Process for removal of 1 , 2-epoxy-5-hexene from epichlorohydrin

Technical field

This invention concerns a process to remove 1 , 2-epoxy-5-hexene from epichlorohydrin which is produced by oxidation of

unpurified allyl chloride comprising at least 1 , 5-hexadiene as impurity .

Background art

Epichlorohydrin (ECH) is currently produced from allyl

chloride, chlorine and water followed by basic treatment

(dehydrochlbronation) to produce the ECH. Using this route the ECH is contaminated with trichloropropane (TCP), the presence _. of TCP could generate problems when ECH is used as in the production of epoxy resins. It is also a toxic compound and harmful to the environment.

One elegant solution to prevent presence of TCP is to produce ^■ ECH by direct epoxidation of the double bond of allyl chloride. However the technical grade of allyl chloride, used in the production of epichlorohydrin (ECH), contains an impurity: 1,5- hexadiene .

When ECH is made by epoxidation of such allyl chloride, part of this impurity is converted into 1 , 2-epoxy-5-hexene .

Unfortunately, 1 , 2-epoxy-5-hexene has a boiling point of 118 to 121°C and hence cannot be separated by rectification from ECH (boiling temperature of 118°C).

The problem of 1 , 2-epoxy-5-hexene is augmented in processes where unreacted allyl chloride, and its impurity, are recycled in the process. In those^ processes the majority of 1,5

hexadiene is converted to 1 , 2-epoxy-5-hexene . The US 4127594 described an efficient way to purify ECH by selective hydrogenation of the olefinic impurities. The 5, 6- ^' epoxyhexene-1 present in minor amount in ECH is selectively converted, with minimal concomitant destruction of -ECH; by hydrogenation in the presence of a catalyst comprising rhodium, platinum or palladium deposited on a non-acidic, refractory support. This method converts unsaturated compounds into their saturated analogues and thus removes double bonds, which might be prone for side reactions in the later production and

application of epoxy resins. Due to no detectable change in boiling point of the new product formed after hydrogenation, it would, however, still remain in the ECH after rectification.

More recently, the CN , 102417490 provides a process for

purification of ECH containing 1 , 2-epoxy-5-hexene . In this reference the contaminant 1 , 2-epoxy-5-hexene is treated with excess chlorine or bromine at a temperature in the range of 5 to 30°C. The 1 , 2-epoxy-5-hexene was then converted into a product with a significantly higher boiling temperature. Next, remaining halogen was removed by flushing with nitrogen.

Subsequently, rectification was used to obtain ECH with a purity of more than 99.8%.

The process of CN'490 is an elegant process. On the ^■ other hand, it has some significant disadvantages. It reduces the overall yield of the process due to the fact that the intermediate formed during the chlorination 1, 2-epoxy-5-hexene can attack ECH yielding an addition product.

Furthermore, the reaction is carried out in a separate reactor, where the halogen is added to the ECH. Therefore, an extra reactor setup is required, increasing capital costs. Also chlorinated organic compounds are produced, which are generally harmful for the environment and do not have direct application. The reaction is carried out at temperatures that require active cooling of the ECH, even below ambient temperatures. The reaction temperature according to this reference is 0-30°C, preferably 0-15°C, more preferably 0-5°C.

Also, this reference specifically teaches that an excess of halogen has to be used (ratio halogen/1 , 2-epoxy-5-hexene between 1/1 and 3/1) .

Moreover, after the reaction, the excess halogen must be removed (here by passing through nitrogen gas) . This nitrogen stream needs to be treated to remove the halogen before being released into the atmosphere-. Thus, there is a potential pollution issue with this process. This would again add complexity and costs.

The current inventors set out to solve the problem arising from allyl chloride containing 1 , 5-hexadiene impurity by an

alternative process that is more economical, requires less investment and that might be used to create valuable side- products rather than waste.

Disclosure of the invention

Accordingly, the current invention provides a process for removing 1 , 2-epo.xy-5-hexene and 1,5 hexadiene from ECH by:

a) catalytic oxidation of the unpurified epichlorohydrin mixture with hydrogen peroxide whereby at least 50% of the moles of 1 , 5-hexadiene reacted to 1 , 2-epoxy-5-hexene are further converted into 1 , 2 , 5 , 6-diepoxyhexane and

b) removing optionally the light boiling components from a) and

c) further removing 1 , 2 , 5 , 6-diepoxyhexane by a rectification step .

