Palm fatty acid distillate (PFAD) is a waste from refining crude palm oil, and it is a cheap low-quality feedstock due to its high free fatty acid (FFA) content. Esterification process is necessary to lower the level of FFA in PFAD. The physical and chemical properties of PFAD were studied and compared with previously reported studies and it was found that most of the PFAD parameters showed comparable values or were within the expected range. GC-MS analysis confirmed that the fatty acid in PFAD is 44.99% palmitic acid and 38.15% oleic acid. The optimized reaction conditions obtained for the esterification of PFAD by using ammonium ferric sulfate-calcium silicate (AFS-CS) as heterogeneous acid catalyst were 2-h reaction time, 12 wt% of AFS-CS catalyst amount and 15:1 methanol to PFAD molar ratio at 65 °C to produce maximum methyl esters conversion of 80%. The rate of leaching at active sites on the catalyst was very high; hence, the catalyst is not suitable to be reused.

Modeling of catalyst characterisation, GC-MS spectrum of PFAFD, and mechanism for esterification of free fatty acid

棕榈脂肪酸馏出物（PFAD）是精炼棕榈油的废料，由于其游离脂肪酸（FFA）含量高，因此是廉价的低质量原料。酯化过程对于降低PFAD中的FFA含量是必要的。对PFAD的物理和化学性质进行了研究，并与先前报道的研究进行了比较，发现大多数PFAD参数显示出可比较的值或在预期范围内。GC-MS分析证实，PFAD中的脂肪酸为44.99％的棕榈酸和38.15％的油酸。以硫酸铁硅酸钙（AFS-CS）作为多相酸催化剂进行PFAD酯化的最佳反应条件为2 h反应时间，12 wt％AFS-CS催化剂量和15：在65°C下1甲醇与PFAD的摩尔比可产生80％的最大甲酯转化率。在催化剂的活性位点上的浸出速率非常高。因此，该催化剂不适合重复使用。

催化剂表征模型，PFFAD的GC-MS光谱以及游离脂肪酸的酯化机理