NO166535B - FLAMMABLE, CROSS-BONDED POLYOLEFIN MATERIAL, AND THE USE OF IT FOR COATING ELECTRICAL CONDUCTORS. - Google Patents

Abstract

A filled cross-linked polymeric material of ethylene-vinyl ester copolymer which exhibits flame-retardant properties to a significant extent by incorporating a double lubricant system which includes a fatty acid and an alkylene-bis-amide. Electrical conductors coated with said polymer mixture are also discussed.

Description

Process for the production of propylene oxide.

The present invention relates to the production of propylene oxide where propylene is reacted with an organic hydroperoxide.

Epoxy compounds such as propylene oxide are very valuable and important commercial materials. In the past, methods have been used for the epoxidation of various olefinic materials, such as propylene, where highly active materials, such as peracids, are used. However, the use of these peracid materials was not satisfactory, due to the high costs and a somewhat non-selective reaction.

In recent times, important progress has been made in the area of epoxidation of olefinic unsaturated compounds to the corresponding oxirane compounds. These important advances have included the recognition that organic hydroperoxides can be used in the appropriate and highly selective epoxidation of olefinic unsaturated compounds.

According to the basic process, propylene and an organic hydroperoxide are converted to propylene oxide and an alcohol corresponding to the starting hydroperoxide. It is common to work with low oleic fines per review, e.g. from 10 to 20% to achieve high selectivity. Consequently, large amounts of propylene must be recycled. In operations on a continuous commercial scale, unconverted propylene is often recycled for economic and other reasons. Whatever method is chosen to utilize the unreacted propylene, difficulties arise. For example impurities have been found which are very difficult to remove from propylene oxide, e.g. methyl formate is present in the product stream, further that the ignition level and also the detonation level for propylene-oxygen mixtures are considered to be reached or exceeded at certain points in the process.

The present invention is based on the recognition that not all oxygen from the hydroperoxide reacts with propylene oxide and that the reactor outlet stream in normal epoxidation, which is either catalyzed or not catalyzed, contains from a few tenths to several percent undissolved oxygen and that the oxygen content in propylene rises cumulatively as long as propylene is recycled. It has further been found that unreacted propylene cannot be reused by recycling unless the oxygen content is reduced to certain critical levels.

A suitable method for reducing the oxygen content in propylene is to pass the reactor outlet stream through a distillation fractionation column or several such columns, where the light fractions are extracted and condensed, and the liquid condensate is separated from non-condensed material. The liquid condensate, which mainly consists of propylene, can be recycled or used for other purposes. The majority of oxygen is present in the non-condensed material, although some is still present in the liquid recycled propylene.

An alternative method of using a distillation column would be to use a combined oil absorption and stripping device. In another method, the unreacted propylene recovered from the reaction mixture can be chemically treated to reduce the oxygen by subjecting the propylene to oxidizing conditions by passing it over an oxidation catalyst to cause a controlled oxidation of the propylene to by-product which can be easily removed without faze to form combustible mixtures or which would be inert in the subsequent treatment of propylene.

It is clear that the oxygen content in the feed to an epoxidation reactor must be low enough to allow the operation of this epoxidation treatment in the non-detonable region. However, it has been found in the present work that much less oxygen is permissible in the recycle stream than would correspond to the non-detonable or non-flammable work in the epoxidizer, even if detonable work is avoided by increasing the total pressure in the epoxidizer to keep oxygen in liquid phase, i.e. so that there would be no gas phase in the device.

