Degradative Solvent Extraction Method Research Articles

Degradative solvent extraction of low rank coal: Structural evolution of extraction products

The degradative solvent extraction method was proposed to convert low rank coals into carbon-enriched products under mild condition. However, limitations in the understanding of the structure evolution of products and reaction mechanism of the extraction process hinder the targeted regulation of the products. Therefore, in this work the structural evolution of products during the extraction for different types of coals and by different types of solvents were investigated. Synthesized molecular structural models of the products were constructed and the reaction mechanism was then discussed. Results show that the industrial compounding solvent (ICS) is capable of extracting more single-ring aromatic organics from coals and increasing the yields of the main products by approximately 10% compared to 1-methylnaphthalene. During the extraction process, the main reaction of the sub-bituminous coal is the breakage of unstable chemical bonds and functional groups, while the reaction of lignite is the thermal decomposition and deoxygenation of massive small molecules in the coal. Moreover, the ICS promotes aromatization reactions during the extraction, which indicates that the ICS is the appropriate industrial solvent for the degradative solvent extraction. This research proved a theoretical guidance for the industrialization of DSE technology and the targeted regulation of the products.

Degradative solvent extraction of subbituminous coal with deep eutectic solvent and effect of reaction conditions on products

A degradative solvent extraction method for upgrading low-rank coal was performed at 200–350 °C for 90 min to obtain a substance dissolved in the solvent at room temperature (Soluble). Because the resulting mixture exhibited a high carbon content without ash, it could be readily used as a fuel. Furthermore, deep eutectic solvents (DESs) have attracted attention for improving the Soluble yield and decreasing the oxygen content in Soluble. DES is known to cleave oxygen-containing functional groups in biomass and is considered effective for deoxidizing low-rank coal. Herein, DES was prepared by mixing choline chloride, FeCl3·6H2O, and Adaro subbituminous coal (AD) and then added to 1-methylnaphthalene (1-MN) in a non-polar solvent, followed by degradative solvent extraction in the range of 200–350 °C. The effects of reaction temperature and added DES amount on the product yield and the composition were evaluated. As the reaction temperature and amount of DES added increased, the Soluble yield and carbon content increased. It was also found that the thermal decomposition temperature and oxygen content decreased with the increasing DES amounts. This decrease indicates that DES promotes the deoxygenation and decomposition of AD and increases the soluble yield of the fuel source.

Degradative solvent extraction of low-rank coal: Role of water on pyrolysis mechanism of low-rank coal in a highly-dispersed medium

A degradative solvent extraction (DSE) method was proposed to upgrade low-rank coals (LRC) for their cascaded utilizations in a highly-dispersed medium. The derived products exhibited well improved properties in comparison to the raw LRCs. Previously, the LRCs were pre-dried to eliminate the potential impact of the varied water content of raw LRCs, but in light of the abundant water in fresh coals, the hydrolyzing effect of water on coals under heating, and the energy cost to pre-dry the LRCs, it is consequently essential to clarify the effect of water so as to verify the necessity of pre-drying process. In this study, the roles of inherent water and extra-added water were respectively investigated, using dried, raw and wet coals from two typical LRCs. The results show that increasing the moisture content of raw LRCs contributed to the extraction ability of DSE method without noticeably changing the elemental composition, chemical structure and thermal decomposition behavior of extractable products, thus pre-drying of LRCs before DSE treatment was proven unnecessary. Additionally, the roles of the inherent water were concluded as: 1) leading to the formation of stable covalent bond during drying process; and 2) acting as H donor to promote extraction ability, while the added water can only function as H donor. Since excessive water will increase the pressure during DSE treatment and lead to the waste water treatment, the LRCs with a water content between 10% and 30% were consequently recommended for the practical application of DSE treatment.

Preparation of carbon nanofiber with specific features by degradative solvent extraction product from biomass wastes

One of the most essential topics in carbon fiber research is seeking a suitable precursor for the carbon fiber preparation. In this work, an extract was obtained from biomass wastes by a degradative solvent extraction method under moderate conditions. This extract had the properties required for carbon fiber preparation, such as high carbon content, low ash content, thermoplastic property etc. The carbon fiber, prepared using the extract by electro-spinning, had a coarser surface with the specific surface area and specific volume respectively reaching to 714.24 m2/g and 164.10 cm3/g, higher than those of PAN-based carbon fiber. The diameter of the extract-based carbon fiber was about 169 nm ~ 200 nm. The R (ID/IG) value was as low as 1.46. The stabilization and carbonization of extract-based and PAN-based fibers were also conducted via a TGA-DSC for a detailed investigation and comparison. It showed that the thermochemical behaviors of both carbon fibers were different. Thus, it proved that the degradative solvent extraction of biomass waste is a promising method for precursor production to prepare nano-scale carbon fiber with specific properties.

