Article pubs.acs.org/EF
Slow Pyrolysis of Deoiled Canola Meal: Product Yields and Characterization Ramin Azargohar,† Sonil Nanda,† B. V. S. K. Rao,‡ and Ajay K. Dalai*,† †
Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, SK, Canada Centre for Lipid Research, Indian Institute of Chemical Technology, Hyderabad, A.P., India
‡
ABSTRACT: Canola meal is a byproduct of the biodiesel industry and abundantly available in Canada. Slow pyrolysis of deoiled canola meal was performed over the temperature range 300−700 °C to study the potential applications of the pyrolysis products as fuels and sources of value-added products. The biochar yield decreased with increasing pyrolysis temperature, but the yield of gas products showed the reverse trend. The bio-oil yield increased up to a pyrolysis temperature of 500 °C and then decreased. The carbon and nitrogen contents of biochars were in the ranges 66−81 and 6−9 wt %, respectively. Van Krevelen’s diagram showed that a higher pyrolysis temperature formed a highly condensed aromatic structure for biochars. Alkaline elements had the largest concentration in the ash present in biochar, followed by P and Fe. Biochars showed a basic pH range, and their electrical conductivity decreased with increasing pyrolysis temperature. A higher heating value of 29.8 MJ/kg was observed for biochar produced at 400 °C. The energy recoveries by biochars and bio-oils were 42−65% and 15−32%, respectively. The bio-oil yield was in the range of 10−24 wt %. Bio-oil produced at a pyrolysis temperature of 400 °C had a higher heating value (30.8 MJ/kg) than bio-oils produced at other temperatures. The concentration of phenolic compounds in bio-oil increased with increasing pyrolysis temperature. The same trend was observed for nitrogen compounds produced at temperatures up to 500 °C. The total acid number for bio-oils was in the range of 96−21 mg of KOH/g. The largest heating value for gas products (14.9 MJ/m3) was observed at a pyrolysis temperature of 500 °C.
1. INTRODUCTION Canola is the most available mustard in the world and is suitable for production in cooler climates. It comes from the plant family of Brassicaceae. The largest share of global production of canola belongs to Canada and the United States. Western Canada and the north-central United States are the main geographical areas used for canola crops.1 Canada is one of the largest canola producers in the world, producing 20% of the world’s canola/rapeseed, and is the largest exporter in the world as well. Canola seed contains ∼40 wt % oil, which is mainly used in the food industry. Besides, it has wide range of applications in biodiesel industries, especially the oil with high chlorophyll and larger free fatty acid (FFA) content. Canola and soybeans are the two main crops widely used to produce biodiesel in Canada. There is a recent Canadian government mandate to replace 1.5 billion liters of petrodiesel per year (5%) with biodiesel by 2015,2 which is expected to foster biodiesel industries. Canola meal is obtained after canola seed is pressed to extract the oil. This solid byproduct is processed into high-protein livestock feed because of its excellent amino acid profile and high vitamin and mineral contents. The growth of biodiesel industries in upcoming years will not only produce byproducts such as canola meal but also result in immense pressure for their utilization. The production of canola meal was 3.5 million tons in 2010−2011, of which 3.0 million tons was exported. It is estimated that production of canola meal will double in 4−8 years.2 The presence of some antinutritional factors such as glucosinolates, tannins, sinapine, and phytic acid in canola meal is considered as a disadvantage of its use for animal and human nutrition.3,4 Low lysine levels and biological energy © 2013 American Chemical Society
values for monogestrics are considered as weaknesses of canola meal in its use for meat-producing animals and feeding poultry.2 Because of its larger fiber content, which is 3 times that of soybean meal, the digestibility of canola meal is less than those other sources of meal.3 In addition, canola meal has to compete with higher-protein sources such as dry distiller’s grains (DDGs) obtained from the ethanol industry. The issue of oversupply and the associated price volatility as well as the reduced profitability from the sale of the byproducts from bioenergy processing plants drive the need to utilize canola meal for renewable energy. Pyrolysis as a thermochemical process can be defined as biomass degradation at high temperatures under an inert atmosphere (absence of oxygen). It transforms biomass and other organic materials into a more stable, high-energy-density liquid known as bio-oil (∼22 MJ/kg), a high-energy-density solid known as biochar (∼18 MJ/kg), and gas products with relatively low energy density (∼6 MJ/kg).5 The pyrolysis of wood and other biomass materials has been studied extensively in the past, but the use of canola meal as feedstock for pyrolysis is new. The main interest in the pyrolysis process is conversion of biomass to potential fuels such as bio-oil and biochar, which can be stored or transported much more easily than biomass. In addition, bio-oil obtained from the pyrolysis process is a source of useful chemicals,6 and biochars can be converted to valueReceived: May 20, 2013 Revised: July 25, 2013 Published: July 30, 2013 5268
dx.doi.org/10.1021/ef400941a | Energy Fuels 2013, 27, 5268−5279
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Article
added products such as activated carbons7 and potentially can also be used for soil amendment.8 The focus of this research was to study the effects of different pyrolysis temperatures (300−700 °C) on the slow pyrolysis of canola meal. The effects of temperature on the yields and properties of the bio-oil, biochar, and gas products of pyrolysis were studied. Different characterization techniques were employed to analyze the fuel properties of the bio-oil and value-added applications of the biochar (e.g., soil application properties and production of activated carbons). Analysis of the gas products was performed to assess their potential for use as synthesis gas (syngas) in the Fischer−Tropsch process to produce liquid fuels based on the molar ratio of hydrogen to carbon monoxide.
