Preparation of nitric humic acid by catalytic oxidation from Guizhou coal with catalysts

Intermational Joumal of Mining Science and Technology 22(2012)75-78International Journal of Mining Science and TechnologyELSEVIERjournalhomepagewww.elseviercom/locata/ijmstPreparation of nitric humic acid by catalytic oxidation from Guizhou coalwith catalystsYang Zhiyuan, Gong Liang, Ran PaSchool of Chemistry and Chemical Engineering, Xi'an University of Science and Technology, xi'an 710054, ChinaARTICLE INFOABSTRACTArtideNitric humic acided by catalytic oxidation between nitric acideived 18 Aatalysts. We investigated catalytic oxidation processes and the factorsfects of different catalysts, including NiSO4 support on active carbon(aAvailable online 17 March 2012icon dioxide(SiO -NiSO) composites of SD4/Fe2O,, Zr-iron and vanadium-iron composite were stud.ied. As well, we investigated nitric humic acid yields and the chemical structure of products by elemenanalysis, FT-iR and E4/E6 (an absorbance ratio at wavelengths of 465 and 665 nm of humic acid alkalineextraction solutions). The results show that the catalytic oxidation reaction with added catalysts canGuizhou coalatalytic oxidationincrease humic acid yields by 18.7%, 16. 36%, 12.94%, 5.61% and 8.59%, respectively. The highest yieldof humic acid, i. e, 36.0%, was obtained with Ac-NiSOa as the catalyst. The amounts of C and h decreasedCatalystswith the amount of nitrogen. The increase in the E4/E6 ratio in catalytic oxidation of (Guizhou)coal shows that small molecular weights and high yields of nitric humic acid can be obtained by catalytxidation reactionp 2012 Published by Elsevier B.V. on behalf of China University of Mining Technology1 IntroductionMany scientists have discussed catalysts in the process of coaloxidation. Kamiya found that Cuo used as oxidation catalyst atAccording to a geological report. the proven reserves of coal 270, as well as molybdenum and vanadium used with oxygenresources in Guizhou account for 5% of the total reserves in China. at 105%C, oxidized low ranked coal 6 Liu investigated FeCl, asGuizhou coal is a low ranked coal with high sulfur and ash con- a catalyst in a H2O aqueous solution at 60C in a mixture of ethyltents, contains a large number of clay minerals and is similar to ether 17). Our earlier research showed that transition metal ionsthe carboxyl, hydroxyl functional groups which contain oxygen. and rare earth metal ions in a photocatalytic oxidation of coalGuizhou coal, when directly combusted, has low calorific value. affected its humic acid content and its chemical structure [8].Athis not only causes an enormous amount of resources to be present, there are many catalysts that can be used to catalyze hu-wasted, but also severe environmental pollution. The process of mic acid in the coal oxidation, but the yield is low and the purity ofcoal oxidation, known as oxygen degradation, is the gradual degra- its product insufficient. How to prepare highly effective catalystsdation from complex coal structures to simple ones during the has becomes a new direction in further research. Our objectivesinteraction between coal and oxygen 1, 2]. Recently, the use of coal were to investigate the effect of catalysts on the high value-added,for making humic acid via oxidation has been reported by ui et al. chemically fine nitric humic acid from Guizhou coal during mildwho showed the preparation of co-polymer material using humic oxidation, to optimize the catalytic reaction and, as well as to disacid from weathered coal and some polymers [3] These kinds of cuss the impact of the catalysts on the yield, composition andmaterial are added to drilling fluids as high-temperature filtrate structure of nitric humic acid.loss reducers and tested in over 70 wells in several oil fields inChina. Kucherenko et al. described some preparations of humic 2. Experimentalcid from alkali-impregnated brown coal and their applicationsin heavy industries 14). It appears that the results of these recentapplications have some positive impact on industrial developmentin regions where low-ranking coal is readily available [5].Coal samples( supplied by the water City Mining Bureau, Guizhou, China)were pulverized into ultrafine powders in particle dso,ing author, Tel +86 29 855831shown中国煤化工 data in the table tharess: zhiyuanyange126 com(h sulfur and ash.CNMHG2095-2686/s- see front matter o 2012 Published by Elsevier B V on behalf of China UniversitZ Yang et a/Intemational Joumal of Mining Science and Technology 22(2012)75-78Table 1Moisture, ash content and analytical results of Guizhou coal (%)diluted to about 100 mL After cooling, three drops of a henanthroline indicator were added and titrated with a 0. 