More specifically, the present invention relates to an integrated process for the production of olefin oxides starting from a C2-Cs alkyl stream.

Even more specifically, the present invention relates to an integrated process for the production of propylene oxide from propane, by the direct oxidation of propylene with hydrogen peroxide.

Olefin oxides, or epoxides, are useful intermediates for the preparation of a wide variety of compounds. For ex- ample, olefin oxides can be used for the production of gly- cols, condensation polymers such as polyol polyethers or polyesters which can be used as such or as useful interme- diates in the synthesis of polyurethane resins, elastomers, sealants, etc.

The preparation of epoxides by the direction oxidation of the corresponding olefins with hydrogen peroxide in the

presence of catalysts such as titanium-silicalite treated with neutralizing substances to neutralize the acid groups present on the surface, is known in literature. Catalysts of this type are described, for example, in European pat- ents EP 230,949, EP 712,852 and EP 940,393 or in published international patent application WO 00/17,178.

In literature, the synthesis of epoxides is therefore described starting from the assumption that the reagents, essentially olefin and hydrogen peroxide, are available as already preformed streams. On an industrial scale, however, the availability of raw materials for the preparation of a product such as an olefin oxide is not always immediate or is not always economically advantageous for the market value of the epoxide.

To solve the problem of the availability of raw mate- rials, the Applicant has now found a process for the pro- duction of olefin oxides in which the preparation of the desired epoxide is integrated with that of the olefin and hydrogen peroxide so that the final synthesis depends ex- clusively on easily available raw materials such as oxygen and the corresponding alkyl hydrocarbon.

The object of the present invention therefore relates to an integrated process for the production of olefin ox- ides which comprises: a) feeding in continuous to a dehydrogenation unit, a par-

affinic stream essentially consisting of at least one C2-C5 alkyl hydrocarbon; b) sending the stream leaving the dehydrogenation unit to a separation unit to produce a stream consisting of hy- drogen, a stream essentially consisting of the non- reacted alkyl hydrocarbon, which is recycled to the de- hydrogenation, and a stream essentially consisting of the dehydrogenated alkyl hydrocarbon (olefin stream); c) feeding the stream of hydrogen together with a stream of oxygen, to a hydrogen peroxide synthesis unit; d) feeding a part of the olefin stream, together with the hydrogen peroxide produced in step (c), to an oxidation unit, the rest of the olefin stream being sent to a storage tank; e) recovering the olefin oxide produced and sending it for storage.

According to the present invention, the paraffinic stream fed to the dehydrogenation can be selected from one or more of the C2-C5 alkyl hydrocarbons even if it is pref- erable to operate with a stream of ethane and/or propane or, even more preferably, with a stream of propane alone.

The paraffinic stream, coming from a refinery with a purity degree higher than or equal to 95%, is fed to the dehydrogenation unit which effects a catalytic dehydrogena- tion at a temperature ranging from 450 to 800°C, preferably

from 550 to 650°C, and at an absolute pressure ranging from 10 to 300 kPa. Any dehydrogenation catalyst for light par- affins can be used in the process, object of the present invention, even if catalysts based on platinum, gallium, chromium, vanadium supported on silica and/or alumina are preferred. Details on the dehydrogenation of paraffins and on the catalysts used are available on SRI International "Alkane Dehydrogenation and Aromatization", Report 203, September 1992.

At the end of the dehydrogenation, the stream produced is sent to a two-step separation unit. In the first step, the hydrogen is recovered whereas in the second step the non-reacted paraffin is separated from the olefin.

The separation of the hydrogen also generally takes place in two steps. In the first step, carried out with a distillation system of the cold box type, a stream of hy- drogen is recovered, still containing significant quanti- ties of impurities, whereas in the second step a purifica- tion is effected, for example by means of membrane separa- tion or PSA (Pressure Swing Adsorption), which allows a stream of hydrogen to be obtained with a purity suitable for the subsequent hydrogen peroxide synthesis reaction.

