## 5 Solvent Evaluation
\begin{table}
\begin{tabular}{l|c c c c c c c c c c c c c} \hline \hline  & \begin{tabular}{c} **Physical** \\ **Solvents** \\ \end{tabular} & \begin{tabular}{c} **Primary** \\ **Amines** \\ \end{tabular} & \begin{tabular}{c} **Secondary** \\ **Amines** \\ \end{tabular} & \begin{tabular}{c} **Tertiary** \\ **Amines** \\ \end{tabular} & \begin{tabular}{c} **Stetically** \\ **Hindered** \\ **Amines** \\ \end{tabular} & \begin{tabular}{c} **Amines** \\ **Blends** \\ \end{tabular} & \begin{tabular}{c} **Phase** \\ **Change** \\ **Solvents** \\ \end{tabular} & \begin{tabular}{c} **Ionic** \\ **Liquids** \\ \end{tabular} & \
\begin{tabular}{c} **Sals** \\ **Ammonia** \\ \end{tabular} &
\begin{tabular}{c} **Sawater** \\ **Degree of** \\ **Criticality** \\ \end{tabular} \\ \hline
**Maturity** & **8** & **8** & **8** & **4** & **4** & **3** & **4** & **4** & **4** & **1** \\ \hline
**Compactness** & **3** & **3** & **3** & **3** & **3** & **4** & **4** & **4** & **3** & **3** & **2** & **1** \\ \hline
**Energy** & **3** & **2** & **3** & **3** & **3** & **4** & **5** & **5** & **4** & **4** & **4** & **1** \\ \hline
**CO\_Loading** & **2** & **3** & **3** & **4** & **4** & **5** & **5** & **5** & **3** & **3** & **1** & **1** \\ \hline
**Health and Safety** & **3** & **3** & **3** & **3** & **3** & **3** & **3** & **4** & **4** & **2** & **5** & **1** \\ \hline
**Operability** & **4** & **4** & **4** & **3** & **2** & **4** & **3** & **4** & **4** & **3** & **3** & **1** \\ \hline
**Impurity** & **2** & **3** & **3** & **3** & **4** & **3** & **3** & **4** & **4** & **4** & **4** & **1** \\ \hline
**OPEX** & **4** & **2** & **2** & **3** & **3** & **1** & **2** & **2** & **2** & **4** & **4** & **5** & **1** \\ \hline
**Other** **Sumables** & **4** & **4** & **4** & **4** & **4** & **4** & **4** & **4** & **4** & **2** & **4** & **2** & **1** \\ \hline \hline \end{tabular} (*) Color coding is a measure of the quality of the KPI, Green (5), good, light green (4) medium-good, yellow (3) medium, orange (2) medium-bad, red (l), bold.  
\end{table} 
Table 3: Comparative assessment of the different solvent classes for CO\({}_{2}\) capture using on board KPIs *. It can easily be seen that no solvent class excels in all categories. On the contrary, there is a large distribution of advantages and disadvantages for almost all solvent types in the different ship requirements. Technological maturity, perhaps one of the most important constraints for direct on-board application of solvent-based membrane CO\({}_{2}\) capture, is ensured by only a few solvent categories that have been extensively tested in different scales and high TRL land-based technological applications. For a given capture target, process compactness can be achieved in a number of ways, i.e., low-density solvents or lower liquid flowrates (equivalently, high cyclic capacity) mostly associated with recently developed solvents such as phase change solvents and ionic liquids. These solvents are being designed to minimize a number of technological constraints, including the process cost per unit of captured CO\({}_{2}\) and the requirements for solvent regeneration, alternatively, the energy penalty coming from the energy integration of the process within the ship. On the downside, however, immediate applicability of PCM and IL systems is limited due to their increased complexity and property uncertainties. On-board safety needs to be addressed with utmost care. Solvent toxicity combined with higher presence in the vapor phase due to their high vapor pressure is a factor that needs to be carefully considered. Operational characteristics of the examined solvent classes, including the sensitivity of their selectivity to CO\({}_{2}\) over other gaseous components and their oxidative stability in the presence of impurities as well as the range of process parameters in which the system maintains acceptable operating levels (e.g., avoidance of thermal decomposition, unfavorable precipitation, etc.)