Cardanol: from cashew nut shell liquid to green chemistry

The use of renewable resources for the production of chemicals and materials is a very important current topic, and has attracted the attention of researchers from academic and industrial sectors worldwide. Indeed, since the very early 2000s, the synthesis of monomers and polymers from renewable resources has been the focus of major research efforts due to the volatility of petroleum product prices, coupled with growing environmental concerns. Renewable resources, also known as biomass, refer to any material of recent biological origin, including plant matter, animal matter, agricultural crops and even co-products and fermentable waste. The most widely used renewable raw materials for the production of chemicals and materials are wood, proteins, cellulose, lignin, tannins, starches, oleochemicals such as vegetable oils, and animal resources such as chitin and chitosan...

A wide variety of chemical substances have already been prepared from these biomass-derived materials, some of which have been industrialized and commercialized. In particular, vegetable oils such as soybean, tung, linseed, rapeseed and castor have for many years produced a wide range of products for a wide variety of applications.

Among these oils, Cashew Nut Shell Liquid (CNSL) is an agricultural co-product abundantly available in many parts of the world, with a unique chemical structure, as it contains a phenolic moiety with a 15-carbon unsaturated side chain. CNSL is not edible, so its use as a chemical feedstock does not compete with the food supply chain, unlike other renewable raw materials such as edible oils. The three main classes of phenolic compounds derived from renewable resources are lignin, tannins extracted from wood and CNSL. While lignin and tannins are massively available in biomass, their commercial availability is limited compared to that of CNSL. As a result, CNSL has the potential to replace phenol in many applications with equivalent or even better results. Greater use of CNSL as a raw material for chemistry and polymer production is possible, given its high production (> 900 kt. per year), low cost and chemical structure opening the way to numerous reactions. Several reviews have been published describing the composition, reactions and applications of CNSL. This article presents the various aspects of CNSL's use in chemistry, focusing in particular on access to CNSL, the different reactions that can be envisaged and the products derived from it. In particular, this article presents CNSL as a precursor for the synthesis of various products such as monomers, polymers and additives.

A glossary of terms is provided at the end of the article.