**3. Results and Discussion**

Catalysts and the optimal process parameter combinations for the quality improvement of biogasoline fractions were determined based on preliminary experimental results to obtain the most favorable experimental results.

The yield of gas and liquid product mixtures obtained from the two different catalysts differed in the function of process parameters. The yield of the gas products obtained in Reactor I from feedstock "A" over the Pt/Al2O3/Cl catalyst was higher than 99.3% in every case. This was due to the low chlorine content of the catalyst, the high liquid hourly space velocity (LHSV), and the low experimental temperature applied in Reactor I. The low chlorine content of the catalyst results in lower acidity, and thus lower cracking activity. The yields of products obtained from Reactor II decreased up to 2.1%, which was higher than in the case of Reactor I. This was due to the higher chlorine content, and thus higher acidity and cracking activity of the catalyst.

According to the above, the yields of the liquid products varied from 97.2% to 99.4% in the function of process parameters, as shown in Table 4. These yield values are high even from an industrial perspective. The lowest acceptable yield value for a light naphtha isomerization unit is 92%. Data in Table 4 illustrate well that the gas production was low (0.6–2.8 %), due to the reasons mentioned above.

The yield of gas phase products (C1–C4) obtained from feedstock "B" on the Pt/H-Mordenite/Al2O3 catalyst was below 5% up to 250 ◦C at every LHSV. At higher temperatures and lower LHSV the yield of gas products sharply increased because the cracking reactions took place to a greater extent (Table 5). About 45% of the gas phase product was i-butane, which can be utilized for alkylate production or as an LPG (propane-butane gas) blending component.


**Table 4.** Yield of the liquid products in the function of process parameters (catalyst: Pt/Al2O3/Cl, feedstock: "A").

<sup>1</sup> LHSV values for the total catalyst volume of Reactor I and II.

**Table 5.** Yield of the gas products as a function of process parameters (catalyst: Pt/H-Mordenite/Al2O3, feedstock: "B").


According to the yield data of gas products, the yield value of the liquid products changed in opposite tendency due to the above-mentioned cracking reactions (Figure 5). The yield of liquid products changed between 85.4% and 99.3%. The lowest values were obtained under the strictest process parameters, at high temperature (T: 270 ◦C) and high residence time (LHSV: 1.0 h−1) in the catalytic system. Curves in Figure 5 illustrate well that iso-paraffins can be obtained with high yield from high n-paraffin containing biogasoline fractions for a wide range of process parameters.

**Figure 5.** Change of liquid product yields as a function of temperature and LHSV (catalyst: Pt/H-Mordenite, feedstock: "B").

Based on the gas and liquid product yields obtained from the different catalysts, it was concluded that the liquid yield obtained from Pt/Al2O3/Cl was significantly higher than in the case of Pt/H-Mordenite/Al2O3. The reason for this was because the cracking reactions took place to a lesser extent due to the lower isomerization temperature.

In order to evaluate the isomerization reaction results, the thermodynamic equilibrium concentration (ATEC) was determined for the individual components in the C5 and C6 fractions as a function of process parameters. The isomerization activity of the catalyst was monitored by the concentration of 2-methyl-butane (2-MB in C5 fraction) and 2,2-dimethyl-butane (2,2-DMB in C6 fraction). Only 2-MB can be formed from n-pentane during isomerization; 2,2-dimethyl-propane (2,2-DMP) cannot be formed due to the steric and reaction mechanism reasons. The 2,2-DMB component has the lowest reaction rate among the hexane isomers; its formation is the rate-determining step of the isomerization of n-hexane, and its equilibrium concentration depends mainly on the reaction temperature [27].

Figure 6a,b demonstrate the ATEC values of 2-MB and 2,2-DMB in the liquid products obtained from feedstock "A" on the Pt/Al2O3/Cl catalyst as a function of process parameters.

**Figure 6.** ATEC of 2-MB (**a**) and 2,2-DMB (**b**) as a function of temperature and LHSV (catalyst: Pt/Al2O3/Cl, feedstock: "A").

As a comparison, ATEC values of 2-MB and 2,2-DMB in the liquid products obtained from feedstock "B" on the Pt/H-MordeniteAl2O3 catalyst as a function of process parameters are shown in Figure 7a,b.

**Figure 7.** ATEC of 2-MB (**a**) and 2,2-DMB (**b**) as a function of temperature and LHSV (catalyst: Pt/H-Mordenite/Al2O3, feedstock: "B").

