Lignite Liquefaction Research Articles

Deduction of lignite liquefaction mechanism based on carbon structure analysis and free radical determination

The liquefaction performance of lignite is closely related to its structural evolution. The carbon structure and the free radical concentrations of Naomaohu (NMH) coal and liquefaction products were characterized by modified nuclear magnetic resonance (NMR) spectroscopy and electron paramagnetic resonance (EPR), respectively. The results showed that the oil yield increased gradually with the increase in temperature, and it reached a maximum of 64.91% at 430 °C. The carbon spectrum of the liquefied oil showed that the increase in temperature had little effect on the aromatic carbon connected with the aliphatic carbon, but had a greater effect on the aromatic proton carbon of the liquefied oil. The stability of aromatic carbon in asphaltene was greater than that of aliphatic carbon, and the temperature rise had a significant impact on the different types of aliphatic carbon of the asphaltene. The aromatic side chain of asphaltene gradually broke, and the bridgehead carbon content of the aromatic carbon increased due to the intensification of the condensation reaction at high temperature. On the other hand, the concentration of free radicals in liquefied oil increased with temperature, while the concentration of free radicals in asphaltene first increased and then decreased with temperature, indicating a positive correlation between its change trend and respective yield. With the increase in temperature, the aromatic ring substances with strong bond energy were gradually opened, the side chains were broken, thus forming more low molecular compounds. In summary, based on the above changes in the carbon structure and free radicals, the lignite pyrolysis and liquefaction mechanism have been deduced at the molecular level.

Hydrocarbon Fuels from Sequential Hydrothermal Liquefaction (HTL) of Lignite and Catalytic Upgrading of Crude Oil

Hydrocarbon Fuels from Sequential Hydrothermal Liquefaction (HTL) of Lignite and Catalytic Upgrading of Crude Oil

Study on liquefaction characteristics of lignite in CO atmosphere

This article investigated the interaction mechanism between carbon monoxide (CO) and lignite organic matter in lignite liquefaction systems. The study found that a CO atmosphere can facilitate lignite conversion, but its hydrogen supply capacity is poor, resulting in lower liquefaction effects compared to an H2 atmosphere. Increasing the initial reaction pressure and CO content can enhance the conversion of lignite to low molecular compounds. In-situ studies on lignite pyrolysis in CO and N2 atmospheres show that CO plays an effective role in promoting the fracture of multiple hydrogen bonds present in lignite, which is linked to the water-gas shift reaction that CO takes part. Additionally, CO can also facilitate the breaking of oxygen-containing ether bonds in lignite, thereby eliminating oxygen and producing CO2 in the gaseous phase. Density functional theory (DFT) calculations demonstrate that CO reacts with the group after the ether bond breaks, which reduces the formation energy of the product and promotes the ether bond breaking. In summary, CO in syngas may benefit the breaking of ether and hydrogen bonds in lignite during liquefaction, thus promoting lignite conversion.

Direct liquefaction of low rank lignite with peach seed kernel and waste polypropylene for alternative fuel production

In this study, alternative fuel potentials to petroleum were investigated by direct liquefaction of peach seed kernel (PSK), Muğla-Yatağan lignite (MYL) and waste polypropylene (wPP) separately and together. The effects of PSK and wPP on the yield and selectivity of oil products obtained by direct liquefaction of MYL were also examined. Direct liquefaction experiments were performed in a batch reactor at 1/3 solid/solvent, reaction temperature of 400 °C and reaction time of 60 min. The highest total conversion and oil + gas yield were 95% and 85% direct liquefaction of wPP, respectively. According to the calorific value analysis of the chars, the highest gross calorific value of chars was 7709 cal/g in the liquefaction of PSK, and the lowest net calorific value was 2783 cal/g in the liquefaction of MYL. PSK and wPP increased oil yield of MLY from 28% to 60% and 68%, respectively. According to the GC-MS analysis of oils (light liquid products), alternative fuels to gasoline can be produced by direct liquefaction of PSK, wPP and wPP/MYL. Alternative fuels to diesel can be produced by direct liquefaction of MYL and PSK/MYL. The co-liquefaction of MYL with wPP and PSK improved the yield and product components of the oils. The oil + gas yield of MYL was approximately increased PSK by 12% and wPP by 6%.

