Experimental study on the effect of pyrolysis pressure, peak temperature, and particle size on the potential stability of vine shoots-derived biochar

Published Date

1 October 2014, Vol.133:163–172, doi:10.1016/j.fuel.2014.05.019

Title 

Experimental study on the effect of pyrolysis pressure, peak temperature, and particle size on the potential stability of vine shoots-derived biochar

• Author 

• Joan J. Manyà ^,
• Miguel A. Ortigosa
• Sergio Laguarta
• José A. Manso

• Thermo-chemical Processes Group (GPT), Aragón Institute of Engineering Research (I3A), University of Zaragoza, Technological College of Huesca, crta. Cuarte s/n, E-22071 Huesca, Spain

Received 5 February 2014. Revised 2 May 2014. Accepted 8 May 2014. Available online 23 May 2014.

Highlights

• •
  A central composite design was applied to assessing the effect of selected factors.
• •
  Stability of the vine shoots-derived biochar was mainly determined by the particle size.
• •
  Using a bed of alumina represents a low-cost way to partly remove tar from the pyrolysis gas.

Abstract

This study examines the effect of three key operating factors (peak temperature, particle size and pressure) on the potential stability of the biochar produced by slow pyrolysis of vine shoots. The following response variables were considered as key indicators of the potential stability of biochar in soils: the fixed-carbon yield, the fraction of aromatic carbon, and the molar H:C and O:C ratios. Slow pyrolysis tests were conducted in a laboratory-scale fixed-bed unit and planned according to a 2-level factorial design. The behavior of the product gas yield and composition at the outlet of the secondary cracking reactor (a fixed-bed of activated alumina particles at 700 °C) was also evaluated as a function of the three factors. The results from the statistical tests revealed that the particle size is the most significant factor in determining the potential stability of biochars. Using larger particles of biomass and, in a lesser extent, operating at higher peak temperatures leads to the production of more stable materials. Unexpectedly, the absolute pressure only plays a significantly positive role in decreasing the tar content in the producer gas at the outlet of a secondary cracking reactor.

Keywords

• Biochar
• Pyrolysis
• Vine shoots
• Pressure
• Particle size

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Nomenclature

GHSV

gas hourly space velocity (h⁻¹)

m_bio

dry mass of biomass sample (kg)

m_char

mass of produced biochar (kg)

adjusted coefficient of determination

x₁

coded variable for pressure

x₂

coded variable for peak temperature

x₃

coded variable for particle size

y_char

biochar yield (kg kg⁻¹ of biomass in a dry basis)

y_FC

fixed-carbon yield (kg kg⁻¹ of biomass in a dry and ash-free basis)

y_gas

yield of producer gas (kg kg⁻¹ of biomass in a dry and N₂-free basis)

y_water

yield of water (g kg⁻¹ of biomass in a dry basis)

y_tar

yield of tar (g kg⁻¹ of biomass in a dry basis)

Greek symbols

β₀

regression coefficient for the intercept term

β₁

regression coefficient for the linear effect of pressure

β₂

regression coefficient for the linear effect of peak temperature

β₃

regression coefficient for the linear effect of particle size

β₁₂

regression coefficient for the interaction term between pressure and peak temperature

β₁₃

regression coefficient for the interaction term between pressure and particle size

β₂₃

regression coefficient for the interaction term between peak temperature and particle size

β₁₁

regression coefficient for the quadratic effect of peak temperature

ρ

Pearson’s correlation coefficient

Acronyms

BET

Brunauer Emmett Teller

CEC

cation exchange capacity

CP-MAS

cross polarization and magic angle spinning

FC

fixed carbon

GC

gas chromatography

NMR

nuclear magnetic resonance

PID

proportional integral derivative

RSM

response surface methodology

TGA

thermogravimetric analysis

XRF

X-ray fluorescence

WGS

water gas shift

 Table 1

Table 1.

Fig. 1.

 Table 2

Table 2.

 Table 3

Table 3.

 Table 4

Table 4.

Fig. 2.

Fig. 3.

Fig. 4.

 Table 5

Table 5.

