focus on Laboratory Products
An Easy to Use Tool for Safe and Reproducible High Pressure Reaction Chemistry
Tom McInally, Martyn Fordham
For the effi cient synthesis of novel molecules, materials and polymers scientists employ a broad range of experimental techniques and equipment. Reactions carried out at very low temperature under an inert atmosphere at high dilution can usually be performed in a conventional round bottom fl ask whereas reactions that require elevated temperature and high pressure need to be carried out in a specially designed high pressure reactor.
A high pressure reactor can offer several advantages over a conventional round bottom fl ask for conducting chemical reactions. It enables reactions to be carried out under elevated pressure and at temperatures higher than the boiling point of the reaction solvent or solvent mixture. These factors can lead to a signifi cant increase in reaction rate to produce the desired product and thereby minimise the decomposition of substrates and/or products leading to a cleaner reaction profi le. It may seem counterintuitive, but carrying out a reaction under pressure in a suitably designed reactor, can lead to an increase in the safety of a procedure by containing potentially toxic materials or gases in a controlled environment. However not all commercial high pressure reactors are the same, they differ considerably in their quality of construction, safety features, ease of set-up and use, ease of maintenance and versatility to handle different corrosive materials and reactants under high pressure.
In the School of Chemistry at the University of Nottingham (UK), high quality cutting edge collaborative research is carried out in many areas including nanotechnology, synthetic methodology, natural product synthesis, materials chemistry and the utilisation of supercritical fl uids as alternative solvents for synthesis. One area of specialism is the use of supercritical fl uids, such as carbon dioxide, as a “green” solvent for polymer synthesis and materials processing. This research is led by Professor Steven Howdle and his group required access to equipment which would enable the development of effi cient synthetic protocols for the preparation and isolation of a variety of polymeric materials quickly, easily and most importantly, given that the reactions would be carried out at elevated temperatures and high pressures, in a safe manner. The group investigated a number of high pressure reactors which were commercially available at the time however they did not meet the groups’ requirements in terms of ease of set-up, operation, cleaning, versatility of use and safety.
Driven by their desire for an affordable high pressure reactor that combined ease-of-use, outstanding performance, ease of maintenance and high operational safety, Professor Howdle embarked on a project with colleagues Martin Dellar, Peter Fields and Richard Wilson based in the University’s workshops, to design and develop a bespoke high pressure reactor.
Design for a New High
Pressure Reactor A major design feature introduced into the new reactor was a novel clamp. This is used to fasten the body of the reactor to the head piece which contains valves to allow the introduction of reagents and gases as well as monitoring the pressure and temperature of the reaction. A clamp design to secure the body to the head was favoured rather than use of a screw thread, as in the latter, there is the possibility of cross threading and accumulation of materials in the screw path required to join the sections together.
As stated above, safety in use was a key design feature required by the scientists who would use the equipment. One potential safety issue which had been identifi ed in a clamp design was the possibility of opening the reactor whilst still under pressure when undoing the clamp. When a regular high pressure valve is opened at the end of the reaction, it could be assumed that the pressure has been released. However it is possible to have a small blockage in a valve leading to some residual pressure. If the clamp was removed under such conditions, the head metal could have suffi cient momentum to fl y off and potentially cause serious injury to the scientist. This required a safety design feature to be developed for the new reactor to ensure that all residual pressure was always released
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