Selective Oxidation Of Coals In Aqueous NaOCl Solution And Fine Separation Of The Products

As important heavy carbon resource, efficient utilization of coal is very important to thesustainable development of our national economy, while the key to effective use is ofknowledgeofitsstructure.Coaloxidationisanimportantapproachforbothunderstandingcoalorganic matter macromolecular network structure and obtaining organic chemicals. Theresearches of under mild conditions in moderate and selective depolymerization of organicmatter in coal as much as possible for the composition of simple organic compounds andoxidativedepolymerizationmechanism are helpfultounderstandcoalstructuralcharacteristics,establish an scientific method of separation and analysis for products and prepare highvalue-added products from coal.Comparedtoother oxidants,NaOClhas someobvious merits,such as cheaper, easy availability, environmental friendly, and higher reactivity toward coaloxidative degradation. These merits, especially for the high reactivity toward coal oxidativedegradation, possibly make coal oxidated under mild conditions, thereforecoal oxidation withNaOClisaworthwhilewaytoexploretheefficientuseofcoal.To provide a reliable theoretical basis and technical support for high value-added utilizationofcoal,oxidativedegradationbehaviors offourdifferent rankcoals anda series ofcoal relatedmodel compounds （CRMCs） with aqueous NaOCl solution, including the reaction processoptimization, separation and analysis of oxidation products and the reaction mechanism, wereinvestigatedinthisstudy.Themainresultsinthisworkareasfollows:The effects of ratio of NaOCl to coal, reaction temperature, pH value and reaction time onthe coal oxidative degradation were investigated. The results show that lignite was more easilyreactive than bituminous coal. The optimum operation conditions for lignite oxidativedegradation are 30 oC, pH, 12.0, NaOCl/coal 1/100 （g/mL） and 24 h and forbituminous coaloxidativedegradationare 40oC,pH10.5,NaOCl/coal1:120（g/mL）and 36h.Coal oxidation products were analyzed with GC/MS. The results indicated that the productswere very complex, and chlorinated compounds, fatty acids, aromatic acids were typical coaloxidation substances. Oxidative product was sequentially extracted with five different polarsolvents and achieved a simple group separation. Oxygen-containing and chlorine-containingorganic compounds could be enriched with ether and ethyl acetate, and the extracts of CS₂contained a large amounts of organic sulfur compounds and alkanes, and hydrocarbons withsmall polar were the main components of petroleum ether, and benzene on the extraction ofhydrocarbons and esters were high extracts, and the content of benzene polycarboxylic acidswithmorethanfourcarboxylicgroupsattachedtobenzenewerehighinsalt.Three solid acids （FC₂） produced from coal oxidation were extracted with ether, CS₂ and methanol sequentially under ultrasonic. It is found that the extraction yield of methanolon thethreesolidacidswashighest,followedbyether,andCS₂ wasminimum.FC₂wasoxidized withNaOCl. The results showed that the kinds of compounds in the oxidative products of FC₂greatly reduced compared with those of raw coal. The compounds were mainly benzenepolycarboxylic acids with more than four carboxy. It is indicated that the structure of FC₂ wasahighercondensedaromaticrings.Four coal oxidation residues （FC1） were extracted with petroleum ether, CS₂, acetone andmethanol underSoxhlet,sequentially.Theextractionyieldofmethanolishighest.BasedontheGC/MS anaysis ofextracts, it is foundthat nonecompounds weredetected from theextracts ofpetroleum ether from Dongtan and Heidaigou oxidation residues and the extracts of acetoneand methanol from all four oxidation residues. The main compounds detected in other extractswereoxygen-containingcompounds,aromaticsandalkanes.Using graded extraction-separation with column chromatography-crystallization technologyto subtly separate the oxidation products, eight kinds of pure methyl benzene polycarboxylicacids were obtained, and their isomers were also effective separated. It is achieved partialoxidation products of the fine coal separation, which provides a new feasible method forobtainingbenzenepolycarboxylicacidsfromnaturalmacromoleculesmaterials, andprovidesanimportanttechnologyforhighvalue-addeduseofcoal.It was found that NaOCl can react with almost all types of compounds by examiningCRMCs reaction with NaOCl. The reaction mechanism is complex due to the presence ofmany competitive reactions, such as oxidation, addition, substitution, and free radicals. Theside chain on the benzene ring is oxidized rather than the benzene ring itself; polycyclicaromatic hydrocarbons （including naphthalene） are more reactive toward NaOCl than sidechain; substituentsonthearomaticringplaysanimportantwaytoinfluenceontheoxidationofaromatic ring; the reactivity of alkane with NaOCl is weak, while it is greatly enhanced byCCl4 addded, so the mechanism of alkane reaction with NaOCl may be by free radical;oxygenated compounds easily react with NaOCl; organic nitrogen and sulfur compounds areeasily oxidized to the corresponding nitrogen oxide and sulfur oxides, and their associatedbondswereeasilybroken.ThemechanismsofcoaloxidationwithNaOClwerealsodiscussed.132figures,67tables,230 references.