High-Performance Materials from Bio-based Feedstocks. Группа авторов

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Figure 2.6 Esterification of fatty acid.

Table 2.4 Comparison of various catalysts for biodiesel production.

Catalyst	Feedstock	Reaction conditions	Yield (%)	References
Alcohol:Oil	Catalyst amount (wt%)	Temperature (°C)	Time
La2O3/CaO	Jatropha oil	25 : 1	3	160	3 h	98.76	[112]
Li/CaO	Jatropha oil	12 : 1	5	65	1–2 h	>99	[113]
ZnO‐TiO2‐Nd2O3/ZrO2	Soybean oil	5.7 : 1	—	195	44 min	99	[104]
/SnO2	Waste cooking oil	15 : 1	3	150	3 h	92.3	[105]
Bio‐based carbon modified with Ni and Na2SiO3	Soybean oil	9 : 1	7	65	100 min	98.1	[114]
Sulfonated modified coconut meal residual	Waste palm oil	12 : 1	5	65–70	10 h	92.7	[115]
Sulfonated modified carbonized coconut shell	Palm oil	30 : 1	6	60	6 h	88.25	[116]
Sulfonated woody biochar	Canola oil	30 : 1	7	315	3 h	48.1	[117]
Sulfonated carbonized bamboo	Oleic acid	7 : 1	6	90	2 h	98.4	[111]
Calcium oxide from eggshell	Waste cooking oil	6 : 1	5.8	Room temperature	11 h	97	[118]

Sulfonated activated carbons from various biomass resources were tested for the production of biodiesel through esterification or transesterification. Various kinds of biomass wastes were activated with H₃PO₄ prior to carbonization and subsequently sulfonated through arylation of 4‐benzenediazonium. The resulting bio‐based activated carbon materials were highly porous with surface areas of 640–970 m² g⁻¹ depending on the biowaste source. Under optimal conditions, conversion of up to 94% could be achieved for esterification [120]. Slow reaction rates, the requirements of high methanol‐to‐oil molar ratios, and high reaction temperatures are, however, weaknesses of the sulfonated carbon catalyst for biodiesel production [122]. A further application with regard to the upgrading of bio‐oil via reactive distillation including water removal, catalytic esterification, and neutralization steps was carried out with p‐toluene sulfonic acid embedded on an activated carbon obtained by activation of sawdust pellets [123]. The catalyst was applied to the catalytic esterification in the reactive distillation procedure. After water removal from the oil, the esterification reaction took place at 80 °C under atmospheric pressure with the acid‐modified activated carbon catalyst and zeolite. The heating value of the upgraded bio‐oil obtained from fast pyrolysis was improved from 14.80 to 23.13 MJ kg⁻¹ and was ascribed to the presence of higher ester and acetic acid contents in the oil according to the reaction in Figure 2.7. The properties of the upgraded oil were consistent with the diesel standard. Interestingly, sulfonated activated carbon catalysts have the potential for bio‐jet fuel production through co‐pyrolysis of biomass and plastic waste [124]. Prior to the sulfonation step, an activated corncob was converted by microwave‐assisted carbonization. The sulfonation temperature was a major factor that influenced the number of SO₃H groups on the catalyst. These active groups benefited the co‐pyrolysis oil yield of nearly 98% at 500 °C for 15 minutes. The obtained oil consisted of aromatic and C₉–C₁₆ alkanes, which was qualified as a bio‐jet fuel.

      A drawback of the sulfonated bio‐based activated carbon catalyst is that its preparation process is environmentally unfriendly owing to the heating of carbon materials in concentrated sulfuric acid for an extended time. Apart from sulfuric acid, tribasic potassium phosphate (K₃PO₄) was recently used to activate carbon materials. The K₃PO₄ impregnated on the activated carbon catalyst benefited the biodiesel production from waste cooking oil. With 5% catalyst loading, the biodiesel yield was 98% in a 12 : 1 methanol‐to‐oil molar ratio at 60 °C for four hours. Only 20% reduction in biodiesel yield was observed when the catalyst was used for five reaction cycles [125].