Solid polymer electrolyte reactor

Cheng, H., Scott, K. and Christensen, P.A. (2004b) Design and operation of a solid polymer electrolyte reactor for electrochemical hydrodehalogenation. Chem. Eng. J. (Amsterdam) 102, 161-170. 

Principles and Applications of Solid Polymer Electrolyte Reactors for Electrochemical Hydrodehalogenation of Organic Pollutants... 

Fig. 13.3 The principle of a chlorine/alkaline solid polymer electrolyte reactor...

Solid polymer electrolyte reactors have been examined previonsly for oxidation and organic electrochemical redaction of organic componnds [56, 72-78]. Ognmi and co-workers studied the electrochemical hydrogenation of nitrobenzene to aniline nsing a Cn-Pt cathode/Naflon mem-brane/Pt anode MEA [76] and the rednction of cyclo-octene, diethyl maleate, ethyl crotonate, and n-bntyl methacrylate (dissolved in either ethanol, diethyl ether, or n-hexane) with MEAs composed of Pt, An, or An-Pt cathode layers deposited onto the snrface of a Nation membrane [72]. In addition, electrochemical rednction of edible oils (snch as soybean or cottonseed) resnlts in a quite different prodnct [79]. 

An, W., Hong, J.K.,Pintauro, P.N., 1998. Current efficiency for soybean oil hydrogenation in a solid polymer electrolyte reactor. Journal of Applied Electrochemistry 28,947-954. 

Cheng H, Scott K, Christensen PA (2005) Paired electrolysis in a solid polymer electrolyte reactor -simultaneously reduction of nitrate and oxidation of ammonia. Chem Eng J 108 257-268... 

Furan was dimethoxylated to give 2,5-dihydro-2,5-dimethoxyfuran, using electrogenerated bromine molecules generated from bromide salts in electrolyte solutions [71]. This reaction was characterized in classical electrochemical reactors such as pump cells, packed bipolar cells and solid polymer electrolyte cells. In the last type of reactor, no bromide salt or electrolyte was used rather, the furan was oxidized directly at the anode. H owever, high consumption of the order of 5-9 kWh kg (at 8-20 V cell voltage) was needed to reach a current efficiency of 75%. 

Fig. 12.2 Plate-and-frame electrolyser schemes (a) undivided cell (b) membrane-divided cell (c) solid polymer electrolyte (SPE) reactor (d) membrane-divided cell with GDE (e) SPE-GDE reactor. Liquid compartments are denoted in grey...

The central part of the electrochemical HDH reactor is the use of solid polymer electrolyte (SPE). A typical membrane material belongs to the fully fluorinated polyethene-based family polytetrafluoroethylene (PTFE) (known by the trade name Teflon), shown in Fig. 13.1. 

Fig. 14. Electrochemical reactor for ozone synthesis using the lead dioxide/solid polymer electrolyte route. (Adapted from [67]).

Synthesis of pure hydrogen peroxide using solid polymer electrolytes (SPE) could eliminate the need to separate the product from liquid electrolytes (basic or acidic). Designs of the (SPE) fuel cell type of reactor could be investigated for such a process. Tatapudi and Fenton [71, 80] demonstrated the basic feasibility of this process (with or without concurrent anodic ozone evolution). However, new cathode materials and... 

Most of the electrochemical reactors fail due to different attacks on the electrocatalysts, where the anodes are attacked faster than the cathodes (electrochemical corrosion, mechanical fissures due to electrodissolution, or bubble formation and evolutions, etc.) [43]. In new technologies, the use of the anode, membrane, or cathode assemblies solves this problem. In the case of the solid polymer electrolytes, the anode and the cathode catalysts are integrated to the membrane promoting the mechanical and electrochemical stability of the device [44,45]. This new technology replaces the problem of the diaphragm-based electrochemical industry that was established in the beginning of the twentieth century [46]. 

Ghosh, D. Vasudevan, Electrolytic synthesis of succinic acid in a flow reactor with solid polymer electrolyte membrane, /. Appl. Electrochem. 2002,... 

H2/O2 fuel cell system for direct formation of H2O2 has been reported [15]. The fuel cell system can be operated safely for the H2O2 production because H2 and O2 are separated by a NaOH or H2SO4 electrolyte membrane [16-18]. Both alkaline and acid H2O2 solutions are useful however, a neutral H2O2 aqueous solution is the most useful and flexible form. Formation of a neutral H2O2 aqueous solution has recently succeeded using anew conceptual solid-polymer-electrolyte membrane reactor and a new electrocatalyst [19, 20], as shown in Fig. 3. 

In other cases, the method of removal depends upon the nature of the product, e.g. gases may be (1) vented from the reactor, possibly via a slight reduction In pressure (2) displaced from the electrolyte via inert gas sparging (3) segregated via a solid polymer electrolyte (section 5.2) or recirculated via a gas-liquid separator. Liquid products may be (1) separated by flotation or settlement if they are immiscible and have a markedly different density to the electrolyte or (2) emulsified by mixing, then swept out of the reactor. Solid products can be separated via (I) flotation or settlement (2) fluidization or tangential shear to remove them from the reactor (3) solvent extraction or incorporation into a mercury phase, e.g. amalgamation of metals. 

As shown in Fig. 5 7(b) the solid polymer electrolyte cell comprises a membrane, fuel cell type, porous electrodes and three further components z carbon collector, a platinized titanium anode support and a cathode support made from carbon-fibre paper The collector is moulded in graphite with a fluorocarbon polymer binder A 25 pm thick platinized titanium foil is moulded to the anode side to prevent oxidation. The purpose of the collector is to bnsure even fluid distribution over the active electrode area, to act as the main structural component of the cell, to provide sealing of fluid ports and the reactor and to carry current from one cell to the next E>emineralized water is carried across the cell via a number of channels moulded into the collector These channels terminate in recessed manifold areas each of which is fed from six drilled ports. The anode support is a porous conducting sheet of platinized titanium having a thickness of approximately 250 pm. The purpose of the support is to distribute current and fluid uniformly over the active electrode area. It also prevents masking of those parts of the electrode area which would be covered by the... 

A more compact reactor design takes advantage of solid polymer electrolytes (SPEs). Hence, cast Nafion membrane and SPEEK were prepared, and used as cationic SPE whereas alkali-doped poly (vinyl alcohol), PVA and Amberlyst resin composites were made, and used as anionic SPE. These SPEs were combined with a cathode made of copper, electrodeposited onto porous carbon paper, and an anode consisting of Pt/C on the carbon paper. The main electroreduction products were formic acid, methanol, formaldehyde, carbon monoxide and methane, while undesired hydrogen gas by-product was also detected [120]. 

Onder E, Koparal A S and Ogutveren U B (2009), Electrochemical treatment of aqueous oxalic acid solution by using solid polymer electrolyte (SPE) reactor , Chem Eng J, 147,122-129. 

---