Effect of catalyst and atmosphere on liquefaction performance of the lignite in optimized two-stage liquefaction process

Since most oxygen containing structures in lignite will break at relatively low temperature and macromolecular structure will pyrolyze at higher temperatures, two-stage liquefaction process is proposed to obtain better liquefaction performance and reduce energy consumption. Different collocations of catalyst and atmosphere were examined and results showed that the total conversion and oil yield could increase with a percentage of 8.12% and 14.04% in maximum. The collocation of CO atmosphere and sodium carbonade had the best adaptability to moisture and a relatively good liquefaction performance. The effect of sodium carbonade on product conversion and feasibility of replacing hydrogen with CO or syngas were discussed. This work is proposing solutions for lignite liquefaction to strengthen the efficient use of low-rank coal resources.

Investigation of the liquefaction possibility of Ermenek lignite as an alternative clean energy source

Coal liquefaction; can be defined as the transformation of coal into products that have a high energy density, can be easily stored and transported and do not create environmental pollution, to meet both fuel and chemical raw material requirements.
 This study was carried out to determine the yields of the products formed as a result of the liquefaction of Konya-Ermenek lignite in the N2 atmosphere and under non-catalytic conditions. Proximate and ultimate analysis of the obtained solid and liquid products was made. The composition of the oil product was determined by GC-MS. As a result of liquefaction, the char yield was 71.37%, the preasphaltene yield was 12.24%, the asphaltene yield was 2.23% and the oil + gas yield was 14.16%. It was determined that the higher heating value of 4199 kcal/kg in raw lignite is twice as high in liquefaction products. It was determined that the sulfur content of 3.94% in raw lignite decreased to 1.54%, 0.85% and 0.44% in char, preasphaltene and oil, respectively.

Preliminary investigations on the catalytic hydrogenation of polycyclic aromatic hydrocarbons via WGSR

The water-gas shift reaction (WGSR) is a crucial reaction in the direct liquefaction of lignite in a syngas (CO + H2) system. In this study, anthracene was utilized as a polycyclic model compound of lignite, to which hydrogen is donated by the H2/D2 produced from CO and H2O/D2O via the WGSR. The results show that the model compound of the polycyclic aromatic hydrocarbon in coal (anthracene) undergoes partial cracking and polycondensation under non-hydrogen-donor conditions at 400 °C. In addition, WGSR catalyzed by NiO can generate hydrogen for the hydrogenation of anthracene. Comparing the mass spectra of deuterated products with those of conventional hydrogenation products by isotope labeling, the alkyl side chain positions of toluene, 1,4-xylene, methylnaphthalene, 1,1-diphenylethylene, methylanthracene and other compounds are prone to deuteration, enabling speculation of the main hydrogenation route of anthracene, which provides theoretical support for the catalytic hydrogenation in direct liquefaction of lignite in a syngas (CO + H2) system.

Investigation of the improvement of Sivas-Kangal lignites liquefaction product yields

In recent years, converting and using coal into the most suitable product according to its properties has emerged as a modern approach. Among the main processes applied to coal are low and high-temperature carbonization, gasification and liquefaction. In coal liquefaction, coal is broken down into free radicals using hydrogen donor solvent and catalyst under high temperature and pressure conditions. Later, these radicals can be used in the production of both liquid fuel and chemical raw materials by being saturated with hydrogen. This study aims to improve the yields of Sivas-Kangal lignite liquefaction products (char, preasphaltene, asphaltene, oil-gas). For this purpose, firstly raw coal, then spiral enriched clean coal liquefaction experiments were carried out. The chemical characterizations of the obtained products were determined by proximate and ultimate analysis. The composition of the oil was identified by GC-MS. As a result of the enrichment, the char yield decreased by 16.5% whereas the oil+gas yield increased by 14.64%. Total conversion increased from 31.74% to 48.24%. It has been concluded that the enrichment process has a positive effect on the liquefaction yields.

In-situ impregnation of β-FeOOH on coal by solid-state reaction toward direct coal liquefaction

Herein, β-FeOOH nanoparticles supported on coal (β-FeOOH@C) were prepared by a solid-state in-situ impregnation and tested for the direct coal liquefaction (DCL) process. The β-FeOOH nanoparticles with ~10–50 nm were uniformly loaded over coal through a solid-state reaction among ferrous chloride, sodium hydroxide and coal. The obtained β-FeOOH@C solid showed enhanced catalytic performance for DCL compared with unsupported β-FeOOH nanoparticles. The conversion and oil yield achieved by β-FeOOH@C were 92.88 and 48.78% in the catalytic liquefaction of Dahuangshan lignite. The solid-state in-situ impregnation with coal as support shows great potential to prepare effective iron-based catalysts toward practical DCL.