Interaction between low-rank coal and biomass during degradative solvent extraction

A degradative solvent extraction at around 350°C for low-rank coal or biomass wastes upgrading and fractionation was proposed in our previous work. The extraction yield of low-rank coal is relatively lower than that of biomass. In this work the blends of low-rank coal and biomass were treated by this method at 350°C to investigate the interaction between them. The results showed that the yields and elemental compositions of the extracts obtained from the blends were slight different to the calculated results, which were calculated by assuming that there was no interaction between the coal and biomass. The slight promotion of yield was judged to be caused by the catalytic action of the minerals in the coal for thermal decomposition of biomass. It was worth to note that the elemental composition, molecular weight distribution, chemical structure, thermal decomposition behavior and thermoplastic behavior of the extracts obtained from low-rank coal, biomass and their blend, were rather similar to each other, independent of the properties of the raw feedstocks. Overall, the interaction between low-rank coal and biomass during the extraction was not significant. On the other hand, the proposed degradative solvent extraction method was fit not only by single low-rank coal and biomass but also by their blends to produce the product having similar physicochemical properties. This implied that an industrial system of degradative solvent extraction can use coal, biomass or their blends as feedstock at the same time without modification or adjustment.

Solvent Recycling Operation of the Degradative Solvent Extraction of Biomass to Minimize the Amount of Solvent Required

The authors have recently presented a degradative solvent extraction method to dewater, upgrade, and convert biomass wastes into three solid fractions which we call Soluble, Deposit, and Residue. The carbon based yield of Soluble, which is the smallest molecular weight fraction, reached as high as 70% for some biomass wastes. Solubles were free from water and mineral matters, and their physical and chemical properties were almost independent of raw materials. Soluble is expected to be utilized for preparing functional carbon materials such as carbon fiber, and hence, it is requested to maximize the Soluble yield with minimum energy requirement from a practical viewpoint. Since the largest energy consumption of this extraction method comes from the separation of Soluble from solvent, it is essential to minimize the solvent to Soluble ratio before separating Soluble from the solvent. On the other hand, a large solvent to biomass ratio is required to disperse the biomass in the solvent during the solvent treatment at around 350 °C. To compromise the conflicting demands and to minimize the solvent to Soluble ratio, a new operating scheme, which uses the Soluble–solvent mixture repeatedly before separating Soluble from the solvent by replacing around 10% of the mixture by fresh solvent on every solvent treatment, was proposed. The validity of this operating scheme was examined by treating Thai rice straw (RS) with a general-purpose petroleum based solvent called A150 through 10 repeated uses of the Soluble–A150 mixture. It was found that the new operation scheme was effective from the viewpoints of quality and the yield of the Soluble produced.

Degradative solvent extraction of low-rank coals by the mixture of low molecular weight extract and solvent as recycled solvent

The authors have proposed a degradative solvent extraction method to dewater, upgrade and separate low-rank coals to upgraded coal, high molecular weight extract (Deposit), low molecular weight extract (Soluble), and a little amount of liquid and gas products. For the practical application of this extraction method, the solvent must be recycled. Furthermore, the separation of the Soluble and solvent, which was implemented by distillation, consumed much energy and added the cost of the whole system significantly. In order to solve these issues, the utilization of the Soluble and solvent as the recycled mixture solvent was proposed and investigated in this work. The results showed that the yields of the Deposit increased by more than two times with the mixture solvent recycle, and got almost stable after 5–7 extraction cycles. This made up for the loss of the part of the extraction product (Soluble) to a large extent. Furthermore, the ratios of O/C, N/C, and S/C of the Deposit decreased with the mixture solvent recycle, indicating that the Deposit was further upgraded. The aromaticity and reactivity of the Deposit decreased and increased with the mixture solvent recycle, respectively. The Cal/Car of the Deposits ranged from 0.35 to 0.84. The ash content of the Deposit increased slightly from 0.25% to 0.29%, and then got almost constant after 4 times of the mixture solvent recycle. Only 0.2–0.4% of the main inorganic elements were transformed from raw coal to the Deposit. The main inorganic elements in the Deposit were Si, Al and Fe. The relatively high contents of some inorganic elements in the Deposit were caused by their high contents and existing form in the raw coal. Thus, it was showed that using the Soluble and solvent as recycled mixture solvent is a feasible way for the practical application of the degradative solvent extraction of low-rank coals.

