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Ind. Eng. Chem. Prod. Res..Dev., VoI. 17. No. 2, 1978
TECHNICAL REVIEW Desulfurization of Organic Sulfur Compounds by Selective Oxidation. 1. Regenerable and Nonregenerable Oxygen Carriers Amir Attar and William H. Corcoran' Chemical Engineering Laboratory, California lnstltute Of Technology, Pasadena, California 9112'5
Amir A t t a r is a n Assistant Professor of Chemical Engineering a t the Department of Chemical Engineering, University of Houston, Houston, Texas 77004. Dr Attar obtained his Ph.D. in Chemical and Enuironmental Engineering from the California Institute of Technology, and his B.Sc. and M S c . from the Technion, Haifa, Israel. Dr. Attar is a n active researcher and consultant on coal desulfurization, liquefaction, and gasification.
William H. C o r c o r a n received his Ph.D. in Chemical Engineering a t the California Institute of Technology in 1948. His research interests have been mainly in applied chemical kinetics and in biomedical engineering. The work in applied chemical kinetics has had special focus on pyrolysis of hydrocarbons and reactions of oxides of nitrogen. His current biomedical engineering activities relate to the fluid mechanics of flow through artificial heart valves. Presently he is President of the American Institute of Chemical E n gineers and has been especially active in chemical engineering education by way of the Engineers' Council for Professional Development a n d the American Society for Engineering Education.
0019-7890/78/1217-0102$0.100/0
Introduction Current desulfurization methods (Horne and McAfee, 1960; Schuman and Shalit, 1970; Schuit and Gates, 1973) react hydrogen and the organic sulfur compound, denoted by RSR', in accord with the equation RSR'
+ 2H2
-
RH
+ R" + H2S
(1)
The effectiveness of the hydrodesulfurization especially depends on the combined form of the sulfur. In particular, when the sulfur is present in thiophenes or aromatic sulfides, the hydrodesulfurization requires high temperatures and partial pressures of hydrogen (Phillipson, 1971). In general, whenever the n electrons of the sulfur can resonate with li electrons, the energy of the carbon-sulfur bond (C-S) becomes practically identical with that of a carbon-carbon bond. Then the selectivity of hydrodesulfurization is reduced, and hydrogenation of carbon-carbon bonds will occur. Loss of selectivity is particularly important for coal and residual oil because most of the carbon atoms are unsaturated, and most of the organic sulfur is in the form of thiophenes and aromatic sulfides (Attar and Corcoran, 1977; Horton and Randall, 1947; Given and Wyss, 1961). Search for alternative desulfurization schemes intensified in 1970, and a new general desulfurization method was formulated (Attar, 1972; Attar, 1973; Corcoran, 1974; Attar and Corcoran, 1975; Attar, 1976). The method used two steps: (1) selective oxidation of the organic sulfur to sulfoxides (I) and sulfones (11) with the latter as the preferable product; the general form of the reaction may he written as IO]
R-S-R' +R-SO-R'
I
[m
R-SO2-R'
(2)
I1
(2) thermal decomposition of the oxidation product, in the presence or in the absence of a base; here the reaction may he represented as
(heat)
R-S02-R'
hydrocarbons
+ SO2
(3)
If a base is present, the SO2 finally appears as a sulfite. The structure of R and R' determines the types of hydrocarbons t h a t will be obtained; e.g., if R is aliphatic, an olefin is obtained (Reid, 1960; Suter, 1944). With dibenzothiophene sulfone, however, a diphenyl phenol is obtained (Wallace and Heimlich, 1968). Aromatic sulfides and sulfones may couple due to the pyrolytic reaction (Went, 1965; Bordwell et al., 1968). With oxidation of the sulfur to the sulfone, the bond energy between the carbon and the sulfur is reduced on the average by 5.2 k c a l h o l for aliphatic sulfides and by 11.8 k c d m o l for
0 1978 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol.
17, No. 2, 1978
103
A review on desulfurization of organic sulfur compounds by selective oxidation is presented. This part 1 is directed to results that have been obtained with both regenerable and nonregenerable oxygen carriers. When a sulfur-containing fossil fuel is oxidized by molecular oxygen, two types of reactions occur of major import in desulfurization. One is the formation of peroxidic species; the other is selective oxidation of the organic sulfur by the peroxides to form sulfoxides and sulfones. Optimal oxygen selectivity would be 0.5, but the optimum is not reached because the peroxides can be decomposed thermally and thus be lost for sulfur attack. In solid fuels, mass transfer effects can decrease oxidative efficiency, and for both liquid and solid fuels, protic solvents such as water and alcohol can decrease selectivity of the oxidation of the sulfur compounds to sulfones.
aromatic sulfides and thiophenes. Thus, the selectivity of the decomposition a t the sulfur-carbon bond is increased. Indeed, organic chemists use decomposition to remove SO2 from organic sulfones (Heldt, 1965; Wallace and Heimlich, 1966; Bordwell et al., 1968).