Biosolubilization of low-rank coal by the newly isolated strain Streptomyces fulvissimus K59

Lignite, as low rank coal (LRC) has some disadvantages compared to hard coal, its use is limited. Therefore alternative and ecological conversion methods are being sought. Microbiological liquefaction of lignite is a clean and cost-effective technology for the treatment of solid waste resources, that allows for recovery of complex aromatic compounds from LRC. These can be further converted into products of agricultural relevance, with added value. In the presented studies 10 microbial strains were isolated from coal samples. One of the strains, identified as Streptomyces fulvissimus K59 was selected and applied in biosolubilization of coal in a liquid culture. Capacity of the K59 isolate for coal decomposition was tested in mineral medium, in modified yeast extract-peptone-glucose medium (YPG) containing 1% unprocessed carbon and in YPG with lignite treated using 2 N, 5 N and 8 N HNO3. A Plackett-Burman design was applied for the screening of influential process parameters. The most efficient biosolubilization process was achieved after substrate processing with 5 N HNO3, in the presence of 10 g/L sucrose and 50 g/L lignite, where the resultant concentration of biosolubilized lignite was 15 times higher as compared to the results obtained using crude coal.

Study on carboxyl groups in direct liquefaction of lignite: Conjoint analysis of theoretical calculations and experimental methods

In order to investigate interactions between carboxyl groups and aromatic hydrocarbons during direct coal liquefaction (DCL), tetralin (THN) and benzene (BZ) were selected to represent hydrogenated and non-hydrogenated aromatic compounds in DCL solvents, respectively. 3-phenylpropionic acid (PA) was used as model compound of fragments with carboxyl groups in lignite. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) coupled with density functional theory (DFT) calculations were employed to evaluate noncovalent interactions between carboxyl groups and aromatic compounds (THN and BZ). Results of DFT calculations were verified by ATR-FTIR. Moreover, influence of hydrogen bonds on reaction behaviors of carboxyl groups was investigated by DCL experiments of demineralized Yunnan lignite (DeYN) in THN, with or without addition of BZ. Results show that stronger hydrogen bonds exist between carboxyl groups and BZ, and consequently C–O bonds in carboxyl groups are significantly weakened, compared to THN. Presence of BZ results in decomposition of more carboxyl groups and production of less CO2, but has little effects on aromatic structure. Conclusions drawn from DCL experiments can be explained by ATR-FTIR and DFT calculations. Hydrogen bonds play crucial roles in reaction behaviors of carboxyl groups in coal-oil slurry during DCL. C–O bonds in carboxyl groups of lignite can be obviously weakened by formation of stronger hydrogen bonds. Consequently, decomposition of carboxyl groups is enhanced but generation of CO2 is suppressed.

Contribution of Lignin Peroxidase, Manganese Peroxidase, and Laccase in Lignite Degradation by Mixed White-Rot Fungi

The catalytic depolymerization of biological enzymes during biological liquefaction of coal is very important. In this study, the effects of medium types, lignite addition, and mixed culture on lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase (Lac) secreted by white-rot fungi are investigated. Fifteen strains of white-rot fungi are used for microbial liquefaction of the Zhaotong lignite in Yunnan. The results show that the activities of LiP, MnP, and Lac are highest in the Czapek-Dox medium (DOX), followed by the Sabouraud Maltose Broth (SMB) medium, and are almost zero in the Potato Dextrose Agar (PDA) medium. In the early stage of fungal growth, the medium contains sufficient nutrients, and lignite addition induces an inhibitory effect on extracellular enzyme secretion, whereas in the late growth stage characterized by nutrient deficiency, it exhibits an enhancing effect. For fungi pair combinations, if only single enzyme activity was considered, the positive synergistic effect of Lac in the mixed culture of s.commune and SL203 would be the highest, with the synergistic coefficient of 233.33. While three enzymes were considered, the integrated effects of ZTW07 and SL203 are the highest, with Lac, MnP, and LiP producing synergistic coefficients of 158.795, 1.217, and 1.006, respectively. It can be seen that the mixed culture can greatly improve the enzyme activity of white rot fungi and is one of the effective methods to improve the liquefaction efficiency.