The discovery that significant amounts of oxygen are formed in the epoxidation reaction forces one to apply a regulation of the oxygen content in the propylene that enters the epoxidation reaction. It has been found in the present invention that the total oxygen content present in the reaction vessel is below 3 mol%, which is achieved by oxygen being removed at least partially from unreacted propylene for return to the reaction vessel. If the amount of oxygen in propylene is higher than that specified, but still below levels for detonation or ignition, many difficulties are involved which make a feasible process unattainable. These difficulties can best be explained as follows: With a normal recycling of propylene, which would contain the cumulative oxygen supply per review, the oxygen level continues to rise in the epoxidizer. The first major effect caused by such an oxygen build-up is that which includes the direct attack of molecular oxygen on propylene in the epoxidation device. It is common knowledge in the field that propylene is oxidized with molecular oxygen in the temperature range used for the epoxidation. This action completely suppresses an advantage obtainable from the reaction of propylene and hydroperoxide, namely the formation of propylene oxide with very high selectivities without any formation of methyl formate. In this case, the oxygen level builds up in the unreacted propylene, and subsequently in the epoxidation reactor as unreacted propylene is recycled, until a permanent state is reached, namely the state at which the net amount of free oxygen in the epoxidation device is consumed by direct oxidation attack on the propylene. This results in very unsatisfactory work due to the fact that unfortunate by-products which are known to occur in ordinary propyl enoxidation with molecular oxygen.

The second difficulty which occurs either together with or before the first is the hazardous and uneconomic work when the oxygen level rises. It is highly undesirable to operate the epoxidation device with a gas phase containing molecular oxygen due to the risk of explosion. This can be avoided by applying a sufficient high pressure to keep all the oxygen dissolved in the liquid phase. However, due to the high volatility of oxygen, the required pressures in the device rise sharply when the concentration of oxygen in the recycled stream increases. Work becomes impractical from an economic point of view or extremely risky because of that effect. Moreover, if the oxygen level is allowed to rise, it is economically impractical to carry out the separation of propylene and oxygen, e.g. by high-pressure distillation without having a gas phase in the fractionation zone, which is within the flammable and explosive area. It is therefore essential that the oxygen is purified to such an extent in the plant's propylene recovery sections that work can be carried out under the potentially explosive area in all sections of the plant.

The hydroperoxides used in the invention are those with the formula ROOH, where R is a substituted or unsubstituted alkyl, cycloalkyl or aralkyl radical with from 3 to 20 carbon atoms. R can be a heterocyclic radical.

Illustrative and preferred hydroperoxides are cumene hydroperoxide, ethylbenzene hydroperoxide, tertiary butyl hydroperoxide, cyclohexanone peroxide, tetrahydronaphthalene hydroperoxide, methyl ethyl ketone peroxide, methyl cyclohexane hydroperoxide. A useful organic hydroperoxide compound for use in the invention is the peroxide product which is formed by oxidation of cyclohexanol in the liquid phase.

Temperatures that can be used in the present invention can be varied quite widely depending on the reactivity and other properties of the particular system. In general, temperatures within the range -20 - 200°C, in particular 0 - 150°C, and preferably 50 - 120°C can be used. The reaction is carried out under pressure conditions sufficient to maintain a liquid phase. Although sub-atmospheric pressure can be used, usually pressures in the range of atmospheric pressure to 70 kg/cm 2 are absolutely most desirable.

The ratio between propylene and organic peroxide compounds can vary over a wide range. In general, molar ratios between propylene and hydroperoxide are used within the range 0.5:1 to 100:1, in particular 1:1 to 20:1, and preferably from 2:1 to 10:1.

The concentration of hydroperoxides in the propylene oxidation reaction mixture at the beginning of the reaction would normally be 1% or more, especially lower concentrations would be effective and can be used.

The propylene oxidation reaction can be carried out in the presence of a solvent, and in practice it is usually desirable that it be used. Usually, aqueous solvents are not used. Among the suitable substances are hydrocarbons, which may be aliphatic or aromatic, and the oxygenated derivatives of these hydrocarbons. Preferably, the solvent has the same carbon skeleton as the hydroperoxide used in order to reduce or avoid problems when separating the solvent.

The epoxidation reaction takes place in the presence or absence of metallic epoxidation catalysts. If these are used, the catalysts may comprise compounds of V, Mo, Ti, W, Se, Mb, Te, preferably the first four mentioned.

