Extraction and sequential elution of a heavy oil from direct coal liquefaction

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Extraction and sequential elution of a heavy oil from direct coal liquefaction Hua-Shuai Gaoa, Zhi-Min Zonga, , Zheng Yanga, Li-Li Huanga, Min Zhanga, Dao-Guang Tenga, Xian-Yong Weia,b ⁎

a b

Key Laboratory of Coal Processing and Efficient Utilization, Ministry of Education, China University of Mining & Technology, Xuzhou 221116, Jiangsu, China State Key Laboratory of High-efficiency Utilization and Green Chemical Enginneering, Ningxia University, Yinchuan 750021, Ningxia, China

ARTICLE INFO

ABSTRACT

Keywords: Direct coal liquefaction residue Microwave-assisted extraction Sequential elution

Microwave-assisted extraction (MWAE) with CH3OH and sequential elution (SE) of a heavy oil (HO) from direct coal liquefaction of Heishan bituminous coal combined with subsequent analyses were conducted to understand the molecular composition of the HO and to explore the possibility of separating pure condensed arenes (CAs) from the HO. The yield of extractable portion (EP) from the HO by the MWAE is 94.2% and the main gas chromatograph/mass spectrometer (GC/MS)-detectable compounds in EP are CAs, especially tricyclic and tetracyclic arenes, along with small amount of normal alkanes. By the SE, much more other types of compounds, e.g., oxygen-, nitrogen-, or sulfur-containning organic compounds, were detected with GC/MS, and pyrene and 1methylpyrene were separated in the purities of 95.2% and 93.4%, respectively.

1. Introduction

2. Experimental procedure

Direct coal liquefaction (DCL) produces light oil, heavy oil (HO), and DCL residue (DCLR) [1–4]. Both HO and DCLR are heavy mixtures (HMs). Related investigations include hydrogenolysis after pretreatment by oxidation [5], hydrotreatment [6,7], and hydrogenation [8–10], but such hydroconversions face difficulties in carbon deposit on the catalyst used. Since HO is rich in condensed aromatics, especially condensed arenes (CAs), and many of the CAs are value-added chemicals because of their unique properties in the scientific areas [11–19], understanding the molecular composition (MC) of HO and separating CAs from HO are of great importance. Ionic liquids [20] and supercritical fluids [21,22] were used to extract valuable components from DCLR, but obtaining pure compounds from either DCLR or HO faces a huge challenge due to their complex MCs. Sequential separation is a feasible approach for the insight into the MC in HMs [23–27]. Herein, microwave-assisted extraction (MWAE) with CH3OH and sequential elution (SE) through a silica gel column were used to isolate a HO and to reveal the MC of the HO by subsequent analysis. Subsequent SE through a gelatin column was adopted to obtain relatively pure pyrene and 1-methylpyrene (1-MP).

2.1. Materials

⁎

The HO is a fraction distilled in the temperature range of 360–380 °C from the reaction mixture of Heishan (Xinjiang, China) bituminous coal liquefaction and denoted as HODCL for convenience in description. CH3COCH3, CS2, CHCl3, CH3OH, petroleum ether (PE, b.p. 60–90 °C), silica gel (SG, 60–100 mesh), and Sephadex LH-20 gelatin are analytical reagents purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). SG was baked at 100–120 °C for 0.5 h before use and Sephadex LH-20 gelatin was swelled in CH3OH for more than 3 h prior to use. 2.2. Separation process As Fig. S1 and Table S1 in the Supplementary material show, pyrene and 1-methylpyrene are the most abundant 2 compounds in HODCL. The separation process of HODCL includes MWAE and SE (Fig. 1). In detail, 4.8974 g HODCL was extracted with 20 mL CH3OH at 35 °C for 0.5 h under microwave irradiation (3 W) using a CEM Discover SP system. The

Corresponding author. E-mail address: [email protected] (Z.-M. Zong).

https://doi.org/10.1016/j.fuel.2019.116319 Received 16 December 2018; Received in revised form 30 August 2019; Accepted 28 September 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.