Methods of Oxidation T h e applicability of a desulfurization scheme depends on the kinetics and the selectivity of the oxidation. The oxidation should be rapid, and the oxidizer should be selective to the sulfur. Selective oxidation of sulfur compounds has been investigated by many researchers. Hartough (1952) reviewed the oxidation of thiophenes, and Reid (1960) reviewed the oxidation of sulfides. T h e most economical oxidizer on an industrial scale, however, is oxygen. Therefore, a method is needed which uses molecular oxygen as the oxidizer. Two schemes have been used to oxidize sulfur compounds with oxygen. They are: (1) Direct application of oxygen or air (Cullis et al., 1968; Capozzi and Modena, 1974); this method is suitable for thiols and is usually carried out in basic solution (Wallace et al., 1965); and (2) indirect oxidation using an oxygen carrier. Oxygen carriers are molecules which can selectively oxidize the sulfur and which can be regenerated or produced using molecular oxygen. Two types of carriers were tried, regenerable and nonregenerable. Methods with Regenerable Oxygen Carriers. The scheme of oxidation of sulfur compounds with a regenerable oxidizer UOz involves two steps: (1) oxidation U02
+ R-S-R'
-+
U
+ R-S02-R'
(4)
(2) regeneration of the oxidizer with molecular oxygen
u +0 2
-
U02
(5)
Nitrogen Dioxide as a Regenerable Oxidizer. Oxidation
regeneration 2N0
+0 2
+
2N02
(7)
Attar and Corcoran (1976) observed that 70% of the sulfur of 65-100 mesh Pittsburg seam coal was oxidized a t 140 "C and atmospheric pressure by a gas stream containing 5% NO:! in Nz. The initial heating value of the coal was 7199 cal/g, and the final value was 7133 cal/g. Relative to the initial weight of the sample, 6% by weight was volatilized, and 3.8 wt % of the original sample was volatilized as water. Of the initial total weight, 0.46% was organic sulfur and 1.23% was in pyrites. Diaz and Guth (1976) patented a desulfurization process based on these reactions under certain conditions. T h e method has potential if two problems can be solved. First, there is a safety
problem due to the possibility of a rapid and explosive reaction between the coal powder and the NO2. Second, there are potential problems of air pollution because of NO, attaching itself to the coal structure and then appearing in the atmosphere as NO, or in other nitrogen compounds. Evidence exists that organically bound nitrogen ends as NO, pollution (Fine e t al., 1974). Chlorine as a Regenerable Oxidizer. Chlorine can be applied to desulfurization with oxidation and hydrolysis proceeding as follows
R
>s R
+ Cl?
-
R\
m ,
R'
In work to date, chlorination of coal in an aqueous carrier (Mukai e t al., 1969), in an organic solvent (Macrae and Oxtoby, 1965), or in the gaseous phase (Sun and Wu, 1974) does not seem to be selective. Sun and Wu (1974) observed excessive gasification and oxidation of the organic matrix. Ganguli et al. (1976) oxidized coal with chlorine at 69 "C in methylene chloride and decomposed the product with water a t 350 "C. They noted that about 1%chlorine remained attached to the organic matrix even after the hydrolysis. In a method which was first proposed by Brown et al. (1948), Attar and coworkers (1975) used chlorine to oxidize dibenzothiophene in a solution of CC14 a t -10 "C and then hydrolyzed the product a t 15 "C. They observed that substantial chlorination of the phenyl groups occurred. Oxidation by chlorine will be useful if the process is conducted so t h a t selectivity for the sulfur is controlled and hydrolysis of the organically bound chlorine is carried to completion. If the hydrolysis is not completed, chlorinated phenols may result. Methods without Regeneration of the Oxidizer. Oxidation of a hydrocarbon by molecular oxygen proceeds via the intermediates of organic hydroperoxides ( H P ) and peroxy acids (PA). The peroxidic species can selectively oxidize sulfur compounds to the corresponding sulfides and sulfones. A detailed discussion and a review of this concept have been presented by Attar (1973), Corcoran (1974), and Attar (1974, 1976). Much of the background material on oxidation of hydrocarbons by oxygen has also been discussed previously by numerous authors, and therefore will only briefly be discussed here. Two excellent reviews were published by Emanuel et al. (1967) and by Sheldon and Kochi (1973). The following points are of special note.
