A new method for the alkali catalytic modification of lignite in subcritical H2O–CO systems is presented, which can greatly improve its caking properties (caking index, >90). Soxhlet extraction technology coupled with GPC (gel permeation chromatography), FTIR (Fourier transform infrared spectroscopy), and 13C-NMR (carbon-13 nuclear magnetic resonance) analysis methods were used to investigate the structural evolution and formation mechanisms of solutes of n-hexane, benzene, and tetrahydrofuran in modified coal (denoted as NS, BS, and TS, respectively), which were the main caking components in the modified lignite. The results showed that the solutes were composed of four kinds of compounds with weight-average molecular weights in the range of 1170–2900, 300–550, 190–300, and 100–150, respectively. Oxygen-containing functional groups appeared in many forms, such as phenolic OH, aliphatic OH, ether bonds, and carbonyl and carboxyl groups, but mainly existed as C–O. When the temperature was <320 °C, NS consisted of aliphatic ring compounds, while BS and TS contained some aromatics, with an average of two aromatic rings per cluster in both. The appearance of monocyclic aromatic structures in the solutes occurred in the 320–330 °C temperature range, with one to three aromatic rings in the BS clusters, while polycyclic aromatic structures with more than five rings appeared in TS. The statistical structural models of the solutes all contained polycyclic aliphatic/aromatic structures as their main bodies, connected with substituents such as monocyclic aromatic structures, aliphatic side chains, and oxygen-containing functional groups. They are consistent with the structure of caking components in caking coal. The formation of caking components in modified lignite therefore underwent four distinct stages: separation of primary solutes, formation of pyrolysis solutes, formation of hydrogenated solutes, and formation of polycondensation solutes. This study provides valuable insights into the caking transition of modified coal and a basis for the high-added value utilization of lignite.

The hydrogen transfer reaction is one of the key chemical processes of coal conversion. The elucidation of the hydrogen transfer mechanism is essential for rational control of the properties and distribution of products. This paper is focused on the hydrogen transfer mechanism of lignite modification in a subcritical D2O–CO system. Using Soxhlet extraction, isotope ratio mass spectrometry, 1H nuclear magnetic resonance, and pyrolysis–gas chromatography–mass spectrometry (Py-GCMS), the deuterium transfer routes in deuterated products and their representative structures were studied. The existing form of deuterium in deuterated products was also proposed. The results showed that the subcritical D2O–CO system can generate active deuterium, which combines with the free radical fragments resulting from coal pyrolysis to form three kinds of deuterated products: n-hexane solute (NS-D), benzene solute (BS-D), and tetrahydrofuran solute (TS-D). Deuterium in the three solutes migrates in the order TS-D → BS-D → NS-D. It was observed that the active deuterium is not transferred to the β sites of the solutes but rather to their ar, α,2, α, and γ sites. Py-GCMS detection results showed that the solutes mainly consist of six representative structures, that is, monocyclic and polycyclic aromatics, alkenes, alkanes, alcohols, and esters. In the modification process, deuterium is incorporated into the monocyclic aromatic structures in the aliphatic side chains first and then in the aromatic ring. For the polycyclic aromatic structures, the active deuterium enters the side chain first and then the aromatic ring having that side chain. A small amount of active deuterium can be incorporated into the alkene and alkane structures directly. However, it mainly transfers to such structures indirectly through thermal cracking of deuterium-containing macromolecular aromatic structures. Active deuterium reduces oxygen in the oxygen-containing structures to form OD or DHO, yet it cannot easily enter the aliphatic and aromatic structures linked to the oxygen-containing structures. This research provides a new perspective for the study of hydrogen transfer routes and can serve as a reference for discussing the molecular mechanisms involved in various coal conversion processes.

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Objectives/Scope As one of the largest emitters in the world, the oil and gas industry needs more efforts on greenhouse gas reduction. Methane, as a potent greenhouse gas, could largely determine whether natural gas could serve as a bridging energy towards a sustainable future. In the past decade, the oil and gas companies in China has significantly enhanced casing gas recovery and reduced large volume of flaring (&gt;20k m3/day). However, the remaining low- to mid- volume flaring gas were left for further recovery. Methods, Procedures, Process Shale gas production in China has met a surge in the number of drilling wells. Those new wells were characterized by a relatively low gas production rate (&lt;1 mill m3/day), in comparison with the shale gas well in the US. As a result, flaring gas during well completion needs to be recycled or used so as to enhance the gas recovery rate. In this study, a pilot demonstration project of flaring gas recovery was carried out to reduce greenhouse gas emission in Weiyuan shale gas region in Sichuan province, China. The technical route of dehydration and natural gas compression was adopted. The recycled natural gas was transformed into compressed natural gas (CNG) and transported to the nearest CNG station for further use. Results, Observations, Conclusions The inlet gas pressure were between 2.85 to 5.82 MPa and the outlet pressure were kept stable around 20 MPa to meet the standard of CNG. The minimum dew point temperature was -65.5 °C and the outlet temperature rise remained below 23 °C. The manufactured device also showed a sound flexibility with recover rate between 523.22 to 1224.38 m3/h, which was the 28% to 157% of the designed capacity. An overall of 21k of natural gas was recoverd. Novel/Additive Information For a single well completion event, a total of 50k of natural gas could be recovered by this device. The device applied in the pilot demonstration has well matched with the local transportation, gas composition, and surface engineering of the well completion and has the potential of popularization and application in the shale gas region in Sichuan. In that case, it could reach a future economic return over 0.6 billion RMB.

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