The hydrogen, together with a stream of oxygen, is fed to a hydrogen peroxide synthesis unit which operates with well-defined operating conditions. In particular, the hy-

drogen peroxide can be prepared by feeding in continuous to a stirred reactor containing, in dispersion, a heterogene- ous catalyst based on platinum and palladium, a stream con- sisting of: - a liquid stream containing an alcohol or an alcohol- water mixture with an alcohol content higher than 50% by weight, and an acid or halogenated promoter; and - a gaseous stream containing hydrogen, oxygen and an in- ert gas, wherein the concentration of hydrogen is lower than 4.5% by volume and the concentration of oxygen is lower than 21% by volume, the complement to 100 being the inert gas, for example nitrogen or a noble gas such as helium or argon.

A liquid stream is extracted in continuous from the synthesis reactor, containing the hydrogen peroxide pro- duced in a concentration ranging from 2 to 10% by weight and a gaseous stream essentially consisting of non-reacted hydrogen and oxygen and the inert gas, which is recycled.

The synthesis reaction is carried out at a temperature ranging from-10 to 60°C, preferably from 0 to 40°C, at a pressure ranging from 1 to 300 bars, preferably from 40 to 150 bars, and with residence times of the liquid medium in the reactor ranging from 0.05 to 5 hours, preferably from 0.1 to 2 hours.

The hydrogen peroxide synthesis catalyst contains pal-

ladium in a quantity ranging from 0.1 to 3% by weight and platinum in a quantity ranging from 0.01 to 1% by weight, with an atomic ratio between platinum and palladium ranging from 1/500 to 100/100. The palladium is preferably present in a quantity ranging from 0.4 to 2% by weight and the platinum in a quantity ranging from 0.02 to 0.5% by weight, with an atomic ratio between platinum and palladium ranging from 1/200 to 20/100. In addition to the two metals men- tioned above, the catalytic system can comprise one or more promoters selected from metals of groups VIII or IB, such as ruthenium, rhodium, iridium and gold, in a concentration generally not higher than that of the palladium.

The catalyst can be prepared by dispersing the active components on an inert carrier by means of precipitation and/or impregnation starting from precursors, for example salts or soluble complexes. The inert carrier can be se- lected from silica, alumina, silica-alumina, zeolites, ac- tivated carbon. Activated carbon with a surface area rang- ing from 300 to 1400 m2/g is preferred.

The catalyst is normally dispersed in the reaction me- dium at a concentration ranging from 0.1 to 10% by weight, preferably from 0.3 to 3% by weight.

The liquid stream consists of one or more Cl-C4 alco- hols or a mixture of these alcohols with water. Among the alcohols, methanol is preferred.

The acid promoter can be any substance capable of gen- erating hydrogen ions in the liquid reaction medium and is generally selected from inorganic acids such as sulfuric, phosphoric, nitric acids or from organic acids such as sul- fonic acids. Sulfuric acid and phosphoric acid are pre- ferred.

The concentration of the acid generally ranges from 20 to 1000 mg per kg of liquid medium and preferably from 50 to 500 mg per kg of liquid medium.

The halogenated promoter can consist of any substance capable of generating halogen ions in the liquid reaction medium. These substances are generally capable of generat- ing bromide ions such as hydrobromic acid and its salts soluble in the reaction medium, for example alkaline bro- mides. The concentration of halogenated promoter generally ranges from 0.1 to 50 mg per kg of liquid medium and pref- erably from 1 to 10 mg per kg of liquid medium.

The reaction product containing hydrogen peroxide, af- ter filtration for recovering the catalyst dispersed therein, is fed directly to the epoxidation unit of the olefin together with the latter. In order to keep the mate- rial balance under conditions of self-sufficiency, the fraction of olefin capable of being oxidized by the hydro- gen peroxide produced with the hydrogen coming from the de- hydrogenation unit, is fed to the epoxidation unit. The re-

maining olefin is sent for storage.

The reagent streams are fed to the epoxidation reactor under such conditions as to have a molar ratio olefin/H202 inside the reaction container, ranging from 10/1 to 1/10, preferably from 6/1 to 1/1. The epoxidation reaction is carried out under stirring, in the presence of the same solvent used in the hydrogen peroxide synthesis, at a pH ranging from 5.5 to 8 and in the presence of a catalyst used in a quantity ranging from 1 to 15% by weight with re- spect to the reaction mixture, preferably from 4 to 10%.