104
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
Table I. Rate Constants for the Oxidation of Sulfur Compounds by Hydroperoxides and Peroxides Sulfur compound
Peroxide
Dibenzothiophene tert-Butyl hydroperoxide Dibenzothiophene Hz02 Dibenzothiophene sulfoxide Dibenzothiophene
H202
Dibenzothiophene
H202
Dibenzothiophene
H202
Dibenzothiophene
H202
Solvent Acetic acid H20, acetic acid, and white oil H20, acetic acid, and white oil White oil, H20, and acetic acid White oil, H20, and acetic acid White oil, H20, and acetic acid White oil, H20, and acetic acid tert-Butyl alcohol
H2Oz
Cyclohexyl methyl tert- Butyl sulfide hydroperoxide Cyclohexyl methyl tert- butyl n-Butyl alcohol sulfide hydroperoxide Cyclohexyl methyl tert-Butyl Methanol sulfide hydroperoxide Cyclohexyl methyl tert-Butyl Ethylene glycol sulfide hydroperoxide Cyclohexyl methyl Cyclohexene tert-Butyl alcohol sulfide hydroperoxide Cyclohexyl methyl tert- Butyl Methanol sulfide hydroperoxide Cyclohexyl methyl Cyclohexene Ethylene glycol sulfide hydroperoxide Cyclohexyl methyl Cyclohexene Benzene sulfide hydroperoxide Cyclohexyl methyl Cyclohexene Cyclohexene s u 1fide hydroperoxide Cyclohexyl methyl tert-Butyl Benzene sulfide hydroperoxide Cyclohexyl methyl tert-Butyl Cyclohexane sulfide hydroperoxide Cyclohexyl methyl Cyclohexene Cyclohexane sulfide hydroperoxide Cyclohexyl methyl tert-Butyl Benzene sulfide hydroperoxide air Isopropyl alcohol p,p’-Dichlorobenzyl p,p’-DichloroH202 Isopropyl alcohol benzyl Isopropyl alcohol p,p’-DichloroH202 benzyl Ethyl alcohol p,p’-DichloroH202 benzyl p,p’-DichloroH202 Acetonitrile benzyl Propionitrile p,p’-DichloroH202 benzyl Diisopropyl ether p,p’-DichloroH202 benzyl tert-butyl alcohol Cyclohexyl methyl tert-Butyl sulfide peroxide
+
Temp, OC
Rate lawb
ka
E, kcall mol
log A ”
5 x 10-6
Reference
40
2nd 1:l
Ford and Young (1965)
100
1st 1:O
9.4 x 10-2
100
1st 1:0
0.13
50
1st 1:0
6.2 X
13.04
8.078
75
1st 1:O
34.0 X
13.04
8.078
85
1st 1:0
48.6 X
13.04
8.078
100
1st 1:0
100.0 X
13.04
8.078
50
2nd 1:l
1.43 X
17.5
50
2nd 1:l
1.71 X
15.0
Bateman and Hargrave (1954)
50
2nd 1:l
2.2 x 10-4
14.1
Bateman and Hargrave (1954)
50
2nd 1:l
2.3 X
12.7
Bateman and Hargrave (1954)
50
2nd 1:l
1.19 X
15.1
Bateman and Hargrave (1954)
50
2nd 1:l
1.65 X
12.6
Bateman and Hargrave (1954)
50
2nd 1:l
1.27 X
11.0
Bateman and Hargrave (1954)
50
3rd 1:2
10.9
Bateman and Hargrave (1954)
50
2.9 0.9:2
8.5
Bateman and Hargrave (1954)
50
2.7 0.7:2
6.5
Bateman and Hargrave(1954)
50
2.40.4:2
Bateman and Hargrave (1954)
50
2.45 0.45:2
Bateman and Hargrave (1954)
50
2.3 0.9:1.4
13.4
Bateman and Hargrave (1954) 7.9476 Overberger and Cummins (1953) 7.9476 Overberger and Cummins (1953) 7.9476 Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Hargrave (1956)
30.2 2nd 1:l
3.1 x 10-5
17.2
39.8 2nd 1:l
7.6 X 10s
17.2
49.8 2nd 1:l
1.91 X
49.8 2nd 1:l
2.02 X
17.2
49.8 2nd 1:l
1.8 x 10-5
49.8 2nd 1:l
0.7 x
49.8 2nd 1:l
1.6 x 10-5
50
9.4 x
2nd 1:l
Heimlich and Wallace (1966) Heimlich and Wallace (1966) Heimlich and Wallace (1966) Heimlich and Wallace (1966) Heimlich and Wallace (1966) Heimlich and Wallace (1966) Bateman and Hargrave (1954)
io-”
17.7
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
105
Table I (continued) Sulfur compound
ha
E, kcall mol
2nd 1:l
7.9 x 10-5
15.5
Hargrave (1956)
50
2nd 1:l
1.01x 10-3
13.1
Hargrave (1956)
Methanol
50
2nd 1:l
1.58 X
14.4
Hargrave (1956)
25
2nd 1:l
3.2 x 10-4
14.4
Modena and Miola (1957)
25
2nd 1:l
2.8 x 10-4
14.4
Modena and Miola (1957)
25
2nd 1:1
1.41 x 10-4
14.4
Modena and Miola (1957)
25
2nd 1:l
2.04 x 10-3
13.5
Modena and Miola (1957)
25
2nd 1:l
2.27 x 10-3