The amount of metal in the solution used as a catalyst in the epoxidation process can vary greatly, although it is desirable to use at least 0.00001 mol and preferably 0.002 mol to 0.03 mol per moles of hydroperoxide present. Quantities larger than approx. 0.1 mol does not seem to give any advantage over smaller amounts, but amounts up to 1 mol or more per moles of hydroperoxide can be used. The catalyst remains dissolved in the reaction mixture during the process and can be reused in the reaction after removal of the reaction products. The molybdenum compounds include molybdenum organic salts, oxidizers, such as MO2O3, MoO3, molybdic acid, molybdenum chlorides and oxychlorides, molybdenum fluoride, phosphate, sulphide and the like. Heteropolyacids containing molybdenum can be used as well as salts thereof, examples are phosphormolybdic acid and sodium and calcium salts thereof. Similar or analogous compounds of other metals of the aforementioned can be used, as well as mixtures thereof.

The catalytic components can be used in the epoxidation reaction in the form of a compound or mixture which is originally soluble in the reaction medium. Although the solubility will depend to some extent on the particular reaction medium used, a suitable soluble substance will comprise hydrocarbon-soluble organometallic compounds, which have a solubility in methanol at room temperature of at least 0.1 g per litres. Illustrative soluble forms of catalytic materials are naphthenates, stearates, octoates, carbonyls, and the like. Various chelates, association compounds and enol salts, such as e.g. aceto-acetonates can also be used. Special and preferred catalytic compounds of this type for use in the invention are naphthenates and carbonyls of molybdenum, titanium, tungsten, rhenium, niobium, tantalum and selenium. Alkoxy compounds, such as tetrabutyl titanate and similar tetraalkyl titanates are very useful. However, four of the listed catalysts have been found to have particular utility in the epoxidation of a primary olefin, such as propylene. These four catalysts are molybdenum, titanium, vanadium and tungsten. It has been found that their activity of epoxidation of primary olefins is surprisingly high, and can lead to high selectivity for propylene to propylene oxide. These high selectivities are achieved by high conversions of hydroperoxide, 50% or higher, which conversion levels are important for the commercial application of this method of operation.

Basic substances can be used in the present invention. Such basic substances are alkali metal compounds or alkaline earth metal compounds. Particularly preferred are compounds of sodium, potassium, lithium, calcium, magnesium, rubidium, cesium, strontium and barium. Of the compounds used, the most preferred are those which are soluble in the reaction medium. However, insoluble forms can be used and are effective when dispersed in the reaction medium. Organic acid compounds such as a metal acetate, naphthenate, stearate, octoate, butyrate and the like can be used. In addition, inorganic salts such as sodium carbonate, magnesium carbonate and trisodium phosphate can also be used. Particularly preferred species for metal salts include sodium naphthenate, potassium stearate, magnesium carbonate. Hydroxides and oxides of alkali and alkaline earth metal compounds can be used. Examples are NaOH, MgO, CaO, Ca(OH)2 and KOH, alkoxides, e.g. sodium ethylate, potassium cumylate, sodium phenolate can be used. Amides such as NaNH2 can be used as well as quaternary ammonium salts. In general, any compound of alkali or alkaline earth metals which gives a basic reaction in water can be used.

The basic compound is used during the epoxidation reaction in an amount of from 0.05 to 10 mol per mol of epoxidation catalyst, in particular 0.25 to 3.0 mol, and preferably 0.50 to 1.50 mol. It has been found that as a result of the incorporation of the basic compound into the reaction system, significantly improved efficiency is achieved when using the organic hydroperoxides in the epoxidation.

That is when using the basic compound, the result is a higher yield of oxirane compound based on hydroperoxide consumed. Moreover, of the consumed hydroperoxide, a larger amount is reduced instead of being converted into other unwanted products by the invention.

Furthermore, by the use of the basic compound it is possible to use lower ratios of propylene to hydroperoxide and thus improve the propylene conversions, while maintaining satisfactorily high reaction selectivities.

During the epoxidation, the organic hydroperoxide is selectively reduced to the corresponding alcohol, which is suitably extracted and/or converted into hydroperoxide and reused or converted into another product.

In the preceding description, the term propylene is to be understood as including mixtures of propylene and propane. Commercially available propylene contains e.g. some propane.

The following examples illustrate the present invention.

