The ammonolysis of esters in liquid ammonia

The rates of ammonolysis of alkyl benzoate and phenylacetate esters in liquid ammonia increase with the acidity of the leaving group alcohol and show relatively large Brønsted βlg values of −1.18 and −1.34, respectively, when plotted against the aqueous pKa of the alcohol. The Brønsted βlg obtained using the pKa of the leaving group alcohol in liquid ammonia is significantly reduced to ~ −0.7, which indicates that the rate-limiting step involves a reaction of the tetrahedral intermediate with little C–OR bond fission in the transition state. The solvolysis reaction is subject to significant catalysis by ammonium ion, which, surprisingly, generates a similar Brønsted βlg indicating little interaction between the ammonium ion and the leaving group. It is concluded that the rate-limiting step for the ammonium-ion-catalysed solvolysis of alkyl esters in liquid ammonia is the diffusion-controlled protonation of the zwitterionic tetrahedral intermediate T+- to give T+, which is rapidly deprotonated to give T0 which is compatible with the rate-limiting step for the uncatalysed reaction being the formation of the neutral T0 by a ‘proton switc

Scope and limitations of aliphatic Friedel-Crafts alkylations. Lewis acid catalyzed addition reactions of alkyl chlorides to carbon-carbon double bonds

Lewis acid catalyzed addition reactions of alkyl halides 1 with unsaturated hydrocarbons 2 have been studied. 1:l addition products 3 are formed if the addends 1 dissociate faster than the corresponding products 3; otherwise, polymerization of 2 takes place. For reaction conditions under which 1 and 3 exist mainly undissociated, solvolysis constants of model compounds can be used to predict the outcome of any such addition reactions if systems with considerable steric hindrance are excluded

Recovery and reuse of discontinuous carbon fibres by solvolysis: Realignment and properties of remanufactured materials

Discontinuous carbon fibre tows were recovered after solvolysis of an aeronautic type composite made with RTM6 epoxy resin. A Sohxlet extraction method was used to quantify the organic residue on the fibre tows and showed that less than 3 wt% was remaining on the surface. The recovered tows were therefore reused directly to manufacture a plate with randomly distributed carbon fibres and then three plates with realigned carbon fibres. The latter were then characterised and tested and the results obtained were compared to the material manufactured using the same type of virgin fibres by the same method. The materials made from recycled carbon fibres showed very good properties in comparison to the virgin fibre material, despite the presence of flaws such as quality of the fibre surface after solvolysis, alignment and voids). This is the first time in the open literature that carbon fibres recovered from solvolysis were reused in this way together with characterisation of the resulting materials

The recycling of OMC's carbon reinforcement by solvolysing thermoset matrix. A way of sustainability for composites.

Originally developed for high-tech applications, carbon fibre/thermoset matrix composites have been increasingly used in leisure and sports industries, for several years. But the carbon reinforcement is the most expensive constituent, and also the most environmentally impacting in the elaboration of a composite part. To this day, no end-of-life solution or recycling process efficiently exists. This paper aims at demonstrating that recovering the carbon reinforcement is possible, technically and economically speaking. Moreover, it is particularly the basis for a life cycle analysis that assesses benefits and environmental challenges of this recycling loop based on the reinforcement recovery by a solvolysis of the organic matrix. Lastly, the lack of data to consider the better end-of-life option (reuse, recycling, energy recovery and material valorisation) will be underlined

Optimisation of solvolysis for recycling carbon fibre reinforced composites

Solvolysis processes have been used to degrade the resin of two different varieties of epoxy based carbon fibre reinforced composite (CFRC) materials. A degradation of up to 98% has been achieved when processing material at a temperature of 320 °C using a supercritical solvent mixture of acetone and water. Increasing the processing time from 1 to 2 hours shows an increase in the degradation of only 10% and there does not appear to be any benefit in processing the material beyond this time. Due to the batch conditions used, it is necessary to rinse the fibres with acetone after processing to remove remaining organic residue. Washing the fibres at supercritical batch conditions, however, does not efficiently remove the residue compared to a simple hand washing with acetone. Shredding the sample prior to processing also does not have a significant effect. The process investigated requires 19 MJ.kg-1 of fibres recovered and, since the process has not yet been optimised, shows strong potential for future development especially since it allows for the recovery and reuse of organic resinous products

Eco-Efficient Synthesis of LiFePO4 with Different Morphologies for Li-Ion Batteries

LiFePO4 is presently the most studied electrode material for battery applications. It can be prepared via solution, although it requires well-controlled pH conditions to master the iron valence state in the newly created material. Here we report its synthesis via the use of "latent bases" capable of releasing a nitrogen base upon heating. This way of controlling the reaction pH enables, in the absence of excess Li, the preparation of Fe+3-free LiFePO4 powders having various morphologies and showing good electrochemical performance. This approach is shown to offer great opportunities for the low-temperature synthesis of various electrode materials