Plasma Science & Technology, Vol.5, No.3 (2003)A New Grade Carbon Black Produced by Thermal Plasma Process*Li Juan (李娟)', He Fangfang(何方方)', Luo Yiwen (罗义文),(!八Yin Yongxiang (印永祥) 1, Dai Xiaoyan (戴晓雁)', Liao Xu (廖旭)”1 School of chemical engineering of Sichuan University, Chengdu 610065, China2 Southwestern University of Science and Technology, Mianyang 621000, ChinaAbstract This paper presents a new route about producing carbon black, by which the naturalgas cracking is carried out in tbe absence of oxygen thanks to an electric energy supply externallygiven by a plasma jet. The carbon black produced by this process has a narrow size distributionand a small average diameter of 38 nm as well as a highly branched aggregate. The higher DBPvalue of 1.40 ml/g shows it should be a high structure carbon black. The FTIR spectra shows thatthere are lots of aromatic cc bonds and a large armount of nitrogen. containing functional groupson the carbon blacks surface, such as -NH, -CN as well as -CH, -OH, -C0OH groups.Keywords: carbon black, thermal plasma, natural gasPACS: 81.05.U; 52.251Introductioncess has been adapted to meet the requirements ofrubber and plastics industries for more than 50 years,Carbon black (CB) is one kind of the importantit is still not certain that this technology will be ablechemical raw materials that has extensive uses into survive the next century and plasma technologyindustries of rubber, plastic, dye et al.l21. From awould ernerge as a solution interesting.chemical point of view, CB manufacturing processesPreparation of CB in thermal plasma mainly in-can be classified into two categories: incomplete com-cludes two ways: one is the AC plasma arc[3] andbustion and thermal decomposition of bydrocarbons,the other is the DC plasma jet. In our experiments,depending upon the presence or absence of oxygen 2].the DC plasma jet was used.Although the partial combustion processes are ableto produce CB at a very low price, satisfying thepresent demand, its application remains to be limited2Experimentalby thermodynamic reactions under operating condi-ions. Depending on the feedstock and on the qualityFig. 1 shows the schematic experimental system.of the product, the furnace process achieves poor CBThis plasma reactor was composed of four parts:yields and is characterized by a high pollution levelplasma generator, reaction chamber, cooling waterof of-gas CO2, NOx, SO2, ... While the furnace pro-net and feedstock injector. The plasma generator中国煤化工"The projet sppred by the National Nature Science Foundation ofMYHCNMHG1815Li Juan et al. : A New Grade Carbon Black Produced by Thermal PlasmaProcessAnodeNitrogenGasCooling waterCH,-→=r+一CH4Gas- solid separatorCoolingwater、2Collection vessel、3Fig.1 Schematic of the experimental system(1) the DC plasma reactor, (2) the gas solid separator, (3) the collection vesselTable 1. Conversion of methane and yield of CB at 20 Nm2/h N2 and 120 kWMethane flow rate (Nm*/h)Methane conversion (%)CB yield (%)197.1439412784(was connected to a DC power supply of 300 kWprocess in the experiments.maximum. The reaction chamber was constructedThe CB product was trapped from the collectionwith a double wall (500 mm long and 50 mm i.d.)vessel. CB samples were analyzed by TEM andof water cooled stainless steel, in which a hot wallFTIR spectrum and were determined according toof a graphite tube was used to keep a highly react-GB/T 7044 -93 by the national CB examination cen-ing temperature and reduce radial temperature gra-ter. Gas chromatography was used for an analysis ofdients. Feedstock injector was equipped with twothe of-gas composition. A part of the of-gas wasports, which was terminated by a tail filter whereelicited from the reactor exit and injected to a mea-CB and gas were separated. .suring cell in which the temperature was maintainedatT= 160 °C. .All the experiments were carried out at atmo-spheric pressure with electric powers varying between3Results90 kW and 200 kW. Nitrogen was used as a workingIn our experimnents, off-gas compositions were ob-gas to generate arc. Natural gas was used as a reac-tive gas and was injected just below the plasma gen-served. CH4, C2H4, CzH2 and CO were identifed,erator. Typical parameters in the experiments wereno cyanides were detected when operating with N2a flow rate of N2 of 20 Nm3/h~ 30 Nm23/h. Wallas plasma gas.Depending on the mass balance, we can calculatetemperature measured in the exit of reaction cham-ber allowed the temperatures to be varied betweenthe, conversion of methane and yields of acetylene中国煤化工ions. The results2100 K and 2300 K. There was no special quenchingandfYHCNMHG1816Plasma Science & Technology, Vol.5, No.3 (2003)Table 2. The analysis of the CB produced by plasma-pyrolyzed natural gasExamination itemsNumerical valueDBP Abs. (ml/g)1.4Reflectivity3Fluidity (mm)22Pyrogenation decremnent (%)Incineration (%)0.23pH3.6Nitrogen S.A. (m2/g)70Specific volume (ml/g)1Pigmentation (%)8(Volatility (%)16.8Notes: (1) We can't test the absorbing value of the iodine because the sample can't be soaked by the I2-KIliquor. (2) We can't test the absorbing value of the hydrochloric acid because the sample can't be soaked bybydrochloric acid. (3) The sample can't be dispersed synnetrically by DDP.23.0021.00752.0019.003430.78838.852923. 