Method for partially and selectively oxidizing alcohols to esters or carboxylic acids

A transition metal electrocatalyst surface (e.g. a porous surface of finely divided Group VIII or Group I-B metal with an attached current collector) is modified by a sulfur treatment, using an oxidized sulfur species of average sulfur oxidation state of about 4 or less, e.g. SO.sub.2 dissolved in aqueous acid. Treatment of the transition metal with SO.sub.2 or the like typically provides up to 100% coverage of the surface electrocatalyst sites with chemisorbed sulfur-containing species and perhaps subsurface effects as well, but washing or other non-electrochemical techniques can remove 5-90% (e.g. 25-70%) of the chemisorbed SO.sub.2 or the like from the surface, leaving substantially only a very strongly bound form of the sulfur-containing species. The strongly bound sulfur-containing species can then be reduced to form a highly beneficial, selectivity-improving pattern of sites containing reduced --S (e.g. sulfur or sulfide) on the electrocatalyst surface. Electrochemical synthesis cells can be constructed from a cathode and/or anode made form the S-treated electrocatalyst and used in highly selective syntheses of useful organic and inorganic compounds from various starting materials, e.g. by reduction of O.sub.2 to H.sub.2 O.sub.2, reduction of NO to NH.sub.2 OH, oxidation of RCH.sub.2 OH to RCOOCH.sub.2 R (R=lower alkyl, etc.), oxidation of RR'CHOH to RCOR' (R and R'=lower alkyl, etc.) or the like.

EXAMPLES 
Example 1: Preparation of Modified Electrocatalyst and Electrogenerative 
Cells 
The unmodified electrocatalyst was an American Cyanamid LAA-2 electrode 
sheet material which can be cut to the desired size (e.g. 5cm.sup. 2) and 
attached to a metal screen and an electrical contact. See S. H. Langer et 
al, Ind. Eng. Chem. Proc. Des. Dev., 22, 264-271 (1983) and S. H. Langer 
et al. J. Electrochem. Soc. 122, 1619-1626 (1975). The LAA-2 
electrocatalyst sheet comprises Pt-black on the face (9 mg/cm.sup. 2) and 
an extremely hydrophobic fluorocarbon polymer (PTFE) coating at the 
opposite face. The porous hydrophobic surface is designed to contact a 
fluid reactant and the Pt-black face is designed for contact with a liquid 
electrolyte such as aqueous sulfuric, phosphoric or perchloric acid. This 
sheet material is available with a current-collecting metal mesh already 
attached; the Pt-black surface is very active and well-suited to use in 
fuel cells and electrogenerative reactors because of its ability to permit 
diffusion of reactant fluids and the formation of a 
reactant/electrocatalyst/electrolyte interface. 
The LAA-2 electrocatalyst material was modified by soaking a clean, 
untreated sheet (current-collecting screen already attached) in SO.sub.2 
-saturated 1M H.sub.2 SO.sub.4 overnight. After this soaking treatment, 
the electrocatalyst sheet was given a soaking wash in freshly prepared, 
aqueous 1 M H.sub.2 SO.sub.4, containing dissolved air, for 18 hours, to 
leach out all weakly bound SO.sub.2 from the electrocatalyst surface. The 
SO.sub.2 -treated and washed electrocatalyst was then subjected to a 
pre-reduction step (after rinsing and superficial drying) in which the 
electrocatalyst sheet, with an electrical lead attached to the current 
collecting mesh, was placed in a cell with gaseous hydrogen and kept at a 
constant potential of 0.0 v. vs. r.h.e. (reversible hydrogen electrode) 
for 0.5 hr to activate the electrode and reduce SO.sub.2 in preparation 
for the polarization curve determination. The total geometric exposed 
surface on this electrode ranges from 5 to 8 cm.sup.2 ; roughness factors 
are of the order of 1500 true cm.sup.2 /geometric cm.sup.2. 
Cyclic voltammetry was used to investigate the sulfur content of the 
electrocatalytic electrode which had been soaked, washed, activated and 
reduced. The cyclic voltammetry apparatus comprised a 250 ml standard high 
purity 3-electrode glass cell specifically modified to hold the LAA-2 
electrode (2.54 cm in diameter). A Princeton Applied Research () model 
175 Universal Programmer and a 173 potentiostat were used in the 
generation and control of the electrode potential program, respectively. 
