Evaluation of hydrochars from lignin hydrous pyrolysis to produce biocokes after carbonization

Abstract

Hydrochars were obtained after hydrous pyrolysis of a pine Kraft lignin using different reaction conditions (temperature, water content and residence time) and the residues were characterized through a wide range of analytical techniques including high-temperature rheometry, solid-state 13 C nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and field emission scanning electron microscopy (FE-SEM). The results indicated that an increase in reaction temperature, an increase in residence time or a decrease in water content reduces the amount of fluid material in the residue. The hydrous pyrolysis conditions studied were not able to increase the maturation of lignin, which would result in an increase in the resolidification temperature, but reduced the amount of mineral matter in the hydrochar produced. On the other hand, the hydrochars obtained from pristine lignin, torrefied lignin (300°C, 1 hour) and their 50:50 wt.%/wt.% blend at temperatures of 350°C after 6 hours using 30 ml of water had lower ash contents (<2 wt.%) than the parent lignin (2.5 wt.%) and a high rank good coking coal (10 wt.%). However, the reactivity of the resulting biocokes (>45%) is excessively high compared to that of the good coking coal (10%) and the microstrength of the biocokes (R 1 <1%) is much lower than that of the coal (R 1 =17%). These findings could be rationalized by the high total porosity (>39%) and high microporous surface areas (>400 m 2 /g) of the biocokes and high alkalinity index of the lignins (>27%) compared to those of the coke (27% and 145 m 2 /g) and coal (0.6%), respectively. Furthermore, the biocoke derived from the hydrous pyrolysed torrefied lignin did not agglomerate, which could not be explained by changes in the chemical properties of the material and requires further investigation.

Evaluation of demineralized lignin and lignin-phenolic resin blends to produce biocoke suitable for blast furnace operation

“…Torrefaction causes significant changes in the chemical structure of pristine lignin. In our previous work [4], it was found that torrefaction causes complete degradation of aliphatic C−C and C−O groups, polysaccharides, carbonyl and carboxylic acid structures, which were very similar to the modifications caused by hydrothermal carbonization of lignin at 350°C for 6 h using 30 mL of water. Torrefaction of demineralized lignin greatly reduces the intensity of the peak at around 147 ppm, which corresponds to aromatic carbons bonded to methoxy groups.…”

“…Previous work by our group [4] indicated that lignin torrefaction reduces the intensity of peaks associated to aromatic rings, guaiacyl groups and methoxy groups (1600−900 cm −1 ). Torrefaction of either pristine lignin or demineralized lignin produces similar structural changes, as indicated by the almost identical spectra for TL and TDL.…”

“…Hydrothermal carbonization (HTC) tests have been described in detail in our previous work [4]. Briefly, the equipment comprised of a Parr 4740 series stainless steel 75 mL cylindrical pressure vessel connected to a pressure gauge rated to 690 bar.…”

“…The possible conversion of Kraft lignin into biocoke through hydrothermal carbonization was investigated by our research group [4]. The hydrochars obtained at 350°C for 6 h using 30 mL of water from pine Kraft lignin, torrefied lignin and a 50:50 wt/wt blend of pristine and torrefied lignins yielded less ash than a good coking coal (i.e.…”

Effect of Charcoal and Kraft-Lignin Addition on Coke Compression Strength and Reactivity

“…The chemical composition of charcoal ash was determined with X-ray fluorescence (XRF) (Bruker AXS S4 Pioneer, Bruker AXS GmbH, Karlsruhe, Germany) and the chemical composition of Kraft-lignin was conducted by an external certified laboratory. The basicity index, BI (%), of the coal, charcoal, and Kraft-lignin was defined as the ratio between the basic and acid components in the ash (Equation (1)) [10]. …”