13.5
Modena and Miola (1957)
25
2nd 1:l
3.37 x lo-"
13.2
7.253 Modena and Miola (1957)
25
2nd 1:l
4.38 x 10-3
Modena and Miola (1957)
25
2nd 1:l
6.34 x 10-3
Modena and Miola (1957)
25
2nd 1:l
7.84 x 10-3
Modena and Miola (1957)
25
2nd 1:l
3.73 x 10-3
25
2nd 1:l
2.03 x
0
2nd 1:l
3.2 x 10-4
13.5
Temp, Solvent
"C
Rate law b
tert-Butyl alcohol
50
Methanol
Peroxide
Cyclohexyl methyl Cyclohexyl sulfide peroxide Cyclohexyl methyl Cyclohexyl sulfide peroxide Cyclohexyl methyl tert-Butyl sulfide peroxide p -Nitrophenylene HzOz methyl sulfide
di-n-butyl sulfide
H202
Thioxane
HzOz
94% CzH50H; 6% HzO; 0.1 N HC104 94% CzHsOH; 6% Hz0; 0.1 N HC104 94% CzHsOH; 6% HzO; 0.1 N HC104 94% CzHsOH; 6% HzO; 0.1 N HC104 94% CzH50H: 6% HzO; 0.1 N HC104 94% C2H5OH; 6% HzO; 0.1 N HC104 94% CzH5OH; 6% HzO; 0.1 N HC104 94% CzH50H; 6% HzO; 0.1 N HC104 94% C2H5OH; 6% HzO; 0.1 N HC104 94% CzH50H; 6% HzO; 0.1 N HC104 94% CzHsOH; 6% HzO; 0.1 N HC104 HzO
Thioxane
HzOz
HzO
25
2nd 1:l
2.58 x 10-3
13.5
Thioxane
HzOz
H20
34.2 2nd 1:l
5.32 x 10-3
13.5
Thioxane
HzOz
DzO
9.7 2nd 1:l
4.5 x 10-4
13.5
Thioxane
HzOz
DZO
25
2nd 1:l
1.54 x 10-3
13.5
Thioxane
H20
25
2nd 1:l
1.35 x 10-4
14.1
H20
45.9 2nd 1:l
6.42 x 10-4
14.1
25
2nd 1:l
1.91 x 10-3
D20
25
2nd 1:l
9.6 x 10-5
D20 + HC104
25
2nd 1:l
2.03 x 10-3
Thioxane
tert-Butyl hydroperoxide tert-Butyl hydroperoxide tert-Butyl hydroperoxide tert-Butyl hydroperoxide tert-Butyl hydroperoxide Ha02
Dioxane
25
3rd 1:2
4.07
Thioxane
HzO2
Dioxane
45.9 3rd 1:2
2.46 x
Thioxane
HzOz
Acetic acid
25
2nd 1:l
2.43 X lov2
Thioxane
HzOz
tert-Butyl alcohol
25
2nd 1:l
9.45 x 10-6
19.3
Thioxane
HzOz
tert-Butyl alcohol
45.9 2nd 1:l
4.0 x 10-5
19.3
Thioxane
HzOz
Methanol
25
6.16 x 10-5
15.1
Diphenyl sulfide
HzOz
m-Chlorophenylene methyl su 1fide Phenyl benzyl sulfide
HzOz
p-Chlorophenylene methyl sulfide Phenyl methyl sulfide
H202
m-Methyl phenylene methyl sulfide p-Methyl phenylene methyl sulfide p-Methoxy phenylene methyl sulfide Benzyl methyl sulfide
HzOz
Thioxane Thioxane Thioxane Thioxane
HzOz
HzOz
HzOz HzOz HzOz
HZ0
+ HC104
2nd 1:l
X
13.2
log A n
Reference
7.253 Modena and Miola (1957) Modena and Miola (1957)
16.3
Dankleff et al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) Dankleff e t al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) -6.77 Dankleff et al. (1968) Dankleff et al. (1968) Dankleff et al. (1968) -4.808 Dankleff et al. (1968) -4.808 Dankleff et al. (1968) -6.338 Dankleff et al. (1968)
106
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
Table I (continued) Sulfur compound
Temp, Peroxide
Solvent
“C
Rate lawb
45.9
2nd 1:1
ka
E, kcal/ mol
logAR
3.27 X lo-*
15.1
-6.338
Reference
~
Dankleff et al. (1968) 4.96 X H2Oz Ethylene glycol 25 2nd 1:1 14.2 -6.120 Dankleff et al. Thioxane (1968) 2.38 X 49.5 2nd 1:l H202 Ethylene glycol 14.2 -6.120 Dankleff et al. Thioxane (1968) 1.54 X 13.5 -6.120 Dankleff et al. Thioxane DzO 25 2nd 1:1 H202 (1968) 2.58 X lop3 13.5 -5.901 Dankleff et al. 25 2nd 1:l H2O Thioxane H202 (1968) 25 2nd 1:l 2.2 X 10-6 H202 N-Methyl 19.3 -4.808 Dankleff et al. Thioxane acetamide (1968) 1.87 X lo-” 45.9 2nd 1:l 19.3 -4.808 Dankleff e t al. H202 N-Methyl Thioxane acetamide (1968) a For first-order reaction, s-l. For second-order reaction, mol/L s. First the overall rate dependence, then the dependence on the sulfur compound and the peroxide, respectively. Thioxane
H202
Methanol
1. Noncatalytic, liquid-phase oxidation of a hydrocarbon (RH) in the presence of excess oxygen proceeds by way of a free-radical mechanism. Initiation can occur with molecular oxjjgen in accord with the reaction 2RH
+0 2
by an initiator I2 12
-
+ H202
2R.