The electrolyte was 0.5 M H.sub.2 SO.sub.4 prepared from Baker Ultrex 
ultrapure H.sub.2 SO.sub.4 and quadruply-distilled water and was deaerated 
with purified nitrogen. A platinum spiral served as the counter electrode 
and the reference electrode was a saturated calomel electrode (SCE) filled 
with aqueous saturated NaCl exhibiting a constant potential of 0.264 V vs 
a reversible hydrogen electrode in the same electrolyte. The sulfur 
pretreated electrode was cycled repeatedly between 1.0 and -0.2 V vs SCE 
at 0.5 V/min and the voltammetric currents were digitally integrated using 
a Bascom-Turner model 4110 digital recorder. The overall sulfur oxidation 
charge was obtained using methodology commonly employed; see, for example, 
Loucka, J. Electroanal. Chem., 31, 319 (1971). 
For electrogenerative oxidation and reduction studies, the reduced sulfur 
dioxide-treated LAA-2 electrode was used as either the cathode (e.g. for 
NO reduction) or the anode (e.g. for alcohol oxidation) in an 
electrogenerative (galvanic) configuration according to S. H. Langer et al 
in Ind. Eng. Chem. Proc. Des. Dev. 22, 264 (1983) and J. Electrochem. 
Soc., 122, 1619 (1975); see also S. H. Langer et al, Environ. Prog. 5, 276 
(1985) and Pure & Appl. Chem., 58, 895 (1986). The barrier electrolyte 
phase was 3M H.sub.2 SO.sub.4 prepared from conc. H.sub.2 SO.sub.4 and 
distilled water. Cell components were machined from KEL-F 
fluorochlorocarbon polymer. 
When the reactant is to be reduced, it is fed as a fluid (preferably as a 
gas) to the cathode gas chamber where it contacts, and can diffuse into, 
the modified LAA-2 electrocatalyst surface. Hydrogen gas at one atmosphere 
is fed to the anode, which is either a treated or untreated (preferably 
untreated) LAA-2 electrode. 
When the reactant is to be oxidized, it is fed as a fluid (preferably 
gaseous also) to an anode chamber containing an exposed modified LAA-2 
electrocatalyst surface. Oxygen (e.g. at 1.0 atm) is fed to the cathode, 
which has an exposed, preferably untreated LAA-2 electrocatalyst surface. 
To provide alcohols to the anode in the gaseous state, an inert carrier 
gas (nitrogen) was passed through a saturator containing the alcohol 
dissolved in water. 
If desired a reference electrode (e.g. a standard calomel electrode) can be 
included, and the electrolyte phase can be separated into a catholyte and 
anolyte with the aid of an ion exchange membrane. The electrodes are 
connected through an external circuit incorporating an ammeter and a 
variable resistance load (to control generated current and consequently 
also the electrode potential). 
Thus, a typical cell configuration for reduction of nitric oxide is: 
##STR1## 
with electrical leads connected to the current collectors, external 
circuitry, etc. 
A typical configuration for oxidation of an alcohol is: 
##STR2## 
with appropriate leads, circuitry, etc. 
According to the lowering of the limiting current in NO reduction at 
potentials below 0.6 volt, the sulfur coverage of the modified electrode 
was 65%. According to S-charge determination with cyclic voltammetry, the 
.theta..sub.s =0.67 (=67% coverage), assuming a 6 electron charge (from S 
at zero oxidation state to S at the +6 oxidation state). The .theta..sub.s 
would be 0.50 (=50% coverage) if an eight electron reaction is involved, 
e.g. from S.sup.= to SO.sub.4.sup.=, i.e. from -2 to +6. The relatively 
close agreement between 67% by cyclic voltammetry and 65% by limiting 
current decrease seems more than coincidental; however, this invention is 
not bound by any theory. The "sulfur" coverage (i.e. coverage by sulfur, 
sulfide or some other species in a low oxidation state) appears to be 
periodic rather than random after the treatment has been completed. 
