Energy & Fuels 1988,2,356-358
366
Table I. Effect of Ultrasound on the Time Required for Regeneration of Dimethyl Polysulfidea S loading after regeneration, w t % time, min init 1.0
2.5 5.0
10 30
with ultrasoundb 100 77 38 23b 23b
with mechanical stirring
100
>95 >95 95 51 22b
loading of the organic phase was determined by comparing its density with the density of dimethyl disulfide and dimethyl polysulfides containing various quantities of sulfur. This analytical procedure has been described in full previ~usly.~ Acknowledgment. We wish to thank B. King for the preparation of the manuscript and Alberta Sulphur Research Ltd. (Calgary, Canada) for financial support. Registry No. S, 7704-34-9;S(CH&, 624-92-0.
"An aqueous solution of sodium sulfide (10 w t 70)was used a t 30 O C . Power was set at 6 W em". bThis figure represents the lower limit possible by this method.
( 5 ) Dowling, N. I.; Lesage, K. L.; Hyne,J. B. Alberta Sulphur Res. Ltd. Q.Bull. 1985, 22, 16-26.
10 wt % of sodium sulfide solution was subjected to ultrasonic radiation over various time periods (Table I). Mixing of the two previously immiscible phases was instantaneous on irradiation, and chemical analysis showed that the sulfur loading was reduced to 23 wt % after a 5-min treatment. In comparison, 30 min of vigorous mechanical stirring was required to achieve the same level of sulfur loading. Note that -20 wt % is the lowest level obtainable by a single treatment because of the equilibrium nature of the reaction of dialkyl polysulfides with sodium sulfide. Ultrasound may be accelerating the regeneration process by two mechanisms: first, it inputs vibrational energy causing mixing of the fluids; second, through the phenomenon of aqueous cavitation, it causes the formation OH') in aqueous solutions and these radof radicals (He, icals will assist the decomposition of the polysulfides, which is known to follow a radical mechanism. Two recent rev i e w cover ~ ~ ~the ~ theoretical and practical aspects of the effect of ultrasound on chemical reactions. Besides the parameters listed in Table I, the effect of temperature, ultrasonic power, and polysulfide/sodium sulfide ratio have been studied. Temperatures in the range 0-80 "C are equally effective but powers >5 W cm-2 were necessary to obtain effective conversion of the polysulfides. All concentrations of sodium sulfide solution gave some regeneration, but optimum rates were obtained when the 10 w t % concentration was reached. Ultrasonic treatment did not cause emulsions between the organic and aqueous phases. Consequently, it should be possible to develop a commercial regeneration procedure by using a flow reactor coupled to an ultrasound source. Reagents. Sodium sulfide and dimethyl disulfide (99% +) from Aldrich Chemical Co. were used without further purification. Water was distilled and deionized. Dimethyl polysulfide (100 wt % S), was prepared by adding sulfur (100 g) to dimethyl disulfide (100 g) containing a trace of diethylamine and previously saturated with H2S. Regeneration Procedure. First, 100 wt % sulfurloaded dimethyl polysulfides (20 g) was added to 10 wt % aqueous sodium sulfide (60 g), and the mixture was irradiated with ultrasound (20 KHz, 6 W cm-? by using a Branson (Model 450) generator equipped with a 2-cmdiameter probe for a set period of time (see Table I). Irradiation intensity was measured in terms of the percentage output of total power available per unit area of the probe tip. Total power is assumed to be that specified by the manufacturer. Heat was removed or added to the system by circulating fluids through an internal coil. After the organic and aqueous phases were separated, the sulfur
K. L. Lesage, J. B. Hyne Department of Chemistry, University of Calgary 2500 University Drive NW Calgary, Alberta, Canada T2N IN4 Received November 30, 1987 Revised Manuscript Received February 11, 1988
(3) Lorimer, J. P.; Mason, T. J. Chem. SOC.Rev. 1987, 16, 239-274. (4) Lindley, J.; Mason, T. J. Chem. SOC.Rev. 1987, 16, 275-311.