A STUDY ON THE INVESTIGATION OF IMPROVEMENT IN COAL LIQUEFACTION PRODUCT EFFICIENCY

The aim of this study is to improvement the yields of Malatya-Arguvan lignite liquefaction products (char, preasphaltene, asphaltene, oil-gas). For this purpose, the liquefaction experiments of coal which firstly raw and then enriched by spiral have been carried out. The chemical characterizations of the obtained products were determined by proximate and ultimate analysis. The composition of the oil was identified by GC-MS. As a result of the enrichment, the char yield decreased by 9.28% whereas the preasphaltene yield increased by 5.31% and the oil + gas yield increased by 4.18%. Total conversion increased from 47.57% to 56.85%. It has been concluded that the enrichment process has a positive effect on the liquefaction yields.

Research on a Mixed Culture Technique of the White Rot Fungi Effect of Extracellular Lignin Peroxidase on Lignite Liquefaction

In order to improve the efficiency of lignite liquefaction, white rot fungi mixed culture technology was applied. Firstly, 15 fungi were used to liquefy Zhaotong lignite. The results show that there is a good linear relationship between liquefaction effect and lignin peroxidase (LiP). But the low activity of LiP is the barrier in real practice. Five strains with the highest LiP activity for combinatorial culture suggested that mixed strains culture is an effective way to improve LiP activity and liquefaction effect, and the average enzyme activity is 76.28 U/L. While the single strain is only 19.24 U/L. Besides, in 10 mixed strains cultures, four of them showing obvious synergy and the one with maximum enzyme activity has increased by 6.7 times. The analysis of lignite and liquefaction products by using 13C NMR shows that the aromatic carbon (fa) decreases, and the phenol or aromatic ether carbon (faP) and oxygen linked fatty carbon (falO) increase, which proves that LiP has undergone ring-opening, oxidation and other reactions in lignite liquefaction.

Understanding the liquefaction mechanism of Beypazarı lignite in tetralin with ultraviolet irradiation using discrete time models

This study has proposed four different liquefaction models consisting of both reversible and irreversible reaction steps with three lumped parameters, asphaltenes, preasphaltenes, and oils, for the liquefaction of Turkish lignite (Beypazarı-Çayırhan). The coal had been liquefied in tetralin using a solvent/coal ratio of 5/1 at four different ultraviolet irradiation light sources of 90, 120, 150, and 180 W. The validity of the proposed models is specified by first order linear discrete-time models with the experimental data. Furthermore, the reaction rates of the proposed liquefaction models are determined using a Matlab program with the use of Kalman filter. The validation of proposed models for the liquefaction of Beypazarı lignite is defined using the sum of the squared differences of the models and experimental data. The results demonstrate that models which consist of reversible steps provide a better fit with experimental data compared to models consisting of irreversible steps. While the liquefaction step from reactive coal to oils demonstrates a maximum reaction rate constant of 2*10−2 h−1, the other steps from reactive coal to either preasphaltenes or asphaltenes show lower reaction rate constants, about 1*10−2 h−1. In addition to the fact that the formation of preasphaltenes and asphaltenes from reactive coal takes place slowly, a major proportion of the oils are formed directly from reactive coal.

Comparative Study of the Catalytic Performances of Na2CO3 and γ-FeOOH in Hydroliquefaction To Propose a Two-Stage Lignite Catalytic Liquefaction Process

High oxygen content in lignite increases hydrogen consumption during hydroliquefaction, and simultaneously the produced water decreases hydrogen partial pressure, which negatively affects lignite liquefaction behaviors. Therefore, the liquefaction performances and oxygen-removal behaviors of Xilinhaote (XL) lignite during liquefaction at different temperatures in the presence of Na2CO3 (NC) and FeOOH (FO) were investigated. Results showed that the oxygen contents of liquefaction residues (LRs) obtained at 330–380 °C were 9.37–13.84% without catalyst and decreased to 7.90–13.02% and 6.38–11.73% with the addition of FO and NC, respectively. The addition of NC could promote the polarized breakdown of aromatic Caryl–Calkyl ether bonds via ionic pathways in the presence of water, which facilitated the depolymerization of lignite macromolecular structures, resulting in significant increase in coal conversions at 330–380 °C. To enhance liquefaction performance, an optimized two-stage catalytic liquefaction process for lignite with high oxygen content was proposed, which integrated the deoxygenation treatment of lignite over Na2CO3 and the hydrogenation of Na2CO3-treated lignite over iron catalyst. In the two-stage catalytic liquefaction processes, coal conversions and oil yields significantly increased to 90.66–92.73% and 52.73–57.56%, respectively, compared to 84.61% and 43.52% in single-stage liquefaction of XL over FO at 450 °C. Furthermore, in the two-stage catalytic liquefaction process, the treatment of XL over NC in stage I presented higher coal conversion (92.73%) and oil yield (57.56%) than those over FO in stage I (90.66% and 52.73%). Surprisingly, H2 consumption of the former (2.17%) was lower than that of the latter (2.91%).