Cyclic voltammetry studies suggest complete (100%) SO.sub.2 coverage 
(.theta..sub.s =1.00) if the washing step is omitted or if the washing 
solution is not exposed to oxygen. Accordingly, the strongly-bound 
SO.sub.2 can probably be assumed to be typically in the range of from 40 
or 50% up to 65 or 75% of the coverage, the balance being weakly 
bound-SO.sub.2, which is removed in the washing step. The weakly-bound 
SO.sub.2, in the form of a reduced sulfur species (S, sulfide, or the 
like), i.e. after the reduction step, appears to be the subject to 
re-oxidation with NO, by chemical and/or electrochemical mechanisms, 
perhaps leading even to its removal, leaving only the strongly-bound 
SO.sub.2, which behaves differently and provides a reliable surface 
modification of electrocatalytic sites. However, chemical or physical or 
physico-chemical, non-electrochemical techniques (e.g. washing) are 
preferred for removal of weakly-bound SO.sub.2, so that substantially only 
the strongly-bound SO.sub.2 is present during the reduction of the 
SO.sub.2 to S,S.sup.= or the like. 
Sulfur coverage determinations were based upon a hydrogen adsorption site 
density of 2.04.times.10.sup.18 H atoms/cm.sup.2, the site density being 
based upon a calculated roughness factor (R) of 1550. 
Except as otherwise indicated, electrogenerative cell operating 
temperatures were in the range of 15.degree.-90.degree. C., most typically 
20.degree.-50.degree. C. Elevated pressures, though permissible, were not 
used. 
Exampe 2: NO Reduction to NH.sub.2 OH and Byproducts 
Two cathode feeds were used: (a) pure nitric oxide (CP grade) and 2.7% NO 
in N.sub.2 (Matheson Certified Standard). Higher nitrogen oxides were 
removed from the cathode feeds by passing them through NaOH in acetone/dry 
ice. Possible reduced-NO products are determined in accordance with 
half-cell reactions in which the electron change per 2 moles NO can range 
from 2e- to 10e.sup.- and the E.degree. vs. NHE (normal hydrogen 
electrode) can range from as much as 1.59 volts down to as little as 0.38 
volt: 
______________________________________ 
Electron (e) 
Products Change/2 mole NO 
E.degree. vs. NHE (v.) 
______________________________________ 
N.sub.2 O + H.sub.2 O 
2e 1.59 
N.sub.2 + 2H.sub.2 O 
4e 1.68 
2NH.sub.2 OH 
6e 0.38 
2NH.sub.3 + 2H.sub.2 O 
10e 0.73 
______________________________________ 
To measure the effect of the modification of the LAA-2 cathode with the 
SO.sub.2 adsorption/wash/SO.sub.2 -reduction treatment, parallel runs were 
carried out with unmodified cathodes ("unmodified cell"). Current 
efficiency studies were carried out on both modified and unmodified cells. 
Current accountabilities and nitrogen balance closures were consistently 
within 10%. 
At potentials above 0.6 volt, both modified and unmodified cells produced 
N.sub.2 O, consistent with S. H. Langer et al, op. cit. in Ind. Eng. Chem. 
Proc. Des. Dev. But pronounced differences were noted at cell potentials 
in the 0-0.6 volt range. The electrocatalyst modification method of this 
invention decreases limiting currents. When a cell of this invention was 
used with the dilute NO feed, two limiting currents were observed, one at 
low and one at high current. The electrocatalyst treatment decreased both 
limiting currents slightly and accentuated the second (higher) one. 
Product analysis and current efficiency studies provided the most striking 
data and indicated increased selectivity for NH.sub.2 OH productions at 
E.sub.cell values below 0.6 volt. 
Feed: Pure Nitric Oxide (5.1 cm.sup.3 /min) 
Excess H.sub.2 Fed to Anode 
Exposed Electrocatalyst Surface at Cathode: 5.07cm.sup.2 
______________________________________ 
Current Efficiencies (%) at Various 
E.sub.cell Values (in Volts) 
______________________________________ 
Unmodified Cell Products* 
0.1 0.2 0.3 0.4 0.55 
______________________________________ 
N.sub.2 O 5 10 50 95 &gt;95 
N.sub.2 17 22 28 12 5 
NH.sub.2 OH 3 3 3 &lt;1 -- 
NH.sub.3 75 62 45 3 3 
______________________________________ 
Modified Cell Products** 
0.1 0.2 .25 .35 .40 .55 
______________________________________ 
N.sub.2 O -- 10 23 62 88 90 
N.sub.2 -- 0 0 0 0 0 
NH.sub.2 OH -- 75 48 22 &lt;5 &lt;1 
NH.sub.3 -- 15 23 18 &lt;5 &lt;1 
______________________________________ 
*Cell internal resistance: 0.34 ohm 
**Cell internal resistance: 0.26 ohm 
(-- indicates no data) 
Example 3: Oxidation of Alcohols to Esters and Ketones 
The cell configuration was as described in Example 2. The modified 
electrode (LAA-2, treated in accordance with Example 1), was the anode, 
and the cathode was an unmodified LAA-2 (9 mg/cm.sup.2 of Pt-black). 