Effect of Solvent on the Degradative Solvent Extraction of Low Rank Coal

We have proposed a degradative solvent extraction method which upgrades as well as dewaters low rank coals and biomass wastes at 350 °C using 1-methlynaphthalene as a model solvent. The proposed solvent treatment is an effective method to produce high quality extracts having similar physical and chemical properties from several kinds of low rank coals and biomasses. Three solid fractions (Residue, Deposit, and Soluble) were fractionated and recovered after the solvent extraction. Soluble and Deposit are expected to be precursors for producing value added products. In this work the effects of solvent on the degradative solvent extraction of two low-rank coals, Loy Yang (LY) and Pendopo (PD), were examined by using four solvents: 1-methylnaphthalene (1-MN), kerosene, a 1 to 1 mixture of 1-MN and kerosene, and a solvent rich in alkyl benzenes, A150. It was judged that the solvent does not affect the degradation reaction at 350 °C, and hence the performance of this degradative solvent extraction method such as selective deoxygenation and effective dewatering is realized by all of the solvents used. The yield distributions of extracted products were dominated by the solubility of solvent used as expected. The Hildebrand regular solution theory seems to represent the differences in the yields and elemental compositions of Soluble fractions. 1-MN, having 21.3 (J/cm3)1/2 of solubility parameter δ, gave the largest yield of Soluble followed by A150 (δ ≅ 18.8 (J/cm3)1/2), the mixed solvent (δ ≅ 19.1 (J/cm3)1/2), and kerosene (δ ≅ 16.7 (J/cm3)1/2). Preparation of solvent treated coals (STCs) from different solvents gave the yields close to the sum of the yields of Soluble, Deposit, and Residue for all solvents used. Most of the heating values of solid products were over 29 MJ/kg and rather close to subbituminous coal. All Solubles were found to melt completely at rather low temperature. The properties of Solubles can be changed by solvents used. It was found that A150 may be utilized as a practical solvent when Soluble is the target product and that kerosene is expected to be a practical solvent for preparing STC from low-rank coal.

Modeling and Kinetic Study of Degradative Solvent Extraction of Biomass Wastes

The degradative solvent extraction (DSE) has been found to be an effective method to convert and upgrade biomass wastes into high-quality extracts with various applications. However, the reaction pathways and kinetics of this DSE process are still not clear and need to be clarified. Hence, in this study, the biomass was treated in 1-methylnaphthalene at various conditions (300–350 °C and 0–90 min) by the DSE method and separated into five products: residue (unreacted biomass), two extracts (deposit and soluble), liquid, and gas. A lumped reaction model was proposed to simulate this biomass DSE process. The kinetic parameters were estimated by the least squares fit based on the experimental data and the model, which was optimized by the MATLAB optimization program. The results showed that the proposed model was valid and well-capable of describing the biomass DSE process. It can be concluded that different conversion pathways existed at 300 and 350 °C. At 300 °C, the dominant reactions were the conversion ...

Conversion of Biomass into High-Quality Bio-oils by Degradative Solvent Extraction Combined with Subsequent Pyrolysis

The rapid depletion of fossil fuels has attracted more attention being geared toward the fast pyrolysis of biomass to produce bio-oils. However, the produced bio-oils usually contain high water, oxygen, and acid contents and low calorific values, which have limited their wide application. Therefore, in this study, a novel two-stage method combining degradative solvent extraction with subsequent pyrolysis was proposed to improve the quality of derived bio-oils. The raw biomass was initially dewatered and deoxygenated using a degradative solvent extraction method to obtain a low-molecular-weight extract (named “Soluble”). The Solubles were then pyrolyzed at 500 °C to prepare bio-oils. The carbon contents and calorific values of bio-oils produced from the Solubles were as high as 90.09% and 44.63 MJ/kg, respectively, which were 1.5–2.0 times higher than those from the raw biomasses. In addition, the water and oxygen contents of bio-oils from the Solubles were significantly lower than the bio-oils from the ra...

