Carbon Materials for Advanced Technologies Episode 7 ppsx

220 Table 9. Effect of blending coal-derived pitches from WVGS 13421 on elemental composition (daf) NMF-soluble 75.25 wt% 25 75 wt% 450°C extract EXT.HEXT EXT HEXT hydrogenation EXT 450 450 HEXT450 C 84 2 85 9 88 6 88.1 H 5.5 53 56 5.8 N 2.1 24 22 22 S os 0.6 0.8 0' 74 3.0 31 C/H atormc 128 134 134 126 ratio +oxygen by difference For the most part, the elemental analysis data for the blends are consistent with a weighted average of the lndividual components. Also shown is the elemental analysis for some of the soluble products form WVGS 13423 in Table 10 As was observed for the WVGS 13421 products, hydrogenation increased the total hydrogen content and decreased the atomic C/H rabo. Table 10. Elemental composition of products from WVGS 13423 NMP-soluble extract 75 25 wt% 450°C hydrogenation EXT EXT: HEXT45 0 HEXT450 C 84.9 86.3 85.5 H N S 0 53 2.0 07 70 5.6 24 59 19 04 34 C/H atormc ratio 133 129 1 26 'oxygen by difference One effect of the degree of hydrogenation is to lower the softening polnt and glass transition temperature, T,, of the pitch as shown in Table 11. The occurrence of a softenlng point and glass transition demonstrates the pitch-like character of the hydrogenated products, although these values are sbll considerably higher than most commercial pitches. Only a limited number of coal-derived pitches were examned by 'H NMR because of their low solubihty in solvents commonly used 111 convenbonal proton magnetic resonance. Table 12 reports the distribubon of hydrogen for three of the pitches. Unlike coal-tar pitches, which typically have over 85% of the hydrogen bonded to aromatic carbon, the matenals listed in Table 12 are characterized by a high content of aliphabc hydrogen. 22 1 Table 11. Characteristics of NMP-soluble pitches from WVGS 13421 NMP-soluble 400°C 450°C 75.25 wt% extract hydrogenation hydrogenahon EXT:HEXT EXT HEXT4OO HEXT450 450 Glass "C Mettler transition T,, ___- '168 *76 *76 softening 4300 173 158 165 pomt, "C +by thermal mechanical analysis, * by differential scanning calonrnetry Table 12. 'H NMR characterlzation of coal-derived pitches WVGS 13421 WVGS 13407 WVGS 13421 75.25 wt% NMP-soluble extract 450°C hydrogenation EXT HEXT450 'H distribution Aromatic H, %Ha 29 39 41 Aliphatic H, %Hal 71 61 59 Size exclusion chromatography (SEC) using trichlorobenzene as a solvent was used to determme the number average molecular weight (MWJ distribution of several of the coal-derived pitches. The molecular weight distribution for all the materials is quite broad, with a considerable amount exceedmg a MW, of several hundreds. Typically, the molecular weight averages were between MW, of 400 and 500. These values are only slightly higher than those for commercial pitches. Moreover, the wdth and shape of the molecular weight distribution curves for the coal extracts are generally simlar to those for commercial pitches. 2 3 Ash reduction in coal-derivedpitches One of the more lmportant considerations in detemmg the end use of synthetic graphte is its contamination with metallic components Metals such as iron, vanadium, and especially in nuclear applications, boron are deleterious to the performance of graphte Table 3 presented the extrachon yields of NMP- soluble material for three biturnnous coals. For these coals, rmneral matter and insoluble coal residue were separated from the extract by simple filtration through 1-2 pm filter paper Table 13 lists the high-temperature ash content m the dry coal, and m their correspondmg NMP-insoluble and NMP-soluble products. The reduced ash content of the extract is typically between 0.1 to 0.3 wt% using traditional filtration techniques for the small-scaled extraction