21.
(12)
(13)
or by the decomposition of intermediates, e.g., the hydroperoxides, RO2H R02H
+
RO.
+ HO.
(14)
The organic radicals HO-, ROz., RO., etc., denoted by A, abstract a hydrogen from a hydrocarbon molecule
A- + R H
+
R.
+ AH
(15)
and produce R.. In turn, R. absorbs oxygen very rapidly, and a peroxy radical RO2. is produced as follows
R- + 0
2
+
ROy
(FAST)
(16)
Peroxy radicals can abstract a hydrogen from another hydrocarbon molecule and produce a hydroperoxide ROy
+ RH
+
RO2H
+ R.
(17)
d[R-S-R’] = hz[R-S-R’] [HP] dt
+ k3[R-S-R’]
[HP]’ (19)
An excellent review of the solvent effect has been published by Curci and Edwards (1970). All of their observations supported a mechanism of oxidation proposed in the early work of Overberger and Cummins (1953) wherein it was postulated that the sulfur was oxidized by a nucleophilic attack on a peroxidic complex which contained peroxidic and protic structures R R“-0 \on: / OH 4- HA + R-SO-R’ (20) H;(3 s,R,-R-
A----H
,
HA denotes the protic molecule, and R”02H is the peroxide. The oxidation of the sulfoxide to the sulfone occurred by the same mechanism. In a protic solvent, the solvent present in excess fulfills the function of HA, and the apparent rate of reaction 19 is first order with respect to the peroxide. In an aprotic solvent, another hydroperoxide molecule will function as HA
2ROOH
H‘
\
I
(21)
or the peroxy radicals can terminate by the reaction 2ROy
-+
RO2R
+
0 2
(18)
or by similar reactions. 2. Hydrocarbons which contain hydrogen with lower bond energies are oxidized more rapidly than those with higher bond energies. The hydroperoxides that result are more stable and therefore are more selective as oxidizers. 3. Hydroperoxides and peracids can selectively oxidize sulfur compounds to the corresponding sulfoxides and sulfones (Overberger and Cummins, 1953; Bateman and coworkers, 1962; Ford and Young, 1965; Heimlich and Wallace, 1966; Barnard et al., 1961). 4. The protic nature of the solvent strongly affects the observed form of the rate equations for the oxidation of sulfur compounds (Overberger and Cummins, 1953). In general, the rate equation has two terms. One accounts for the protic aspect of the solvent, and the other accounts for the degree of association of the hydroperoxide ( H P ) in accord with the equation
Therefore, in an aprotic solvent the apparent rate of reaction 19 depends on the second power of the concentration of hydroperoxide. The data that were published on the rates of oxidation of sulfur compounds by hydroperoxides are given in Table I. 5 . A special case of interest is that of the peroxy acids which are formed by oxidation of the primary oxidation products, especially aldehydes. Peracids can form intramolecular, cyclic peroxidic complexes. Then in most cases the rates of oxidation of the sulfur compounds depend on the first powers of the concentrations of acids as suggested by the equation
,OH
R
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
107
Table 11. Rate Constants for the Oxidation of Sulfur Compounds by Peracids
E, Sulfur comDoundC
Acid
Solvent
Temp, “C
Rate lawa
kb
kcall mol
log. A b
Tetramethylene sulfide Di-n-butyl sulfide
Peracetic
To1u ene
-70
2nd 1:l
4
Peracetic
Toluene
-70
2ndl:l
3.2
Di-sec-butyl sulfide
Peracetic
Toluene
-70
2ndl:l
1.47
Di-tert-butyl sulfide
Peracetic
Toluene
-70
2ndl:l
0.83
8.6
9.164
Di-tert-butyl sulfide
Peracetic
Toluene
-50
2ndl:l
5.65
8.6
9.164
Phenyl methyl sulfide Peracetic
Toluene
-49
2nd 1:l
0.097
9.6
8.338
Phenyl methyl sulfide Peracetic
Toluene
-39.1
2nd 1:l
0.24
9.6
8.338
Phenyl methyl sulfide Peracetic
Toluene
-30.0
2nd 1:l
0.53
9.6
8.338
Phenyl methyl sulfide Peracetic
Toluene
-20.0
2nd 1:l
1.7
9.6
8.338
Diphenyl sulfide
Peracetic
0
2nd 1:l
0.268
9.6
7.166
Diphenyl sulfide
Peracetic
10
2nd 1:l
0.483
9.6
7.166
