OHMIC

Project Title
Development of Organic Synthesis Methodologies Based on an Ohmic Heating Reactor
Project Type
Nacional / Public
Funding Body
Funding Program
PTDC
Reference
QUI-QUI/102454/2008
Funding
  • CEB: 7 320,00
  • Total: 157 696,00
Start
01-06-2010
End
31-05-2013
Partnership
Universidade de Aveiro, Universidade do Minho, Faculdade de Ciências da Universidade do Porto e Instituto de Ciências e Tecnologias Agrárias e Agro-Alimentares
External link

Principal Investigator

Team Members - CEB

Abstract

For most chemical processes, a major adverse effect on the environment is the consumption of energy for heating and cooling. To overcome this problem it is highly desirable to develop efficient methods that use alternative energy sources. In particular, the use of microwave energy to directly heat chemical reactions is becoming an increasingly popular technique in the scientific community. The main benefits of performing reactions under microwave irradiation are the significant rate enhancements and the higher product yields that can be frequently observed. However, important questions relating to the existence of “non-thermal” microwave effects, the scalability and the use of poor-absorber microwave solvents remain unresolved [Kap04, Hoz05]. The challenge of this project is to find an alternative heating process for organic synthesis, with potential advantages in terms of performance to the conventional oil-bath processes and microwave-assisted synthesis. Ohmic heating is an advanced thermal processing method where the reaction mixture or the medium, which serves as an electrical resistor, is heated by passing electricity through it. Electrical energy is dissipated into heat with high efficiency (more than 90%), which results in rapid and uniform heating (temperature homogeneity) and an increase of movement of the charged species. This process of energy transfer depends on the electrical impedance of the medium and the applied voltage. In common with microwave heating, electrical energy is transformed into thermal energy. However, unlike microwave heating, the depth of penetration is virtually unlimited and the extent of heating is governed only by the spatial uniformity of electrical conductivity throughout the product and its residence time in the heater [Vic06]. Although there are many applications of ohmic heating in the food industry [Vic06], as far as we know the application of this process in organic synthesis has not been reported to date. Since a standard system for organic synthesis is not available, the objectives of this research project are to design, construct and test an ohmic heating micro-reactor. We expect to achieve a significant reduction of reaction time and increase energetic efficiency of the chemical reactions that will be studied. Understanding ohmic heating process in chemical reactions is essential for process validation, an actual demonstration of the accurate reliability and safety of the process. Mathematical modelling provides insight into the heating behaviour of the ohmic processes. Therefore, we intend to propose a numerical model for simulation of micro-reactor thermal and electrical characteristics. After the optimization and validation of the micro-reactor for organic synthesis, we will assay some representative reactions, focusing our attention on the reactions in aqueous solutions, such as C-C cross-coupling reactions (Suzuki and Heck) (Scheme 1a,b), 1,3-dipolar cycloadditions (Scheme 2a,b), Michael additions (Scheme 3), hydrolyses (Scheme 4a,b) and synthesis of six-membered heterocycles (Scheme 5a,b). The evaluation of yields, rate enhancements, regioselectivity and energy efficiency of the reactions will be considered important in order to compare the results obtained in ohmic heating with those obtained under microwave-assisted synthesis and conventional oil-bath processes. Another advantage of the ohmic heating is the scale-up. Therefore in the last stage of the project we will choose a reaction to be run in a continuous flow ohmic heating process. The development of this project will take advantage of the large experience of our group at the Chemistry Department of University of Aveiro (DQ/UA) in organic synthesis [VS06, Pinto05, Lac06, AMS05]. The existing scientific collaborations with other research groups namely at Department of Chemistry, Faculty of Science of the University of OPorto (FC/UP and REQUIMTE) and at the Department of Biological Engineering of University of Minho (CEB/UM), will allow performing the design and construction of the micro-reactor and the development of the numerical model for process validation. A positive impact is expected from this project, since this work can lead to the development of a better, simpler and environmentally friendly process for organic synthesis with reduced maintenance costs and with high energetic efficiency.