An Inter-laboratory Comparison of CO 2 Isotherms Measured on Argonne Premium Coal Samples A. L. Goodman,* ,† A. Busch, | G. J. Duffy, ⊥ J. E. Fitzgerald, § K. A. M. Gasem, § Y. Gensterblum, | B. M. Krooss, | J. Levy, ⊥ E. Ozdemir, ‡ Z. Pan, § R. L. Robinson, Jr., § K. Schroeder, † M. Sudibandriyo, § and C. M. White † U.S. Department of Energy, National Energy Technology Laboratory, Pittsburgh, Pennsylvania, Chemical and Petroleum Engineering Department, University of Pittsburgh, Pennsylvania, School of Chemical Engineering, Oklahoma State University, Stillwater, Oklahoma, Institute of Geology and Geochemistry of Petroleum and Coal, Aachen University, (RWTH), Aachen, Germany, and CSIRO Energy Technology, Lucas Heights Science and Technology Centre, Lucas Heights, NSW, Australia Received December 18, 2003. Revised Manuscript Received April 20, 2004 Adsorption isotherms, which describe the coal’s gas storage capacity, are important for estimating the carbon sequestration potential of coal seams. This study investigated the inter- laboratory reproducibility of carbon dioxide isotherm measurements on dry Argonne Premium Coal Samples (Pocahontas No. 3, Upper Freeport, Illinois No. 6, Wyodak-Anderson, and Beulah Zap). Four independent laboratories provided isotherm data for the five coal samples at temperatures of either 22 °C or 55 °C and pressures up to 7 MPa. The differences among the data sets in this study appeared to be rank-dependent in that the data among the laboratories agreed better for high-rank coal samples than for low-rank coal samples. A number of parameters such as sample size, equilibration time, and apparatus dimensions were examined to explain the rank effect, but no trend could be found that explained the differences. The variations among the data are attributed to different procedures for removing moisture to obtain the “dried” coal. Introduction Recently, carbon dioxide (CO 2 ) sequestration in coal seams has been identified as an attractive option that may aid in mitigating emissions of greenhouse gases. 1-5 Of special interest is the CO 2 storage capacity of coal seams at various pressures. Most often, a coal seam’s CO 2 storage capacity is estimated from isotherm mea- surements using the coal of interest. Measurement of the amount of CO 2 adsorbed per unit mass of coal with increasing pressure produces an isotherm that describes the coal’s gas storage capacity. Although individual laboratories often determine their own intra-laboratory isotherm reproducibility, inter-laboratory isotherm re- producibility has not been reported. This makes it difficult to compare the results obtained from different laboratories. Thus, questions arise concerning the extent to which differences in results can be attributed to the coal sample rather than to the details of the measure- ment technique. Strict control must be placed on experimental meth- odology and variables in order to obtain reproducible results. 6 The need for inter-laboratory accuracy is well recognized by regulatory agencies and industry. This need drives the development of standard methods. 7 Further, the research community recognizes that sev- eral factors including the operator, the equipment, the calibration of the equipment, and the laboratory envi- ronment including temperature and humidity can influ- ence the variability of a test result. Because no standard method or equipment for obtain- ing CO 2 isotherm data is available, labs reporting isotherms use their own, usually home-built, apparatus and procedures. Thus, it is possible that various labo- ratories report different storage capacities for the same coal samples. To investigate the inter-laboratory repro- * Author to whom correspondence should be addressed. Tel: 1-412- 386-4962. Fax: 412-386-5920. E-mail: angela.goodman@netl.doe.gov. † U.S. Department of Energy, National Energy Technology Labora- tory. ‡ University of Pittsburgh. § Oklahoma State University. | Aachen University. ⊥ CSIRO Energy Technology, Lucas Heights Science and Technology Centre. (1) Reeves, S. Geologic Sequestration of CO2 in Deep, Unmineable Coalbeds: An Integrated Research and Commercial-Scale Field Dem- onstration Project. 2001. SPE paper 71749 presented at the Annual Technical Conference and Exhibition, Society of Petroleum Engineers, New Orleans, LA, September 30-October 3. (2) Gentzis, T.; Hirosue, H.; Sakaki, T. Energy Sources 1996, 18, 119-129. (3) Gentzis, T. Int. J. Coal Geol. 2000, 43, 287-305. (4) Allis, R.; Chidsey, T.; Gwynn, W.; Morgan, C.; White, S.; Adams, M.; Moore, J. Natural CO 2 Reservoirs on the Colorado Plateau and Southern Rocky Mountains: Candidates for CO2 Sequestration. DOE/ NETL-2001/1144-CDROM, 1-19. 2001. NETL Publications. 5-14-2001. (5) White, C. W.; Strazisar, B. R.; Granite, E. J.; Hoffman, J. S.; Pennline, H. W. J. Air Waste Manage. Assoc. 2003, 52, 645-715. (6) Mavor, M. J.; Owen, L. B.; Pratt, T. J. Measurement and Evaluation of Coal Sorption Isotherm Data. 1990. SPE paper 20728 presented at the 65th Annual Technical Conference and Exhibition, Society of Petroleum Engineers, New Orleans, LA, September 23-26, pp 157-70. (7) ASTM E 691-99 Standard Practice for Conducting an Interlabo- ratory Study to Determine the Precision of a Test Method. In Annual Book of ASTM Standards; West Conshohochken, PA, 2000; pp 264- 285. 10.1021/ef034104h CCC: $27.50 © xxxx American Chemical Society PAGE EST: 7.4 Published on Web 00/00/0000