1 mol/L ferrousammonium sulfate solution to a red brick finish In additio673.0303325937825.0 mL sodium pyrophosphate alkaline extraction and 15 mL ofconcentrated sulfuric acid were respectively, added into the5.0 mL at 0.068 mol/L of potassium dichromate solution, Giventhese conditions, oxidation and titration were performed and theThe other reagents, concentrated sulfuric acid, nitric acid, ferricreference value of was firstly deteoxychloride, ferric chloride ferric oxide ammo-metavanadate, silicon dioxide, nickel sulfate, ammonia water. 2.5. Analysis and characterizationpyrophosphate, sodium hydroxide, phenanthroline, ferrousammonium sulfate and dichromate were all of reagent grade qualNexus 870 Fourier transform infrared spectroscopy from theity and obtained from the Xi'an Chemical Reagent Factory(Xi'an,merican NICOLET Company was used to measure the infrared patterns of the coal samples with a spectrometer resolution of 4 cm-Ia scanning frequency of 32 per second, a measurement range of2.2. Catalyst preparation400-4000 cm"and a deuterated triglycine sulfate (DTGS)detectorThe optical density measurements on the extraction solution ob-A method of impregnation was used to obtain the activated car-lined from the extraction processes were determined by a tu-bon supported catalysts. The activated carbon was treated by nitric 1900 double-beam UV-vis spectrophotometer(Beijing PurkinjeGeneral Instrument Co, Ltd )at 465 and 665 nm, with averages ofous nickel sulfate solution with Niso4 water (6g: 140 mL). The three readings. The absorbance ratio(EA/E6)of humic acid in thesolution was then strongly stirred for ih, washed with distilled alkaline solution at 465 and 665 nm wavelengths is one of thewater and dried and held in reserve we obtained the activated important indices to characterize the composition and structurecarbon supported Niso 4 catalyst(AC-NISO) The silicon dioxide of humic acid. The amounts of C. H. N and S of the residue weresupported NiSO4 catalyst(SiO -NiSO4). the vanadium-iron com- determined by a Vario EL Ill CHNS type element analyzer Coal sam-posite solid acid catalyst, the solid Zr-iron composite acid catalyst ples were dried for 4 h at 105C in a vacuum oven, a specificand the solid So2/Fe20, acid catalyst were prepared according amount of coal samples were obtained on an analytical precisionto the protocols described by the references cited 19-12elemental analyzer produced by the German Ai Le Man analy23, Catalytic oxidation of Guizhou coal with nitric acidsystem. By switching the C H N. s mode, the C h, N s contentsof the coal samples were determined.A vibration-type ball milling system of ZM80 was used to grindfresh Guizhou coal into ultra-fine coal samples for nitric acid oxi- 3, Results and discussiondation [13]: the particle sizes were measured by a laser particlesize analyzer as Dso< 10 um. Orthogonal tests were used which 3. 1. Effect of oxidation conditions on the yield of humic acidselected the ratio of nitric acid to coal, the reaction temperatureand the reaction time as the catalytic oxidation condition variablesThe yields of humic acid in orthogonal tests of different oxidaFrom these results, the optimal oxidation conditions were found tion conditions are shown in Table 2. In the following, we discussand under these optimal oxidation conditions, 10.0000 g samples the results from the orthogonal analysis. There are two sets of optiwere mixed with specific amounts of catalysts and nitric acid in mal parameters in coal catalytic oxidation: 1)the ratio of acid tothree post mixed flasks inter bath with a designed tempera- coal 4: 1 (mL/g) a reaction temperature of 80oC and a reaction timeture. Oxidative degradation was performed for 40-80 min, the of 80 min and(2)the ratio of acid to coal 4 1(ml/g), a reactionnitric oxidized solution was vacuum filtered and washed with dis- temperature of 95c and a reaction time of 80 min,tilled water to a level close to neutral.24. Experiments of alkali solution extraction from nitrification coal32. Eject of catalysts on humic acid yieldand yield determinationGiven these optimal oxidation conditions i e, a ratio of acid tocoal 4: 1(mLg) a reaction temperature of 95oCand a reaction time2.4.1. Extractionof 80 min, coal samples and nitric acid were mixed with a specificWe added 0. 