P.D. Clark,* R. A. Clarke
Characterization of a Solvent-Swollen Coal by Small-Angle Neutron Scattering
Sir: It is known that bituminous coals will swell in solvents such as pyridine.' The phenomenon of coal solvent swelling is being used to characterize coal structure especially in the determination of molecular sizes between cross-links. In addition, swelling can affect coal reactivity in thermolysis reactions. Also, it is important to note that swelling increases reagent accessibility in chemical modification of coals.2 The objective of this study is to determine changes that occur in the physical structure of coals upon swelling in an organic solvent. Small-angle neutron scattering (SANS) is being used to examine the changes in pore structure in a Pittsburgh No. 8 seam hvA bituminous coal, Argonne Premium Coal Sample No. 4,3 upon exposure to two perdeuteriated solvents, benzene for nonswollen and pyridine for swelling conditions. The deuteriated solvent provides a large contrast between the solvent and the solid coal for neutron scattering. Coal porosity has been studied by SANS in the dry stateH and in nonswelling deuteriated ~ o l v e n t a . These ~*~ studies suggested that this technique can be useful for examinhg pore structure. Our current results demonstrate that the pore structure of a coal swollen in pyridine is dramatically altered from ita original state. The SANS measurements were made at Argonne National Laboratory's Intense Pulsed Neutron Source (IPNS) by using the small-angle diffractometer (SAD).Neutrons were produced in pulses by spallation from 450-MeV protons followed by moderation by solid methane (18 K) to produce wavelengths of 0.5-14 A. A 64 X 64 array position sensitive multidetector was used to detect neutrons scattered by the sample while the wavelength of the neutrons (A) was determined by time-of-flight. The data were corrected for scattering from the cell and incoherent (1) Green, T.; Kovac, J.; Brenner, D.; Larsen, J. W. In Coal Structure; Meyers, R. A., Ed.; Academic: New York, 1982; pp 199-282. (2) Liotta, R. Fuel 1979,58, 724-728. (3) Vorres, K. 5.;Janikowski, S. K. Prepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. 1987,32(1) 492-499. (4) Kaiser, H.; Gethner, J. S. Proc.-Int. Conf. Coal Sci., 1983,1983, 300-303. \ (6) Tricker, M. J.; Grint, A.; Audley, G. J.; Church, S. M.; Rainey, V. S.; Wright, C. J. Fuel 1983,62, 1092-1096. (6) Gethner, J. S.J . Appl. Phys. 1986,59, 1068-1085.
0887-062418812502-0356$01.50/0 0 1988 American Chemical Society
Energy & Fuels, Vol. 2, No. 3, 1988 357
Communications -0
scattering. Finally, the relative intensity (I)was expressed as a function of the scattering vector Q Q = (47r/X) sin B (1)
a
where B was half the scattering angle and
I(Q) = K(
1
(P, - pm) exp(iQr) d3r)
(2)
where K included all the experimental constants and p s and pm were the scattering length densities of the solvent and the matrix. A Q range of 0.005-0.35 A-1 is accessible on the SAD instrument a t IPNS.' The preparation of the Argonne Premium Coal Sample has been d ~ r i b e d A. ~-100 mesh APCS No. 4 sample was used. (Anal. Found on a maf basis: C, 83.2; H, 5.3; N, 1.6; S, 0.9; O(difference1, 9.0; ash (dry), 9.) A sealed glass ampule containing the coal was broken open in a nitrogen-atmosphere glovebox. The coal was well mixed and a portion transferred to a 2 cm diameter X 1.85 mm thick quartz cell leaving enough room for swelling. Perdeuteriated solvent was added to the coal, and then the cell was sealed. In the case of pyridine-d, the sample was allowed to sit for several days before doing the SANS experiment to insure complete swelling. In both cases the sample transmission relative to empty quartz cell was about 82% and thus multiple scattering will be essentially very small. A Guinier plot: based on the relationship shown in eq 2, for both solvents is shown in Figure la. Even though benzene-d6 and pyridine-d6 have similar scattering length densities, 5.35 X 1O'O and 5.69 X 1O'O cm-2 respectively, there is a striking difference between the scattering data from the two solvents. For both solvents the Guinier plots were nonlinear throughout the Q range of 0.005-0.25 A-1 which may be due to a wide distribution of pore sizes. This is consistent with a few SANS and SAXS studies on several coals.H The scattering data from the pyridine-swelled coal are not consistent with a fractal surface as a linear dependence in log I vs log Q plots is not seen in a wider Q range, which should be the signature for the fractal surface. Instead, we see a linear dependence in log (QI) vs Q2plot in a wider Q range yielding a negative slope that is more applicable to a rod-shaped void. The difference in the scattering between the coal and swollen coal may be in the shape of the pores. From small-angle scattering it is possible to estimate the shape of the pore or particle by using a modified Guinier a n a l y ~ i s . ~There J~ are three general types of pore shapes: spherical, elongated (tubular), and lamellar. From the Guinier analysis one can determine the radius for spherical shapes, cross sectional radius for elongated shapes and thickness for lamellar shapes due to the following scattering laws for the latter two shapes: elongated:
I = IAl/Q)
I = It(1/Q2) To investigate the possibility of elongated pores In (QI) is plotted versus Q2 in Figure Ib. For benzene-d, there is no correlation, but for the pyridine-d, a negative slope is found. At low Q, tubular pores with a radius of 9-11 A lamellar:
~~
(7) Epperson, J.E.; Thiyagarajan, P.; Klippert, T. E. "SAD Manual"; available from IPNS, Argonne National Laboratory, Argonne, IL 60439. (8) Guinier, A.; Fournet, G. Small Angle Neutron Scattering; translated by Walker, C. B., Kudowitch, K. L.; Wiley: New York, 1955; pp 19-23. (9) Kratky, 0.; Pilz, 1. Q. Reu. Biophys. 1978, 11, 39-70. (10)Hjelm, R. P. J. Appl. Crystallogr. 1985,18 452-460.
