Oxidation of Shenmu char powder with aqueous hydrogen peroxide–acetic anhydride

• Conditions for Shenmu char powder (SCP) oxidization with AHPO–AAH were optimized.
• SCP consists of aliphatic, aromatic, and carbonyl carbon species.
• Malonic and succinic acids are the main alkanedioic acids produced from SCP oxidation.
• Main BCAs are benzenetricarboxylic and benzenetetracarboxylic acids from SCP oxidation.

The mild oxidation of Shenmu char powder (SCP) with aqueous hydrogen peroxide (AHPO)–acetic anhydride (AAH) was carried out under different conditions, including volume-to-mass ratio of AAH to SCP (AAH/SCP), temperature, volume ratio of AHPO to AAH (AHPO/AAH), and time. Each reaction mixture was filtrated and then extracted with methanol to afford residue and extract. The optimal conditions were determined to be 60/1 of AAH/SCP, 50 °C, 2 of AHPO/AAH and 60 h based on the extract yield. The extracts from SCP oxidation after different periods of time ranging from 12 to 72 h were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and atmospheric pressure solid analysis probe/time-of-flight mass spectrometer (ASAP/TOF-MS). In total, 46 compounds were identified in the extracts by GC/MS analysis and carboxylic acids are predominant. Malonic acid and succinic acid were detected in the extracts and their total mass content in the extracts is up to 56.5%. A series of long-chain alkenedioic acids or long-chain cycloalkanedioic acids with molecular formulae C29H56(CH2)n(COOH)2 (n = 0–6) were detected in the extracts with ASAP/ TOF-MS.