The procedure was based on our previous study with slight modifications (Li et al., 2015). Briefly, CCR and 0.5% hydrochloric acid (based on the total weight of acid in the mixture) was mixed with 88% FA at a liquid-to-solid ratio of 30 mL/g, and then placed in an oil bath at 95◦C for 30 min with magnetic stirring at 500 rpm. Upon completion, the flask was immediately cooled down to room temperature with running water and the mixture was centrifuged at 8000 rpm for 5 min. Subsequently, the supernatant liquor was collected and the FA was recovered by distillation. The gel-like solid obtained was wash by deionized water at least 8 times followed by centrifugation (8000 rpm for 5 min) to remove excess acid.