Please cite this article as: Hua-Shuai Gao, et al., Fuel, https://doi.org/10.1016/j.fuel.2019.116319

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Nomenclature

IEP MC 1-MP MPRE NCAs NMRs PE PRE R1 R2 R3 R4 R5 R1-1 R1-2 R1-3 R1-4 R1-5 R2-1 R2-2 R2-3 R2-4 R2-5 RC SE SG TIC VR

AC AR CAs CP CMP CMPcp

absolute content aromatic ring condensed arenes crude pyrene crude 1-MP crude 1-MP from CP elution with CH3OH/CHCl3 (VR of 4:1) DCL direct coal liquefaction E1 eluate from EP with PE eluate from R1 with PE/EA (VR of 1:1) E2 E3 eluate from R2 with PE/EA (VR of 1:2) eluate from R3 with CH3COCH3 E4 E5 eluate from R4 with CH3OH EA ethyl acetate EP extractable portion ES effluent solution ES1-1-ES1-4 ES from E1 elution with CH3OH/CHCl3 (VR of 1:1) ES2-1-ES2-5 ES from E1 elution with CH3OH/CHCl3 (VR of 4:1) GC/MS gas chromatograph/mass spectrometer GPC gelatin-packed column HACAs heteroatom-containing condensed aromatics HACOC heteroatom-containing organic compound HMs heavy mixtures 1 H NMR 1H nuclear magnetic resonance 13 C NMR 13C nuclear magnetic resonance HODCL heavy oil from direct coal liquefaction extraction was repeated until the last extract solution turned to colorless. Then, the mixture was separated by filtration to extractable portion (EP) and inextractable portion (IEP). About 2.2647 g EP and 2 g SG were transferred into 10 mL CS2. After evaporating CS2, the EP/SG mixture was placed into a SG-packed column (50 mm inner diameter and 700 mm height). Then EP was eluted with PE to obtain eluate 1 (E1) and retentate 1 (R1), followed by eluting R1 with isometric PE/EA to obtain eluate 2 (E2) and retentate 2 (R2), eluting R2 with PE/EA volume ratio (VR) of 1:2 to obtain eluate 3 (E3) and retentate 3 (R3), eluting R3 with CH3COCH3 to

obtain eluate 4 (E4) and retentate 4 (R4), and eluting R4 with CH3OH to obtain eluate 5 (E5) and retentate 5 (R5). EP, IEP, and E1-E5 were analyzed with an Agilent 7890/5973 gas chromatograph/mass spectrometer (GC/MS) and detailed information on the analysis was introduced in the Supplementary material (Figs. S1–S6 and Tables S1–S18). About 1.0663 g E1 was dissolved in small amount of PE, transferred into a gelatin-packed column (GPC, 10 mm inner diameter and 250 mm height), and eluted with isometric CH3OH/CHCl3 to collect 240 mL effluent solution 1-1 (ES1-1), followed by eluting retentate 1-1 (R1-1) to collect 210 mL ES1-2, eluting R1-2 to collect 120 mL ES1-3, and eluting R1-3 to collect 90 mL ES1-4, as demonstrated in Fig. 2. Since the MC of ES1-3 is similar to that of ES1-4 according to the analysis with GC/MS (Fig. S8) and pyrene is predominantly abundant in both ES1-3 and ES1-4, ES1-3 and ES1-4 along with the aftermentioned ES2-4 were incorporated as crude pyrene (CP). Another 0.9364 g E1 was eluted with 4:1 (VR) of CH3OH/CHCl3 through the GPC to collect 120 mL ES2-1, followed by eluting R2-1 to

HODCL MWAE with CH3OH EP

IEP

elution with PE E1

inextractable portion molecular composition 1-methylpyrene 1-MP-rich eluent nitrogen-containing aromatics nuclear magnetic resonances petroleum ether pyrene-rich eluent retentate 1 retentate 2 retentate 3 retentate 4 retentate 5 retentate 1-1 retentate 1-2 retentate 1-3 retentate 1-4 retentate 1-5 retentate 2-1 retentate 2-2 retentate 2-3 retentate 2-4 retentate 2-5 relative content sequential elution silica gel total ion chromatogram volume ratio

R1

E1 elution with CH3OH/CHCl3 = 1 : 1 (240 mL)

elution with PE/EA = 1 : 1 E2

R2

ES1-1

elution with PE/EA = 1 : 2

E3

R3

ES1-2

elution with CH3COCH3 E4

analysis with GC/MS

R5

R1-2 elution with CH3OH/CHCl3 = 1 : 1 (120 mL)

ES1-3

R4

elution with CH3OH E5

R1-1 elution with CH3OH/CHCl3 = 1 : 1 (210 mL)

R1-3 elution with CH3OH/CHCl3 = 1 : 1 (90 mL) R1-4

ES2-4 ES1-4 ad dit ion incorporation

analysis with GC/MS

CP

Fig. 1. Procedure for MWAE of HODCL and SE of EP.

