Maikel M. van Iersel et al. / Ultrasonics Sonochemistry 17 (2010) 315–317
317
Table 1
Methyl chloride synthesis using ultrasound irradiation.
4. Conclusions
Gas feed composition (v%)
Time to steady
state (min)
Methyl chloride
yield
This work has demonstrated that ultrasound irradiation allows
a more sustainable process towards methyl chloride as
for
CH4
Cl2
Ar
compared to the current industrial chlorination of methane. The
extreme conditions inside the imploding cavities enable radical
formation at ambient bulk conditions. Furthermore, this ultrasonic
route is intrinsically safe as the reaction is performed under diluted
conditions and the reaction stops when the ultrasounds source is
switched off. Accurate control of the cavity contents is crucial for
obtaining significant yields in such gas-phase reactions. Addition
of a monoatomic gas is necessary to achieve the required temper-
ature rise, whereas the reactant concentration inside the cavity is
relevant for the chemical effect. When aiming at a particular reac-
tant concentration inside the cavity, non-equilibrium thermody-
namics have to be taken into account. Due to rapid cavity
dynamics, the composition of the cavity interior does not equal
the gas feed composition, yet strongly corresponds to the relative
solubilities of the gases in the liquid.
4.09
0.22
0.22
0.22
0.22
95.69
83.58
53.22
10.79
90
4
16.20
46.56
88.99
170
170
170
19
15
7
predominantly induces transient cavitation, the cavities have
insufficient time to fully equilibrate with the surrounding liquid
[27]. The aqueous solubilities of methane and argon are approxi-
mately equal at 293 K. As ethylene is more soluble in water than
argon, a relatively large amount of ethylene is likely to be present
inside the cavity when it forms. This would correspond with the
observation that the hydrogen formation rate for ethylene has a
maximum at a hydrocarbon concentration lower than in the case
of methane. The same argument holds for a gas feed containing
iso-butane.
References
[1] K.A. Marshall, Chlorocarbons and chlorohydrocarbons, survey, Kirk-Othmer
Encyclopedia of Chemical Technology, vol. 6, Wiley & Sons, New York, 2003.
[2] M.T. Holbrook, Methyl chloride, Kirk-Othmer Encyclopedia of Chemical
Technology, vol. 16, Wiley & Sons, New York, 2003.
[3] M. Rosberg, W. Lendle, G. Pfleiderer, A. Tögel, E-L. Dreher, E. Langer, H.
Rassaerts, P. Kleinschmidt, H. Strack, R. Cook, U. Beck, K-A. Lipper, T.R.
Torkelson, E. Löser, K.K. Beutel, T. Mann, Chlorinated Hydrocarbons, Ullmann’s
Encyclopedia of Industrial Chemistry, Wiley-VCH, Verlag GmbH & Co. KgaA,
Weinheim, 2006.
[4] P. Tundo, A. Perosa, F. Zecchini, Methods and Reagents for Green Chemistry: An
Introduction, Wiley, Hoboken, 2007.
[5] P.T. Anastas, J.C. Warner, Green Chemistry Theory and Practice, Oxford
University Press, New York, 1998.
[6] M. Lancaster, Green Chemistry: An Introductory Text, Royal Society of London,
Cambridge, 2002.
[7] V.K. Ahluwalia, M. Kidwai, New Trends in Green Chemistry, Kluwer Academic
Press, Dordrecht, 2004.
[8] Y. Peng, W. Zhong, G. Song, Ultrason. Sonochem. 12 (2005) 169.
[9] S. Puri, B. Kaur, A. Parmar, H. Kumar, Ultrason. Sonochem. 16 (2009) 705.
[10] J.L. Luche, Synthetic Organic Sonochemistry, Plenum, New York, 1998.
[11] T.J. Mason, J.P. Lorimer, Applied Sonochemistry: The Uses of Power Ultrasound
in Chemistry and Processing, Wiley-VCH, Weinheim, 2002.
[12] L.H. Thompson, L.K. Doraiswamy, Ind. Eng. Chem. Res. 38 (1999) 1215.
[13] G. Cravotto, P. Cintas, Angew. Chem., Int. Ed. 46 (2007) 5476.