Mechanism study of degradative solvent extraction of biomass

We have recently proposed a novel and effective degradative solvent extraction method to upgrade and convert various types of biomass feedstocks into high-grade carbonaceous materials under rather mild conditions. The feasibility of this method has been preliminarily proven in our previous work. However, the conversion mechanism of this process remains unknown. Hence, in this study the conversion process of the degradative solvent extraction of biomass was investigated in detail. A typical biomass (fir sawdust) was treated in 1-methylnaphthalene at 350°C with the residence time from 0 to 90min. Three solid products, which were the fraction soluble in the solvent at room temperature (termed Soluble), the fraction soluble in the solvent at treatment temperature but insoluble at room temperature (Deposit) and the unextractable fraction (Residue), were obtained. The products were then characterized by various analysis methods in detail. The oxygen, carbon and minerals in the raw biomass were mainly recovered as CO2/H2O, Deposit/Soluble, and Residue, respectively. With the residence time increasing from 0 to 45min, the soluble yields increased obviously but the deposit yields decreased significantly. The yield variations of the Solubles and Deposits obtained at residence time longer than 45min were not significant. The chemical structure and properties of Solubles were independent of the residence time, while those of Deposits varied obviously with residence time. According to the results, the conversion process of the degradative solvent extraction of biomass was proposed. The process can be divided into two stages. The first stage took place at heating up stage from 250 to 350°C and the beginning of the isothermal stage at 350°C. In this stage, the thermal extraction, deoxygenation and aromatization reactions of the raw biomass occurred significantly. The main product was Deposit. The oxygen was removed as CO2 and H2O. At the second stage, the Deposit was further deoxygenated and converted into Soluble. In this stage, the Deposit underwent complex reactions, such as the cleavages of oxygen containing cross-links and slight aromatization reactions. The oxygen was mainly removed as H2O at the second stage.

Two-Stage Conversion of Low-Rank Coal or Biomass into Liquid Fuel under Mild Conditions

The authors have recently proposed a novel degradative solvent extraction method that upgrades and fractionates various types of low-rank coals or biomass wastes into several different molecular weight fractions at around 350 °C. The lowest molecular weight fraction that was recovered as solid (termed soluble) by the yield of 19.4–71.7 wt % on a carbon basis had unique and almost raw-material-independent properties: almost free from ash and moisture, average molecular weight of around 300, carbon content of as high as 81.5–84.8 wt %, and oxygen content of as low as 6.5–12.1 wt %. In this work, the combination of the proposed extraction method and the liquefaction of the soluble under mild conditions was investigated as a two-stage liquefaction method to produce liquid fuel. A rice straw (RS) and a brown coal (LY) were extracted by the proposed extraction method to produce solubles by the yields of 31.5 and 21.7 wt %, respectively. The solubles produced were then liquefied at 400 °C using FeOOH/sulfur as t...

Upgrading and multistage separation of rice straw by degradative solvent extraction

Upgrading and multi-stage separation (UMSS) of rice straw was conducted at different temperatures using 1-methylnaphthalene (1-MN) as solvent. Three main solid products were obtained: low molecular weight extract (soluble), high molecular weight extract (deposit) and extraction residue (residue). The elemental composition, chemical structure and physicochemical characteristic of each component were analyzed in detail. Alkali and alkaline earth metal (AAEM) contents of solid products and rice straw were also measured by ICP-MS. The results showed the yield of soluble increased with temperature, and the carbon-based yield of soluble reached 33.48% at 350°C. The carbon content and oxygen content of three solid products (soluble, deposit, and residue) increased and decreased with temperature, respectively. The carbon content of soluble and deposit reached up to 82.36% and 80.59% respectively. Meanwhile the oxygen contents of them were as low as 9.50% and 12.03% respectively. More than 86.99% oxygen of rice straw was removed as H2O and CO2. Soluble was almost free from ash, and the ash content of deposit was also less than 1.50%. The higher heating values (HHV) of three solid products were significantly higher than that of rice straw. The FT-IR results indicated that not only dehydration reaction and decarboxylation reaction occurred, but also including obvious aromatization reaction. The contents of Na, Mg and K of soluble and deposit were extremely low, and they decreased with temperature gradually. In conclusion, the degradative solvent extraction method realized dehydration, deoxygenation and multistage separation of biomass under mild condition, and obtained a variety of products of low ash and oxygen content as well as high carbon content and HHV.