0.00
X
0.01
0.02 Q 2(
l/A *)
0.03
0.04
I
I
...
0.004
0.008
0.016
0.020
0.004
0.008
0.016
0.020
Figure 1. Guinier analysis of the scattering data for pyridine-& (A)and benzene-d6(0) imbibed coal: (a) normal presentation of the Lnjintensity)as a function of the scattering vector squared; (b) presentation modified to investigate the existence of tubular pores; (c) presentation modified to investigate sheet pores.
are found. Figure ICshows that lamellar pores are not seen in either sample since no negative slopes are observed for both samples. From these preliminary results we conclude that in the good swelling solvent the tertiary structure of this bituminous coal undergoes major rearrangement. Whereas the original coal contains a broad size range of roughly spherical pores, the swollen coal seems to contain elongated pores with definite cross sectional radius. The pyridine appears to be filling up the pores with the cross sectional radius measured (about 9 A); about five pyridines can be fitted perpendicular to the axis of the elongated pore. The size of the pyridine molecule has been estimated from space-filling computer models based on the van der Waals radii of the individual atoms. It is important to note that we are observing relatively narrow elongated pores. These results could be explained by invoking hydrogen bonding between the pyridines and the phenols or other acidic hydroxyls on the surface of the tubular pores. In addition, NMR and ESR experiments have shown that the motion of pyridine in a coal is restricted.ll Our SANS data imply that the tertiary structure in the coal may be to a great extent determined by the hydrogen bonding, which was broken up by pyridine upon swelling, and this structure is rearranged to tubular channels filled with pyridine. Since the lamellar shapes were not seen in the scattering of both benzene- and pyridine-contacted coals it seems (11) Silbemagel, B. G.; Ebert, L. B.; Scnlosberg, R. H.; Long, R. B. In Coal Structure; Gorbaty, M. L., Ouchi, K., Eds.; Advances in Chemistry 192; American Chemical Society: Washington, DC, 1981; pp 23-36.
358 Energy & Fuels, Vol. 2, No. 3, 1988
unlikely that the coal had a layered polycyclic aromatic structure.
Acknowledgment. This work was performed under the auspices of the Office of Basic Energy Sciences, Divisions, of Chemical Sciences and Material Sciences (IPNS), U.S. Department of Energy, under Contract No. W-31-109ENG-38. Registry No. Neutron, 12586-31-1.
