Electrochemical routes for industrial synthesis

Abstract

Esta revisão examina as razões que justificam um interesse crescente da indústria química pelos processos eletrolíticos. Reveem-se as indústrias químicas, nas quais compostos orgânicos e inorgânicos são processados e descrevem-se os avanços tecnológicos mais relevantes. Inicialmente, abordam-se processos bem estabelecidos, como as indústrias cloroalcalinas de produção de alumínio, p-aminofenol, adiponitrila, etileno glicol, antraquinona, produtos perfluorados, ácido glioxílico e L-cisteína. Face à grande quantidade de informação disponível, o assunto é tratado com base científica, mas de modo bastante simplificado. Posteriormente, descrevem-se processos orgânicos e inorgânicos emergentes, nomeadamente processos eletroquímicos mediados e síntese em líquidos iónicos. Estabelecem-se paralelos entre síntese química e síntese eletroquímica. Estimula-se o interesse nos processos de eletrossíntese, particularmente em líquidos iónicos, não desmerecendo a importância das vias puramente químicas de síntese orgânica e inorgânica.This review examines the reasons for increasing interest towards electrolyses by the chemical industry, reviews the electrochemical industries as most of them now exist, and provides a status report on the key technological advances which are occurring to meet present and future needs. Classical industries like those of chloroalkali, aluminium, p-aminophenol, adiponitrile, ethylene glycol, anthraquinone, perfluorinated products, glyoxylic acid and L-cysteine are initially covered. Considering the large amount of available publications in these topics of electrochemical engineering, the covered relevant information is treated at a scientific level, although in a simplified way. Then the paper deals with emerging inorganic and organic processes, e.g. electrosynthesis in ionic liquids and mediated electrochemical processes, and finishes by assessing what the future development trend might be given the electrochemical and non electrochemical competing influences. With this approach it is hoped to stimulate the interest of chemical engineers and scientists non-specialised in electrochemical routes, and to review some cutting edge research, particularly as far as electrosynthesis in ionic liquids is concerned.

Hydrogen production by alkaline water electrolysis

“…51 The solvent should generally have the following properties: (i) it must be liquid at the operational temperature, (ii) it must dissolve the electrolyte to provide a conducting solution, (iii) it must be chemically/electrochemically stable, and (iv) it must present fewer problems in storage or handling.…”

“…198 The main problem with ILs is that they normally have high viscosity and low water solubility. 51,199,200 This hinders mass transfer, and leads to low current densities and, consequently, low hydrogen production rates. ILs with higher conductivities and better water solubility are required to enhance ionic transfer and improve the water electrolysis process.…”

The Electrode/Ionic Liquid Interface: Electric Double Layer and Metal Electrodeposition

“…[7,8] As a consequence, opportunities arise in the applied aspects of electrochemistry such as electrodeposition, [19] batteries and supercapacitors, [20] and electrochemical synthesis. [21] In fact, ionic liquids also provide new types of media for investigation of metals whose equilibrium potentials…”

Electrochemical Synthesis in Microreactors

“…They conclude that not one general protocol can be effective for a variety of electron rich and deficient aromatics and each substrate requires individual optimisation to achieve the highest yields. Carbon-carbon cross coupling reactions have recently been achieved in an electrochemical microreactor consisting of borondoped diamond (BDD) anode and a nickel cathode reported by Waldvogel et al [28] The electrodes were separated by both sides using adhesive tape as previously described, to leave a reactor channel with the dimensions 1 x 3.5 cm 2 . The coupling reaction between 17 and 18 (Scheme 7), gave a total yield of the two coupling products 19 and 20 of 90% at current densities of 2.8 mA cm -2 .…”

“…This is not only due to the advances in equipment and understanding of electrochemical reactions, but also because of the advantages it can offer to organic synthesis [1][2][3][4].…”