Available electrocatalyst surface at the anode was approximately 5 
cm.sup.2 as in Example 2. The cation exchange membrane dividing the 
electrolyte was an RAI Research 4010. The anolyte compartment was 3 mm 
thick, and the catholyte compartment was 4 mm thick. The cathode feed was 
pure oxygen at atmospheric pressure. 
For an unmodified cell (see R. L. Pesselman et al, Chem. Eng. Comm. 38, 
265-273 [1985]and S. H. Langer et al, Pure & Applied Chem., 58, 895-906 
[1986]), the overall reaction for vaporized aqueous lower aliphatic 
straight-chain primary alcohols having 2 or more carbon atoms has been 
shown to be 
EQU O.sub.2 +2R--CH.sub.2 OH.fwdarw.2R--CHO+2H.sub.2 O, 
with some CO.sub.2 and possibly RCOOH as byproducts, wherein R is CH.sub.3 
--, C.sub.2 H.sub.5 --, etc. 
In the modified cell, however, substantially the only reaction with a 
vaporized aqueous lower aliphatic straight-chain primary alcohol appeared 
to be 
EQU O.sub.2 +2RCH.sub.2 OH.fwdarw.R--COOCH.sub.2 R+2H.sub.2 O. 
No CO.sub.2 was detected. A major amount of ester was found in the gaseous 
effluent from the anode chamber (the "gas" side of the anode). Small 
amounts of ester do pass into the electrolyte, some of which is then 
hydrolyzed to RCOOH. 
When a secondary alcohol feed is used, the overall reaction appears to be: 
EQU O.sub.2 +2R--CH(R')OH.fwdarw.2R--CO--R'+2H.sub.2 O, 
(with little or no CO.sub.2 byproduct), where R and R' are the same or 
different and are lower alkyl or the like. For an interesting electrolytic 
esterification involving substantial power input, cf. T. Shono et al, 
Tetrahed. Letters, 40, 3861-3864 (1979). 
Apparently, limited ensembles of surface adsorption sites prevent 
degradation of the initially adsorbed alcohol to carbon dioxide. 
Suppression of CO.sub.2 formation is important in view of the relatively 
high cost of alcohol starting materials. Ester formation is of interest as 
an alternative to butane oxidation (which uses a petroleum-based feedstock 
instead of a biomass-based feedstock) and Fischer esterification, which is 
a readily reversible reaction requiring two starting materials (RCOOH and 
RCH.sub.2 OH) instead of one. The electrochemical (e.g. electrogenerative) 
cell configuration permits most of the ester product to be conducted away 
from the catalytic zone as an effluent stream before it can come into 
intimate contact with the acid electrolyte. The continuous distillation 
feature of a Fischer esterification is intended to accomplish the same 
objective, but permits a far greater degree of contact between ester and 
acid, hence a less favorable equilibrium position. 
Ethanol to Ethyl Acetate 
Ethanol ("EtOH") conversion to ethyl acetate ("EtAc") provided an excellent 
model reaction for primary alcohols (especially C.sub.2 -C.sub.12 
alkanols) and also has commercial significance in the chemical synthesis 
industry, where Fischer esterification is one of the preferred routes to 
ethyl acetate. 
The anode feed was obtained by passing O.sub.2 -free nitrogen through a 
saturator containing 50 or 75% (v/v) ethanol dissolved in water. The anode 
was modified in accordance with Example 1. Cell and feed temperatures were 
within the range of 21.5 to 26.degree. C. Flow to the anode was 35 to 40 
cm.sup.3 /min.; cell internal resistance was 0.27-0.34 ohm. 
The overall electrode reactions with current generation appear to be: 
EQU ANODE: 2C.sub.2 H.sub.5 OH.fwdarw.CH.sub.3 COOC.sub.2 H.sub.5 +4H.sup.+ +4e 
(H.sup.+ transported to cathode in the electrolyte phase) 
EQU CATHODE: O.sub.2 +4H.sup.+ +4e.fwdarw.2H.sub.2 O. 
