## 4 Waste Conversion for Fuel Gas Production
### Specialized Additives and Catalysts to Increase the Efficiency of Pyrosis and Gasification of Waste
Catalytic pyrolysis of waste cooking oil was investigated by [PERSON] et al. [101]. The effect of nickel-cobalt catalyst and reaction temperature on hydrogen production was studied. The maximum volume concentration of hydrogen (42 vol%) at a temperature of 750 \({}^{\circ}\)C was registered using a catalyst containing 20 wt% Ni and 30 wt% Co. It was found that the maximum hydrogen concentration of 43.5 vol% was reached at 800 \({}^{\circ}\)C. A further increase in temperature caused sintering of the catalyst and subsequent loss of activity. The study also concluded that single metal catalysts exhibit a higher deactivation rate and lower catalytic effect than bimetallic catalysts [101]. [PERSON] et al. [54] found that the addition of catalysts significantly improves the efficiency of water-semicoke slurry gasification and hydrogen yield. Compared to 4.66 mol/kg without catalyst, the hydrogen yield increased to 55.78, 54.43, 51.06, and 53.79 mol/kg after the addition of K\({}_{2}\)CO\({}_{3}\), KOH, Na\({}_{2}\)CO\({}_{3}\), and NaOH, respectively. With an increase in the proportion of K\({}_{2}\)CO\({}_{3}\) (0-5%), the number of porous structures on the surface of the char increased. Mesoporous structures increased the contact area between char particles and water molecules, which increased the efficiency of gasification. The increase in the amount of catalyst promoted the steam reforming reaction (C + H\({}_{2}\)O \(\rightarrow\) CO + H\({}_{2}\)). The advantages of potassium-containing catalysts were also discussed in [102; 108]. [PERSON] et al. [102] showed that, with an increase in KOH concentration from 0 to 5 wt%, the hydrogen content in the gaseous pyrolysis product of pyrocatechol (model compound for lignin in biomass and for aromatic compounds in wastewaters) increases from 16 vol% to 48 vol%. [PERSON] et al. [108] explained the emerging catalytic effect when using potassium-containing catalysts (KOH, K\({}_{2}\)CO\({}_{3}\)) by the enhancement of the water gas shift reaction due to the intermediate formation of the salt (HCOO-K). The formation of the formate salt in the presence of K\({}_{2}\)CO\({}_{3}\) can be shown by the reactions: K\({}_{2}\)CO\({}_{3}\) + H\({}_{2}\)O \(\rightarrow\) KHCOO + KOH, KOH + CO \(\rightarrow\) HCOOK, HCOOK + H\({}_{2}\)O \(\rightarrow\) KHCO\({}_{3}\) + H\({}_{2}\). As a result, CO reacts with KOH to form HCOOK. Potassium formate then reacts with water to form H\({}_{2}\). However, further decomposition of KHCO\({}_{3}\) leads to the formation of additional CO\({}_{2}\), which is also confirmed by the experimental results. CO\({}_{2}\) concentrations increased by 16-54% (depending on biomass and catalyst type). At the same time, the studies [50; 98; 104] confirm that the CO concentration significantly decreased (up to 95%) when using potassium-containing catalysts. The reason for this is the enhancement of the water-gas shift reaction. [PERSON] et al. [44] studied the catalytic effect of KOH on the characteristics of liquid products of pyrolysis of oil sludge. The experiments were carried out in a horizontal quartz tube reactor with a fixed bed at a temperature of 600 \({}^{\circ}\)C. With the addition of 10 wt% KOH, the liquid product yield decreased from 60.1% to 52.8%. The shares of solid residues and gaseous product increased from 16.6% to 19.4% and from 23.3% to 27.8%, respectively. [PERSON] et al. [44] found that the addition of KOH improved the quality of the resulting oil product. Its calorific value increased by 22%, and viscosity decreased significantly (up to 70%).