285121 1629.711 456.0044.5717.00000 300020001500 1000400cm'Fig.2 FTIR spectra of carbon blackwere summarized in Table 1. The methane conver-cluding the two main morphological properties: spesion was approximately 97% of methane injectioncific surface area and DBP absorption. Specifc sur-rates about 10 Nm3/h. The yield of CB was foundface area is 80 m2/kg and DBP is 1.4 ml/g. Accord-to be 43% of a methane injection rate of 10 Nm' /h,ing to the information published, the DBP of the CBand 41% of a methane injection rate of 15 Nm3/h. .produced by conventional method is not more thanFurther increase in methane injection rate resulted1.0 ml/g. As we know, the CB with a higher DBP isin a decrease in methane conversion and CB yield.a kind of high-structured CB.中国煤化工。Table 2 lists the analytical results of the CB, in-Fig.t is clear thatMHCNMHG1817Li Juan et al. : A New Grade Carbon Black Produced by Thermal PlasmaProcess13%、30%02300m60%Fig.4 Aggregse morphology ef carton blnck ot 7200magnifed hy TEMFig.3 Diameter distribution of the plasma carbon blackproducts: 30% for 20 nm ~ 30 nm, 50% for 30nm ~ 4093Enm,18%for40nm~60um,2%for60nm~150nmthe CB produced by DC plasma technology havesome special surface structure. In addition, theFTIR spectra reveals that there exist some aromaticCC bonds and a large amount of nitrogen-containingfunctional groups in the CB, such as -NH, -CN aswell as -CH, -OH, -COOH groups. About the -OH,Fig.5 Aggregate morphology of carton black at 19000-COOH groups in the FTIR spectra, we think thatmagnifed by TEMit should be led by the oxygen from the very fewimpurity of nitrogen. Also it shows that complexgate morphology of CB at 72000 magnified and 19000molecules can be synthesized from simple moleculesmagnifed by TEM. From Fig.4, we can see the prod-by plasma process. Because the main aim of theucts are abundant in an aggregate and highly fusedarticle is to describe production of CB, the mecha-together to form the aggregate. This high aggrega-nism of synthesizing -OH, -COOH groups won't betion was in line with the good performances obtaineddiscussed here.with DBP absorption for most of these blacks. FromA study conducted by TEM is decisive to charac-Fig. 5, TEM analysis of carbon structure shows theterize the texture (ie, elemental particles and theirproducts have an obvious boundary and are charac-aggregation) as well as the structure of CB[5).terized by a high level of graphitisation. These blacksThe texture was analyzed following two diferentpredict interesting properties for electrical conduc-scales, the particle size and the aggregate morphol-tive applications (batteries, conductive plastics, .. .ogy [3]. The blacks obtained by DC plasma werecharacterized by a rather small primary particle.Fig. 3 shows the profle of the size distribution of the4 ConclusionsCB particles. It is clear that the minimum size is20 nm, the maximum size is 150 nm, the average size中国煤化工. was investigated ex-is 38 nm. Fig. 4 and Fig. 5 show respetively aggre-_sma jet. The resutsYHCNMHG1818Plasma Science & Technology, Vol.5, No.3 (2003)show that the natural gas undergoes very fast andCB. It will of course bring new grades of CB to thecomplex reactions with a high temperature plasmaworld. In a further step, the development of thejet and decomposes completely to produce C2 andplasma process will be carried out simultaneously inCB. The CB produced by this process have a nar-various areas ranging from CB, new carbon nanos-row size distribution and a small average diametertructures including nanotubes.of 38 nm, and its electrical conductivity is as well asa highly branched aggregate. The DBP is 1.40 ml/gand it is a high structure CB. The FTIR spec-tra shows that there exist some aromatic Cc bondsReferencesand a large amount of nitrogen-containing functional1 Li Bingyan. The handbook of carbon black's pro-groups in the CB, such as -NH, -CN as well as -CH,duction and application. Bejing : Chemical In--OH, -COOH groups.dustry Press (in Chinese), 2000, 12Compared with the furnace process, the plasma? Boyd J W. Ulmann's Encyclopedia of Industiralprocess is an environmentally friendly process. ThChemistry, Weinheim: VCH Verlags Geellschaft,principle of the new process consists in replacing the1986, A5: 140Fulcheri L, Nprobst. Carbon, 2002, 40: 169~ 176incomplete cormbustion by directly spliting the hy-drocarbon into CB and C2 thanks to exterior elec-4 Zhao Huaqiao. Plasma chemistry and process,tric energy supply. The major objectives of the newHefei: Science and Technology Press, 1993, 2:4≈5process are: a better use of the feedstock thanks to5Bourrat X. Structure of carbons and carbon arti-the better conversion of the hydrocarbon into CBfacts. In: Marsh H, Rodriguer Reinoso F, editors,and C2, the production of new carbon grades thanksSciences of Carbon Materials, Alicante: Publica-to reaction temperatures and specific ehthalpies un-ciones Universidad de Alicante, 2000, 1 ~ 97reachable by the conventional combustion process.(Manuscript received 30 December 2002)The plasma process opens a totally new area forE-mail address of Li Juan: xiaolizi0068@sohu.com中国煤化工MYHCNMHG1819

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