458
Ind. Eng. Chem. Prod. Res. Dev. 1984, 23, 458-466
on reaction rate as well as yield of benzaldehyde, implying that in this range k1 and k2 are independent of cobalt acetate concentration. Oxidation of p -Methoxytoluene to p -Anisaldehyde.
The process for oxidation of toluene to benzaldehyde could be extended to the oxidation of p-methoxytoluene for the production of p-anisaldehyde. Thus p-methoxytoluenewas oxidized in a medium of acetic acid, with cobalt acetate (0.02 g-mol/L) as a catalyst and sodium bromide (0.16 g-mol/L) as a promoter at 10 kg/cm2 pressure and 125 "C temperature to obtain almost quantitative yield of panisaldehyde, when the overall conversion of p-methoxytoluene was restricted to about 20%. Conclusions
Up to 10% conversion, the use of either sodium bromide or paraldehyde as a promoter gave more than 90% yield of benzaldehyde. At higher conversions, the yield of benzaldehyde decreased markedly and benzoic acid was obtained as a coproduct. The use of sodium bromide was preferred to paraldehyde because relatively higher reaction
rates were obtained in the former case. In the range of 20 to 40% conversion, the yield of benzaldehyde was also higher with sodium bromide than that obtained with paraldehyde. Under suitable conditions (toluene, 28.56 % w/v of reaction mixture; solvent, acetic acid; cobalt acetate, 0.02 g-mol/L; sodium bromide, 0.16 g-mol/L; temperature, 110 O C ; pressure 10 kg/cm2; air flow rate 3 L/min) it was possible to get 40% yield of benzaldehyde, provided the overall conversion of toluene was restricted to 20%. Registry No. Toluene, 108-88-3; benzaldehyde, 100-52-7; sodium bromide, 7647-15-6;cobalt acetate, 71-48-7;paraldehyde, 123-63-7;p-methoxytoluene, 104-93-8;p-anisaldehyde, 123-11-5. Literature Cited Fields, E. K.; Meyerson. S. A&. Chem. Ser. 1968, No. 76(2), 395. Kamath, S. S.; Chandalia, S. B. J . Appl. Chem. Blotechnol. 1973, 23, 469. Kamiya, Y. A&. Chem. Ser. 1968, No. 76(2), 193. Morlmoto, T.; Ogata, Y. J . Chem. Soc., Sect. B 1967, 62. Ravens, D. A. S. Trans. Faraday. Soc. 1959, 55, 1768. Ray, S. K.; Mukherjee, P. N. Indian J . Technol. 1983, 21(4), 137.
Received for review September 22, 1983 Accepted March 5, 1984
Kinetics and Efficiency of Solar Energy Storage in the Photochemical Isomerization of Norbornadlene to Quadricyclane Constantine Phlllppopoulor and John Yarangozls Laboratory of Chemlcal Process Engineering, National Technlcal University of Athens, Athens, eeece
The conversion of norbornadiene to quadricyclane by polychromatic radlation in a solar simulator was investigated. Parameters examined were photosensitizers, reactant and sensitizer concentrationsJnsolationpower, and temperature. The rate of conversion and the efficiency of solar energy storage were measured and have been quantitatively correlated. The most efficient sensitizers were Michler's ketone, acetophenone, and benzophenone in that order. A mixture of the sensitizers performed worse than the less efficient sensitizer, perhaps due to a mechanism of intersensitizer energy transfer. Data have been obtained by exposing the system to the actual sunlight, and repeated cycles of photochemical conversion and thermal reverslon of the reaction were made. The kinetics of the thermal reverse reaction were investigated and presented. This information is considered to be useful in the development of a photochemical solar energy storage system.
Introduction
Photochemical conversion and storage of solar energy was recently being investigated in various laboratories around the world [Hautala et al. (1979); Scharf et al. (1979); Jones et al. (1979)j. Part of this interest is directed to the valence photoisomerizations of organic molecules. In particular, the norbornadiene (N)-quadricyclane (Q) system has been identified as a promising one for the storage of solar energy [Jones et al. (1979); Philippopoulos et al. (198311. The efficiency and kinetics of conversion of norbornadiene upon monochromaticirradiation (A = 254 nm) in the presence of solvents and photosensitizers has recently been reported [Phdippopoulos et al. (1983)l. The quantum efficiency was found to be a function of norbornadiene concentration, the largest value being 0.91 in pure norbornadiene with acetophenone as sensitizer. Acetophenone was found to be the most quantum efficient sensitizer followed by benzophenone and Michler's ketone. 0196-4321/84/1223-0458~01.50/0
It was suggested that the energy transfer from the excited photosensitizer to N is inversely proportional to the difference of triplet energy between the excited molecule and the acceptor. The present paper aims at studying the kinetics and efficiency of storage of polychromatic solar radiation under controlled solar simulation in the laboratory and under conditions of exposure to the sun. Also other objectives were to study the reverse thermal reaction Q N and to carry out a number of cycles of the process to determine possible product deterioration. It is hoped that this information may be useful in the development and improvement of a viable process for photochemical solar energy storage.
