Palm empty fruit bunch oil (palm EFB oil) is a waste product that can be used to produce biodiesel at a low cost. However, high free fatty acid (FFA) content is the primary obstacle to biodiesel production. Before the transesterification process can begin, the oil must be esterified to reduce its acid content. This study seeks to employ dual-frequency ultrasound at frequencies of 28 kHz (200 W) and 40 kHz (200 W) to aid in the esterification and transesterification of ZSM-5-38 and CaO catalysts, respectively. Central composite design and response surface methodology were used to determine the optimal conditions for the three primary parameters of methanol to oil (M:O molar ratio), catalyst loading and reaction time. A 12:1 M:O molar ratio, 11.36 wt% catalyst loading (ZSM-5-38) and 60 min of reaction duration were the optimal conditions for esterification to achieve a FFA conversion of 91.51%. The reusability of ZSM-5-38 revealed a decrease in FFA conversions of 87.36, 75.11, 67.13 and 58.68% with each reused cycle. The optimal transesterification conditions were a 3.28:1 M:O molar ratio, 4.62 wt% catalyst loading (CaO) and 64 min of reaction time, yielding 83.58% biodiesel. The viscosity value (D 445), the flash point (D 93) and the heating value (ASTM D240) of biodiesel produced under optimal conditions were evaluated. The biodiesel properties were determined to be 4.7931 mm²/s, 176°C and 40 398 kJ/kg, respectively.

中文翻译：

---

两阶段生物柴油生产的超声波强化：棕榈油工业副产品棕榈空果串油的优化

棕榈空果串油（棕榈 EFB 油）是一种废品，可用于低成本生产生物柴油。然而，高游离脂肪酸（FFA）含量是生物柴油生产的主要障碍。在酯交换过程开始之前，必须将油酯化以降低其酸含量。本研究试图采用频率为 28 kHz (200 W) 和 40 kHz (200 W) 的双频超声波来分别帮助 ZSM-5-38 和 CaO 催化剂的酯化和酯交换反应。使用中心复合设计和响应面方法来确定甲醇与油的三个主要参数（M:O摩尔比）、催化剂负载量和反应时间的最佳条件。12:1 M:O 摩尔比、11.36 wt% 催化剂负载量 (ZSM-5-38) 和反应时间 60 分钟是酯化反应实现 91.51% FFA 转化率的最佳条件。ZSM-5-38 的可重复使用性表明，每次重复使用循环后，FFA 转化率分别降低了 87.36%、75.11%、67.13% 和 58.68%。最佳酯交换条件为3.28:1 M:O摩尔比、4.62 wt%催化剂负载量(CaO)和64 min反应时间，生物柴油产量为83.58%。评价了在最佳条件下生产的生物柴油的粘度值（D 445）、闪点（D 93）和热值（ASTM D240）。测定生物柴油的特性分别为4.7931 mm ² /s、176℃和40 398 kJ/kg。