Some cell operating data under various conditions including steady state 
are presented in Table 1. For the reported polarization experiment, a 
stable cell potential was established well within the five minutes at each 
operating condition; the indicated product analyses were performed after 
this. Conditions were then changed to obtain the next set of data. Carle 
gas chromatographs with an OV-101 dimethylsilicone phase to identify 
acetate and additional standard columns were used for product analyses. 
Ethyl acetate was the only volatile product observed in the anode chamber 
effluent; identification was confirmed with GC/mass spectrometry on 
trapped effluent during steady state operation. Surface analysis on the 
modified LAA-2 anode using ESCA showed a sulfur-platinum surface ratio of 
close to 1:1. The polarization of the LAA-2 oxygen electrode is 
reproducible to within +15 mV and some data are shown in Table 1. These 
data were obtained against an isolated reference calomel electrode later 
calibrated against a reversible hydrogen electrode (RHE). Thus, 
calculations can be made for the potential at the ethanol and propanol 
oxidizing anode. 
The data of Table 1 demonstrate significant ethyl acetate formation over a 
range of voltage. Washed/reduced-SO.sub.2 anodes did not lose their ester 
forming properties even after 5 hours of operation. The small amount of 
ethyl acetate in the anode effluent on open circuit reflects some product 
accumulation in the electrolyte where it is also subject to hydrolysis. 
Some ethanol vapor dissolves with ethyl acetate in the 3M sulfuric acid 
electrolyte during operation. The material balance improves with steady 
state operation (one hour) as shown in Table 1B. Within the limits of 
analytical error it is seen that about seventy percent of the generated 
current at steady state can be ascribed to ethyl acetate found in reactor 
effluent. Actually selectivity is greater since ethyl acetate dissolved in 
the electrolyte at the interface diffuses into the bulk from where much of 
it can be analyzed. Gas chromatographic head space analysis on the 
electrolyte with standards confirmed that absent product in the anode 
effluent is a consequence of ester dissolution; total ethyl acetate 
accounts for at least ninety percent of the generated current. With 
formation occurring under hydrolyzing conditions, minor amounts of acetic 
acid, identified by liquid chromatography, have been produced either 
directly or from hydrolysis. 
TABLE 1 
__________________________________________________________________________ 
Electrogenerative Oxidation of Aqueous Ethanol Vapor 
Polarization Experiment (T = 23.degree. C.), EtOH Feed = 7.1 .times. 
10.sup.-5 mol/min in N.sub.2 
Cell Voltage 
Current 
EtOH .times. 10.sup.-5 
(IR Corrected) 
Density 
mol/min EtAc .times. 10.sup.-5 
% Current 
mV mA/sq.cm. 
Product mol/min Conversion.sup.g 
Accountability.sup.e 
__________________________________________________________________________ 
794.sup.a 
open circuit 
2.7 0.14 -- -- 
510 2.0 3.1 0.03 .01 19.5 
370.sup.b 
8.3 2.6 0.37 .10 56.8 
298 16.2 2.0 0.62 .18 48.7 
209.sup.c 
31.1 1.8 1.32 .37 53.8 
193 34.3 1.9 1.54 .43 56.9 
157 37.5 1.4 1.52 .43 51.6 
115.sup.d 
45.3 2.0 1.27 .36 35.6 
802 open circuit 
1.7 0.16 -- -- 
One Hour Steady State Operation.sup.f 
208 (34 min) 
28.4 3.5 1.6 .45 71.9 
207 (45 min) 
28.2 3.5 1.5 .43 69.5 
201 (62 min) 
27.4 3.0 1.4 .40 66.1 
__________________________________________________________________________ 
.sup.a-d Cathode potential versus RHE values from separate experiments 
allow calculation of anode potential: a, 221; b, 530; c, 646; d, 725 (mV) 
.sup.e based on ethyl acetate in vapor product stream. 
.sup.f in other experiments under similar conditions analysis for acetic 
acid and dissolved ethyl acetate in the electrolyte brought the current 
accountability to close to 100 percent (within experimental error). 
.sup.g single pass, conversion = 2x ethyl acetate effluent molar flow in 
N.sub.2 /(ethanol molar feedflow). 
