Seiji Nishida

Reaction of Coal with Nitrogen in a Microwave Discharge

The reaction between nitrogen and coal in microwave discharge system at low pressure was studied, using two Japanese coals, 4 Canadian coals and a spectroscopic carbon.HCN, CO and small quantities of (CN) 2 were the main gaseous products. Although reactivity-expressed as a function of total gaseous product yieldtended to vary in an, inverse sense with coal rank, (CN) 2/HCN ratio generally increased with rank. The Japanes coals yielded slightly more product gas and higher (CN) 2/HCN ratios than the Canadian coals, possibly because of their greater content of low molecular weight volatile matter which can easily react with active nitrogen in the gas phase. The reaction of several model hydrocarbons under similar conditions suggests that in low-rank coals the aliphatic structure was largely, while in high-rank coals some of the aromatic structure was affected. Activation energies for formation of HCN and (CN) 2 increased sharply above 230°C, probably due to an interaction of volatile matter with active nitrogen superimposing itself upon the normal surface reaction.

Behavior of Gaseous Products Containing Nitrogen in NHO3 Oxidation of Coal

石炭の硝酸酸化機構をこの反応で発生する窒素系ガスとモデル物質の酸化時のガス組成とを比較することによって検討した。低石炭化度炭に12.7% の硝酸を80℃ で作用させるといずれもNO に富んだガスが発生し, それらのガス組成は反応時間,反応温度によって,つぎのように変化した。1)反応後半ではNO/N2+N2Oが小さくなる,2)反応温度の低下にともなって,NO/N2+N2O が小さくなる, 3)反応開始時にはN2>N2Oであるが, 反応途中で生成量が逆転する。一方80℃ で12.9% の硝酸と反応する有機物はごく限られており, この内NO に富んだガスを発生するのはフェノール類のみであることが見出された。さらにo-クレゾールの硝酸酸化で発生する窒素系ガスの挙動は石炭の場合と非常によく類似していることが明らかになった。これらの結果から「低石炭化度炭の硝酸酸化では石炭分子中のフェノール構造が崩壌してフミン酸が生成する」とした前報の推論が支持された。

Mechanism of Nitric Acid Oxidation of Low Rank Coal

3種の石炭{C=76.2%(I),70.9%(II),67.9%(III)}を12.7%硝酸と80℃ で反応させ,フミン酸が生成する段階で硝酸によって崩壊される石炭分子中の化学構造を検討した。石炭化度の低下にともなって硝酸に対する反応性が増大したが, それらの差異は各炭の内部表面積によっては説明できない。II, IIIの酸化では-COOH 基のみが増加したが, Iでは-COOH基とフェノール性OH 基両者の増加が見られた。これらの結果は石炭の酸化過程ではフェノール性OH基の生成と崩壊とが並列に起こっていることを示唆している。再生フミン酸の分子量は試料炭の石炭化度が低くなるにつれて小さくなり,硝酸によって石炭分子が選択的に崩壊されていることが推測された。再生フミン酸と各試料炭の組成の比較からII, IIIがフミン酸に転化する際には石炭分子中のH/C=1に近い部分が崩壊するが,Iでは水素に富んだ部分が消失することが明らかになった。これらのことから低石炭化度炭にはフェノール構造が多く,それらが希硝酸によって容易に崩壊されるためにフミン酸がすみやかに生成するのであろうと推定した。

Nitric Acid Oxidation of Coal (II)

The properties of carboxyl groups in the oxidized coals obtained from Tenpoku-Fujita (C: 70.9%a.m.f.) and Sumiyoshi (C: 76.2%a.m.f.) coals by HNO3 treatment were studied by using the methods of ion exchange with Ca (CH3COO) 2 aq.sol.and infrared absorption spectra.Carboxyl groups in oxidized Fujita coals were subjected to Ca (CH3COO) 2 aq.sol.exchange completely under N2 atmosphere 18°C, 20hrs. While oxidized Sumiyoshi coals had later exchange rate than Fujitas, and yet exchange reaction proceeded after 7 days. But the exchange rate of the humic acid extracted from oxidized Sumiyoshi coal did not vary significantly from Fujita humic acid.These results were accessible by assuming a rate-determing diffusion of Ca++ ion into oxidized coals. In the case of treating the oxidized coals in much amount of Ca (CH3COO) 2 aq. sol., it could be seen that other acidic groups (probably phenolic) exchanged with Ca (CH3COO) 2. When the oxidized coals were heated in Ca (CH3COO) 2 aq. sol., a remarkable increase of exchange capacities was seen. These increase may be reduced to the action of CO2 given by decarboxylation and newly produced carboxyl groups.