biomass. The crystalline structures of the starting material and biochars were analyzed by X-ray diffraction (XRD) using a Bruker D8 Advance X-ray diffractometer. The scans for all samples were collected from 10 to 50° (2θ scale) using Cu Kα radiation (40 kV, 130 mA) with a scanning speed of 0.5°/min. The sample was finely ground and loaded into the aperture of a silicon sample holder. The DIFFRAC plus XRD Commander software system was used to collect the data, and the EVA database was used for phase identification. 2.3.2. Chemical Characterizations. The IR spectra of bio-oil samples were obtained using diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). Samples were scanned and recorded using a spectroscope (Spectrum GX, PerkinElmer) with 256 scans at a resolution of 4 cm−1 over the wavenumber range from 4000 to 400 cm−1. 1H and 13C NMR data for the samples were acquired on a Bruker Advance 500 MHz NMR spectrometer (Bruker Biospin, Canada) equipped with a 5 mm inverse triple resonance probe (TXI). Samples were prepared by dissolving them in deuterated chloroform. GC analysis of bio-oils was carried out using a Varian CP-3800 gas chromatograph equipped with a flame ionization detector (FID) and a 30 m/0.25 mm column coated with 0.25 μm film thickness (DB-5 column). Helium was used as the carrier gas at a flow rate of 1.2 mL/ min with a column pressure of 22 kPa. Each sample was injected into the injection port of the GC using a split ratio of 50:1. For analysis of chemical compound separation, a linear temperature program from 50 to 250 °C (5 °C/min) was used. The total run time was 45 min. The percentage composition was calculated using the peak normalization method. GC/MS analysis was carried out on a Varian Saturn 2200 GC/MS fitted with the same column and temperature program as described earlier. Peak identification was carried out by comparison to the mass spectra available in the NIST-1 and NIST-II libraries. To analyze the gas product, the gas from the pyrolysis unit was collected in Tedlar bags and injected into the gas chromatograph (Agilent 7890A), which was equipped with two thermal conductivity detector (TCD) columns and one flame ionization detector (FID) column. Higher heating values (HHVs) of biochars and bio-oils were determined in a static oxygen bomb calorimeter (Parr 1108) using ∼1.0 g of sample. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of biochar samples was performed using a Sciex Elan 5000 ICP-MS instrument (PerkinElmer). A Renishaw inVia Raman microscope was used for Raman spectroscopy of biochars in the backscattering configuration. The source of radiation was a laser operating at a wavelength of 514 nm. Biochar pellets were prepared for analysis under the laser. The spectral resolution was 4 cm−1 with 10% laser power and 10 s of exposure time along with a total of 15 acquisitions. The Raman spectra between 1100 and 1800 cm−1 were curve-fitted using the WiRE Raman software. Thermogravimetric analysis (TGA) was performed to determine the devolatilization characteristics of feedstock and biochars using a Pyris Diamond TG/ DTA instrument (PerkinElmer). The samples were analyzed at an argon flow rate of 40 mL/min with a heating rate of 7 °C/min. The rate of weight loss with respect to temperature was recorded. The total acid number (TAN) of bio-oil samples was determined according to ASTM D D664-09a. The TAN is defined as the mass (in mg) of KOH per gram of sample that is required to titrate a sample in a mixture of toluene and propan-2-ol to which a small amount of water is added. A 0.1 mol/L alcoholic KOH solution (in propan-2-ol) and 0.10−0.25 g of sample were used for the titration. Titrations were performed using a combination of an indicating electrode and a reference electrode (Ag/AgCl). Carbon, hydrogen, nitrogen, and sulfur percentages were measured using an Elementar Vario EL III analyzer provided by PerkinElmer.
