaction, ie <1, preferably between 0.15 and 0.85, more preferably between 0.3 and 0.7. The spatial feed rates of the alcoholic-hydrocarbon stream must be less than 50 h <-1>, preferably less than 30 h <-1>, more preferably between 1 and 15 h <-1>

The iso-olefins and primary alcohols are mainly converted in the reaction zone, however also part of the n-olefins can be converted to a useful product; in principle, there are no limits to the concentration of iso-olefin in the hydrocarbon fraction even if it is preferable to have concentrations between 15 and 60%; there are no limits in the relationship between linear isoolefins and olefins. It should be noted that in the case of currents deriving from dehydrogenation of isobutane, there are no significant concentrations of linear butenes in the feed.

The process effluent is then sent to a separation zone where the primary alcohol, the unreacted olefins and the saturated C4-C5 hydrocarbons are separated from the reaction products. Various apparatuses can be used for this separation, among them also the reactor-column. Since the conversion on alcohol is always very high in the typical conditions of the process, object of the present invention, separation techniques can be exploited for the complete removal of the primary alcohol, typical of modern etherification technologies (exploiting the formation of azeotropes between the alcohol and the hydrocarbon stream C4-C5>.

Finally, in the event that total conversions of the C4-C3 isoolefins have not been achieved in the reactor where the joint production of the ether and the high octane hydrocarbons takes place, depending on the particular use of the unconverted stream of C4-C5 hydrocarbons, the separated effluent of head can also optionally be sent to a second etherification reactor, as is customary in modern technologies for the production of tert-alkyl ethers (P.R. Sarathy, G.S.Suffridge, Hydrocarbon Proc., Febr. 1993,45). Again this reactor can be of different configuration (adiabatic, column reactor or any other type that is considered useful for the specific application). The reaction product leaving this finisher reactor can then optionally be combined with that obtained in the first reactor.

Examples are now provided for the purpose of better illustrating the invention, it being however understood that it is by no means limited thereto.

Example I.

This example illustrates the use of the process of the present invention in a jacketed tubular reactor whose design is shown in figure 1 where it is indicated with:

I - liquid inlet

2-liquid outlet

3-thermostatic liquid inlet

4-thermostatic liquid outlet

5-thermocouple

6-porous septum (100 micron)

In this stainless steel reactor, with an internal diameter of 1.4 cm and equipped with valves for the inlet of the reagents and the outlet of the products, 20 cc of cation exchange resin, functionalized with sulphonic groups, Amberlyst, were loaded 15.

The reaction heat, developed by the two exothermic reactions, is removed by the circulation of a cooling fluid (water at 40 ° C) in the reactor jacket.

The thermal profile (an indicative one is shown in figure 2 - where the reactor length is represented in the abscissa and the temperature in the ordinates) obtained by the process, object of the present invention, showed in all the tests carried out a maximum temperature in the first third of the catalytic bed in which the reaction rate is highest.

A constant pressure of 1.5 MPa was maintained in the reactor, sufficient to keep the reagents liquid.

In this test methanol was used as the primary alcohol and a mixture of C4 hydrocarbons with a composition similar to that coming out of an isobutane dehydrogenation plant (isobutene 48% by weight, isobutane 52% by weight) as the hydrocarbon stream. The feed mixture, in which the methanol / isobutene molar ratio is 0.6, was sent to the reactor at a rate of 2 cc / min so as to have an LHS V space rate of 6 volumes / hour per volume of catalyst ( 6 h <-1>).

Operating under these conditions it was possible to obtain (once the steady state was reached) average conversions of methanol and isobutene of 98 and 78% respectively, with a molar selectivity to dimers of 92%.

The maximum temperature reached in the reactor was 72 ° C.

In the steady state, reached under the present conditions in less than 0.5 h, a product was obtained having the following composition:

Example 2 (Comparative)

This example shows how by carrying out the reaction in the absence of primary alcohols it is not possible to limit the formation of heavy oligomers.

This test was carried out with the same equipment and under the same operating conditions described in example 1.

In this example, only a hydrocarbon type feed was used which could be assimilated to a stream leaving an isobutane dehydrogenation plant (isobutane 51% by weight and isobutene 49% by weight).

In the absence of alcohol, controlling the temperature inside the reactor is much more problematic (Tmax = 90-100 ° C).