EXAMPLE I

1,000 g of ethylbenzene oxidate produced by air oxidation of ethylbenzene, and a mixture containing 120 g of ethylbenzene hydroperoxide, 365 g of a mixture consisting of 66 mol% propane and 4 mol% oxygen and 1.3 g of raw lybdenooctanoate solution are introduced into an epoxidation reactor contains 5% by weight of molybdenum.

The epoxidation reaction is carried out at 135°C and 70.31 kg/cm<2>. Under these conditions, no gas phase is present. After 60 minutes of the reaction time, the hydroperoxide conversion is essentially complete. The selectivity of propylene oxide, defined as moles of propylene oxide per mol of hydroperoxide converted is 50 mol%.

The same kind of impurities are observed in the reactor which are formed by direct molecular oxygen attack on propylene. These include acids, esters and CO2. Most damaging to the working process, however, is the observation of the presence of methyl formate which cannot be separated from propylene oxide by ordinary distillation techniques.

Unreacted propylene is separated from the reactor by fractional distillation from material with a higher boiling point.

It turns out that the level of oxygen in unreacted propylene

leading to the presence of an explosive mixture of oxygen-propylene in the gas phase and in the sections of the system from which propylene is recovered. E.g. would a normal propylene recycling scheme for the above process provide up to 50% oxygen in a

gas phase containing propylene-propane in at least the same proportion in the recycling system. It is not economically possible to avoid this oxygen build-up in normal recycling work.

EXAMPLE II

An experiment similar to Example I was carried out with the following batch: 1.00 g of ethylbenzene oxidate containing 120 g of ethylbenzene hydroperoxide, 350 g of a mixture of fresh and recycled propylene comprising 69.2 mol% propylene, 30 mol% octanoate containing 5 wt. -% molybdenum.

In this experiment, the epoxidation is carried out at 135°C and 59.76 kg/cm<2> for 60 minutes. Conversion of hydroperoxide is complete and selectivity defined in example T is 60 mol%.

Recycled propylene in this reaction is produced by separation from the reactor outlet stream in example I by fractional distillation. The oxygen level of the unreacted recycled propylene is reduced by a high pressure fractionation of oxygen from propylene to give a liquid propylene phase containing approx.

0.08 mol% oxygen. This propylene phase is combined with an

part of the gas phase from such a fraction, so that the combined recycled and fresh propylene contained 0.8 mol% oxygen.

The reduction in the reaction between propylene and oxygen is observed.

Most important is the observation that propylene oxide of commercial quality

obtained from the reactor outlet stream by a simple distillation technique

nod.

EXAMPLE III

The unreacted propylene which is obtained by the following process

example I is treated in the following way because it is recycled:

The propylene in gas phase is fed over a vanadium oxidation catalyst

sator. The degree of oxidation is regulated to maintain an oxygen-oxygen concentration in the outlet stream of oxidation of approx. 0.1

mole %.

EXAMPLE IV

350 g of unreacted propylene, whose oxygen content has been reduced according to the procedure in example II, is fed to a reactor together

but with 1000 g of ethylbenzene oxidate containing 120 g of ethylbenzene hydroperoxide and 1.35 g of molybdenum octanoate containing 5% by weight of molybdenum. In this case, only the liquid phase from the high pressure fractionation zone is recycled.

The epoxidation is carried out at 135°C and 49.21 kg/cm<2> for 60 minutes. Ethylbenzene hydroperoxide conversion is essentially complete

with a selectivity to propylene oxide of 69%.

In this case, the reactor effluent stream contains a non-

noticeable amount of methyl formate. Moreover, a simple fractionation of this outlet stream gives a propylene oxide which does not contain methyl formate.

Claims (1)

1. Process for the production of propylene oxide where propylene is reacted with an organic hydroperoxide at temperatures between -20 and 200°C under pressure sufficient to maintain a liquid phase, whereby propylene oxide is formed in the presence of unreacted propylene, characterized in that oxygen is removed at least partly from unreacted propylene for return to the reaction vessel, so that the total O2 content in the reaction vessel is below 3%.