Chemical Structures of Swine-Manure Chars Produced under Different Carbonization Conditions Investigated by Advanced Solid-State ¹³C Nuclear Magnetic Resonance (NMR) Spectroscopy

Abstract

Two types of swine-manure chars, hydrothermally produced hydrochar and slow-pyrolysis pyrochar, and their raw swine-manure solid were characterized using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. In comparison to raw swine-manure solid, both hydrochars and pyrochar displayed significantly different structural features, with lower alkyl carbons, NCH, OCH3, O-alkyl, and COO/N−CO groups but higher aromatic/olefinic and aromatic C−O groups. The chemical structures of four hydrochars varied with different processing conditions. In comparison to the hydrochar with only water wash (HTC-swine W), washing hydrochar with acetone (HTC-swine A) removed the soluble intermediates deposited on the hydrochar, as shown by the decrease of O-alkyl (primarily carbohydrates), corresponding increase of aromatic/olefinic carbons and complete removal of OCH3 groups. With citric acid prewash and acetone wash (HTC-AW-swine A), aromatic C−O and aromatics/olefinics were increased and alkyls were decreased, with O-alkyls totally removed in comparison to just acetone wash (HTC-swine A). Citric acid catalysis and acetone wash (HTC-AC-swine A) increased aromatic C−O and non-protonated aromatics/olefinics, decreased alkyls further, and reduced protonated aromatics/olefinics compared to citric acid prewash and acetone wash (HTC-AW-swine A). The ratios of non-protonated to protonated aromatic/olefinic carbons for HTC-swine W, HTC-swine A, and HTC-AW-swine A hydrochars were quite similar but enhanced for HTC-AC-swine A hydrochar. Obviously, citric acid catalysis and acetone wash (HTC-AC-swine A) provided deeper carbonization than other hydrothermal processes. Hydrothermal carbonization (HTC) processes were associated with the hydrolysis and subsequent decomposition of major biopolymer components in swine manure. The increase of aromaticity during HTC was likely due to condensation polymerization of the intermediates from the degradation of carbohydrates. Pyrochar produced from slow pyrolysis was structurally different from HTC hydrochars. The dominant component of pyrochar was aromatics, whereas that of hydrochars was alkyl moieties. The aromatic cluster size of pyrochar was larger than those of hydrochars. Slow pyrolysis at 620 °C provided deeper carbonization than HTC processes.

Chars produced by slow pyrolysis and hydrothermal carbonization vary in carbon sequestration potential and greenhouse gases emissions

“…The carbon and ash content of HTC was much higher than PC, and had higher hydrogen and oxygen concentrations and were similar to those were recorded by other studies (Cao et al, 2010;Fuertes et al, 2010;Schimmelpfennig and Glaser, 2012).…”

“…Lower pH is achieved with addition of low strength acids (e.g. citric acid) which also enhance dehydration and improve the overall reaction rate of hydrothermal carbonization (Cao et al, 2010;Hu et al, 2010). In contrast, slow pyrolysis produces char with pH values generally above neutrality, and these generally increase, along with ash content, with the temperature of pyrolysis (Ueno et al, 2008).…”

Comparative Evaluation of Physiochemical Properties of a Solid Fuel Derived from Adansonia digitata Trunk using Torrefaction

“…The hydrochars produced between 200 °C and 250 °C showed H/C ratios of 0.11 to 0.09 and O/C ratios of 1.15 to 1.07. These ratios were clearly different from those obtained with swine manure (H/C = 1.50, O/C = 0.57) (Cao et al 2011), digested maize silage (H/C = 1.26, O/C = 0.24), and cellulose (H/C = 1.17 and O/C = 0.35) (Mumme et al 2011). The differences may have been due to the differences in the starting material composition and the torrefaction process conditions.…”

Chemical, structural and energy properties of hydrochars from microwave-assisted hydrothermal carbonization of glucose

“…The peaks between 170 and 200 ppm are due to the presence of carboxylic acid, aldehydes or ketones moieties [36]. The spectrum also shows carbohydrate resonances (specifically CH 2 OH groups around 62 ppm, CHOH groups around 72 ppm, and anomeric O-C-O carbons around 90 ppm) in the O-alkyl region between 60 and 100 ppm [37,38]. These functional groups have already been indicated by the FT-IR result.…”