Reusability Investigation of a Ruthenium Catalyst during Ruthenium Ion-Catalyzed Oxidative Depolymerization of Lignite for the Production of Valuable Organic Acids

Abstract

A clean and efficient conversion process is essential for the utilization of low-rank coals. Lignite, a typical representative of the low-rank coal family, has huge potential for the production of valuable chemicals via the oxidative depolymerization reaction. Ruthenium ion-catalyzed oxidation (RICO) is an effective route for lignite depolymerization under mild conditions, but the high cost of precious Ru limits the potential large-scale application of RICO. How to recycle and reuse Ru is critical to promote the application of RICO. In this work, a novel and efficient approach for reusing Ru through recycling the solvent mixture containing Ru was established for RICO. First, the influence of different reaction parameters on the depolymerization degree of lignite and benzene polycarboxylic acid (BPCA) yields was investigated. Second, the distribution of Ru in the organic phase (OP), aqueous phase (AP), and residual solid phase (RSP) was analyzed after the RICO reaction. Finally, based on the distribution of Ru in different phases, a novel route of recycling Ru by reusing the Ru-containing solvents was proposed. The results showed that the dosage of RuCl 3 and NaIO 4 had a significant influence on both the depolymerization degree of lignite and BPCA yields. The distribution of Ru had a close relationship with the depolymerization degree of lignite and the dosage of NaIO 4 . After the depolymerization reaction, the CCl 4 phase containing Ru was reused directly as the solvent for the next run, which could fulfill the reuse of both CCl 4 and Ru. The results proved that the Ru-containing CCl 4 phase could maintain catalytic performance for 5 runs. This work provides an efficient route to reuse Ru for the RICO depolymerization of lignite into valuable organic acids. As far as we know, this is the first report concerning the recycling and reuse of Ru during the RICO of lignite. This work is important for the application of RICO in lignite depolymerization.

Novel Approach of Reusing the Precious Ru in the Wastewater Derived from the Depolymerization of Lignite to Prepare Ru–AC Catalysts Doped with Nb2O5

“…In this work, Shengli demineralized lignite was depolymerized by RICO according to the reported procedures . Typically, 0.4 g SL + , 40 mg RuCl 3 , CCl 4 : CH 3 CN: H 2 O with a volume ratio of 2:2:3 (total volume, 70 mL) and 8 g NaIO 4 were put into a 250 mL spherical flask.…”

“…Typically, 0.4 g SL + , 40 mg RuCl 3 , CCl 4 : CH 3 CN: H 2 O with a volume ratio of 2:2:3 (total volume, 70 mL) and 8 g NaIO 4 were put into a 250 mL spherical flask. Then, the slurry was allowed to react at 35 °C for 6 h. After the reaction, the Ru-containing organic phase was obtained by phase separation, and Ru was mainly present in the form of RuO 4 in the organic phase characterized by FTIR and Raman spectra in our previous study . Then, the Ru species was extracted with 9 wt % HCl (aqueous/organic phase volume ratio of 1:1) from the organic phase for three times.…”

“…In this work, Shengli demineralized lignite was depolymerized by RICO according to the reported procedures. 33 Typically, 0.4 g SL + , 40 mg RuCl 3 , CCl 4 : CH 3 CN: H 2 O with a volume ratio of 2:2:3 (total volume, 70 mL) and 8 g NaIO 4 were put into a 250 mL spherical flask. Then, the slurry was allowed to react at 35 °C for 6 h. After the reaction, the Ru- containing organic phase was obtained by phase separation, and Ru was mainly present in the form of RuO 4 in the organic phase characterized by FTIR and Raman spectra in our previous study.…”

“…Then, the slurry was allowed to react at 35 °C for 6 h. After the reaction, the Ru- containing organic phase was obtained by phase separation, and Ru was mainly present in the form of RuO 4 in the organic phase characterized by FTIR and Raman spectra in our previous study. 33 Then, the Ru species was extracted with 9 wt % HCl (aqueous/ organic phase volume ratio of 1:1) from the organic phase for three times. Subsequently, the HCl was removed via distillation under reduced pressure, and the waste Ru compound was obtained.…”

Ruthenium ion catalytic oxidation depolymerization of lignite under ultra-low dosage of RuCl3 catalyst and separation of the organic products with inorganic salts

“…In our previous study, the efficient recycling procedure of the homogeneous ruthenium catalyst using CCl 4 extraction was established. 27 It was proved that the ruthenium catalyst could be reused for at least 5 times with no obvious decrease of the BPCAs yields. The dosage of the ruthenium catalyst in the reported work is often high, with mass ratio of RuCl 3 /lignite as high as 1 : 10, which makes it impossible to be adopted in real application.…”