Also in this case very high conversions of isobutene were obtained (85%) but the molar selectivities to dimers are very low (55%). In the steady state, a product was obtained having the following composition:

Example 3

This example shows how it is possible to limit the formation of heavy oligomers also by carrying out the reaction in the presence of an ether, such as MTBE, used in place of the alcoholic component (MeOH).

This test was carried out with the same apparatus and under the same operating conditions described in example 1 using a molar ratio MTBEAsobutene of 0.33. Operating under these conditions it was possible to obtain average conversions of isobutene of 80%, with molar selectivity to dimers of 83%.

The maximum temperature reached in the reactor was 68 ° C.

In the steady state, a product was obtained having the following composition:

Example 4

This example shows how other ion exchange resins are also active in the process, object of the present invention. Also in this case the apparatus described in example 1 was used using, however, 20 cc of cation exchange resin, functionalized with sulphonic groups, Amberlyst 35 as catalyst.

This test was also carried out with a methanol / isobutene molar ratio of 0.4 and a hydrocarbon filler composed of isobutane (53% by weight) and isobutene (47% by weight). This mixture was fed to the reactor at a rate of 2 cc / min so as to have a space rate of 6 volumes / hour per volume of catalyst.

Operating under these conditions it was possible to obtain average conversions of methanol and isobutene of 99 and 85% respectively, with a molar selectivity to dimers of 90%. The maximum temperature reached in the reactor was 76 ° C. In the steady state, a product was obtained having the following composition:

Example 5

This example shows how the presence of linear olefins (2-butene) in the hydrocarbon feedstock does not modify the reaction rate and the selectivity to dimers of the process, object of the present invention.

This test was carried out with the same equipment and under the same operating conditions described in example 4.

In this case, however, a C4 hydrocarbon stream was used with a composition similar to that which would occur at the output of an FCC unit, after isomerization of 1-butene to 2-butene.

The composition of the fed C4 cut was therefore as follows: isobutane 33% by weight, isobutene 23% by weight, 2-butene 44% by weight.

Under these conditions it was possible to obtain average conversions of methanol and isobutene of 98 and 88% respectively, with a molar selectivity to dimers (and codymeles) of 87%. The maximum temperature reached in the reactor was 64 ° C.

In the steady state, a product was obtained having the following composition:

The presence of codymeles between isobutene and 2-butene does not worsen the quality of the product as these hydrocarbons, once hydrogenated, have octane characteristics (RON and MON) similar to those of isooctane.

Example 6

This example shows how the process, object of the present invention, can also be extended to higher primary alcohols such as ethanol.

This test was carried out with the same equipment and under the same operating conditions described in example 4. Under these conditions it was possible to obtain average conversions of ethanol and isobutene of 98 and 85% respectively, with molar selectivity to dimers of 92 %.

The maximum temperature reached in the reactor was 73 ° C.

In the steady state, a product was obtained having the following composition:

Claims (9)

CLAIMS 1) Process for the joint production of ethers and high octane hydrocarbons starting from hydrocarbon cuts containing C4-C3 iso-olefins, by oligomerization with acid catalysts characterized by conducting the oligomerization reaction in the presence of primary alcohols in such quantities as to have a molar ratio of primary alcohols / iso-olefins C4 + C5 lower than 1 and / or in the presence of teralkyl ethers in a quantity such as to have a molar ratio of teralkyl ethers / iso-olefins C4-C3 lower than 1, operating, preferably, at a reaction temperature comprised between 30 and 100 ° C, at a pressure lower than S MPa and at spatial feed rates lower than 50 h <'1>. 2) Process according to claim 1 wherein in feed the molar ratio of primary alcohols / iso-olefins C4 + C5 is comprised between 0.15 and 0.85. 3) Process according to claim 2 wherein in feeding the molar ratio of primary alcohols / iso-olefins C4 + C5 is comprised between 0.3 and 0.7. 4) Process according to claim 1 where the spatial feed velocities are less than 30 h <-1>. 5) Process as in claim 4 wherein the spatial velocities in feeding are comprised between 1 and 15 h <-1>. 6) Process according to claim 1 wherein in feed the molar ratio of teralkyl ethers / iso-olefins is comprised between 0.2 and 0.8. 7) Process according to claim 1 wherein the primary alcohol has a number of carbon atoms from 1 to 5. 8) Process according to claim 7 wherein the primary alcohol is methanol. 9) Process according to claim 7 where the primary alcohol is ethanol. 0) Process according to claim 1 where the teralkyl ether is selected from MTBE, ETBE, TAME and TAEE.