6 Characterization of Petroleum Pitches Used for Coke Production
Downloaded by UNIV OF QUEENSLAND on April 21, 2017 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch006
W. Ε. SMITH, B. NAPIER, and O. J. HORNE Union Carbide Corp., Nuclear Division, Oak Ridge Y-12 Plant, Oak Ridge, Tenn. 37830
This report describes the use of nuclear magnetic resonance (NMR) spectrometry as an aid in structural characterization of pitch materials and was part of a larger study on characteriza tion and reproducibility of petroleum-derived products. (1) Discovery and implementation of pitches as bonding agents are re corded in some of the earliest known documents, and their usage in all probability long predates recorded history. Current usage reflects the desirable properties of pitch materials as numerous industries have been built around such applications as road surfacing, roofing materials, various adhesive and sealant formulations, and electrode fabrication. Though the use of pitch is an ancient art and represents a high-volume market today, characterization and control of pitches have not been emphasized since typical high-volume applications do not warrant such an emphasis. However, pitch from natural sources represents a complex mixture of structures and varies in composition with the location of the source and with the methods used to extract the pitch. The latter can be standardized, but must also compensate for variations in the source if a reproduc ible pitch is to be made. Currently, some specialty applications require a high degree of characterization and control of starting materials, and i t has been these users who continue to support efforts designed for that purpose. Fabricators of specialty items, in general, face less cost restraints and have a higher degree of precision in design and fabrication efforts. An application in which pitch materials are being widely used is as a binder in the fabrication of specialty composite structures which can subsequently be pyrolyzed to yield carbon. Such fabrication schemes place emphasis on pitch materials that exhibit appropriate properties both as plastics at fabrication temperatures and as ceramic-type materials after carbonization. Since the properties of the latter are quite dependent on the characteristics of the raw material and the chemical and mech anical events that accompany carbonization, the fabrications engineer becomes interested in such subjects as pitch properties, 63 Deviney and O'Grady; Petroleum Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
PETROLEUM DERIVED CARBONS
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64
Impurity contents, coke y i e l d s , and volume yields as they relate to the mechanical and e l e c t r i c a l properties of the end product. To optimize and Insure reproducibility of such a fabrication scheme, close control of both materials and processing 1s required. This, 1n turn, suggests the need for better characterization of pitch materials which w i l l necessitate the adaptation and development of more sophisticated analytical techniques than have t r a d i t i o n a l l y been used for describing these materials. NMR spectrometry promises to aid 1n characterization of pitch materials by providing considerable Information about the molecular structure and composition of quite complex mixtures. Using the method of NMR data analysis developed by Williams (2,3), Information on the a l i p h a t i c , al1cycl1c, and aromatic content 1n a sample of petroleum feedstock and a derived pitch was determined and 1s presented i n the following paragraphs. Experimental Studies Materials. Petroleum materials used 1n this study were supplied by the Ashland 011 Company, Ashland, Kentucky. The feedstock sample was f l u i d and was analyzed as received. Prior to analysis, the pitch sample was powdered and dried under a vacuum of < 100 urn for 20 hours at 25° C. Properties of these materials are compared 1n Table I. Analytical Methods. Average molecular weight data were obtalned using a Hewlett-Packard Model 302 vapor pressure osmometer. Sucrose octaacetate was used as a standard. Prior to analysis, chloroform Insolubles were removed by a standard procedure. Samples were analyzed as tetrahydrofuran solutions. Benzene Insolubles were determined as per ASTM D-2317. Carbon and hydrogen contents were determined by combustion 1n a carbon t r a i n using quantities of evolved carbon dioxide and water to calculate the carbon and hydrogen contents, respectively. Oxygen contents were determined by neutron activation analysis using a Kaman Model 711 neutron generator and beryllium as a standard. Analysis for the sulfur content Involved combustion 1n a bomb followed by a gravimetric determination of sulfur as barium sulfate. Ash contents were determined by f i r i n g samples to 900° C in a i r and weighing the residuals. High-resolution spectra were obtained using a Bruker HFX15 90-megahertz spectrometer. Other Instrument conditions are l i s t e d in Table II. Method of Data Analysis. This approach follows that described by Williams (2,3) and makes use of elemental composition and molecular-weight 3ata i n conjunction with proton distributions
Deviney and O'Grady; Petroleum Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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Downloaded by UNIV OF QUEENSLAND on April 21, 2017 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0021.ch006
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