Catalytic upgrading of citric acid to environmental friendly tri-butyl citrate plasticizer over ultra stable phosphonated Y zeolite

•Esterification of citric acid (CA) to tributyl citrate (TBC) plasticizer was performed.•USY and phosphonated USY catalysts were used for TBC synthesis.•Phosphonated USY showed higher catalytic activity than parent USY.•2% (w/w) P/USY catalyst exhibited 100% CA conversion and 93% TBC yield.•The catalyst was found to be reusable for 5 catalytic cycles.

The catalytic synthesis of non-toxic/eco-friendly tributyl citrate (TBC) plasticizer by esterification of renewable citric acid (CA) with butanol would be completely sustainable route. In this context, catalytic performance of parent ultra stable Y (USY) and phosphonated USY catalysts were investigated for TBC synthesis. Parent USY and phosphonated USY catalysts were characterized by powder X-ray diffraction (XRD), N2 adsorption–desorption, NH3 temperature programmed desorption (TPD), pyridine-Fourier Transform Infrared Spectroscopy (FTIR), FTIR, SEM, ICP. The influence of various process parameters such as phosphorous (P) loading (0 to 4 wt/%), catalyst loading (5–25%), molar ratio of CA to n-butanol (1:4 to 1:12), reaction temperature (383–423 K) and reaction time (1–5 h) have been investigated over USY catalyst with aim to maximize CA conversion and TBC yield. Amongst the studied catalysts, the 2% (w/w) P/USY was found to be highly potential catalyst with complete CA conversion (100%) and 93% TBC yield. The present method of using 2% (w/w) P/USY catalyst for the synthesis of TBC would be environmentally benign in the context of bio-renewable synthetic route, high catalytic activity, non-toxic product, long term stability and reusability of catalyst (five catalytic cycles).

Graphical abstract2% (w/w) P/USY was found to be an environmentally benign catalyst with 100% citric acid (CA) conversion and 93% tributyl citrate (TBC) yield at optimum process parameters: 20% catalyst loading, 1:10 (CA:butanol) molar ratio, 413 K reaction temperature and 4 h reaction time.Figure optionsDownload full-size imageDownload high-quality image (104 K)Download as PowerPoint slide