2. EXPERIMENTAL SECTION 2.1. Feedstock. Canola meal was provided by Bungi Oil Industries (Saskatoon, Canada) and used as the feedstock for the pyrolysis process. Particle size analysis of the feedstock showed that 10, 50, and 90 vol % of the particles were smaller than, 114, 533, and 1461 μm, respectively. The canola meal (100 g) was deoiled by the Soxhlet extraction method9 using hexane (500 mL) as the solvent. The deoiled meal was made free of solvent and used as the pyrolysis feed. 2.2. Pyrolysis Process. Pyrolysis of the canola meal was performed in a fixed-bed Inconel tubular reactor (22 mm i.d.). A furnace mounted vertically on a steel frame was used to supply heat to the reactor. For pyrolysis, 20.0 g of canola meal was placed in the reactor on an Inconel web welded to the wall of the reactor. Argon was used as the carrier gas, and its flow rate was controlled by a mass-flow controller (Brooks Instrument 5850S/B). The temperature of the furnace was controlled by a temperature controller (Eurotherm 2416). The reactor temperature was increased to the desired value at a heating rate of 7 °C/min and then held constant for 30 min. The solid product (biochar) was removed from the reactor after the pyrolysis process. Bio-oil was collected in glass containers placed in an ice bath after the reactor. Bio-oil remaining in the outlet line was collected using acetone. Gas samples were collected from outlet line of the reactor in a Tedlar bag after the pyrolysis temperature was reached and then analyzed by gas chromatography (GC) . 2.3. Characterization Methods. 2.3.1. Physical Characterizations. Viscosities of bio-oils were measured at 40 °C using an RV or LV (depending on the range of viscosity) cone and plate viscometer. A Brookfield digital viscometer (DV-I) was used for this analysis. To measure electrical conductivity (EC), biochar was soaked with deionized water at a biochar/water ratio of 1:5 for 24 h with intermittent agitation. The slurry was then measured for EC using an Accumet AP85 Portable pH/conductivity meter (Fisher Scientific, Canada). The moisture and ash contents of biochars and biomass were determined according to ASTM D 2866-94 (approved 1999). The pH of biochar samples was determined according to ASTM D 3838-80 (approved 1999). Particle size distributions (PSDs) for feedstock and biochars were determined from the laser beam diffraction patterns of the particles with a Malvern Mastersizer S long-bench particle size analyzer (Malvern Instruments Ltd., Malvern, UK) using the dry and wet methods, respectively. The accuracy of the measurements was ±2% . Brunauer−Emmett−Teller (BET) surface areas and total pore volumes of biochars were determined by an ASAP 2020 automated gas adsorption analyzer (Micromeritics Instruments Corp., Norcross, GA, USA). After the samples were degassed at 200 °C to a vacuum of 550 μmHg, nitrogen adsorption−desorption isotherms at −196 °C were measured using this equipment. The BET surface area was calculated using the BET equation. For each analysis, ∼0.2 g of sample was used. The accuracy of the measurements performed with this equipment was ±5%. The volatile matter in the biomass was determined by the procedure given in ASTM D 3175-07. The biomass sample (1.0 g) was placed in a muffle furnace maintained at 950 ± 10 °C for 7 min, after which the crucible was removed from the furnace and placed in the desiccator. The loss of weight was given as the volatile matter in the
3. RESULTS AND DISCUSSION 3.1. Canola Meal Deoiling. The canola meal feed contained 3.2 wt % oil. The meal was subjected to Soxhlet extraction to recover the residual oil present in it. The concentrations of oil, carbohydrate, protein, fiber, moisture, and ash content in the original canola meal were 3.2, 34.0, 36.7, 5269
dx.doi.org/10.1021/ef400941a | Energy Fuels 2013, 27, 5268−5279
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Article
Figure 1. Thermogravimetric analysis of deoiled canola meal in argon at heating rate of 7 °C/min.
Figure 2. Yields of pyrolysis products at different pyrolysis temperatures.
based on very slow biochar decomposition at higher temperatures beyond 600 °C.14 The total weight loss observed for the feedstock was 68%, and a weight loss of 66% happened up to 600 °C. The largest weight loss (∼29 wt %) occurred between 300 and 400 °C and the lowest weight loss (