More specifically, it provides a process for removing 1,2- epoxy-5-hexene from ECH, which is produced by oxidation of unpurified allyl chloride comprising at least 1 , 5-hexadiene as impurity in more than 0.05 % by weight of 1, 5-hexadiene, by: (a) contacting a mixture comprising at least allyl chloride,

ECH, 1, 5-hexadiene, 1 , 2-epoxy-5-hexene with hydrogen peroxide and a transition metal complex containing compound as catalyst.

(b) separating unreacted allyl chloride, unreacted 1,5- hexadiene and other low boiling components by distillation

(c) separating 1 , 2 , 5 , 6-diepoxyhexane and possibly .other high boiling components from ECH and 1, 2-epoxy-5-hexene by

distillation .

The current invention allows to employ allyl chloride

feedstocks in an epoxidation process that are contaminated with 1 , 5-hexadiene . The product of the contaminant is ^' 1,2,5,6- diepoxyhexane , also known as 1 , 5-hexadiene diepoxide. This has a boiling point of.l88°C (62°C at a reduced pressure of 30Ό mm Hg) . Its boiling point is therefore' significantly different from ECH, which facilitates the separation of the product ^' . The 1 , 2 , 5 , 6-diepoxyhexane may be used, for instance in resin compositions. The ^' latter is a significant advantage over other processes, like chlorination, where the products formed are considered useless.

Mode for carrying out the invention

Step (a) is preferably carried out by contacting the organic phase of a mixture comprising at least allyl chloride,

epichlorohydrin, 1 , 5-hexadiene and 1 , 2-epoxy-5-hexene . The preferred oxidant for the reaction is hydrogen peroxide.- Other oxidants may be used, i.e. as precursor to the hydrogen

peroxide, but. given the availability and to reduce

environmental impact hydrogen peroxide is the preferred

oxidant. Hydrogen peroxide has strong oxidizing properties. It is typically used in an aqueous solution.

The oxidation catalyst is preferably chosen from transition metal catalysts active in oxidation or epoxidations with hydrogen peroxide as the oxidant. Typical catalysts contain transition metals like manganese, tungsten, titanium,

molybdenum, rhenium, silver, vanadium and iron.

More preferably the oxidation is conducted with a homogenous catalyst, such as manganese or tungsten. However, there are many different suitable catalysts that have a favourable solubility in either water or the organic phase, desired reactivity towards epoxidation and stability against

decomposition. Somebody ordinary skilled in the art can derive examples from overview articles and books such as "Mechanisms in homogenous and heterogeneous epoxidation catalysis, T.S. Oyama".

One preferable class ^" of catalyst comprises manganese complexes incorporating cycling nitrogen containing compounds, the manganese catalyst preferably contains a tertiary substituted nitrogen ligand.

Another preferable class of catalysts comprises tungsten salts or their acids in the presence of phosphates. Also

phosphotungstate salts or their acids can be used. These compounds are used in the absence of organic ligands, but in the presence of a phase transfer agent. Somebody ordinary skilled in the art can derive variations of such tungsten based catalytic epoxidation systems from overview articles and books such as "Modern Oxidation Methods, Jan-Erling Backvall" or "Mechanisms in homogenous and heterogenous epoxidation

catalysis, T.S. Oyama". To ensure optimal oxidant efficiency, the oxidant is preferably added to the aqueous reaction medium at a rate about equal to the reaction rate of the catalytic oxidation. The catalytic oxidation may be performed in a batch process, in a continuous process or in a semi-continuous process. Preferably, step (a) is performed in a common stirred tank reactor provided with a means of stirring. The catalyst, aqueous reaction medium ^' and reactants may be added, in batch, or the reactants may be added over a period of time. If hydrogen peroxide is added during the reaction, then it is added to either the (stirred) organic phase comprising the crude ECH or the (stirred) aqueous reaction medium. In (semi) continuous operations, various recycling streams may be used to control the reaction conditions and to optimize the production rate. In terms of process design, a settler may be added to optimize ^" the gravitational separation of the organic phase containing the ECH . Likewise, a membrane unit may be used to recycle the. agueous reaction medium with reduced loss of catalyst.

The reaction is conducted at or above atmospheric pressure. The precise pressure is not critical so long as the reaction mixture is maintained substantially in a non-gaseous phase. Typical pressures vary from about 1 to about 100 atmospheres. After step (a) , the product comprising crude ECH which is subjected to rectification steps (b) and (c) . Rectification conditions, such as distillation and fractional distillation, are known in the art .

