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3.4. Characterization techniques

3.4.1. Proximate analysis

The proximate analysis provides the percentage composition of moisture, volatile matter, inorganic residue (ash) and fixed carbon in the fuels. The moisture content (ASTM D 3173-03), volatile matter (ASTM-3175-07), ash content (ASTM-3174-04) in the solid fuels are evaluated as per the ASTM methods (Saydut et al., 2008).

3.4.2. Ultimate analysis

The ultimate analysis provides the elemental composition of carbon, hydrogen, nitrogen, sulphur and oxygen. The ASTM D 3176-09 method is followed for the analyses. This analysis is performed in Biotech Park, IIT Guwahati.

3.4.3. Bomb calorimeter

The gross calorific value (GCV) of the solid fuels is measured using a Bomb calorimeter as per the Indian standard (IS: 1359- 1959) method (Model: CC01/M3, Make: M/s Toshniwal Technologies Pvt. Ltd, India).

3.4.4. Brunauer-Emmett-Teller (BET) analysis

BET analysis estimates the surface area of the solid fuels (Model: TriStar II, Make:

Micromeretics, USA). The samples are kept at 110 ˚C overnight to remove the moisture from the fuel surface. Nitrogen gas is used as the adsorbate for the analysis at 77 K. The surface area obtained from the analysis is expressed in m2/g of solid.

3.4.5. X-ray diffraction (XRD)

XRD is used to identify the crystalline components present in the powdered sample (Model: Smartlab, Make: Rigaku Technologies, Japan). The formation of any complex compounds after the thermal process could be identified using XRD analysis. The


oxygen carriers with fuel ash could also be detected. The fuel samples are scanned with a step size of 0.03° with a 2ϴ angle in the range of 10-80°. It is analyzed in the Central Instrumental Facilities (CIF) of IIT Guwahati.

3.4.6. X-ray fluorescence (XRF)

XRF analysis quantifies the metals in the OPCB and its respective oxides present in the oxidized e-waste. A 4g of powdered OPCB sample is mixed with boric acid (binding agent) and compressed into small discs. The pelletization is done by using the hydraulic press method (Bouraoui et al., 2015). It is analyzed in IIT Kharagpur (Model: Pan Analytical, Make: Axios FAST XRF spectrometer, Netherland).

3.4.7. Fourier transform infrared spectroscopy (FTIR)

Table 3.3. FTIR spectra bands of functional groups.

Functional groups Wavenumber (cm-1)

O-H stretching 4000-3500

C-H aliphatic (aliphatic hydrocarbon) 3000-2800

C=O (aromatic ester) 1900-1650

C=C (aromatic hydrocarbon) 1500-1400

C-O (aromatic ester) 1200-1050

C-O-C (aromatic ether) 1270-820

Si-O-Al 900-670

Ca-O 525

Fe-Ca 1064

N-H 1695

The functional groups present in fuels and their respective ash samples are characterized by FTIR analysis. The IR spectrum is recorded in the range 4000-500 cm-1 by the KBr pellet method. The mass ratio of 1:100 (sample: KBr) is maintained for the analysis.

Table 3.3 highlights the functional groups and their respective wavenumbers (Lin et al., 2019, Singh & Zondlo, 2017, Meng et al., 2014). It is analyzed in the Department of


Chemical Engineering, IIT Guwahati (Model: IRAffinity-1, Make: M/s Shimadzu, Japan).

3.4.8. Gas chromatography-mass spectrometer (GC-MS)

The tar composition is analyzed using a GC-MS under a helium atmosphere. A 200 mg of coal tar is dissolved in dichloromethane, and the solution is filtered using filter papers (100 nm pore size). About 1µL of the filtered solution is injected into the GC-MS for analysis. The injector temperature is set to 280℃. The oven temperature is held at 60℃

for 3 minutes. It is then increased to 320℃ at 5℃/min (Jiang et al., 2007, Morgan et al., 2008, Shi et al., 2010). It is analyzed in the Department of Chemical Engineering, IIT Guwahati (Model: 450-GC, 240-MS, Make: M/s Varian, Netherland).

3.4.9. Field emission scanning electron microscope (FESEM)

FESEM images (Model: Sigma 300, Make: M/s Zeiss, United Kingdom) provide the surface morphology of the solid fuels. The detailed information about sintering, agglomeration can be confirmed by this analysis. It has the ability to magnify 10x to 3,00,000x. The interaction of coal, biomass with oxygen carriers after the reduction process can be analyzed using FESEM images. This equipment is found in the Central Instrumental Facilities (CIF) of IIT Guwahati.

3.4.10. Gas chromatography (GC)

The gas chromatography technique is used to find the composition of the gas from the reactor outlet. Argon is used as the carrier gas for the analysis. A standard gas calibration chart is prepared to estimate the composition of the unknown samples. The standard gas canister is purchased from Chemix. Gas samples are analyzed using a gas chromatograph (Model: CP-3800; Make M/s Varian, Netherland).


3.4.11. Thermogravimetric analyser (TGA)

Thermo-gravimetric analysis (TGA) is conducted for the CLC and non-CLC process of

the coal under non-isothermal conditions in the temperature range of 25-1000°C at a heating rate of 10°C/min under CO2/N2 atmosphere. Further, the reactivity of char (coal and rice straw) with oxygen carriers (Fe2O3, OPCB) are tested for estimating the solid- solid interaction under an inert atmosphere using a TGA (Model: TG 209 F1 Libra; Make M/s Netzsch, Germany). Synergistic effect of coal and biomass

The synergistic effect of the coals (LAC, HAC) and biomass (RS) is assessed by comparing the estimated weight loss based on individual fuel behaviour in unblended conditions (theoretically) and the actual weight loss (Wact) under blended conditions (Equation 3.1) using a coal-biomass mixture of 1:1 ratio by weight. The theoretical weight loss (Wtheo) is predicted by using the individual weight loss of coal and RS estimated under the unblended condition and is given as,

Wtheo= x1W1+ x2W2 (3.1)

xi denotes the mass fraction of each component (0.5 for each case); Wi is the weight loss of individual fuels in unblended conditions. The difference in weight loss between Wtheo

and Wact indicates a measure of synergistic effect on the co-blending of coal and RS. Kinetic studies using TGA Data

The activation energy is estimated using different models such as the reaction order model and shrinking core model (SCM). The Coats-Redfern method is used for fitting the various models considered to determine the thermo-kinetic parameters. Table 3.4 describes the different reaction models, such as the shrinking core model and volumetric


models to determine the activation energy. The integral form of the Coats–Redfern equation is as follows,

ln [G(α)

T2 ] = ln [AR

βE] − E

RT (3.2)

Where G(α) is the integral form, T is the absolute temperature in K, E is the activation energy, β is the heating rate (10 K/min), A is the pre-exponential factor. The activation energy is obtained by plotting ln (G(α) T⁄ 2) and 1/T and the slope of the straight line gives the value of E/R.

Table 3.4. Different reaction models for the estimation of kinetic parameters.

Model Integral form G (α)

Shrinking core model (SCM)

Contracting volume 1 − (1 − 𝛼)1/3

Reaction models

First order −𝑙𝑛(1 − 𝛼)

Second order (1 − 𝛼)−1− 1

Third order [(1 − 𝛼)−2− 1]/2

The pre-exponential factor (A) and activation energy (E) can be calculated with the plot of ln (G(α)/T2) versus 1/T. These values are calculated at three different temperature intervals in the range of 350-600°C for volatiles reactivity, 600-800°C for higher hydrocarbon reactivity and 800-1000°C for char reactivity.