Book Reviews Randall E. Winam* Chemistry Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, Illinois 60439 P. Thiyagarajan
IPNS Division, Argonne National Laboratory 9700 South Cass Avenue, Argonne, Illinois 60439 Received December 23,1987 Revised Manuscript Received March 21, 1988
Book Reviews
The author claims to cover all aspects of methanol from the conversion of coal to syngas to special chemical productions based on methanol and the use of methanol as an energy and transportation fuel. In fact the book covers all these aspecta in a rather broad and descriptive manner in 10 chapters. After a rather nondescriptive introduction, the different routes for syngas and then for methanol synthesis (95 pages) are given. The following sections deal with methanol as fuel for transportation and energy production (79 pages) and methanol-based synthesis for liquid hydrocarbons, syngas, and hydrogen (92 pages). Chapter 8 contains a rather broad survey on direct and indirect coal hydrogenation hardly reflecting methanol (67 pages). The last sections cover all processes for basic chemicals from methanol but is restricted to C1-CI compounds and a short review on single cell protein production. In a rather descriptive way all aspects are thoroughly covered, and the 384 pages contain 94 pages of literature references updated to 1983/1984 but mostly covering the literature from 1950 to the late 1970s. This book is neither a text book nor a true engineering display but a comprehensive and detailed source of basic information. For this,a section presenting all chemical and physical data for methanol should have been added. A very good keyword register provides easy access to all information. The book is a good source of information for anybody interested in or in need of a broad survey. It is, however, limited in full chemical or engineering details. H. H. Oelert, Technische Universitat Clausthal
scribing structural elements of these compounds. The second chapter presents a technical discussion of the application of graph theory to PAH structure. This is the basis for the author's 'Formula Periodic Table for PAHs", which is used to organize the PAHs into logical groups. The next chapter describes methods that the author used to determine the numbers of isomers for PAHs, numbers that are given later in the compilation. Auxiliary information derived from these isomer counting procedures are also discussed. The final discussion chapter describes general spectroscopic features of PAHs, including ultraviolet absorption, photoelectron spectroscopy, infrared spectroscopy, and NMR. A summary of simple methods for estimating Huckel MO eigenvalues for use in UV and photoelectron spectroscopy is also given. The compilation of properties takes up the last 264 pages and considers about 500 compounds. Data for each are given on a half-page form. This form contains space for the following information: formula; name; properties (mp, bp, solubility), Huckel .n-energy,number of Kekule structures, Hackel HOMO energy; number of benzenoid isomers; brief information on synthesis and/or iaolation; syctral properties (W,NMR, photoionization); carcinogenic activity (a "yes" box and a "no" box are given for each); uses and references. When information could not be found by the author, the entry is left blank (perhaps 75% of the entries are blank). In summary, this book organizes the properties of benzenoid PAHs into a logical framework and uses this framework for an extensive compilation of chemical properties. It should be of value to anyone who routinely refers to the basic chemical/physical properties of these substances. Stephen E. Stein, National Bureau of Standards
Handbook of Polycyclic Hydrocarbons. Part A. Benzenoid Hydrocarbons. By J. R. Diaz. Elsevier: Amsterdam, The Netherlands. 1987. xii + 387 pp. ISBN 0-444-42802-X.
Catalytic Activation of Carbon Dioxide. ACS Symposium Series 363. Edited by William M. Ayers. American Chemical Society: Washington, DC. 1988. 212 pp. $49.95.
This book presents a general discussion and extensive compilation of properties of polycyclic aromatic hydrocarbons (PAHs). The focus of this volume is on benzenoid PAHs, that is, molecules composed entirely of fused, six-membered aromatic rings. Classification and much of the discussion is couched in terms of "graph theory", a method of analysis that deals solely with the molecular geometry. Although the application of these methods is not always straightforward and is accompanied by some specialized terminology, the result is an easily understood, intuitive method of structural description. For instance, the major level of grouping is based simply on the number of internal carbon atoms in the PAH. In a sense, graph theory serves to express structural ideas that would otherwisebe represented in a leas exact way by using illustrative chemical structures. Because of the often very complex structures of PAHs, a more precise means of discussing structural features can be of real value. The first 123 pages summarize the properties of benzenoid PAHs, making extensive use of the terminology of graph theory. The first chapter is devoted to nomenclature, which represents a particularly difficult communications problem for researchers studying PAHs. Graph theory is well suited to the task of de-
This book was developed from a symposium sponsored by the Division of Colloid and Surface Chemistry at the 191st meeting of the American Chemical Society in New York in April, 1986. It covers a subject of increasing importance because it is believed that carbon dioxide buildup from combustion of fossil fuels is a worldwide problem that will require both research and development for its solution. The evolution of carbon dioxide from fossil fuels, particularly from coal and coal gasification, threatens the atmospheric balance of the world and the world climate. The book consists of 14 chapters discussing catalytic routes for the use and conversion of carbon dioxide as well as some thermodynamic and equilibrium data. Some of the chapters briefly discuss the economic outlook of various process routes. Overall, the book provides a good introduction to a number of ideas and projects for conversion of carbon dioxide, and the various chapters contain lengthy references for those wanting more detailed study of particular routes of carbon dioxide removal. A major weakness of the book is the fact that it consists of chapters written by different authors and, therefore, there is little crossreferencing and continuity between the different chapters. Additionally, most of the chapters are rather brief and can be con-
Methanol-Chemie und Energierohstoff (Methanol-Raw Material for Chemistry and Energy). By Friederich Asiiger. Springer: West Berlin. 1986. 384 pp + 93 figures (German). $108.90.