experments 222 To reduce the quantity of ash in the extracts even further, steps were implemented using a sequential solids removal scheme that entailed a combination of centrifugation and filtration. Following extraction of the coal Table 13. Ash content in WVGS coals and coal products Weight % ash WVGS ID 13407 13421 13423 Coal, dry 14.0 3.2 3.8 Residue 29.3 4.6 4.7 Extract 0.2 0.1 0.3 Yield of extract (daf) 66.3 35.7 34.2 with NMP, the mixture was placed in a centrifuge during which time the particulates were subjected to 2000 G for two hours. The supernatant liquid was removed from the solids by simply decanting and then filtering through 1-2 pm filter paper. The resulting filtrate was centrifuged again for an extended period of time (overnight) at 2000 G. Again the supernatant liquid was separated by decanting and then filtered through 0.2 pm filter paper. Table 14 shows the results using the above process for WVGS 13421 coal where it can be seen that significant ash reduction is possible. Table 14. Results of de-ashlng experiments using centrifugation and filtration of WVGS 1342 1 Material Weight % ash Dry coal 3.2 Raw extract 0.1 Second centrifugation 0.05 While the quantity of ash in the extracts is rather low, after coking and calcining the ash constituents are slightly concentrated in the carbons because of the small volatile matter loss from the extracts. For example, Table 15 shows the ash content of products from WVGS 13421. The extract was obtained using the large-batch extractor as described earlier. The product was de-ashed by first centrifuging at 2000 G for 90 minutes followed by filtration through 1-2 pm filter paper. The product was recovered, dried, and converted to green and calcined coke. Table 15. Ash content of WVGS 13421 and its products Raw coal NMP-extract Residue Green coke Calcined coke Ash. wt% 3.03 0.04 3 34 0.15 0.24 To determined if the ash removal steps could be simplified, experiments were performed on hydrogenated coals. Hydrogenation experiments were conducted at 400°C in tetralin and the pitch isolated from the insoluble mmeral matter and 223 coal by centrifugation alone at 2000 G for 60 minutes without the use of NMP. The supernatant liquid was decanted and dried under vacuum at 150°C. Table 16 lists the yield of products and their ash contents. Table 16. Ash content of raw coal and their hydrogenated coal products, wt% Supernatant liquid Insoluble solids Yield Yield Coal sample Raw product Ash content product Ash content WVGS 13407 13.6 43 <o. 1 52 19.3 WVGS 13421 3.0 38 <o. 1 55 5.4 coal Note that the yield of extract product presented here is lower than that reported earlier in Table 4 because the hydrogenated products were not extracted with NMP but were centrifuged directly. The data show that centrifugation by itself, and without any accompanying filtration, appears to provide pitches of acceptable purity, albeit with an associated lower yield. The coal-derived pitch precursors for WW-1, WW-2, and WW-3 test graphites were de-ashed by the combined centrifugation and filtration method while all of the other pitches were de-ashed by centrifugation alone (2000 G, 90 minutes). 3 Preparation and Characteristics of Cokes Produced from Solvent Extraction 3.1 Preparation of green and calcined cokes Two reactor types were used to convert coal-derived pitches into green coke. A heavy, carbon-steel pipe (about 0.75 m long by 5 cm inside diameter) was machined at both ends such that plugs could be inserted to seal the system. The coking reactor was filled approximately 213 full with pitch, flushed with nitrogen, and then sealed. The coking reactor was inserted into a ceramic tube furnace and heated in two stages. In the first stage the coal pitch was heated