3.1.2. Exergy Profit of Input Acetic Acid Streams

Next, we consider the acetic acid inlet to the VAM production process (see Figure 8, derived from Figure 6). The potential upstream process and the boundary need to be defined to evaluate the exergy footprint/profit of the input acetic acid stream. A similar case study is used to demonstrate the exergy accounting for the input stream. The specific process example evaluated is the VAM production process. The acetic acid feed stream is chosen for evaluation.

**Figure 8.** Exergy profit evaluation of inlet acetic acid stream.

Equations (2), (3) and (8) are applied to the evaluation, taking the following form:

$$\text{EX}\_{\text{liabilities},\text{AA feed}} = \sum\_{i} \text{EX}\_{\text{input},i} + \text{EX}\_{\text{add}} \tag{13}$$

$$\mathbb{E}\mathbb{X}\_{\text{asset,AA\,feed}} = \sum\_{j} \mathbb{E}\mathbb{X}\_{\text{output},j} \tag{14}$$

$$\mathbb{E}\mathbb{X}\_{\text{profit, AA feed}} = \mathbb{E}\mathbb{X}\_{\text{asset}, \text{AA feed}} - \mathbb{E}\mathbb{X}\_{\text{liability}, \text{AA feed}} \tag{15}$$

where EXadd represents the exergy to be added to the upstream process, *i* represents the set of input material *i* in the upstream process, and *j* represents the set of output material *j* in the upstream process.

Table 4 shows the calculation results, assuming a value of 100 kg/h of the acetic acid stream is fed to the VAM production process. The detailed calculation steps are provided in Part 2 of the Supplementary Materials. The exergy liability is much higher than the exergy of the acetic acid stream. The original exergy content of the acetic acid stream is −0.000069 MW. The results show that the actual exergy required to produce 100 kg/h of acetic acid from the chosen upstream process is higher than the exergy of the stream itself. The exergy profit shows how much exergy input is needed to produce the acetic acid input stream.

**Table 4.** Calculation results of input acetic acid stream, on the basis of a value of 100 kg/h of the acetic acid input stream.


\* The exergy content of the acetic acid stream is supposed to be 0.000069 MW. However, since this is an input stream, this means that work is needed to produce this stream (a liability) from the reference conditions. A negative sign is thus shown for the exergy value.