Preferably, unreacted allyl chloride (for recycle purposes) and light ends, such as 1 , 5-hexadiene , chloropropanes , and

chloropropenes and the like, are removed as part of step (b) in one or more stages from the crude ECH first. A typical ECH composition (crude after reaction) is as follow:

The crude ECH is subjected to distillation, preferably in a perforated-plate column, bubble-cap plate column and/or packed column. This may be a single column or a series of columns.

The column is preferably equipped with an evaporation or heating device (or an evaporation or heating area or zone) located at or near the bottom of the column (or below the first plate) . It is furnished with means to introduce an inlet stream at a point intermediate between the bottom and the top of the column; means to withdraw a lower-boiling stream at or near the top of the column, and means to withdraw a hi.gher-boiling stream at or near the bottom of the column and possibly means to withdraw a product stream at- an intermediate point on the column .

Preferably, a lower-boiling stream is continuously drawn off at the head of the column and a higher-boiling ^' stream is

continuously drawn off at the foot of the column.

Next, 1 , 2 , 5 , 6-diepoxy-hexane and other heavy end e.g.

components such as monochlorohydrins and dichlorohydrins and the like, with boiling points greater than 118 °C are separated from ECH. This is again done in a distillation column or series of columns, operating however at lower pressure and/or higher temperature conditions then the conditions for removal of the light ends. Moreover, the product stream is drawn off at the head of the column or at an intermediate point between feed point and the head of the column.

The TCP was not detectable in the crude ECH. Further

purification by distillation lead to a ECH purity of superior to 99% and further optimization up to 99.5% purity of the ECH. According to the. invention, the 1 , 2-epoxy-5-hexene in the ECH is converted into a higher boiling product, this is achieved by epoxidizing the mono-epoxide into the corresponding diepoxide. By ensuring that the 1 , 2-epoxy-5-hexene is converted into a high boiling product, this contaminant can effectively be removed. Moreover, this may lead to the production of 1,2,5,6- diepoxyhexane that can be cleanly separated and form an

alternative attractive epoxy resin-type product.

In the preferred embodiment the reaction conditions during epoxidation of crude ECH are such that on molar basis at least 45% of the contaminant 1 , 5-hexadiene is converted into 1,2,5,6- diepoxyhexane and thus can be collected during distillation in the fraction that has a higher boiling point than ECH.

Desired reaction conditions according to this inventio are those in which the rate of the consecutive reactions are such that formation of 1 , 2 , 5 , 6-diepoxyhexane from 1, 2-epoxy-5-hexene. is at least 0.50 that of the formation of 1 , 2-epoxy-5-hexene from 1 , 5-hexadiene . Somebody ordinary skilled in the. art ca derive those conditions from theoretical considerations as ^' for example explained in Chemical Reactor Development, Dirk Thoenes or by variation of reactor types and reaction conditions such as phase ratio or residence time.

The most optimal reaction conditions for maximal removal of

1 , 2-epoxy-5-hexene can lead to reduced peroxide yields defined as the molar ratio of ECH produced over hydrogen peroxide charged. It can also lead to a reduction in turn over numbers defined as molar ratio of ECH produced over catalyst charged. Without being bound to any specific theory it is fair to assume that a high conversion of 1 , 2-epoxy-5-hexene to 1,2,5,6- diepoxyhexane is coupled to relatively low concentrations of allyl chloride in the reaction media which results in side, reactions of the epoxidation becoming more favourable, such as decomposition of peroxide and decomposition of ECH .

Accordingly, this invention might be best practised when the removal of 1 , 2-epoxy-5-hexene is high, while the decrease in Yield and TON is small to nihil.

The present invention of removal of 1 , 2-epoxy-5-hexene via epoxidation can be combined with other techniques known in the , art. This includes "bleeding" a fraction of the allyl chloride recycle stream removing low boiling side products of the allyl chloride productions that will accumulate or chlorination of - remaining 1 , 2-epoxy-5-hexene in epichlorohydrin .

Due to circumventing ECH synthesis via addition of chlorine to allyl chloride and making use of the oxidative manufacturing of the ECH from allyl chloride, the latter ECH and all its

derivatives will not contain detectable amounts of TCP, even in the most crude quality or grades. Since the main impurities 1 , 2-epoxy-5-hexene and 1 , 2, 5 , 6-diepoxyhexane contain, like the ECH, an epoxide group, these compounds will be build-in the derivatives and thus not leach into its surrounding when applied as epoxy resin.