Study on the thermal liquefaction of Xilinguole lignite in solvent at high temperature

In this paper, thermal liquefaction (TL) of Xilinguole lignite (XL) in the range of 400–540 °C have been carried out in toluene, tetralin (THN) and their mixed solvent, respectively. Results indicated that the conversion of XL primarily depends on the hydrogen donor ability of solvent. The highest conversions of XL in toluene and THN were obtained at 480 °C, which are 25.8% and 98.6%, respectively. The condensation of pyrolytic free radicals dominates the TL in toluene solvent but there is hardly obvious coking occurred in THN at below 510 °C. In toluene and THN mixed solvent, the conversion of XL increases with the THN content. The products of TL in toluene mainly consist of oil and gas (O + G) fraction, but the asphaltene (AS) and preasphaltene (PA) factions prevail in the products of TL in THN. Hydrogen donor solvent has obvious improvement on the deoxygenation in the TL process. Therefore, TL in hydrogen donor solvent is a potential conversion technology of XL due to low reaction pressure and without H2 and catalyst used.

A Preliminary investigation of CO effects on lignite liquefaction process

This paper made a preliminary investigation of CO effects on lignite liquefaction process. The Schütze method coupled with an elemental analyzer was adopted for directly determining the O contents of liquid and solid materials, and the O balance, variation amounts of water, and CO consumptions were calculated quantitatively for liquefaction processes. It was found that the two reactions which were the water-gas shift reaction and the reaction between CO and organic structures of coals, occurred distinctly in the liquefaction process with CO atmospheres, and were simultaneously strengthened by the catalysts. The simultaneous occurrence of the two reactions played the roles of reducing the water production, elevating the coal conversion, and promoting the asphaltene (AS) and preasphaltene (PA) production.

Catalytic Liquefaction of Lignite by Supercritical Ethanol

Catalytic hydrogenation liquefaction by supercritical ethanol is an effective method for the efficient utilization of lignite. The liquefaction efficiencies of lignite 1(L1) and lignite 2(L2),which were collected from Zhaotong, Yunnan, were compared. It was found that the liquefaction efficiency of L1 was better than L2 but the gas yield of L2 was higher than L1 under the same reaction conditions, indicating that both of them could be effectively conversed. The yields of lipids and phenols in the components of liquefaction products were significantly different, and the liquefaction of L2 could achieve the desired conversion effect by changing the reaction conditions. Increasing the amount of ethanol could promote liquefaction efficiency, however, when the ratio of ethanol to coal(E/C) were 20 and 30, the growth rate of the yield of liquefied oil was quite lower than the previous stages. This phenomenon indicated that with the decrease of lignite concentration, the mass transfer effect of ethanol as a solvent in the reaction was getting better and better, and the liquefaction rate increased rapidly. But the higher system pressure was not conducive to liquefaction in high temperature conditions. In addition, the esterification reaction between ethanol and the intermediates of hydrocracking reaction could facilitate liquefaction reaction.

Study on the preheating stage of low rank coals liquefaction: Product distribution, chemical structural change of coal and hydrogen transfer

Preheating stage of direct liquefaction of Yunnan lignite (YN) and Hami sub-bituminous coal (HM) in tetralin at temperature range of 200–350°C was investigated under nitrogen atmosphere. In order to reveal the product characteristics and hydrogen transfer between coal and solvent during preheating process, thermo-gravimetric analyzer coupled with mass spectrometer (TG–MS), X-ray photoelectron spectroscopy (XPS) and gas chromatography coupled with mass spectrometer (GC–MS) were employed. The results show that yields of light products, i.e., oil, gas, and water, increase with raising temperature during the preheating process. YN and HM achieve 51.69% and 44.19% (daf) light products yields at 350°C, respectively. Moreover, oxygen-containing functional groups, such as carboxyl, ethers, and alcohols in raw coal are reduced after preheating. In addition, hydrogen transfer achieves a perceptible extent even at 200°C and the amount of transferred hydrogen increases with raising temperature. A positive dependence of hydrogen transfer on conversion is observed during preheating stage. Comparing the two coal samples, YN obtains higher conversion and hydrogen transfer due to its higher thermal reactivity at this temperature range. However, HM achieves higher oil yield than YN does at 350°C since high hydrogen transfer amount and H/C ratio of raw coal promote the oil yield.