Thermal degradation of crab shell biomass, a nitrogen-containing carbon precursor
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Thermal degradation of crab shell biomass, a nitrogen‑containing carbon precursor Zoltán Sebestyén1 · Emma Jakab1 · Andrea Domán2 · Péter Bokrossy2 · Imre Bertóti1 · János Madarász3 · Krisztina László2 Received: 3 September 2019 / Accepted: 11 February 2020 © The Author(s) 2020
Abstract Waste and low-cost lignocellulosic biomasses are well studied and widely used as raw materials for porous carbon adsorbents. Much less attention is given to the exploration of the potential of marine biomasses, though these materials contain also nitrogen, which—if preserved during the processing—has a beneficial influence on the sorption properties of the porous carbon obtained. Here, we report a multi-technique investigation into the conversion of crab shell to porous carbon adsorbent. Thermogravimetry and pyrolysis-GC/MS studies were used to reveal the thermal degradation of this natural polymer and follow the decomposition process through the identification of the products. Almost 40 various volatile degradation products were distinguished released at 500 °C pyrolysis temperature. Based on the TGA/DTG results, two temperatures, 350 and 500 °C, were selected to obtain pyrolytic samples in macroscopic quantities in order to characterize the morphology and surface chemistry of the solid fraction. More than 50% of the nitrogen atoms were still in the carbonaceous matrix after the 500 °C pyrolysis in the C–N=C, C–NH and 3C–N-type bonds. The ash content 1 g, 16 h, 600 °C in air). The low ash content was also confirmed by the TGA measurement in synthetic air. Based on XRD, the ash contains hydroxylapatite-type crystalline matter [Ca5(PO4)3OH]. The ash, and consequently the Ca content, is certainly below the values reported by Dai et al. [12] and in different chemical forms like in the sample used for an in situ templating by Gao et al. [26].
Thermal degradation of crab shell biomass, a nitrogen‑containing carbon precursor
Fig. 1 SEM images of the precursor (a), C350 (b) and C500 (c) samples
Relative intensity/a.u.
400
Ash
300
Assignation
C500
200
C350
100
0
Table 1 Results of the XPS analysis. Surface composition of the crab shell and the pyrolyzed samples and the distribution of the identified species
Precursor 10
20
30
40
50
60
70
80
2θ /° Fig. 2 Powder X-ray diffractograms of the precursor, the pyrolyzed C350, C500 samples and the ash remained at 600 °C
According to Fig. 1 the integrity of the matrix is retained after the pyrolytic treatments in spite of the respective 30 and 24% yield at 350 and 500 °C. XRD, however, revealed that the orthorhombically ordered chitin (poly (N-acetyl-βd-glucosamine), (C8H13O5N)n) structure [27] of the biopolymer gradually disappeared (Fig. 2). The appearing lowintensity hump above 2θ = 20° indicates the presence of a developing colloidal size layered carbon structure as seen in the case of several precursors [28]. The small amount of the inorganic impurities does not allow the identification of the calcium compound in the crab shell itself. The residual nitrogen- and
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