With the oxygen electrode behavior characterized, an estimate of the anode 
potential at highest production rate for ethyl acetate is 0.66 V (vs. RHE) 
comparable to that for acetaldehyde at an untreated electrode. 
The mechanism of ethyl acetate formation is not presently known. Although 
this invention is not bound by any theory, it might be explained with 
surface acetyl formation or diadsorbed CH.sub.3 COH surface intermediate. 
Both theories have some support in the literature. With the diadsorbed 
species, two protons and two electrons are presumably released in a first 
step, followed by attack on the diadsorbed species by an ethanol molecule, 
presumably resulting in ester formation and release of the other two 
protons and the other two electrons. 
Example 4: Other Electrolytes 
Example 3 was carried out with a perchloric acid electrolyte and then with 
a prosphoric acid electrolyte. Results were substantially the same as with 
the sulfuric acid electrolyte. 
Example 5: Propanol Feed Materials 
Example 3 was repeated, again using 3M H.sub.2 SO.sub.4 electrolyte, but 
with 30cc/min of a 2-propanol feed (from a saturator containing 50 vol.-% 
aqueous 2-propanol). A similar run was carried out with 1-propanol. The 
2-propanol feed provided selective acetone production with no detectible 
byproduct CO.sub.2. When an unmodified anode was used, however, 
significant CO.sub.2 was produced. The 1-propanol feed gave propyl 
propionate as the product, indicating a rather general reaction for 
straight-chain primary alcohols of C.sub.2 and higher. 
Example 6: Liquid Phase Reactant/Packed Bed Electrode 
The purpose of this Example was to demonstrate liquid phase oxidation of 
ethanol, i-propyl alcohol and n-propyl alcohol. In all runs, the alcohol 
was dissolved in the anolyte (immediately before the run). In order to 
bring about effective contact between the aqueous alcohol/anolyte phase 
and the anode, various packed bed designs were used for the anode. The 
preferred packed bed anodes, which could be mounted inside the anode 
electrolyte compartment, had one of the two following configurations: 
(a) Five American Cyanamid AA-1 (9 mg/cm.sup. 2 Pt) electrodes with 80 
U.S.-mesh tantalum screens in conjunction with a gas-diffusion electrode 
(of the type used in the preceeding Examples) to recover vapor phase 
products. The gas-diffusion electrode was either an American Cyanamid 
LAA-2 (9 mg/cm.sup.2 Pt) or an LSE graphite electrode. 
(b) Platinum supported on either graphite felt or porous graphite sheet, 
with no gas-diffusion electrode associated with the packed bed. The oxygen 
counter-electrode was an American Cyanamid LAA-2, described in the 
previous Examples. 
Electrolyte Flow System 
The anolyte containing dissolved alcohol reactant flowed from a 1-liter 
reservoir into the cell through a three-way stopcock at the bottom of the 
anode electrolyte chamber. The stopcock facilitated draining the anolyte 
after the experiment was finished. The anolyte exited the cell through a 
"Teflon" (PTFE)/glass needle valve which was used to control the flowrate. 
Anolyte flowrate was determined by measuring with a stopwatch the time 
necessary to collect 5-10 ml in the graduated cylinder. Anolyte product 
samples were also collected in this manner. 
Static catholyte was employed in all experiments. Excess catholyte was 
maintained in two catholyte reservoirs (drying bulbs) connected to top and 
bottom nipples of the cathode electrolyte chamber. 
Gas Flow System 
In all experiments excess oxygen was fed to the cathode. In the case of the 
AA-1 packed bed (packed bed "a"), nitrogen was passed over the anode LAA-2 
or LSE to recover vapor or gaseous products. In the experiments with the 
Pt/graphite packed bed (Packed bed "b"), no gas diffusion electrode was 
used with the packed bed; thus there was no anode gas stream. 
Electrode Pretreatment 
In experiments involving the AA-1 packed bed, hydrogen gas was passed over 
the gas diffusion electrodes at the anode and cathode, while the cell was 
shorted for thirty minutes. After this time, the resistance across the 
unshorted cell was measured with a Keithley model 502 milliohmmeter. 