Curves in Figure 6a,b and Figure 7a,b demonstrate well that the concentrations of the two emphasized isomers increasingly approach the thermodynamic equilibrium concentrations by increasing the reaction temperatures and decreasing the LHSV. However, the extent of the increase in ATEC values lessened by increasing the temperature, especially at 125–145 ◦C and 250–270 ◦C, respectively, at lower LHSV. The reason for this is that the process parameters have less impact on the reaction rate near to the equilibrium concentrations. This is also supported by the fact that in case of the Pt/Al2O3/Cl catalyst, the ATEC values of 2-MB at the temperature of 125–145 ◦C and LHSV

of 1.0–1.66 h−<sup>1</sup> were 87.8–93.0%, with an absolute difference of 5.2%, while, in the case of 2,2-DMB, these values changed between 67.5% and 85.6%, with an absolute difference of 18.1%. However, in the case of the Pt/H-Mordenite/Al2O3 catalyst, the ATEC values of 2-MB at a temperature of 250–270 ◦C and LHSV of 1.0–1.5 h−<sup>1</sup> were 87.0–92.8%, with an absolute difference of 5.8%, while, in the case of 2,2-DMB, these values changed between 32.1% and 86.8%, with an absolute difference of 54.7%.

Based on the results of a previous publication [28] it was shown that among the C6 i-paraffins obtained, the ATEC value of 2,3-dimethylbutane (2,3-DMB), 2-methylpropane (2-MP), and 3-methylpropane (3-MP) were significantly higher than in the case of 2,2-DMB. To prove this phenomenon in the present study, ATEC values of 2-MP obtained from both feedstocks on the applied catalysts are illustrated in Figure 8a,b.

**Figure 8.** ATEC values of 2-MP (**a**) (catalyst: Pt/Al2O3/Cl, feedstock: "A"); and 2-MP (**b**) (catalyst: Pt/H-Mordenite/Al2O3, feedstock: "B") as a function of temperature and LHSV.

The highest ATEC values of the individual i-paraffins presented in the figures were obtained at 145 ◦C (Pt/Al2O3/Cl) and at 270 ◦C (Pt/H-Mordenite/Al2O3) at LHSV of 1.0 h<sup>−</sup>1. However, the liquid yields were the lowest due to the high hydrocracking activity of catalysts at these process parameters. It is also important to emphasize that the highest possible equilibrium concentrations of 2-MB and 2,2 DMB at the highest experimental temperature are the lowest, because these values are decreasing approximately exponentially with increasing temperature due to the exothermic skeletal isomerization reactions [4].

Based on the results obtained from the two different catalysts, the most favorable process parameter combinations for the isomerization of benzene containing bio-originated C5-C6 fractions are the following: temperature, 125–135 ◦C; LHSV, 1.0–1.33 h−<sup>1</sup> (Pt/Al2O3/Cl); and: temperature, 260 ◦C; LHSV, 1.0–1.5 h−<sup>1</sup> (Pt/H-Mordenite/Al2O3). The benzene content of the target products was <0.05 mg/kg, and oxygenate content was not detected, thus the hydrogenation was complete. The main properties of the liquid products obtained over both catalysts at favorable process parameter combinations are summarized in Table 6. From the results, it was concluded that in the case of the Pt/Al2O3/Cl catalyst the yield of the liquid products and their research octane number was higher with ca. 5% and 4–5 units, respectively, compared to the results obtained on Pt/H-Mordenite/Al2O3. When the n-paraffins and the mono-methyl pentanes having low octane number were recirculated with 95%, the RON of the products could reach 92. This is a good result taking into account that the feedstock was benzene free. It is noted that benzene has a high research octane number (101), and its hydrogenation to cyclohexane results in a lower octane number (84). This decrease in octane should be compensated for by the production of isomers having a very high RON. These i-paraffins are free of sulfur and aromatics; consequently, during their application in internal combustion engines compared to current engine fuels, the pollutant emission is lower and contains less harmful pollutants.

**Table 6.** Main characteristics of liquid products obtained over Pt/Al2O3/Cl and Pt/H-Mordenite catalysts at favorable process parameters (respectively: temperature, 125–135 ◦C; LHSV, 1.0–1.33 h<sup>−</sup>1; and temperature, 260 ◦C; LHSV, 1.0–1.5 h<sup>−</sup>1).