Oxidation Mechanism of Low Rank Coal

In order to elucidate the chemical structure of the parts which are destroyed in the transition from low rank coal to humic acid, chemical and infra-red spectroscopic examination of the solid products obtained byHNO3-oxidationn and wet O2-oxidation of coals were tried and also their reactioncharacteristics were compared with those of various model compounds.Three kinds of coals (C=76.2‰I, 70.9‰II, 67.9‰III) were oxidized with 12. 7 HNO3 at 80°C. The lower the rank of coal was, the more it is reactive toHNO3. Infra-red spectra of their solid products suggested that in the process of coal oxidation formation and destruction of phenolic OH group took place consecutively.Molecular weight of humic acid decreased with lowering of the rank of parent coal. The comparison of the composition of humic acids with their parent coals showed that in II and III, the part near H/C=1 in coal molecule was destroyed inthe process of humic acid forma-tion, however, in I hydrogen rich part was attacked NO rich gas was evolved in oxidation of low rank coals with diluteHNO3 and the composition of gaseous products cotaining nitrogen varied regularly with reaction temperature and time. It was found that only phenols gave the gas rich in NO and that the behavior of gaseous productsevolved in the oxidation of o-cresol was so similar to it on the cases of the coals. It is possible to conclude from the results given above that in the processof humic acid formation from low rank coal by HNO3-oxidation, phnolic structure in coal molecule might be destroyed.In the oxidation of II in water under the initial O2 pressure of 75 kg/cm2 at 105°C, ammonium molybdate (Mo) accelerated the formation of humic acid selectively, while ammonium metavanadate (V) accelerated the entire oxidation rate unselectively. The oxidation rate of the coal decreased in CH3COOH medium and molecular weight of humic acid obtained in this reaction was larger than that in water. From the results of decomposi-tion of H2O2 and oxidative destruction of pyrogallol, it was presumed that V had strong activities in the destruction of phenolic structure as well as the decomposition of in coal molecule whereas Mo had a slight activity in former and that the destruction and production of phenolic structure in coal molecule might be inhibited in CH3COOH medium. It was therefore suggested that in O2-oxidation humicacid was also produced after destruction of phenolic structure in coal molecule.

Air Oxidation of Coal on Wet Process. I. Production of Humic Acid by Air Oxidation of Coal, in Acetic Acid

従来の硝酸酸化に代るものとして湿式空気酸化によるフミン酸の生成条件を検討した。希酢酸媒体中で空気圧40kg/cm2(反応温度における圧力)では反応温度の影響が大きい。すなわち,150℃ 以上の高温では希アルカリに可溶なフミン酸の生成速度は大きいが,多量の炭酸ガスが発生し,固形生成物の収率は低下する。100℃ ではほとんど反応が進行せず,固形生成物はアルカリに難溶であり,130℃ 付近にフミン酸生成の最適温度条件がある。一方,この反応は媒体である酢酸水溶液の濃度により,かなり様相を異にする。すなわち,低濃度媒体を用いると,媒体に可溶な低分子有機酸が多量に生成し,フミン酸収率は低下するが,50%程度の酢酸水溶液中では,固形生成物の収率も高く,しかもフミン酸含有率も高い。しかし100%近い高濃度媒体を用いると,フミン酸の生成速度が小さく,反応時間5時間程度では,生成物は希アルカリにはほとんど不溶であり,酸性基を多く持った酸化炭となる。さらにこの反応では,酢酸コバルト,臭化アンモニウム両者を添加すると,固形生成物の収率の低下もなく,フミン酸含有率が顕著に増加することがわかった。