Any epoxidation catalyst can be used in the process, object of the present invention even if titanium-silicalite having the general formula: XTio2 (l-x) sio2 is preferred, wherein x represents a number ranging from 0.0001 to 0.04, preferably from 0.01 to 0.025. This cata- lyst is described in the patents U. S. 4,410,501,4,824,976, 4,666,692,4,656,016,4,859,785,4,937,216.

The epoxidation reaction of the olefin is carried out at a temperature ranging from 20 to 150°C, preferably from 40 to 100°C, even more preferably from 55 to 90°C and a such a pressure as to keep the olefin dissolved in liquid phase at the reaction temperature.

The stream leaving the epoxidation reactor is sent to a purification section from which the olefin oxide produced

is recovered and sent for storage, together with the sol- vent which is recycled both to the hydrogen peroxide syn- thesis reactor and to the oxidation reactor of the olefin.

In the process, object of the present invention, the . most critical section is the separation section of the ole- fin from the corresponding alkyl hydrocarbon as the prod- ucts to be separated, for example ethane/ethylene or pro- pane/propylene have very similar boiling points and also because the separation may require the use of a cryogenic unit whose running involves problems of a technologi- cal/economic nature. To reduce the incidence of this prob- lem, it is possible, according to the present invention, to use the epoxidation unit as an additional partial separa- tion section of the hydrocarbon mixture leaving the dehy- drogenation unit.

A further object of the present invention therefore relates to an integrated process for the production of ole- fin oxides which comprises: a) feeding in continuous to a dehydrogenation unit, a par- affinic stream essentially consisting of at least one Cs-Cs alkyl hydrocarbon; b) sending the stream leaving the dehydrogenation unit to a first separation unit to produce a stream consisting of hydrogen and a mixed stream essentially consisting of the non-reacted alkyl hydrocarbon and the dehydrogenated

alkyl hydrocarbon (olefin); c) feeding the stream of hydrogen together with a stream of oxygen, to a hydrogen peroxide synthesis unit; d) feeding a part of the hydrocarbon stream coming from the first separation section, together with the hydrogen peroxide produced in step (c), to an oxidation unit; e) feeding the stream leaving the epoxidation unit to a second separation unit to recover a stream containing the olefin oxide produced and a stream essentially con- sisting of the non-dehydrogenated alkyl hydrocarbon which is recycled to the dehydrogenation; f) feeding the remaining part of the hydrocarbon stream coming from the first separation section to a third separation section to recover a paraffinic stream, recy- cled to the dehydrogenation, and an olefin stream sent for storage.

Also in the additional process, object of the present invention, in order to keep the material balance under conditions of self-sufficiency, a fraction of mixed hy- drocarbon stream which contains a quantity of olefin ca- pable of being oxidized by the hydrogen peroxide pro- duced with the hydrogen coming from the dehydrogenation unit, is fed to the epoxidation unit.

The process, object of the present invention, can be better described by referring to the drawings of the en-

closed figures which represent an illustrative but non- limiting embodiments, wherein: Figure 1 represents a block scheme of the present pro- cess wherein a fraction of the olefin produced after the dehydrogeriation phase is fed to the epoxidation unit; and Figure 2 represents a block scheme of the present pro- cess wherein a fraction of the mixed stream still con- taining both the olefin and non-dehydrogenated corre- sponding paraffin is fed to the epoxidation unit.

With reference to the figures, D represents the dehy- drogenation unit, H represents the hydrogen peroxide syn- thesis unit, E represents the epoxidation unit, S1-S3 are three separation units, P represents a purification unit of the hydrogen stream, R is a recovery unit of the solvent whereas PR and PO represent the storage tanks of the olefin and epoxide respectively.

The integrated process for the production of olefin oxides, object of the present invention is evident from the enclosed figures and following description. In particular, a paraffinic stream coming from a refinery, for example propane with a purity of over 98%, is fed by means of line (1) to the dehydrogenation unit D. The outgoing stream is subjected to a first separation, for example in a distilla- tion system of the cold box type S1, to recover the hydro-

gen (2) which, after purification in P (membrane separation or PSA), is fed, by means of line (3), to the hydrogen per- oxide synthesis unit H together with the stream of oxygen and inert gas (9).

