**2. Reaction System**

## *2.1. Synthesis of Butyric Anhydride*

The reaction of acetic acid with butyric anhydride is homogeneous; it is also a series of reversible reactions without a catalyst, which is carried out in two steps as shown by Equations (1) and (2). The reaction rates of the two steps are quite di fferent, and the rate of Reaction (1) is much greater than that of the second step. According to Li et al. [10], the most suitable reaction temperature is 343.15 K.

$$\begin{array}{l} \text{CH}\_3\text{CH}\_2\text{CH}\_2\text{COOH} + \text{CH}\_3\text{(CO}\_3\text{C)}\text{CH}\_3 \Leftrightarrow\\ \text{CH}\_3\text{CH}\_2\text{CH}\_2\text{(CO}\_3\text{C)}\text{CH}\_3 + \text{CH}\_3\text{COOH} \end{array} \tag{1}$$

$$\begin{array}{l} \text{CH}\_3\text{CH}\_2\text{CH}\_2\text{COOH} + \text{CH}\_3\text{CH}\_2\text{CH}\_2\text{(CO}\_3\text{C)}\text{CH}\_3 \Leftrightarrow\\ \text{CH}\_3\text{CH}\_2\text{CH}\_2\text{(CO}\_3\text{C)}\text{CH}\_2\text{CH}\_2\text{CH}\_3 + \text{CH}\_3\text{COOH} \end{array} \tag{2}$$
