Pyrolysis of Colombian spent coffee grounds (SCGs), characterization of bio-oil, and study of its antioxidant properties

Figures & data

Figure 1. Schematic of the pyrolyzer design by Universidad Santo Tomás.

Table 1. Results of the elemental analysis and comparison on a dry basis with the reported values.

Compound	Fraction (%)
	This work	D.R. Vardon et al. (2013)	Li, Strezov & Kan (2014)	Kan, Strezov & Evans (2014)	Matrapazi & Zabaniotou (2020)	Bok et al. (2012)	Lee et al. (2021)
Carbon (C)	48.74	56.10	54.50	51.80	47.96	54.61	47.63
Hydrogen (H)	6.53	7.20	7.10	6.40	1.57	6.59	6.57
Oxygen (O)	40.94	34.00	34.20	39.57	44.05	34.83	45.80
Nitrogen (N)	2.08	2.40	2.40	2.08	6.42	3.97	2.93
Sulfur (S)	0.14	–	0.10	0.15	–	0	0

Table 2. Proximal analysis and comparison.

Compound	Fraction (%)
	Authors	Ballesteros, Teixeira and Mussatto (2014)	Mata, Martins and Caetano (2018)	Lee et al. (2021)
lignin	17.90	23.90	32.50	34.94
cellulose	14.81	12.40	8.60	16.78
hemicellulose	29.15	39.10	36.70	48.22

Figure 2. Thermogravimetric analysis (TGA) of spent coffee grounds at different heating rates.

Figure 3. Differential thermogravimetric analysis (DTG) of spent coffee grounds at different heating rates.

Figure 4. Application of the KAS method to obtain the activation energy Ea.

Figure 5. Application of the OFW method to obtain the activation energy Ea.

Figure 6. Activation energy ${\mathrm{E}}_{\mathrm{a}}$ vs. reaction progress α.

Figure 7. Conversion profiles of the thermal decomposition of SCGs as a function of temperature for five heating rates and the selected range of temperature for analysis.

Figure 8. Normalized conversion profiles of the selected range of thermal decomposition of SCGs as a function of temperature for five heating rates.

Table 3. Calculated E and A by the KAS and FWO methods

α	Range of temperature	KAS			FWO
		E (kJ/mol)	R^2	A (s^−1)	E (kJ/mol)	R^2	A (s^−1)
0.20	200–250 °C	153.29	0.8566	4.3 × 10^12	161.94	0.8697	9.4 × 10^34
0.25		167.61	0.7701	4.6 × 10^13	176.54	0.7880	1.4 × 10^37
0.30		169.28	0.8561	2.7 × 10^13	178.45	0.8688	3.3 × 10^36
0.35	250–300 °C	153.21	0.8869	3.7 × 10^11	162.58	0.8983	1.9 × 10^32
0.40		129.91	0.8309	1.5 × 10^8	139.39	0.8497	8.6 × 10^26
0.45		121.86	0.7612	1.2 × 10^9	131.47	0.7877	9.1 × 10^24
0.50		142.40	0.7574	1.2 × 10^10	152.16	0.7809	6.1 × 10^28
0.55	300–370 °C	182.11	0.8549	3.0 × 10^13	192.04	0.8675	1.7 × 10^36
0.60		207.61	0.9308	2.7 × 10^15	217.77	0.9367	3.4 × 10^40

Table 4. Comparison of the activation energy between this work and other reports.

Biomass	Activation Energy (kJ/mol)	Method	Reference
Spent coffee grounds (this work)	153.29	KAS	–
	162.56	OFW
Spent coffee waste	109.00	FWO	Polat and Sayan (2020)
	104.40	KAS
Coffee grounds	96.80	Coast-Redfern	Jin et al. (2018)
Sewage sludge and coffee grounds mixtures	166.80	KAS	Chen et al. (2017)
	168.80	OFW
Spent coffee ground wastes	197.26	KAS	(Lee et al. 2021)
	196.08	OFW

Source: Elaborated by the authors.

Table 5. Yield of pyrolysis tests (%).

Temperature (°C)	Ramp (°C/min)	Yield (%)		Higher calorific power (MJ/kg)
		Oil	Coal	Oil
400	15	22.46%	21.40%	28.91
	30	17.21%	21.02%	30.19
500	15	14.80%	21.91%	31.48
	30	17.85%	23.44%	30.33

Figure 9. Fourier transform infrared (FTIR) spectroscopy for spent coffee ground bio-oil. Source: Elaborated by the author.