to 400°C. In this stage the material becomes a molten mass. The tube was kept at ths condition for 12 hours. In the second stage, the tube reactor contents were then raised to 600°C and held at this temperature for one hour, whereupon the tube was permitted to cool to room temperature. The product was then recovered and weighed. The green coke precursors for WW-1, WW-2, and WW-3 test graphites, WVGS 13407 NMP-soluble extract, NMP-soluble extract from 350°C hydrogenated WVGS 13407, and WVGS 13421 NMP- soluble extract, respectively, were made with this system. 224 All subsequent green coke operations were made in a second coker, which was fashioned from steel pipe approximately 18 cm in diameter and 25 cm in length. A metal plate was welded to one end and a metal collar was welded to the other end such that a steel lid could be bolted to the system. Typically, about 250 to 500 g of pitch were sealed under nitrogen in the coker reactor and the system placed in a large temperature-programmable furnace. The heat treatment process was as follows. The temperature was raised 5"C/min to 350 "C and then l"C/min to 425°C and the temperature held at 425°C for 90 minutes. Finally the temperature was raised further at 3"C/min to between 500 and 600"C, and held there for 3 hours. The coker was cooled to room temperature and the material recovered to determine green coke yield. The green cokes were calcined by placing a weighed amount of green coke into an alumina tube. The tube was fitted with end caps to allow for a constant purge of nitrogen. The alumina tube was then inserted into a high-temperature furnace and the temperature raised to about 1000°C for a period between 30 and 60 minutes. The furnace was turned off, cooled to room temperature, and the product recovered to determine the calcined coke yield. The effect of hydrogenation on the yield of green coke is shown in Table 17. Thermogravimetric analysis (TGA) was also conducted for comparison. It can be seen that the pitch from unhydrogenated coal results in a fairly high yield of green coke. As the severity of hydrogenation increased the green coke yield decreased, probably because of molecular weight reduction and loss of low- molecular weight species during coking. Also, in general, TGA yields are lower than the yields obtained from the green coking operation. Undoubtedly, during the green-coke process in the sealed reactor, some reflux occurred, promoting additional condensation and enhanced carbon yield. The TGA experiment, which involves rapid heating under a flowing inert gas atmosphere, tends to promote enhanced distillation of volatile species. Tables 18 and 19 show the effects of blending extracts of hydrogenated coal with those from untreated coal for WVGS 13421 and WVGS 13423, respectively. For both coals, the amount of hydrogenated material in the blend causes a reduction in coke yield. Again, the TGA yields are generally lower than the yields obtained using the coking reactor. This is particularly pronounced for the WVGS 13423 coal following hydrogenation at 450"C, where the TGA yield is only 34 wt%. As noted previously, the hydrogenated products from WVGS 13423 are relatively volatile. 