Diphenyl sulfide
Peracetic
Benzene + 10 N acetic acid Benzene 10 N acetic acid Toluene
20
2nd 1:l
0.880
9.6
7.166
Dibenzothiophene
Peracetic
Benzene
15
2nd 1:1
0.0049
14.7
8.572
Dibenzothiophene
Peracetic
Benzene
30
2nd 1:1
0.0091
14.7
8.572
Dibenzothiophene
Peracetic
Benzene
40
2nd 1:1
0.0168
14.7
8.572
Dibenzothiophene
Peracetic
Benzene
50
2nd 1:1
0.0357
14.7
8.572
Dibenzothiophene
Peracetic
Benzene
60
2nd 1:l
0.0694
14.7
8.572
Dibenzothiophene
Peracetic
15
2nd 1:1
0.00433
14.8
5.8596
Dibenzothiophene
Peracetic
30
2nd 1:l
6.0157
14.8
5.8596
Dibenzothiophene
Peracetic
40
2nd 1:1
0.0329
14.8
5.8596
Dibenzothiophene
Peracetic
50
2nd 1:1
0.0725
14.8
5.8596
Dibenzothiophene
Peracetic
60
2nd 1:l
0.142
14.8
5.8596
Benzothiophene
Peracetic
Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene
40
2nd 1:l
0.0026
5.8596
Benzothiophene
Peracetic
40
2nd 1:l
0.0017
5.8596
Thiophene
Peracetic
40
2nd 1:1
6 X low5
5.8596
Tetramethylthiophene 2,5-Dimethylthiophene 2-Methylthiophene
Peracetic
40
2nd 1:1
0.0368
40
2nd 1:l
0.00186
40
2nd 1:l
4.1 x 10-4
3-Methylthiophene
Peracetic
40
2nd 1:1
3.4 x 10-4
p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide
p -Methoxy
+
+ + + + +
Peracetic Peracetic
.
perbenzoic p-Methoxy perbenzoic p-Methoxy perbenzoic p-Methoxy perbenzoic p -Methoxy perbenzoic p-Methoxy perbenzoic
+ + + + + +
Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Benzene 10 N acetic acid Toluene
-65
2ndl:l
0.61
6.6
6.6881
Toluene
-55
2nd 1:1
1.32
6.6
6.6881
Toluene
-45
2nd 1:l
2.44
6.6
6.6881
Isopropyl alcohol
-35
2nd 1:l
0.19
9.9
8.382
Isopropyl alcohol
-25
2nd 1:l
0.44
9.9
8.382
Isopropyl alcohol
-15
2nd 1:l
0.95
9.9
8.382
Reference Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young ( 1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Ford and Young (1965) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Curnmins (1953) Overberger and Cummins (1953)
108
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17, No. 2, 1978
Table I1 (continued)
Sulfur compound p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide p,p’-Dichlorobenzyl sulfide 3-Methoxythionaphthene 3-Methylthionaphthene Thionaphthene
Acid
Solvent
Temp, “C
Rate lawa
kb
E, kcall mol
logAb
Peroxybenzoic
Toluene
-65
2nd 1:1
1.29
5.2
5.646
Peroxybenzoic
Toluene
-55
2nd 1:
2.50
5.2
5.646
Peroxybenzoic
Toluene
-45
2nd 1:1
4.17
5.2
5.646
Perbenzoic
Isopropyl alcohol
-40
2nd 1:l
0.15
9.6
8.2516
Perbenzoic
Isopropyl alcohol
-30
2nd 1:l
0.38
9.6
8.2516
Perbenzoic
Isopropyl alcohol
-20
2nd 1:l
0.79
9.6
8.2516
p -Methyl perbenzoic p -Methyl perbenzoic p-Methyl perbenzoic p -Chloroper benzoic p -Chloroperbenzoic p -Chloroperbenzoic p -Nitroperbenzoic p-Nitroperbenzoic p-Nitroperbenzoic Perbenzoic
Isopropyl alcohol
-40
2nd 1:l
0.11
11.3
9.5979
Isopropyl alcohol
-30
2nd 1:l
0.29
11.3
9.5979
Isopropyl alcohol
-20
2nd 1:l
0.70
11.3
9.5979
Isopropyl alcohol
-45
2ndl:l
0.17
9.6
8.4687
Isopropyl alcohol
-35
2ndl:l
0.45
9.6
8.4687
Isopropyl alcohol
-25
2ndl:l
0.89
9.6
8.4687
Isopropyl alcohol
-55
2ndl:l
0.43
6.9
6.5578
Isopropyl alcohol
-45
2ndl:l
0.88
6.9
6.5578
Isopropyl alcohol
-35
2nd 1:l
1.60
6.9
6.5578
CHzC12
30
0.61
Perbenzoic
CHzClz
30
0.112
Perbenzoic
CHZC12
30
0.0057
Dioxane-HZ0 25 Perbenzoic Thionaphthene 0.004 3-MethoxythioPerbenzoic CHZC12 30 0.08 naphthene sulfoxide 3-MethoxythioPerbenzoic CH2C12 30 0.032 naphthene sulfoxide Thianaphthene Perbenzoic CH2C12 30 0.050 sulfoxide Perbenzoic Dioxane-HzO 25 0.0029 Thianaphthene sulfoxide Dioxane-HzO 25 5.0 Diphenyl sulfide Perbenzoic Diphenyl sulfoxide Perbenzoic Dioxane-HZO 25 0.0032 Dioxane-HzO 25 0.0396 Dibenzothiophene Perbenzoic Dibenzothiophene Dioxane-HnO 25 0.0037 Perbenzoic sulfoxide a Overall order, then order with respect to the sulfide and the oxidizer, respectively L/mol s. From different suppliers. Used as received.