The following examples will more fully illustrate selected embodiments of this invention. All parts, percentages and.

proportions referred to herein and in the appended claims are by weight unless otherwise indicated.

EXAMPLES

Example 1:

In a typical continuous reaction, the flows of the components are 0.24 mol per hour of hydrogen peroxide, 9.0 micromol per hour of catalyst, 2.5 millimol per hour of oxalic acid and 0.79 mol per hour of crude ECH. pH is maintained between pH 3.2 and 4.0. Temperature ¹ . is set at 15 °C and the reaction volume is controlled at about 200 ml. The catalyst used is a [Mn ₂ (μ- 0) 3(1,4, 7-trimethyl-l , 4 , 7-triazacyclononane } ₂ ] ²⁺ salt.

The starting allyl chloride contains 0.4 wt% 1 , 5-hexadiene as starting feedstock to produce the crude ECH. This results in a steady state yield of ECH based on the peroxide added of 72 % ^■ and a diepoxide/monoepoxide (DO/BO) ratio of 1.

Example 2 :

As in example 1, but the allyl chloride contains 1.2 wt% 1,5- hexadiene as starting feedstock to produce the crude ECH. This results in a steady state yield based on the peroxide added of 69 %, and a DO/BO ratio of.1.

Example 3:

As in example 1, but the allyl chloride contains 1.2 wt% 1,5- hexadiene and the ally chloride flow was 0.316 mol/h. This results in a steady state yield based on the p.eroxide added of 72.9 %,■ a turnover number of 19300 and a DO/BO ratio of 3. Example 4 :

Crude epichlorohydrin (126 grams) containing 0.2 wt% of 1,2- epoxy-5-hexene is reacted in a aqueous medium (125 ml) .

containing 0.1 ml of 35wt% hydrogen peroxide, [Μη ₂ (μ- 0) ₃ { 1, 4., 7-trimethyl-l, 4, 7-triazacyclononane } ₂ ] ²⁺ salt (240 microM) and oxalic acid (20 rti ) . 35 wt% hydrogen peroxide solution is added in a rate of 4 ml/h over 10 minutes at .30 °C . The pH is controlled between 3.4 and 3.8 by addition of small amounts of oxalic acid and NaOH. Conversion of 1 , 2-epoxy-5- hexene by oxidation is 91%. The purity of the ECH was > 99.7 wt%

Example 5:

As in example 4, but with 25 ml of aqueous phase. Conversion of 1 , 2-epoxy-5-hexene by oxidation is .55.4%. The purity of the ECH was > 99.5 wt%

Example 6:

As in example 4, but with 26 grams o'f ECH. Conversion of 1,2- epoxy-5-hexene by oxidation is 98%. .The purity of the ECH was > 99.8 wt% .

Example 7 :

Allyl chloride containing 1.2 wt% 1 , 5-hexadiene (50 ml) is reacted with a solution of 25 ml hydrogen peroxide (35 wt%) in 150 ml water. Phosphotungstic acid and Aliquat® 128 are added and the pH is controlled at pH 2. After 2 hours, at 35 °C, the organic phase is removed, from the mixture and analysed by gas chromatography. The organic phase contains 22 wt% of ECH with a DO/BO ratio of 1.23. Example 8 :

The product of the organic phase of examples 1-7 are further purified by distillation according to a method as given above in the description. The crude composition of the organic phase has an average composition as given of the table below:

Additional distillation can be performed to remove light (allyl chloride) and heavy boiling components further (DO).

Distillation was performed at 60°C and under reduced pressure. Pressure was. slowly decreased to obtain the purity of the ECH. The ECH obtained had the following composition, as was determined by gas chromatography.

component Weight percent

ECH 99.1

Allyl chloride 0.4

Butenyl oxirane ^' (BO) 0.06

1, 2-di (oxiran-2-yl) ethane (DO) 0.006

trichloropropane < 0.001

Total light ends (lower boiling 0.6

than ECH)

Total heavy ends (higher 0.2

boiling than ECH) Example 9:

Such an ECH distillation can be further optimized; A person skilled in the art would use Aspen simulation . software to optimize the distillation. Such an optimization of. distillation of the mixture coming from, example 1 would results in. the following composition:

The EGH-.purity obtained by the process has given in the above examples is superior to 99.10 weight % and free, of

trichloropropane..