225 Table 17. Effect of hydrogenation on green coke yields WVGS 13407 71.4 71.0 Coal Green coke yield, wt% TGA yield, wt% EXT 60.3 HEXT3 50 WVGS 13421 EXT 71.2 80.0 HEXT400 62.8 HEXT450 57.1 51.0 WVGS 13423 EXT 70.3 61.5 HEXT450 52.3 34.0 Table 18. Effect of blending hydrogenated coal-derived pitch and coal extract on green coke yields, WVGS 13421 Blending ratio Green coke yield, wt% TGA yield, wt% 100.0 EXTHEXT450 71.2 80 0 75.25 EXTHEXT450 69.6 25:75 EXT:HEXT450 62.9 0.100 EXT.HEXT450 57.1 63.5 52.9 51.0 Table 19. Effect of blending hydrogenated coal-derived pitch and coal extract on green coke yields, WVGS 13423 Blending ratio Green coke yield, wt% TGA yeld, wt% 1OO:O EXT:HEXT450 70.3 61.5 75:25 EXT:HEXT450 61.7 57.7 25:75 EXTHEXT450 47.2 40.4 0:lOO EXT:HEXT450 52.3 34.0 Table 20 reports the yield of calcined cokes for several of the graphite precursors. The high-coke yields indicate that most of the volatiles were lost during the green coking operation. Since no visible tar or smoke occurred during calcinabon, most of the weight loss is attributed to evolution of hydrogen, non-condensable hydrocarbons, and other light gases. 3.2 Analysis of cokes by optical microscopy Polarized light photomicrographs were taken of the green and calcined cokes, as well as their corresponding test graphites. The untreated extract cokes are characterized by very small anisotropic domains on the order of 3 microns or less. This type of optical structure is believed to be highly desirable for nuclear graphite applications. 226 Table 20. Yield of calcined coke for WVU test graphites WVGS 13421 Calcined coke yield. wt% HEXT4OO 75:25 EXT:HEXT400 60:40 EXT:HEXT350 EXT 75:25 EXT:HEXT450 25:75 EXT:HEXT450 HEXT450 93.8 96.1 95.5 92.8 91.6 92.7 94.2 WVGS 13423 EXT 87.0 75 :27 EXT:HEXT450 91.1 25:75 EXT:HEXT450 93.1 HEXT450 92.0 In contrast, the hydrogenated extracts show much larger anisotropic domain structures, increasing in size with increasing hydrogenation severity, which is consistent with the reduced coefficient of thermal expansion (CTE) exhibited by the test graphtes as discussed later. Further, blending hydrogenated material with untreated extract results in anisotropic domains of an intermediate size. Thus by varying the process parameters, a variety of cokes can be prepared to produce tailored graphites with a range of anisotropy. Figure 1 shows the effects of blending on the development of optical texture. Indeed, the manufacture of graphites ranging from very isotropic to highly anisotropic is possible from a single coal source by controlling blending composition and hydrogenation. This finding was also substantiated by Seehra et al. [22] in a recent publication. 3.3 Ash analysis of cokes Table 21 reports the ash content and ash composition (determined by inductively coupled plasma-atomic emission spectroscopy, ICP-AES) for all of the calcined cokes used to fabricate the test graphites. It can be seen that the amount of ash and its make-up are variable, but are within the range observed for petroleum-based calcined cokes. Although the ash contents in all of the calcined cokes appear rather high, these materials may still be acceptable because many of the metallic species are driven off during graphitization. This aspect is addressed in the next section. 227 Figure 1. Optical photomicrographs of green cokes derived from WVGS 13421 pitches: top, EXT; middle, 75:25 EXT:HEXT450; bottom, HEXT450 Table 21. Ash content and composition of calcined cokes used to make the WW graphites 00 wvu- wvu- wvu- wvu- wvu- wvu- wvu- wvu- w- ww- wvu- wvu- ww- 1 2 3 4 5 6 7 8 9 10 11 12 13 13421 13421 13421 13421 13423 13423 75~25 25175 75:25 60:40 25:75 75~25 EXT. EXT: 13423 13407 13421 13421 EXT: EXT: EXT: EXT: Precur 13407 HEXT 13421 HEXT HEXT HEXT HEXT HEXT HEXT 13423 HEXT HEXT HEXT EXT 350 EXT 400 450 400 350 450 450 EXT 450 450 450 sor Sulfur wtyo 0.53 0.45 0.56 0.54 0.40 0.60 0.65 0.46 0.64 0.62 0.56 0.36 0.32 Ash wt% 0.76 0 76 0.29 0.29 0.24 0.34 0.29 0.16 0.47 0.61 0.91 0.25 0.43 Metals PPm B 6.8 5.3 2.1 3.8 31 3.1 3.0 2.6 3.6 3.0 2.4 3.4 3.3 Na 346.0 36.0 37.0 56 0 16.0 81.0 79.0 20.0 51.0 27.0 37.0 17.0 126.0 Mg 1470 380 12.0 8.8 58 80 2.3 8.6 9.5 11.0 15 0 60.0 17.0 A1 274.0 239.0 41.0 94.0 35.0 57.0 19.0 80.0 115.0 93.0 188.0 57.0 297.0 Si 474.0 