**2. Methodology**

The research methodology comprises several activities described in even detailed and specific manner.

## **2.1 Extracting experimental IL inhibition ability**

As a relatively new study, it is very important to gain acknowledgment and recognition from peers. Hence, as mentioned earlier, the experimental value of IL inhibition ability will be obtained from several past studies that are highly recognized. For instance, paper from Xiao et al. is chosen as it is the pioneer of IL inhibitor research. The full list of papers that were chosen for development or correlation and later for validation work is shown in **Table 1**.

As observed from table, experimental values from four papers will be collected. All of them studied hydrate formation in the presence of methane gas for the thermodynamic hydrate inhibitor. In all these papers, the effectiveness of an IL as THI was reported in the form of IL-hydrate equilibrium curve. Generally, a larger temperature depression signifies that the IL is good in inhibiting and shifting the equilibrium curve. However, since IL-hydrate equilibrium curve is not quantifiable and thus is not possible to develop correlation, average temperature depression will be used to represent IL inhibition ability in our work. This average temperature depression value can be calculated through the following equation [9, 13, 30]:

$$
\overline{T} = \frac{\sum\_{i=1}^{n} T\_i}{n} = \frac{\sum\_{i=1}^{n} T\_i}{n} = \frac{\sum\_{i=1}^{n} (T\_{0,\text{pl}} - T\_{1,\text{pl}})}{n} \tag{1}
$$

$$
\overline{T} = \frac{\sum\_{i=1}^{n} T\_i}{n} = \frac{\sum\_{i=1}^{n} (T\_{0,\text{pl}} - T\_{1,\text{pl}})}{n} \tag{1}
$$

where *T*0, pi is the dissociation temperature of methane in a blank sample without IL and *T*1, pi is the dissociation temperature of methane in a sample with IL inhibitor. The values of both dissociation temperatures should be obtained from


#### **Table 1.**

*Chosen papers for experimental values for this work.*

**147**

**Figure 2.**

could be run.

*Pre-Screening of Ionic Liquids as Gas Hydrate Inhibitor via Application…*

**2.2 Simulation of fundamental properties value in COSMO-RS**

to input the right information to extract the desired output.

*Flowchart of predicting thermodynamic properties through COSMO-RS.*

entire computational method of COSMO-RS.

After obtaining the data of IL inhibition ability, now it is the time to collect another set of data, which is the fundamental property value of IL-hydrate system. Here, COSMO-RS software will be used to carry out the simulation. In COSMO-RS, all calculation works are performed based on density functional theory (DFT), utilizing the triple-zeta valence polarized (TZVP) basis set [50]. **Figure 2** shows the

As regards **Figure 2**, COSMO-RS first requires the input of molecular structure

[51]. After this, the charge density of a segment on each molecule surface will be calculated in a virtual conductor. The distribution of this charge density on the entire surface of the molecule will then generate a sigma profile (*σ*-profile) through the use of COSMOtherm software [52]. Then, the *σ*-profile will now be used as the basis by COSMO-RS to predict the desired thermodynamic properties. Nevertheless, it is to be noted that among the computational process being shown in **Figure 2**, a user is only required to insert the input, while all the computational process will be carried out by the software itself. Therefore, it is utmost important

The input or simulation method of COSMO-RS in this work has been conducted by referring to the work of Kurnia et al. [39, 53]. **Figure 3** shows the required input for calculating hydrogen bonding value before a proper simulation

As observed from **Figure 3**, the required inputs are temperature and the mole fraction of IL-hydrate system. For this work, the temperature is fixed at

the same pi, and n refers to the number of pressure point considered. For example, **Figure 1** shows the IL-hydrate equilibrium curve from Keshavarz et al. [49] for blank hydrate system (without IL) and hydrate system with 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4). Now, it is seen that with IL that acts as an inhibitor, the region of hydrate formation has reduced. It is also clear that the favorable pressure for hydrate to form has increased and the favorable temperature has reduced. This, in turn, made it hard for hydrate to form. Now to calculate average temperature depression, for instance, at 4 MPa, *T*0, pi is equal to the temperature of blank hydrate without IL; the temperature would be around 277.5 K. On the other hand, T1, pi that refers to the temperature of IL-hydrate system will be around 277 K. The difference between these two values is then the temperature depression. Several temperature depression values will be collected at different pressure points along the curve. Lastly, the average of these values will become the average tem-

*DOI: http://dx.doi.org/10.5772/intechopen.86847*

perature depression value.

**Figure 1.** *Hydrate-IL equilibrium curve from the work of Keshavarz et al.*

*Pre-Screening of Ionic Liquids as Gas Hydrate Inhibitor via Application… DOI: http://dx.doi.org/10.5772/intechopen.86847*

*Solvents, Ionic Liquids and Solvent Effects*

*<sup>T</sup>*̶

*Chosen papers for experimental values for this work.*

**2.1 Extracting experimental IL inhibition ability**

and later for validation work is shown in **Table 1**.

As a relatively new study, it is very important to gain acknowledgment and recognition from peers. Hence, as mentioned earlier, the experimental value of IL inhibition ability will be obtained from several past studies that are highly recognized. For instance, paper from Xiao et al. is chosen as it is the pioneer of IL inhibitor research. The full list of papers that were chosen for development or correlation

As observed from table, experimental values from four papers will be collected.

*<sup>n</sup>* (*T*0,pi <sup>−</sup> *<sup>T</sup>*1,pi) \_\_\_\_\_\_\_\_\_\_\_\_\_\_ *<sup>n</sup>* (1)

All of them studied hydrate formation in the presence of methane gas for the thermodynamic hydrate inhibitor. In all these papers, the effectiveness of an IL as THI was reported in the form of IL-hydrate equilibrium curve. Generally, a larger temperature depression signifies that the IL is good in inhibiting and shifting the equilibrium curve. However, since IL-hydrate equilibrium curve is not quantifiable and thus is not possible to develop correlation, average temperature depression will be used to represent IL inhibition ability in our work. This average temperature depression value can be calculated through the following equation [9, 13, 30]:

> = \_\_\_\_ ∑*T <sup>n</sup>* <sup>=</sup> <sup>∑</sup>*i*=1

where *T*0, pi is the dissociation temperature of methane in a blank sample without IL and *T*1, pi is the dissociation temperature of methane in a sample with IL inhibitor. The values of both dissociation temperatures should be obtained from

**146**

**Figure 1.**

**Table 1.**

*Hydrate-IL equilibrium curve from the work of Keshavarz et al.*

the same pi, and n refers to the number of pressure point considered. For example, **Figure 1** shows the IL-hydrate equilibrium curve from Keshavarz et al. [49] for blank hydrate system (without IL) and hydrate system with 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4). Now, it is seen that with IL that acts as an inhibitor, the region of hydrate formation has reduced. It is also clear that the favorable pressure for hydrate to form has increased and the favorable temperature has reduced. This, in turn, made it hard for hydrate to form. Now to calculate average temperature depression, for instance, at 4 MPa, *T*0, pi is equal to the temperature of blank hydrate without IL; the temperature would be around 277.5 K. On the other hand, T1, pi that refers to the temperature of IL-hydrate system will be around 277 K. The difference between these two values is then the temperature depression. Several temperature depression values will be collected at different pressure points along the curve. Lastly, the average of these values will become the average temperature depression value.