[14] B.M. Teo, W. Prescott, M. Ashokkumar, F. Grieser, Ultrason. Sonochem. 15
(2008) 89.
Starting from the insights obtained by these hydrogen forma-
tion experiments, the feasibility of methane chlorination at ambi-
ent conditions has been explored. Relatively high concentrations
of an inert monoatomic gas in the feed are required to assure a suf-
ficient temperature rise upon collapse. Secondly, because the ratio
of chlorine to methane in the cavity should be close to stoichiom-
etric and the pronounced effect of gas solubility on the composi-
tion of the cavity interior, the difference in water solubility of the
two reactants should be accounted for. During the experiments
the concentration of chlorine in the gas feed was kept constant
at a value of 0.22 v/v% and the ratio between methane and argon
was varied. The steady state concentration of methyl chloride
was measured by GC-analysis of the outgoing gas flow and from
this the methyl chloride yield has been calculated. The results of
these experiments are presented in Fig. 2 and Table 1.
The experiments have demonstrated that ultrasound enables
the formation of methyl chloride under diluted and mild reaction
conditions. By optimizing the ratio of argon to methane in the
gas feed, methyl chloride yields as high as 19% have been observed.
At lower methane concentrations the low reactant concentration
inside the cavity limits the overall yield, whereas above the opti-
mum concentration the decrease in hot-spot temperature results
in lower conversions. In accordance with previous work, the high-
est product yield is obtained for a gas feed containing a higher frac-
tion of methane as that corresponding to the maximum hydrogen
formation rate from water [19]. This shift can be explained by the
improved methane to chlorine ratio dissolved in the liquid. For a
methane concentration in the feed of 50 v/v% this ratio equals
approximately unity, leading to a more similar cavity concentra-
tion for both reactants. The head space contained no detectable
amounts of dichloromethane, indicating that multiple chlorination
of methane hardly occurred. This high selectivity in methyl chlo-
ride can probably be explained by the relatively low methyl chlo-
ride concentration in the reactor compared to the methane
concentration. The acquired GC-spectra, however, suggested the
formation of higher hydrocarbons [19].
[15] S. Biggs, F. Grieser, Macromolecules 28 (1995) 4877.
[16] T.J. Mason, C. Petrier, Ultrasound Processes, in: Advanced Oxidation Processes
for Water and Wastewater Treatment, IWA Publishing, London, 2004.
[17] M.P. Brenner, S. Hilgenfeldt, D. Loshe, Rev. Mod. Phys. 74 (2002) 425.
[18] W.B. McNamara III, Y.T. Didenko, K.S. Suslick, Nature 401 (1999) 772.
[19] E.J. Hart, C.H. Fischer, A. Henglein, J. Phys. Chem. 91 (1987) 4166.
[20] Supeno, P. Kruus, Ultrason. Sonochem. 9 (2002) 53.
[21] K. Makino, M.M. Mossoba, P. Riesz, J. Am. Chem. Soc. 104 (1982) 3537.
[22] C.H. Fischer, E.J. Hart, A. Henglein, J. Phys. Chem. 90 (2) (1986) 222.
[23] A. Henglein, Z. Naturforsch. 40b (1985) 100.
[24] B.E. Poling, J.M. Prausnitz, J.P. O’Connell (Eds.), Specific Heat Capacities have
been Determined from Temperature Dependent Correlations Given in
Properties of Gases and Liquids, fifth ed., McGraw-Hill, London, 2001.
[25] P.J. Lindstrom, W.G. Mallard (Eds.), Aqueous Solubilities have been Derived
from Henry Coefficients Provided in NIST Chemistry WebBook, NIST Standard
Reference Database Number 69, National Institute of Standards and
Technology, Gaithersburg MD, 20899, 2005.
[26] M.M. van Iersel, J. Cornel, N.E. Benes, J.T.F. Keurentjes, J. Chem. Phys. 126
(2007) 064508.
[27] G.J. Price, M. Ashokkumar, M. Hodnett, B. Zequiri, F. Grieser, J. Phys. Chem. B
109 (2005) 17799.