281.0 60 0 279.0 173.0 88.0 12.0 70.0 341.0 4.0 298.0 80.0 594.0 K 32.0 29.0 8.8 5.7 4.3 0.6 3.9 5.9 11.8 9.0 26.0 __ 39.0 Ca 759.0 365.0 87.0 65.0 128.0 20.0 16.0 15.0 16.8 38.0 121.0 132.0 128.0 Ti 429.0 509.0 77.0 125.0 6.6 87.0 94.0 ____ 59.8 206.0 139.0 60.0 40.0 V 20.0 17.0 4.9 7.9 1.9 1.7 I .8 2.8 5.6 11.0 12.0 6.0 2.0 Cr 28.0 61.0 9.4 23.0 17.0 84.0 63.0 5.0 55.2 300.0 294.0 72.0 170.0 Fe 778.0 1879.0 999.0 643.0 537 0 1209.0 286.0 504.0 1795.0 1779.0 37040 597.0 645.0 Mn 11.0 29 0 22.0 10 0 30.0 15 0 12.0 __ 18.1 44.0 57 0 40.0 50.0 NI 13 0 25 0 13.0 20.0 15.0 43 0 33.0 38.0 32.7 162.0 152.0 38.0 38.0 Cu 252.0 25.0 111 0 74 0 444.0 92 1 294.0 412.9 1036.0 653.0 4490- 227.0 Zn 240 12.0 207.0 77.0 220 1060 100 __ 8.4 61.0 98.0 27.0 15.0 P ____ 45.0 0.4 1.1 ____ 04 0.2 52.0 0.4 ____ ____ __-_ ____ 229 4 Preparation and Evaluation of Graphite From Coal-Derived Feedstocks Test graphites were made from calcined coke which was initially milled into a fine flour so that about 50% passed through a 200 mesh Tyler screen. The coke flour was then mixed with a standard coal-tar binder pitch (1 1 0°C softening point) at about 155°C. The ratio of pitch to coke is about 34:100 parts by weight. After mixing with the liquid pitch, the blend was transferred to the mud cylinder of an extrusion press heated to about 120°C. The mix was then extruded into 3-cm diameter by 15-cm long cylinders and cooled. These green rods were then packed in coke breeze and baked in saggers to 800°C at a heating rate of 60"Ckour. The baked rods were graphitized to about 3000°C in a graphite tube furnace. In most cases, the graphite rods were machined into rectangular specimens 2-cm wide by 15-cm long for measurement of the CTE. 4. I Analytical characterization c f graphites In order to assess the loss of inorganic contaminants during graphibzation, the ash composition of most of the graphites was analyzed by ICP-AES. The total ash contents of the WW graphites are compared to those for the precursor calcined cokes in Table 22. Also included are data for H-45 1 and VNEA, which are the current qualified nuclear-grade graphites. The elemental ash composition for most of the graphites, as measured by ICP- AES, are compiled in Table 23. The results show that most of the inorganic matter is removed during the graphitization process. The elemental compositions of the WW graphites are in the same range as the commercial nuclear graphites which have presumably undergone extensive additional halogen purification. Table 22. Ash contents of calcined cokes and thelr processed graphites (ppm) WJ- 1 7600 290 ww-2 7600 370 ww-3 2900 680 ww-4 2900 380 ww-5 2400 70 WW-G 3400 130 ww-7 2900 1020 WVU-8 1 GOO 100 WVU-9 4700 100 VNEA ____ 220 60 H-45 1 ____ Calcined coke Graphitc [...]... 22nd Biennial CofiferenceOR Carbon, American Carbon Society, San Diego, CA, 1995, pp 244 245 Irwin, C., and Stiller, A,, Carbon products and the potential for coal-derived 234 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 feedstocks Paper presented at Carbon Materials for Advanced Technologies, American Carbon Society Workshop, Oak Ridge, TN, 18 May 1994 Mantell, C L., Carbon and Graphite Handbook,... 6 .7 66 6.5 VNEA 10 1.1 14 11 22 0.1 07 01 _ _ WVU-9 3.O 01 1.o 11 0.8 2.1 17 5.6 4.3 17 4.0 0 .79 0.10 4 .7 -1.1 13 45 5.1 43 _- H-451 5 .7 1.1 12 23 12 1.6 0.84 24 0 10 7. 1 - 0.42 0.13 1.o Table 24 Some properties of WW coal-derived calcined cokes and their graphites WVU -1 WW2 WVU3 WVU4 WVU5 WVU6 WWI WW8 WW9 WVU- WVU11 WVU12 WW- 10 CTE 4.42 2.89 528 1.59 071 4.52 3 .77 1.19 3 12 5.28 5 07. .. 1.8 WVU-2 8.6 2.5 10 9.9 11 19 71 11 - _ WVU-3 5.5 1.1 79 51 73 96 66 47 _ 58 0.21 1.8 0.14 0.10 0.94 37 0.42 18 0 11 0.11 0 95 WVIJ-4 4.6 1.6 9.1 14 11 91 55 50 " _ 15 0 49 0.82 0.18 _ - 0.50 WVU-5 2.2 1.3 2.5 4.0 8.2 23 56 0.1 12 0.52 0.38 0.21 0.10 0.51 WVU-6 4.0 0. 