Conversion of a Wide Range of Low-Rank Coals into Upgraded Coals and Thermoplastic Extracts Having Similar Chemical and Physical Properties Using Degradative Hydrothermal Extraction

Abstract

We have recently presented a method that converts low-rank coal into upgraded coal and thermoplastic extract through the hydrothermal degradative extraction in a flow of hot water at less than 350°C. To examine the validity of the presented method and to characterize the upgraded coals and the thermoplastic extracts obtained in more detail, seven kinds of low-rank coals, a biomass, an O-methylated brown coal, an oil rock, and a bituminous coal were subjected to the hydrothermal degradative extraction at either 300 or 350°C. The elemental compositions of the upgraded coals were found to be rather close to each other, and their carbon and oxygen contents were larger than 71% and less than 23%, respectively, meaning that the heating values are well over 30 MJ/kg on a dry ash-free (daf ) sample basis. The solid extracts (deposits) obtained at 350°C from the variety of samples were very close to each other in elemental composition, molecular-weight distributions, pyrolysis behavior, and softening/melting behavior. All of the deposits interestingly completely melted without decomposition below 200°C. Thus, the proposed method was found to be effective to convert low-grade carbonaceous resources into solid fuel having a higher heating value and compounds having thermoplastic property under rather mild conditions.

Molecular composition of extracts obtained by hydrothermal extraction of brown coal

“…It indicates that all the UCs and deposits obtained from LY, NM, and YN (a, b and c) were located in the directions of dehydration and decarboxylation relative to their parent coals. All of the deposit fractions have 0.97-1.24 of H/C and 0.13-0.18 of O/C, both of which are within the ranges reported previously [15]. When the H/C of the deposit prepared from LY in this study is compared with that in Ref.…”

“…There have been many studies applying extraction methods to recover useful components from brown coal, such as supercritical gas extraction [2], supercritical fluid extraction [3,4], alkali extraction [5], solvent extraction [6][7][8], and hydrothermal extraction [9][10][11][12][13][14][15].…”

“…Such hydrothermal extractions convert brown coal into four fractions: extraction residue (upgraded coal, UC), gaseous product (gas), solid extract (deposit), and water-soluble extract (soluble) [13,14]. In a previous study, we clarified that the deposits obtained at 350°C from various coals were similar in elemental composition, molecular weight distributions, pyrolysis behavior, and softening/melting behavior, and had an interesting thermoplastic property under mild conditions, which made possible their use as an effective binder for metallurgical coke [15]. This result suggested that the deposits might be the most valuable product from the hydrothermal extraction of coal, due to their potential applications and multiple sources.…”

Production of carbonaceous microspheres from wood sawdust by a novel hydrothermal carbonization and extraction method

“…2, as reported previously. [27][28][29][30] In a typical experiment, 1.5 g of wood sawdust (JRP or JB) was placed on a lter (Filter 1 in Fig. 2, Swagelok, SUS316; outer diameter: 11.2 mm; pore size: 0.5 mm) in the reactor.…”

Physicochemical properties of wastewater produced from the microwave upgrading process of Indonesian lignite

“…Lignite upgrading and utilization are receiving considerable attention after proper processing [6][7][8][9][10][11]. Demineralization and dewatering of lignite to improve energy density are essential pretreatment steps in lignite utilization processes [12,13]. A promising process for removing hazardous trace metals and other minerals with mixed bacteria has been proposed to obtain clean coal [14][15][16][17][18].…”