The stream (5) leaving S1 goes to the separation sec- tion S2, to recover the non-dehydrogenated paraffin (6), which is recycled to the unit D, and the olefin (8) which, according to the scheme of figure 1, is partly stored in PR and is partly sent, by means of line (7), to the oxidation unit E. The light products or impurities (methane, ethane, ethylene, heavy products), which are discharged from sec- tions Sl, S2 and P are sent to the torch by means of line (4).

The stream (14) containing hydrogen peroxide in solu- tion is fed to the oxidation unit E, together, as already mentioned, with the olefin (7). The solvent is recovered in the unit E from the stream (11), which is separated in R and recycled both to the hydrogen peroxide synthesis, by ; means of (12), and to the oxidation unit, by means of (13), as diluent of the hydrogen peroxide solution (10) leaving the synthesis. The olefin oxide produced (16) goes to the separation/purification section S3 from which the non- reacted olefin (17) is recovered, which is recycled to E, and the epoxide (18) stored in PO.

The excess water formed during the cycle is separated

from the solvent in R, treated with means not illustrated in the figures, and discharged to the sewage by means of line (15).

In the variations of Figure 2, the hydrocarbon stream (7) is fed to the oxidation unit. In particular, the stream (5) leaving the separation unit S1 is partially fed to the oxidation unit E, by means of (7), and partially to the separation section S. The reaction product (16) leaving unit E is sent to the separation/purification section S3 from which, in addition to the epoxide, the stream (17) containing the non-dehydrogenation paraffin and the non- reacted olefin in E, is recovered. This stream is recycled to the dehydrogenation unit D.

An illustrative but non-limiting example is provided for a better understanding of the present invention and for its embodiment.

EXAMPLE The procedure is adopted according to the scheme of Figure 1. The dehydrogenation step is carried out using a fixed bed reactor and a chromium catalyst on alumina. The dehydrogenation temperature is 650°C, the pressure 70 kPa.

The hydrogen peroxide synthesis is effected in a sol- vent (methanol) in which a catalyst consisting of palladium and platinum on coal, is dispersed at a concentration of 1% by weight. 200 mg of H2SO4 per kg of liquid medium and 6

mg of HBr per kg of liquid medium, are used as reaction promoters. The reaction temperature is 25°C, the pressure is 10 MPa. A hydrogen peroxide solution at 7% is obtained, which, after dilution to 3.5%, is fed to the epoxidation unit.

The latter is effected using titanium silicalite dis- persed in a concentration of 6% by weight in the aqueous reaction medium kept at a pH of 6.5 by the addition of NH40H. The reaction temperature is 50°C, the pressure 1.3 MPa.

The material balances are indicated in the following table. Component Stream 1 2 3 4 5 6 7 8 9 g/h w % g/h w % gh w % g/h w % g/h w % g/h w % g/h w % g/h w % g/h w % Propylene 257 55.5% 7 3.5% 197 100.0% 53 100.0% Propane 289 97.0% 198 42.7% 198 94.5% Hydrogen 12 45.0% 11 100.0% 1 2.5% Other hydrocarbons 9 3.0% 15 55.0% 47 97.5% 9 1.8% 4 2.1% Oxygen 219 100.0% Hydrogen peroxide Water Solvent Other oxygen.hydrocarbons Propylene oxide Total 298 100% 27 100% 11 100% 48 100% 464 100% 209 100% 197 100% 53 100% 219 100% Component Stream 10 14 12 13 11 15 16 17 18 g/h w % g/h w % g/h w % g/h w % g/h w % g/h w % g/h w % g/h w % g/h w % Propylene 492 65.0% 492 100.0% Propane Hydrogen Other hydrocarbons Oxygen Hydrogen peroxide 160 7.2% 160 3,6% Water 78 3.5% 142 3.2% 64 3.0% 64 3.0% 226 5.2% 98 89.9% Solvent 2067 89.3% 4133 93.2% 2067 97.0% 2067 97.0% 4133 94.6% Other oxygen.hydrocarbons 11 0.3% 11 10.1% Propylene oxide 265 35.0% 265 100.0% Total 2305 100% 4435 100% 2131 100% 2131 100% 4370 100% 110 100% 757 100% 492 100% 265 100%