Figure 10. Test chromatogram 500 °C – 30 °C/min. Source: Elaborated by the author.

Figure 11. Families of bio-oil compounds from spent coffee grounds. Source: Elaborated by the author.

Vardon, Derek R., Bryan R. Moser, Wei Zheng, Katie Witkin, Roque L. Evangelista, Timothy J. Strathmann, Kishore Rajagopalan, and Brajendra K. Sharma. Oct. 2013. “Complete Utilization of Spent Coffee Grounds to Produce Biodiesel, bio-oil, and Biochar.” ACS Sustainable Chemistry and Engineering 1 (10): 1286–1294. https://doi.org/10.1021/sc400145w.

 Web of Science ®Google Scholar

Li, X., V. Strezov, and T. Kan. 2014. “Energy Recovery Potential Analysis of Spent Coffee Grounds Pyrolysis Products.” Journal of Analytical and Applied Pyrolysis 110: 79–87. https://doi.org/10.1016/j.jaap.2014.08.012.

 Web of Science ®Google Scholar

Kan, T., V. Strezov, and T. Evans. Jan. 2014. “Catalytic Pyrolysis of Coffee Grounds Using NiCu-Impregnated Catalysts.” Energy & Fuels 28 (1): 228–235. https://doi.org/10.1021/ef401511u.

 Web of Science ®Google Scholar

Matrapazi, V. K., and A. Zabaniotou. 2020. “Experimental and Feasibility Study of Spent Coffee Grounds Upscaling via Pyrolysis Towards Proposing an eco-Social Innovation Circular Economy Solution.” Science of the Total Environment 718: 137316.

 PubMed Web of Science ®Google Scholar

Bok, J. P., H. S. Choi, Y. S. Choi, H. C. Park, and S. J. Kim. Nov. 2012. “Fast Pyrolysis of Coffee Grounds: Characteristics of Product Yields and Biocrude oil Quality.” Energy 47 (1): 17–24. https://doi.org/10.1016/j.energy.2012.06.003.

 Web of Science ®Google Scholar

Lee, Xin Jiat, Hwai Chyuan Ong, Wei Gao, Yong Sik Ok, Wei Hsin Chen, Brandon Han Hoe Goh, and Cheng Tung Chong. May 2021. “Solid Biofuel Production from Spent Coffee Ground Wastes: Process Optimisation, Characterisation and Kinetic Studies.” Fuel 292: 120309. https://doi.org/10.1016/J.FUEL.2021.120309.

 Web of Science ®Google Scholar

Ballesteros, L. F., J. A. Teixeira, and S. I. Mussatto. 2014. “Chemical, Functional, and Structural Properties of Spent Coffee Grounds and Coffee Silverskin.” Food and Bioprocess Technology 7 (12): 3493–3503. https://doi.org/10.1007/s11947-014-1349-z.

 Web of Science ®Google Scholar

Mata, T. M., A. A. Martins, and N. S. Caetano. 2018. “Bio-refinery Approach for Spent Coffee Grounds Valorization.” Bioresource Technology 247: 1077–1084. https://doi.org/10.1016/j.biortech.2017.09.106.

 PubMed Web of Science ®Google Scholar

Polat, S., and P. Sayan. Mar. 2020. “Assessment of the Thermal Pyrolysis Characteristics and Kinetic Parameters of Spent Coffee Waste: A TGA-MS Study.” Energy Sources Part A: Recovery, Utilization, and Environmental Effects, 1–14. https://doi.org/10.1080/15567036.2020.1736693.

 Web of Science ®Google Scholar

Jin, L., H. Zhang, and Z. Ma. 2018. “Study on Capacity of Coffee Grounds To Be Extracted oil, Produce Biodiesel and Combust.” Energy Procedia 152: 1296–1301. https://doi.org/10.1016/j.egypro.2018.09.185.

 Google Scholar

Chen, Jiacong, Jingyong Liu, Yao He, Limao Huang, Shuiyu Sun, Jian Sun, KenLin Chang, Jiahong Kuo, Shaosong Huang, and Xunan Ning. 2017. “Investigation of co-Combustion Characteristics of Sewage Sludge and Coffee Grounds Mixtures Using Thermogravimetric Analysis Coupled to Artificial Neural Networks Modeling.” Bioresource Technology 225: 234–245. https://doi.org/10.1016/j.biortech.2016.11.069.

 PubMed Web of Science ®Google Scholar