Process intensification for recovery of anacardic acid from Cashew Nut Shell Liquid (CNSL) using ion exchange resin: Optimization of operational parameters by response surface methodology

Cashew nut shell liquid (CNSL) is an abundant agro-industrial byproduct rich in anacardic acid, a high-value phenolic lipid. This study developed a selective adsorption process using ion-exchange resin (IER) for its recovery. The weak base resin Lewatit® PH 3021 exhibited higher adsorption capacity (820 mg/g) than strong base resins due to selective interaction with the carboxyl functionality. Among the screened organic solvents, xylene provided suitable solubility and mass transfer. Response surface methodology (RSM) optimization identified optimum conditions of 3.81% w/v CNSL concentration, 33.3 °C, 0.224 g adsorbent and 9.9 h, with a predicted adsorption capacity of 921.6 mg/g. Triplicate validation resulted approximately 840 mg/g. Equilibrium data followed the Sips isotherm (R 2 = 0.995), while adsorption kinetics indicated contributions from surface adsorption and diffusion. Desorption exceeding 90% was achieved using 5% HCl-ethanol, resulting anacardic acid at 82.8% yield and 95% purity. FT-IR, XPS, solid-state, 13 C NMR and EDX supported changes in functional groups, nitrogen chemical environments and resin composition during adsorption, desorption and regeneration. A plausible mechanism involving proton transfer between the anacardic acid carboxyl group and resin dimethylamine sites, forming a protonated amine-carboxylate ion pair, is proposed. Desorption occurs through HCl treatment via chloride exchange, followed by triethylamine-mediated resin regeneration. The isolated anacardic acid structure was confirmed by 1 H NMR. Solvent recycling and resin regeneration demonstrated process robustness, while preliminary techno-economic analysis indicated cost-effectiveness and scalability.