87 68 5.9 90 17 49 7. 6 25 _-_- 0.58 0.12 0 10 0 .78 WW -7 6.4 1.9 7. 8 432 12 11 33 6.1 0.21 36 0. 17 0.32 0.15 0.16 0.60 WVU-8 09... Huntington, N Y , 1968 Eser, S., and Jenkins, R G., Carbonization of petroleum feedstocks I relationships between chemical constitution of the feedstocks and mesophase development, Carbon, 1989, 27, 877 8 87 Lewis, I C., Chemistry of pitch carbonization, Fuel, 19 87, 66, 15 27 1531 Derbyshire, F J., Vitrinite structure: alterations with rank and processing, Fuel, 1991, 70 , 276 284 Song, C., and Schobert, H H., Non-fuel... development [l] Model Mandated Test Cerhficabon Year Sales Area Method Standard 1 970 California Carbon Trap 6 grams HC 1 971 49 States 6 grams HC Carbon Trap 1 972 50 States 2 grams HC Carbon Trap 1 978 50 States SHED 6 grams HC 1980 California SHED 2 grams HC 1981 50 States SHED [8] 2 grams HC 1995 California VT SHED [9] 2 grams HC I995 Callfornia Run Loss 0.05 g/mile 1996 50 States VT SHED 2 grams HC 50 States... 2 3 4 5 Reis, T., To coke, desulfurize, and calcine, Hydrocarbon Processing, 1 975 , 54, 145 156 Yamada, Y ,Imamura, T., Kakiyama, H., Honda, H., Oi, S., and Fukuda, K., Characteristux of meso -carbon microbeads separated from pitch, Carbon, 1 974 ,12,3 07 319 Edie, D D., and Dunham, M G., Melt spinnmg pitch-based carbon fibers, Carbon, 1989, 27, 6 47 655 The Stansberry, P G., Zondlo, J W., Stiller, A H., and... 1.09 0.96 R 13.16 10.01 13 16 998 11.85 14 .71 15 10 10.18 11.56 896 1 377 10.10 1 1 76 density 1.51 1. 57 1. 57 148 CTE X 10-6/"C, R in pohm-m; density i gicm' n 138 1. 57 1.50 1.48 159 1.51 161 1. 47 1.42 graphite 13 e c 232 00 10 05 15 20 25 30 WewM Percent Hydrogen Added to Coal (daq Figure 2 Effects of hydrogenation on CTE of coal-based graphites 0 1 0 25 50 75 100 Weight Percent EXT m Blend w t h HEXT450... understanding of the performance of activated carbon in hydrocarbon adsorption over a larger range of operation Properties of activated carbons produced by Westvaco for automotive applications are presented in Table 5 Table 4 Properties of selected activated carbon products Reprinted from [l 11, copyright 0 1992 John Willey & Sons, Inc., with permission Liquid-Phase Carbons Gas-Phase Carbons Manufacturer... graphite manufacture, Journal cf Materials Science, 1983, 18, 3 161 3 176 King, L F., and Robertson, W D., A comparison of coal tar and petroleum pitches as electrode binders, Fuel, 1968, 47, 1 97 212 Hutcheon, J M., Manufacture technology of baked and graphitized carbon bodies In Modern Aspects cf Graphite Technology, ed L C F Blackman Academic Press, New York, 1 970 , pp 49 78 Shah, Y T., Reaction Engineering... Applications/characteristicsof activated carbon The activated carbon materials are produced by either thermal or chemical activation as granular, powdered, or shaped products In addition to the form of the activated carbon, the fiial product can differ in both particle size and pore structure The properties of the activated carbon will determine the type of application for which the carbon will be used 2.2.1 Liquid phase . 27. 0 37. 0 17. 0 126.0 Mg 1 470 380 12.0 8.8 58 80 2.3 8.6 9.5 11.0 15 0 60.0 17. 0 A1 274 .0 239.0 41.0 94.0 35.0 57. 0 19.0 80.0 115.0 93.0 188.0 57. 0 2 97. 0 Si 474 .0 281.0 60 0 279 .0 173 .0. 5 07 1.09 0.96 CTE 4.42 2.89 528 1.59 071 4.52 3 .77 1.19 3 12 5.28 R 13.16 10.01 13 16 998 11.85 14 .71 15 10 10.18 11.56 896 1 377 10.10 11 76 density 1.51 1. 57 1. 57 148 138 1. 57. 294.0 72 .0 170 .0 Fe 77 8.0 1 879 .0 999.0 643.0 5 37 0 1209.0 286.0 504.0 179 5.0 177 9.0 370 40 5 97. 0 645.0 Mn 11.0 29 0 22.0 10 0 30.0 15 0 12.0 __ 18.1 44.0 57 0 40.0 50.0 NI 13