Enhancement of Gasification Reactivity of Low-Rank Coal through High-Temperature Solvent Treatment

We have recently proposed a degradative solvent extraction method to upgrade and fractionate various types of low-rank coals by a nonpolar solvent at temperatures below 350 °C. The main products obtained are solvent-soluble fractions (extracts) and an insoluble fraction, which we call “upgraded coal (UC)”. The UC samples were prepared from eight low-rank coals and one bituminous coal in this work. It was found that the gasification reactivities of the UC chars prepared from seven coals of the eight low-rank coals were larger than those of the raw coal chars. The CO2 gasification rates of the UC chars prepared from an Australian brown coal, Loy Yang (LY/UC), and an Australian bituminous coal, Gregory (GR/UC), were surprisingly larger than the gasification rates of the corresponding raw coal chars by 2.4–1.9 times. The mechanism of gasification reactivity enhancement was examined from the viewpoints of the catalytic effect of coal inherent minerals, pore surface area, and carbon structure of the chars. The ...

Degradative solvent extraction of demineralized and ion-exchanged low-rank coals

Dehydration and upgrading are essential pretreatment methods for efficient utilization of low-rank coal. In previous works the authors employed degradative solvent extraction method to dehydrate and upgrade low-rank coals and fractionate them into several fractions. For further study of this method, two low-rank coals (MM and LY) were pretreated by acid washing for demineralization or acid washing and Na/Co ion-exchange. The pretreated and raw coals were then extracted by 1-methylnaphthalene (1-MN) at 350°C and fractionated into upgraded coal (UC), high molecular weight extract (deposit), low molecular weight extract (soluble), as well as a little H2O and gas products. The results show that both acid washing and ion-exchange enhance the yields and carbon contents of the two extracts. Ion-exchange obviously promotes the removal of oxygen-containing functional group during extraction. The yield of high molecular weight extract of demineralized MM increases from 3.5% to 9.5%, and the carbon content and oxygen content of low molecular weight extract of Na ion-exchanged LY are as high as 85.3% and less than 6.4%, respectively. Ion-exchange has a distinct influence on physical and chemical properties of the extracts. The influence of Na ion-exchange is especially remarkable. Thus, demineralization and ion-exchange have evident promotion for the degradative solvent extraction of low-rank coal.

Preparation of High-Grade Carbonaceous Materials Having Similar Chemical and Physical Properties from Various Low-Rank Coals by Degradative Solvent Extraction

Eight kinds of low-rank coals including lignites and sub-bituminous coals were subjected to a degradative solvent extraction method that treats carbonaceous resources in a non-hydrogen donor at around 350 °C. The low-rank coals were separated into the residue which cannot be extracted by solvent at 350 °C (termed residue), the fraction which can be extracted at 350 °C but precipitates from solvent at room temperature (deposit), the fraction which is solvent soluble even at room temperature (soluble), and liquid fraction mainly consisting of water and gaseous products mainly consisting of CO2. The soluble fraction was finally recovered as solid by removing solvent. The moisture of the coals was completely removed without phase change, and the ash was almost completely concentrated in the residue. The carbon based yields of the three solid fractions were 19.4–31.2% as solubles, 4.2–16.8% as deposits, and 54.7–69.2% as residues when 1-methylnaphthalene was used as the non-hydrogen donor solvent. Overall, more than 94.4% of carbon was recovered as solid fractions. Meanwhile 30.5–54.9% of oxygen was removed as either H2O or CO2. The interesting findings were that the solubles and deposits obtained from all of the coals were respectively very close to each other in elemental composition, chemical structure, molecular weight distribution, thermal decomposition behavior, and thermoplastic behavior. Elemental compositions of solubles were C = 81.8–84.8 wt %, H = 7.5–8.1 wt %, and O = 6.5–10.2 wt %, which were rather close to the elemental composition of bituminous coal. Thus, the degradative solvent extraction method was found to be effective in converting various types of low-rank coals into residues and compounds having very similar chemical and physical properties without losing heating values. Detailed characterization of the solid fractions showed potential utility of the fractions as solid fuel or precursors of chemicals and carbon materials.