Fig. 2. Procedure for isolating CP. 2

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clusters and thereby released much more compounds from the clusters, facilitating detecting the compounds. Therefore, SE is an effective approach for understanding the detailed MCs of HMs, including HO. The most abundant compounds in the eluates is pyrene detected in E1 (Table S3). As Fig. S7 exhibits, the most abundant group component in E1 is NSCAs, followed by OAs, AAs, SNs, ASPs, and HAs, i.e., only arenes rather than any heteroatom-containing organic compound (HACOC) were eluted with PE, since the weak polarity of PE facilitates retaining the HACOCs. In contrast, ONCAs are predominantly abundant in E2, followed by amides, HAs, QMCCs, OOs, ASPs, ketones, and NSCAs. The elution of so many HACOCs is related to the addition of EA. Nitriles and amines were only detected in E3. Other group components detected in E3 are CMCCs, ONCAs, QMCCs, and NSCAs. All the nitrogen-containing species detected in the eluates contain an aromatic ring (AR) or ARs. This result indicates that more addition of EA leads to more elution of nitrogen-containing aromatics (NCAs). The π-π interactions between > C=O in EA and ARs in the NCAs along with the hydrogen bonds, such as > N-H⋯O=C < and > N-H⋯OC=O bonds between the CMCCs and EA, should be responsible for eluting the NCAs. MAs are the most abundant group components in both E4 and E5, and their elution should be caused by the π-π interactions between > C=O in both the MAs and CH3COCH3 and hydrogen bonds, i.e., > C=O⋯OH and O=CO⋯OH bonds between the MAs and CH3OH. Other group components in E4 include NAs, NSCAs, OAs, SNs, and OOs, while only OOs were detected in E5 except for the MAs.

E1 elution with CH3OH/CHCl3 = 4 : 1 (120 mL) ES2-1

R2-1 elution with CH3OH/CHCl3 = 4 : 1 (120 mL)

ES2-2

R2-2 elution with CH3OH/CHCl3 = 4 : 1 (140 mL)

ES2-3

R2-3

elution with CH3OH/CHCl3 = 4 : 1 (90 mL)

analysis with GC/MS ES2-4

R2-4 elution with CH3OH/CHCl3 = 4 : 1 (90 mL)

ES2-5

R2-5

CMP

Fig. 3. Procedure for isolating CMP.

collect 120 mL ES2-2, eluting R2-2 to collect 140 mL ES2-3, eluting R2-3 to collect 90 mL ES2-4, and eluting R2-4 to collect 90 mL ES2-5, as demonstrated in Fig. 3. According to the analysis with GC/MS shown in Fig. S9, pyrene and 1-MP are predominantly abundant in ES2-4 and ES2-5, respectively. ES2-4, ES1-3, and ES1-4 were incorporated as CP mentioned above, while ES2-5 was used as crude 1-MP (CMP). Then 0.1563 g CP was eluted with 4:1 (VR) of CH3OH/CHCl3 through the GPC to collect pyrene-rich eluent (PRE, 200 mL) and 1-MPrich eluent (MPRE, 100 mL), which was followed by mixing with 0.0964 g CMP. The mixture was also eluted with 4:1 (VR) of CH3OH/ CHCl3 to collect PRE (200 mL) and MPRE (100 mL), as demonstrated in Fig. 4. Finally, pure pyrene and 1-MP were obtained by sequential elution. The relatively pure pyrene and 1-MP were analyzed with GC/ MS and nuclear magnetic resonances (NMRs), including 1H NMR and 13 C NMR, operated at 400 MHz using DMSO‑d6 as the solvent. All the solvents were recycled.