Fig. 5.

• ⁎ 
  Corresponding author. Tel.: +34 974292649; fax: +34 974239302.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0016236114004669

Influence of heating temperature and holding time on biochars derived from rubber wood sawdust via slow pyrolysis

Published Date

May 2014, Vol.107:31–39, doi:10.1016/j.jaap.2014.01.021

Title 

Influence of heating temperature and holding time on biochars derived from rubber wood sawdust via slow pyrolysis

• Author 

• A. Shaaban ^a
• Sian-Meng Se ^a,,
• M.F. Dimin ^a
• Jariah M. Juoi ^a
• Mohd Haizal Mohd Husin ^b
• Nona Merry M. Mitan ^c

• aDepartment of Engineering Materials, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
• bDepartment of Automotive, Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
• cDepartment of Plant and Maintenance, Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia

Received 2 November 2013. Accepted 30 January 2014. Available online 7 February 2014.

Highlights

• •
  Biochars were derived from rubber wood sawdust via slow pyrolysis.
• •
  Heating temperatures (HT) ranged from 300 to 700 °C and retention time (RT) ranged from 1 to 3 h.
• •
  They were characterised by XRD, FT-IR, Boehm titration, pH, BET, SEM and SEM–EDX.
• •
  At low HT and RT, biochar consists of more acidic groups with lower pH.
• •
  At high HT and RT, biochar obtained larger surface area and total pore volume.

Abstract

Biochar samples were produced from rubber wood sawdust (RWSD), which is a by-product from sawmills, via slow pyrolysis. Biochar is a potential additive for agricultural soil as a soil amendment and for agronomics. The approach proposed in the current study considers the effects of heating temperature and holding time on the surface functional groups and morphologies of RWSD-derived biochars. The pyrolysis was performed in a vertical tube furnace heated at 5 °C/min from room temperature to maximum heating temperatures of 300 °C, 400 °C, 500 °C and 700 °C under nitrogen gas purging at a rate of 30 ml/min. Two sets of biochars were produced with holding times of (i) 1 h and (ii) 3 h. Proximate and ultimate analyses were performed on the raw RWSD using thermogravimetric analysis (TGA) and carbon–hydrogen–nitrogen (CHN) elemental analysis. The influence of heating temperature and holding time on biochar surface functional groups and porosities was investigated using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Boehm titration, pH alkalinity, Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM) and SEM with energy-dispersive X-ray (SEM–EDX) spectrocopy. The FT-IR spectra indicated the presence of acidic functional groups, such as carboxylic, phenolic and lactonic groups, and these groups were quantified by Boehm titration. The number of acidic functional groups decreased as the heating temperature and holding time increased. The maximum amount of acidic functional groups was determined to be 1.9 mmol/g at 300 °C for a 1-h holding time compared to 1.3 mmol/g for a 3-h holding time and 1.0 mmol/g with a 1-h holding time at 700 °C. All of the biochars produced at heating temperatures above 400 °C were alkaline, and the pH value increased as the heating temperature and holding time increased. The biochar produced at 300 °C with a 1-h holding time had a pH of 6.72 and the sample produced with a 3-h holding time had a pH of 7.67. In addition, the sample produced when the temperature was increased to 700 °C with a 1-h holding time had a pH of 11.44. The BET surface area analysis reported maximum values of 5.49 m²/g, and the total pore volume was 0.0097 cm³/g at a heating temperature of 700 °C with a 3-h holding time. SEM micrographs clearly showed the development of well-defined pores in the biochars, and the SEM–EDX spectra indicated localised carbon and oxygen content in all the samples. The results indicated that biochars produced from RWSD are potentially beneficial as soil amendments. However, an extensive study of biochar sustainability is worth investigating.

Keywords

• Rubber wood sawdust
• Slow pyrolysis
• Biochar
• Surface functional groups
• BET specific surface area

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 Table 1

Table 1.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

 Table 2

Table 2.

Fig. 6.

Fig. 7.

Fig. 8.

• ⁎ 
  Corresponding author. Tel.: +60 6 3316069; fax: +60 6 3317075.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0165237014000230