Energy & Fuels 1988,2, 355-356
l
40
100
140
100
l
220
270
Temp r C ]
Figure 5. Gas chromatograms of the aliphatic fractions (A-1) of the (A) original coal THF extract and (B)heat-treated A-3 and A-4 mixture for Illinois No. 6. Conditions were as in Figure 2. Numbers denote the number of carbons of n-alkanes.
compounds such as alkylbenzenes, alkylnaphthalenes, phenanthrene, and alkyl hydroaromatic triterpanes, presumably formed by pyrolysis of the high molecular weight fractions. Figure 4 shows a mass spectrum which was tentatively identified as alkyl pentacyclic hydroaromatics.
355
The gas chromatograms of the A-1fraction of the original coal extract and of heat-treated A-3 and A-4 mixtures are shown in Figure 5. The differences between the chromatograms demonstrate the occurrence of pyrolysis reactions. We have shown that low molecular weight compounds are produced by very mild pyrolysis of some coal extracts. They were not physically trapped in the coal but are formed by decomposition of higher molecular weight compounds. While we have not demonstrated that the increase in extractability caused by mild heating of coals is due to pyrolyses, we have demonstrated that it may be due to pyrolysis in some coals. The relatively small molecules (a mobile phase) isolated after pyrolysis need not be present as clathrates inside cages in the macromolecular network (an immobile phase). Our data are clearly inconsistent with the claim that no coal pyrolysis occurs at temperatures below 350 0C.37 Coal pyrolysis can begin at temperatures as low as 250 OC and is presumably continuous above that temperature. Unimolecular bond scission of single u bonds is improbable at this temperature, and the low-temperature processes probably involve chain reactions and/or electrocyclic processes.
Acknowledgment. We thank Drs. Ron Liotta and Mike Siskin for helpful comments on an earlier version of this manuscript. (37) Schulten, H.-R.; Marzec, A. Fuel 1986, 65, 855-860.
Communications Ultrasound-Assisted Regeneration of Sulfur Solvents Used in Sour Gas Production
Sir: Sulfur deposition in production tubulars has become a more common occurrence as higher H2S containing natural gas reservoirs are developed.' These reservoirs are important new sources of elemental sulfur produced from H2S by the Claus process. So-called supersour (>60% H2S) gas reservoirs likely cannot be produced without use of a suitable solvent to dissolve elemental sulfur that is precipitated as the pressure and temperature along the production flowpath decrease. At present, when a well plugs with sulfur, dimethyl disulfide or a mixture of alkyl disulfides (1) is displaced down the well string. These materials react with sulfur in the presence of basic catalysts, producing liquid polysulfides that can be flowed from the well: RNHi
RSSR + Ss RS,R 1 2 R = CH,, C2H6;x 2 2 For sour gases containing 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