The published data on the rates of oxidation of sulfur compounds by peracids are summarized in Table 11. Peracids are stronger oxidizers than hydroperoxides. 6. A larger oxidation potential is required to convert sulfoxides to sulfones than to oxidize sulfides to sulfoxides. Thus, if the oxidizer is a hydroperoxide in a protic medium the reaction may stop after sulfoxide is formed (Attar, 1976). 7. When the n electrons of the sulfur can resonate with the p electrons of the organic radical, a larger oxidation potential will be required to effect the oxidation than for cases where resonance does not exist. Therefore, it is more difficult to
Reference Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Overberger and Cummins (1953) Kucharczyk and Horak (1969) Kucharczyk and Horak (1969) Kucharcyzk and Horak (1969) Greco et al. (1960) Kucharczyk and Horak (1969) Kucharczyk and Horak (1969) Kucharczyk and Horak (1969) Greco et al. (1960) Greco et al. (1960) Greco et al. (1960) Greco et al. (1960) Greco et al. (1960)
For first order, s-l. For second order,
oxidize thiophene than aryl and alkyl sulfides (Modena e t al., 1960; Ford and Young, 1965; Heimlich and Wallace, 1966).
Application to the Desulfurization of Fossil Fuels A fossil fuel can be described as a n assembly of organic groups which may compete for a given quantity of reagent in a reactor. When a sulfur-containing fuel is oxidized by molecular oxygen, two types of reactions occur: (1)oxidation of the hydrocarbon part of the fuel t o produce peroxidic species (PSI. 2RH 2 0 2 2ROzH (23)
+
-+
Ind. Eng. Chem. Prod. Res. Dev., Vol. 17,No. 2, 1978
( 2 ) selective oxidation of the organic sulfur by the PS to yield sulfoxides and sulfones. 2R0,H
+ S9 R'
-
2ROH
+ O,S, /
R (24)
R
The reactions show t h a t even if the in situ oxidation of the sulfur were absolutely selective, two hydrogens would be oxidized to hydroxy groups for each molecule of sulfone formed. In other words, the optimal oxygen selectivity that can be expected is 0.5. In reality, much larger losses are observed because many peroxidic groups decompose thermally and do not oxidize a sulfur atom. Where the sulfur is bound to a solid structure, as in coal, mass-transfer limitations will decrease the selectivity and rate. Protic solvents, such as water or alcohols, will also decrease the selectivity. Oxidation in a protic media very often ends with the sulfoxide. Sulfoxides do not always decompose to SO2 and a hydrocarbon but often to sulfide and sulfone (Suter, 1944). The nonselectivity of the oxidation results in a loss of heating value of the processed material. T h a t loss can be reduced, however, if the temperature and pressure of oxygen are closely controlled. Analysis of the optimal processing conditions will be given in part 2 of this series.
Acknowledgment This presentation was prepared as part of a program sponsored by the National Science Foundation and the Caltech Energy Program. T h a t support is gratefully acknowledged. Literature Cited Attar, A., M.S. Thesis (in Hebrew), Department of Chemical Engineering, Technion, Israel Institute of Technology, Haifa, Israel, 1972. Attar, A., "Selective Oxidation of Organosulfur Compounds", Progress Report, Department of Chemical Engineering, California Institute of Technology, Pasadena, Calif., 1973. Attar, A., Corcoran, W. H., "Desulfurization of Coal and Char by Selective Oxidation with Nitrogen Dioxide", proposal submitted to the Director's Discretionary Fund, Jet Propulsion Laboratory, Pasadena Calif. (Funded 1976). Attar, A., Corcoran, W. H., lnd. f n g . Chem. Prod. Res. Dev., 16, 168 (1977). Attar, A., Forgey, R., Corcoran, W.H., unpublished work, 1975. Barnard, D., Bateman, L., Cunneen, J. I., Chapter 21 in "Organic Sulfur Compounds", Vol. I, N. Kharasch, Ed., Pergamon Press, New York, N.Y., 1961. Bateman, L., Cain, M., Colclowgh, T., Cunneen, J. I., J. Chem. Soc., 3570 (1962). Bateman, L.. Hargrave, K. E., Proc. Roy. SOC. London, Ser. A, 224, 399 (1974). Benson, S. W., Shaw. R., Chapter 2 in "Organic Peroxides", Vol. i, D. Sween, Ed., Wiley, New York, N.Y., 1970. Bordwell, F. G., Williams, J. M., Hoyt, E. E., Jr., Jarvis, B. B., J. Am. Chem. SOC., 90, 429 (1968).