2 g(accurate to 0.0002 g) nitrification coal of lessthan 0.2 mm in size in a 250 mL conical flask. After adding150 mL sodium pyrophosphate as an alkali extraction solutiothe conical flask was placed in a boiling water bath to saturate Yield of humic add under different oxidation conditionthe coal samples, then, extracted for 2 h while constantly shaking, Sample Oxidation conditionso that all residues had deposited. After the liquids and residueReactionvere cooled, they were moved into a 250 mL volumetric flaskto coal〔mLgmperature time(min)diluted with distilled water, shaken and kept for 1 day.6.5972.4.2. Determination of the total yields of humic acidfter filtration withqualitative filter paper and clarification, the extraction solution with an accuracy of 5.0 mL was placed中国煤化工8into a 250 mL conical flask. A potassium dichromate solution of5 mL at 0.068 mol /L and 15 mL concentrated sulfuric acid were雪YHCN MHG80added with an accurate pipette, oxidation followed for 30 min ina boiling water bath, then cooled to room temperature and finallyGZC9 46026969Z Yang et aL/Intemational Joumal of Mining Science and Technology 22 (2012)75-78Sample I Sample ll Samplelll SampleIV Sample V SampleFig. 1. Effect of catalysts on humic acid yield.40003600320028002400200016001200800400Wave numbers(cm)amount of catalysts(amounting to 1% of the quality of coal in theFig. 2, Infrared spectra of extraction residues.three post mixed flasks in a water bath with designed temperatures). Oxidative degradation was performed for 40-80 min; whenthe temperature dropped to room temperature. We removed the The experiments prove the formation of a small amount of co, innitric acid oxidation of the liquid from the solid-liquid separation the process of coal oxidation by nitric acid. Sulfur sequestrationof the mixture with a vacuum filtration device and washed the was also credited to the oxidation process. The content of n wascake with distilled water repeatedly until the cake was close toennannced to the highest level with Ac-NiSOa as the catalyst. theneutral, i. e, we obtained nitrated coalresults correspond to the infrared spectrum analysis and theFig 1 shows the effect of different catalysts on the yields In the Nh, -NO -Cn and -N-C=-C-, which are clearly strengthenedcatalyst: sample Ill: vanadium-iron composite as catalyst; sampleⅣV:SO42f/Fe2O3 as calmple V: AC-NiSOA as catalyst: sam- 3.3. 2 Infrared spectroscopy of extraction residueple VI: silicon dioxide-NiSO4 as catalyst. The yields increased in theInfrared spectrum analyses of nitrated coal extraction residueexpected order. It is seen that the yields from silicon dioxide and from all samples are shown in Fig. 2. This figure indicates thatactivated carbon supported NiSO4 as catalysts were higher than the structural differences of humic acid from Guizhou coal oxithose of the other catalysts and those without catalysts. The result dized with various catalysts are largely as follows: the absorptionndicates that nitric acid oxidized Guizhou coal can greatly im- peaks of stretching vibration attributed to the hydrogen bond asso-e the yield of nitric humic acid in the presence of catalysts. ciations-OH. -NH and-NH2 at 3445 cm"have clearly strengthctivated carbon supported nickel sulfate(Ac-NisO4)as the cata- ened: the peaks of the spectrum of sample V, ie, the infraredlyst embodied the best catalytic effect and the highest yield of hu- spectra of nitrated coal extraction residue under the condition ofmic acid. the yield increased by 18. 71% when AC-NiSO4 as catalyst AC-NiSO a as the catalyst, are strong, suggesting that double andas added, compared with the yield without a catalyst, caused by triple bonds could be formed easily or under sound conservation.its special molecular structure and excellent adsorption properties. The relative intensity at 1638 cm", attributed to carboxylate radcals, the aromatic double bond C=C and carbonyl through th3.3. Structural analysis of nitric acid oxidized productsassociation of the hydrogen-bond >C-0 at 1518 cm"attributee of side chains in the carbon skeleton of the extraction coal reThe element analysis of extraction residue from the six samples idue decreased considerably. Because of the coupling between theL, IL, IlL. IV, V and vi are shown in Table 3. It can be seen that the stretching vibration of single-bonds and the deformation vibrationamounts of C and S are reduced, while those of N, H and the H/C ra- of C-h bonds within the fingerprint area from 1380 to 650 cm", ittio increased in the extraction residue of nitric acid oxidized coal, was rather complicated to define these bonds or decide whetherindicating