-
Theoretical Section
The main criterion which can be used for the screening of various proposed photochemical systems for the storage of solar energy is the overall storage efficiency, qw. As has 0 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 3, 1984
459
Table I. Calculation of Efficiency Values of Various Photochemical Systems for the Concersion and Storage of Solar Energy m a n 1 , -%
AH, compd compd B A norbornadiene sensitizer 1. acetophenone quadricyclane 2. benzophenone 3. CUCl 4. Michler's ketone dimethyl 2,3-norbornadiene dimethyl dicarboxylate sensitizer quadricyclane
kJ/mol (J/g)
112 (1190)
Q
7.
A,,
nm
?E
366 380 388 410
0.34 0.35 0.36 0.38
380 480 610 380
%* 5%
reverse thermal reaction
AMP
AM2b factorc
AM0
AM2
0.9 0.8 0.4 (0.8)
0.06 0.08 0.09 0.11
0.008 0.01 0.015 0.07
0.31 0.28 0.14 0.30
2.00 2.24 1.26 3.30
0.25 0.28 0.21 2.1
0.22 0.31 0.17
0.5 0.3 0.2
0.08 0.17 0.3
0.022 0.140 0.275
0.11 0.09 0.034
0.90 1.53 1.02
0.24 1.26 0.94
115-180
0.22
0.4
0.08
0.01
0.09
0.72
0.09
140-190
$JB~
135-200
77.7 (370)
1. benzophenone 2. camphorquinone trans-diacetylindigo
cis-
dicyclopentadienone
bishomocubanone
34 (100) 68.6
50-60
(500) dianthracene 35 400 0.12 (0.1) 0.075 0.01 0.1 0.10 0.075 220-250 dimer of 189 370 0.58 (0.05) 0.065 0.008 0.03 0.20 0.024 190-260 naphthalene butyl ester "AM0 = irradiation of the sun outaide the atmosphere. *AM2 = spectrum of the sun for angle of incidence radiation to the normal of earth 60". 'Q factor = 7E X @BA. anthracene naphthalene butyl ester
been suggested in the literature [Bolton (1977); Archer (1978);Scharf et al. (1979)],the overall storage efficiency is the ratio of the chemical energy stored into the system (through a photochemical transformation) to the solar energy incident on the collector, namely
where m is the moles of product B produced in the photochemical conversion hv
A-B
(m
is the molar reaction enthalpy stored in B (to be recovered in the reverse reaction), t B is the insolation time, F is the collector's area, and JAis the incident radiation power per unit area per unit wavelength X. The efficiency qwhas been analyzed as the product of four basic efficiency factors [Scharf et al. (1979)] fw
= qE#BAqaqabs
(3)
A detailed analysis of these four factors is justified to explain their significance. The efficiency factor qE above represents the ratio of the stored molar enthalpy AR to the energy of 1 mole of photons, namely
(4) where A, is the ground wavelength for the transfer of (A or sens) from ita basic energy state to its first activated singlet state. This factor ?')E has been computed by Bolton (1977). The quantum efficiency factor 4 B A of eq 3 is defined as the ratio of photons absorbed by substance A (which produced molecules of product B), to the total number of photons absorbed by A. This efficiency is measured experimentally. It must be remarked that for photosensitized incorporates the efficiency transformations the factor bA of energy transfer from the sensitizer to A. The product (9E4BA) has been termed the &-factor and has been used as a criterion of energy storage [Calvert and Pitts (1977)l.
The third factor involved, la,has been termed as the available or useful energy and is defined as
In words, qa representa the ratio of the energy of one mole of photons of wavelength X, (multiplied by the fraction of available moles of photons with X IA,), to the total incident solar energy. Finally, the efficiency factor qab represents the ratio of the photons absorbed by A (or the sensitizer or the photocatalyst) to the total incident photons with X IA,, i.e.
S,"JA qabs
- 10-f~)dX
X(tAk/eJ(l
> k,(A). In this case, the rate equation becomes first order with respect to (A)
+
The other limiting case is when energy transfer is much faster than intersystem crossing and fluorescence, i.e. (k, + kf)