3.2. Separation and characterization of pyrene and 1-MP Compared to isometric CH3OH/CHCl3, 4:1 (VR) of CH3OH/CHCl3 is more polar. The fact that CP and CMP tended to be eluted with isometric CH3OH/CHCl3 and 4:1 (VR) of CH3OH/CHCl3, respectively, suggest that pyrene is preferentially eluted with a weakly polar eluent and increasing the polarity of the eluent facilitates the preferent elution of 1-MP because of the stronger polarity of 1-MP than pyrene. Finally, 0.1234 g pyrene and 0.0676 g 1-MP were gathered, and both of them are light yellow crystals. The purities of pyrene and 1-MP are 95.2% and 93.4%, respectively (Fig. S10). Their structures were confirmed by their mass, 1H NMR, and 13C NMR spectra (Figs. S11–16 and Table 1).

3. Results and discussion

4. Conclusions

3.1. MCs of HODCL, EP, IEP, and E1-E5, and the mechanisms for the extraction and elutions

MWAE with CH3OH and SE along with subsequent analysis with GC/MS proved to be effective for understanding the MC of HODCL by destroying the complex molecular clusters in HODCL. As a result, HODCL mainly consists of tricyclic and tetracyclic CAs along with small amounts of NAs and pyrene and 1-MP were isolated with relatively high purities. Separating value-add chemicals from HO is an effective approach for HO application. SE is an effective approach for understanding the detailed HO. By SE, much more other types of compounds, e.g., oxygen-, nitrogen-, or sulfur-containning organic compounds are detected. The SE not only effectively released much more compounds from the clusters, facilitating detecting the compounds but also separated value-add chemicals such as pyrene and 1-MP.

The EP yield of HODCL is 94.2%, indicating that most of HODCL is extractable with CH3OH. As shown in Fig. S1 and Table S1, the MC of GC/MS-detectable compounds in HODCL is largely similar to that in EP, mainly consisting of tricyclic and tetracyclic CAs with smaller amount of normal alkanes (NAs), while IEP is only composed of NAs. The enrichment of NAs in IEP should result from the poor solubility of the NAs in CH3OH, while –OH⋯π interactions [28] between CH3OH and the CAs lead to the dissolution of the CAs in CH3OH. Pyrene and 1-MP are the most abundant 2 compounds in HODCL with the absolute contents (ACs) of 20.9% and 16.0%, respectively. The yields of E1-E5 are 56.8%, 13.2%, 2.2%, 5.7%, and 4.9%, respectively. As summarized in Figs. S2 and S6 along with Tables S2–S18, in total 63 compounds were detected in E1-E5 and the compounds can be classified into 17 group components (Table S19, in which the full names of the group components and their nomenclatures are included), whereas only 15 compounds were detected in HODCL, EP, and IEP, i.e., most of the compounds detected in E1-E5 were not detected in HODCL, EP, and IEP. The main reason could be the formation of some molecular clusters by the complex intermolecular interactions among the compounds in HODCL and EP. These clusters are less volatile so that they cannot be detected with GC/MS. The SE effectively destroyed the

CP elution with CH3OH/CHCl3 = 4 : 1 pyrene

CMPcp

CMP

elution with CH3OH/CHCl3 = 4 : 1 analysis with GC/MS H NMR and 13C NMR

1

1-MP

Fig. 4. Procedure for isolating pyrene and 1-MP. 3

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Table 1 1 H NMR and Sample

13

C NMR data of pyrene and 1-MP.

Chemical shift (ppm) 1

13

8.32 (d, J = 7.65 Hz, 4H), 8.21 (s, 4H), 8.10 (m, 2H) 8.30–8.22 (m, 3H), 8.20–8.15 (m, 2H), 8.13–8.07 (m, 2H), 8.04 (t, J = 7.64 Hz, 1H), 7.92 (d, J = 7.77 Hz, 1H), 2.91 (s, 3H)

131.08, 127.78, 126.64, 125.51, 124.25 132.63, 131.36, 130.93, 129.63, 129.05, 128.47, 127.91, 127.55, 126.77, 126.54, 125.35, 125.29, 125.24, 124.46, 124.44, 124.18, 19.77

H NMR

Pyrene 1-MP

Acknowledgements

C NMR

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