that the oxidation process gives rise to high decarburiza- they form a group frequency, but changes in the absorption peakstion compared with raw coal. The residues were observed under a of the spectrum of samples ll, IV, v and Vi show similar regularitymicroscope and prove that the effects of nitric acid are not confined and are largely different from the fingerprint area spectrum ofto the particle surface of coal. The cause of carbon sequestration Guizhou raw coal. We can conclude that the macro-molecularwas that the functional group of coal macro-molecules was oxistructure of coal is greatly affected by nitric acid oxidation. Thisdized extensively, followed by oxidative cracking of the molecules. is possibly caused by free radical chain-reactions, which after theFinal analysis of Guizhou coal residue in catalytic oxidation.mpleron composite1908中国煤化工Silicon dioxide-NiSO4YHCNMHGx by weight daf (dry ash free).b By difference.Z Yang et al /Intemational Jourmal of Mining Saence and Technology 22(2012)75-78(AC-NiSO4>silicon dioxide-NiSO4>S042-/Fe203>Zr-iron com-Absorbance values of E4 and E5 and the ratio E4/E6 in the extraction solution of posite>vanadium-iron composite without catalyst) for coalsamples with or without catalysts. AC-NiSo4 is the most efficientEAcatalyst. The structure of coal macro-molecules is greatly affected0016during the process of nitric acid oxidation, possibly caused by freecompositeanadium-iron compositeradical chain-reactions. the humic acid with small molecular2375weight and lower aromaticity can be obtained by oxidation withAC-NiSOaa ratio of acid to coal of 4: 1 (mL/g), extracted at 95oC and insilicon dioxide-NiSO.80 min with AC-NiSOA as the catalyst. Higher yields can be realizedin this process.catalyst activation coal active functional group, produce free AcknowledgmentsradicalsThe project was sponsored by the shaanxi33.3.E4/E6ratTechnological Project, China(No. 2010K07-20The absorbance ratio at wavelengths 465 and 665 nm of the Science and Technology Major Project(Nohumic acid alkaline extraction solution (referred to as the ea/e6 and as authors, we thank them for their financiratio), is characterized by its humic acid compositiothe important indicators. It is the condensation of aromatic humicacid molecular weight or the characteristic function and its negative correlation. The absorbance values and the E4/E6 ratios for dif-[1 Alvarez R Clemente C, Gomez Limon D. The infuence of nitric acid oxidatioferent nitrated coal extraction resolutions are shown in Table 4low rank coal and its impact on coal structure. Fuel 2003: 82(15-Table 4 shows that the E4/E6 ratio of the[2]Iglesias M]. Peunte G, Fuente E. Pifrom nitrated coal oxidation without a catalyst is the smallescompared with AC-NiSO, as the catalyst with the largest ratio. This [3] Song Chunshan, Harold SH. Opportunities for developing specialty chemicalsindicated that a small molecular weight and lower aromaticity ofhumic acid was obtained by oxidation with nitric acid with ac-NisOa as the catalyst. The EA/E6 ratio had nothing to do with theGmc如山number of humic acid molecules but show[5] Arslan G. Edebali S, Pehlivan E. Physical and chemical factors affecting thwith the size of the humic acid molecules or the degree of condensorption of CrVi)via humic acids extracted from brown coals. Desalinationformed the following sequence (AC-NiSo4>50NO4>S9021闭(∝00灿ums2sation, usually decreasing with an increase in humic acid molecu- 16) Burke S, Jarvie AwP. Gaines AF A moar weight or the degree of condensation (14 The E4/E6 ratiFe 03>Zr-iron composite vanadium-iron compositDissertation. Xuzhou: China University of Mining and Technologycatalyst) for coal samples with or without catalysts.TheItio [8] Yang ZY. Mechanism, kinetics and application of ultra-fine coal powder onincreases under catalytic oxidation conditions. It provethe most efficient catalyst because of it has the largest E4/E6 ratio (1o Song. Cui P. Yang mo ride fuel Process Technol 1997 se by leaching withysts can promote oxidative degradation of coal. Theof all the catalysts usec111l Song XM, Ling Q Cui P. The research of Fe-v composi4. Conclusions[121 Ling Q, Cui P, Sun Y]. Research of Fe-Zr composite solid acid catalyst applied toThe amounts of carbon and hydrogen de[131 Ling Q Cui P, Wang GH Develid the valueof H C, but the amounts of nitrogen and ox2dung4 Shenfu so a after门dmrent density maceralsoxidative coal degradation. The EA/E6 ratioy Min Technollytic oxidation conditions. The EA/ E6 ratios formed the sequence2006:36(5628-32中国煤化工CNMHG