Development of a Continuous Clean Alkene Epoxidation Process Technology for the Production of Commercially Important Epoxide Building Blocks

Alkenes (or olefins) are a class of oil-derived hydrocarbons that represent key starting materials for much of the organic chemical industry. A very important step in the conversion of alkenes into molecules that are even more valuable building blocks for the synthesis of a wide variety of products (e.g. pharmaceuticals, plastics, coatings, paints, adhesives, personal products, domestic products and other industrial products) is their selective oxidation to form a new class of molecules called alkene oxides or epoxides. Many of the commercially important procedures for converting alkenes to epoxides employ reagents which are potentially very hazardous, and multi-step processes which by modern standards are of low environmental acceptability. These procedures are also carried out in so-called batch reactions i.e. effectively in a large stirred reactor, with a fixed amount of epoxide being prepared in each batch. Isolating, recovering and purification of the epoxide are additional separate processes involving considerable handling of the product.The work proposed here is aimed at developing a novel process for converting alkenes into their epoxides. The essential features of this have already been demonstrated to be successful and are in the process of being patented. Essentially this involves alternative chemistry to that currently used. It employs an oxidizing agent that is inherently more safe than the currently used agent, and one whose activity needs to be triggered by use of a particular catalyst, adding further to the safety aspects. In addition the process is a continuous rather than a batch one, i.e. the quantity of product generated can be controlled simply by how long the process is allowed to run. This offers the manufacturer significant business flexibility with their customers. The process is also carried out in a special reactor referred to as a Reactive Distillation Column (RDC). In essence this is a vertical tube arrangement with three connected sections. The middle part is a reactor section in which the solid catalyst particles are contained and the chemical reaction takes place, the top and bottom sections are used as separator sections where in effect the epoxide product is isolated. This compact single unit arrangement is extremely convenient and efficient, bringing with it many advantages. It considerably reduces the multi-step handling of the product associated with the existing processes, the 'footprint' and complexity of all the apparatus is reduced, and the ability to switch from one alkene feedstock to a completely different one is considerably facilitated. As a bonus the organic by-product from the oxidizing agent is itself a useful chemical building block and so overall the efficiency of use of all the organic chemical species (referred to by chemists as the 'atom efficiency') is very high.Overall therefore this new process provides many advantages to potential users: feedstock flexibility, 'atom efficiency', flexibility of scale of production, reduced unit costs and improved profitability. Importantly as well, the new process makes a big impact on the environmental acceptability of epoxide production.

The proposed project deals with a continuous clean alkene epoxidation process technology for the production of commercially important epoxide building blocks. The process is considered to be clean as (i) it is a single unit process combining reactor and separator, (ii) it employs an efficient and selective heterogeneous catalyst, (iii) it is solvent less, (iv) it uses a benign oxidant which becomes active only on contact with the catalyst and (v) it is atom efficient and the alcohol by-product itself is an important chemical feedstock. This novel process technology is highly efficient and selective, continuous rather than batch, which potentially provides a reliable, lower cost, safer and more environmentally acceptable method, with the following advantages: (i) Capital cost of the equipment is reduced because reaction and distillation units are coupled together in a single unit. (ii) The exothermic heat of reaction is utilized for supplying the desired heat of reaction for distillation. (iii) The production costs are reduced. (iv) Use of lower mole ratios of reactants, and yet being able to overcome the thermodynamic equilibrium limitations encountered in simple reactions that limit the conversion in fixed bed reactors to a low or moderate level. Simultaneous removal of the products from the reacting mixture, while the reaction is progressing, enables the reaction to proceed to a much higher level of conversion than otherwise possible. This reduces the recycle costs of the excess reactant. (v) Significantly reduced catalyst requirement for the same degree of conversion. (vi) Side reactions are suppressed by separating the product(s) from further reaction as they are formed, thereby improving product selectivity. (vii) Downstream processing is reduced. (viii) Avoidance of hot spots and runaways using liquid vaporisation as thermal fly wheel. (ix) Easy temperature control. In the present case the smaller integrated plant design would lead to lower capital cost of new plant, and very importantly to lower recurrent costs in terms of energy and materials (water, steam etc.) costs. Overall, therefore, such an integrated process also provides a more environmentally acceptable process technology, hence contributing to improving the quality of life of the UK public. Epoxides are versatile and useful intermediates in organic synthesis and as a consequence the epoxidation of olefinic compounds is highly important for industrial manufacturers. Apart from the very large scale production of ethylene and propylene oxides (which are unique gas phase processes), more highly value-added epoxides such as cyclohexene oxide, 1,2-limonene epoxide, pinene epoxide, etc. are produced in liquid phase batch-type reactions employing peroxyacids as the oxidation reagent. Such processes are very dated, employing relatively inefficient stoichiometric oxidation chemistry, with a major requirement in terms of work-up and product isolation and purification procedures. Its safety and environmental acceptability are also low. Many of the potential epoxides that could be produced using this technology are ubiquitous chemical building blocks for the pharmaceutical and related businesses (perfumes, flavours etc.) possibly also in some plastics manufacture. This approach is overall a more efficient process in that it is catalytic, it offers flexibility in terms of the alkene feedstock and the potential volume of production, coupled with a safe and more environmentally acceptable oxidant. Overall such a process offers the prospect of a lower unit cost, and improved profitability. This technologically enhanced process can be utilised by the epoxides manufacturers, who will gain additional products to sell that are superior to their existing product line, and end-users who will actually use these improved quality products.