109
Brown, R. K., Christiansen, R. G., Sandm, R. B., J. Am. Chem. Soc., 70, 1748 (1 948). Capozzi, G., Modena, G., Chapter 17, p 785, in "Chemistry of the Thiol Group", S. Pata, Ed., Wiley, London, 1974. Corcoran, W. H., "A Study of the Applied Chemistry in the Selective Oxidation of Sulfur Compounds in the Desulfurization of Fuel Oil", Proposal submitted to NSF (1974) (Funded 1975). Cullis, C. F., Hopton. J. D., Trimrn, D. L., J. Appl. Chem., 18 (9), 330 (1968). Curci, R., Edwards, J. O., Chapter IV in "Organic Peroxides", Vol. I, D. Sween, Ed.. Wiley, New York. N.Y., 1970. Dankleff, M. A. P., Curci, R., Edwards, J. O., Pyum, Hai-Yung, J. Am. Chem. SOC., 90, 3209 (1968). Diaz, A. F., Guth, E. D., U.S. Patent 3 909 211 (1976). Emanuel, N. M.. Denisov, E. T., Maims. 2. K., "Liquid Phase Oxidation of Hydrocarbons", Plenum Press, New York, N.Y., 1967. Fine, D. H., Slater, S. M., Sarofins, A. F., Williams, G. C., Fuel, 53, 120 ( 19 74). Ford, J. F., Young, V. O., Am. Chem. Soc., Div. Petrol. Chem., Prepr., 10 (2), C - I l l (1965). Ganguli, P. S., Hsu, G. C., Gavalas, G. R., Kalfayan, S. H., Am. Chem. Soc., Dlv. FuelChem., Prepr., 21 (7), 118 (1976). Given, P. H., Wyss, W. R., BCURA Mont. Bull., XXV (5), 166 (1961). Greco, A,, Modena, G., Todesco, P. E., Gazz. Chem. ltal., 90, 671 (1960). Hammett, L. P., "Physical Organic Chemistry", McGraw-Hill, New York. N.Y., 1940. Hartough, H. D., "Thiophene and Its Derivatives", Interscience. New York, N.Y ., 1952. Hargrave. K. R., Proc. Roy SOC.London, Ser. A, 235, 55 (1956). Heimlich, B. N., Wallace, T. J., Tetrahedron, 22, 3571 (1966). Heldt, W. Z., J. Org. Chem., 30, 3897 (1965). Horne, W. A., McAfee, J., Chapter 5 in "Advances in Petroleum Chemistry and Refining", Vol. 3, K. A. Kobe and J. J. McKetta, Ed., Interscience, New York N.Y., 1960. Horton. L., Randall, R. B., Fuel, 26 ( 5 ) , 127 (1947). Horton, L., Randall, R. B., Fuel, 33 ( 5 ) ,389 (1954). Horton, L., Randall, R. B., Chem. lnd., 1885 (Nov. 5, 1966). Kucharczyk. N., Horak. V., Collect. Czech. Chem. Commun., 34, 2417 ( 1969). Macrae, J. C., Oxtoby, R., Fuel, 44 (6), 395 (1965). Magelli, I. L., Shappard, C. S., Chapter I in "Organic Peroxides", Vol. I, D. Sween, Ed., Wiley, New York, N.Y., 1970. Modena. G.. Miola, L., Gazz. Chim. ltal., 87, 1306 (1957). Mukae, S., Araki, Y., Konlshi, M., Otomurou, K., Neuryo Kyodaishi, 48 (512), 905 (1969). Overberger, C. G., Cummins, R. W., J. Am. Chem. SOC.,75, 4250 (1953). Phillipson, J. J., "Kinetics of Hydrodesulfurizationof Light and Middle Distallates", paper presented at the American Institute of Chemical Engineers Meeting, Houston, Texas, 1971. Pinchin. F. J., Fuel, 37, 293 (1958). Reid, E. E., "Organic Chemistry of Bivalent Sulfur", Vol. 11, Chemical Publishing Co., New York, N.Y., 1960. Schuit, G. C. A., Gates, B. C., AlChf J., 19 (3) 417 (1973). Schuman, S. C., Shalit, H., Catal. Rev., 4 (2), 245 (1970). Sheldon, R. A., Kochi, J. K., Oxid. Combust. Rev., 9, 135 (1973). Snow, R. D., lnd. fng. Chem., 24 (a), 903 (1932). Sun, S.-C., Wu, M.-T., "Desulfurization of Coal by Physicochemical Process of Flotation and Volatilization", paper presented at the AlME Annual Meeting, Dallas, Texas, 1974. Suter, C. M., "The Organic Chemistry of Sulfur", Wiley, New York, N.Y., 1944. Wallace, T. J., Heimlich, B. N., Tetrahedron, 24, 1311 (1966). Wallace, T. J., Pobiner, H., Baron, F. A., Schricsheim, A,, J. Org. Chem., 30, 3147 (1965).
Received f o r reuieu: D e c e m b e r 14, 1977 Accepted M a r c h 2,1978