In experiments involving the Pt/graphite packed bed, since no gas diffusion 
electrode was employed at the anode, a different pre-treatment procedure 
was developed. Here, a constant current supply in series with an ammeter 
was connected across the cell. Also connected across the cell was a 
voltmeter. The current source (neative terminal connected to anode) was 
adjusted to force about 10ma through the cell, while hydrogen gas was fed 
to the cathode. A slight production of hydrogen gas bubbles at the packed 
bed anode was observed. Reduction was maintained under these conditions 
for about one hour; the cell resistance was then measured as above. 
Experimental Procedures 
In all runs, two polarization curves were performed for each set of 
experimental conditions. In the first curve, cell potential was changed 
every four minutes. In the second curve, cell potential was varied every 
five minutes and gas chromotography (GC) analyses of the anode effluent 
gas (in cases where a gas diffusion electrode was present at the anode) 
were performed at the end of each 5 min. period. Steady state experiments 
were also carried out. Here, after the two polarization curves were 
finished, the cell potential was adjusted to a region of interest and 
allowed to reach steady operation for about 25 minutes. After this period, 
GC samples of the anode effluent vapor were analyzed (in experiments where 
a gas diffusion electrode was present at the anode) while a 5-10 ml sample 
of the anolyte effluent was obtained. This anolyte sample was immediately 
analyzed using headspace chromatography. Other steady state potentials 
were then investigated using the same procedure. The anolyte samples were 
analyzed by HPLC (high performance liquid chromatography) the day after 
each experiment. 
Chemical Analyses 
Gas chromatographic analysis of the anode effluent vapor was accomplished 
on Carbowax 1540 (C.sub.2 H.sub.5 OH, CH.sub.3 CHO, C.sub.2 H.sub.5 
OCOCH.sub.3, i-propyl alcohol, acetone), Porapak-Q (CO.sub.2) and OV-101 
silicone (n-propyl alcohol, n-propyl propionate) columns. Headspace 
analysis was performed using the same columns. In this procedure, a small 
(500 .mu.l) sample of the anolyte effluent was placed in a 50 ml sealed 
("Teflon" Mininert valve) vial and allowed to equilibrate for 10-20 
minutes before a sample of the vapor above it was analyzed by gas 
chromotography. Calibration curves of several liquid standards bracketing 
the sample vapor concentrations were performed the same day as the 
electrogenerative experiment. 
The anolyte was also analyzed with HPLC for acetic (ethanol runs) and 
propionic (propanol runs) acids using a derivative technique based on 
esterification with phenacyl bromide. 
Run Summary 
Anolyte flow rates (cm.sup. 3/min): from 0.4 to 2.3. 
Concentration of alcohol in feed: from 0.25 to 1.0 M. 
Internal cell resistance (ohms): from 0.27 to 0.45. 
Steady state cell potential (mV): from 188 to 295, with current densities 
above 5mA/cm.sup.2 and up to about 60 mA/cm.sup.2. 
When the AA-1 packed beds (type "a", above) were not modified in accordance 
with this invention and the feed was ethanol, typically at least about 1% 
of the current was attributed to CO.sub.2 production, the major amount of 
current (about 50-90%) could be attributed to acetaldehyde, and a minor 
amount of current was accounted for by acetic acid. With reduced 
--SO.sub.2 treated AA-1 packed bed anodes, on the other hand, no CO.sub.2 
whatever could be detected, about 60-75% of the current was accounted for 
by acetic acid, and no acetaldehyde was detected. 
In runs with reduced SO.sub.2 -modified AA-1 (type "a") packed bed anodes 
and 0.5 M i-propyl alcohol or 0.5 M n-propyl alcohol feeds, no CO.sub.2 
was detected. In the case of i-propyl alcohol, the sole product produced 
appeared to be acetone, and in the case of n-propyl alcohol, no 
propionaldehyde was detected, but 57-82% of the current could be accounted 
for by propionic acid production. 
In type "b" (Pt/graphite sheet) experiments, wherein no gas-phase products 
were recovered with a nitrogen gas stream, the amount of carboxylic acid 
production was increased relative to the aldehyde production, even without 
S-treatment; however, the effect of the reduced-SO.sub.2 treatment is to 
provide a still higher proportion of carboxylic acid. 
Ambient temperature (20.degree.-25.degree. C. ) and pressure (atmospheric) 
conditions were used in all of the foregoing Examples, but these processes 
are operative over a broader range, e.g. temperatures of 
15.degree.-90.degree. C..