Production of hydrogen peroxide

Hydrogen peroxide is produced by a process which uses solid, insoluble, supported anthraquinone as catalyst. The catalyst is reduced to supported anthrahydroquinone using a hydrogen-donating organic substrate such as an alcohol, followed by reaction with oxygen, suitably photochemical reaction, to regenerate anthraquinone and to form hydrogen peroxide, which can be solvent extracted from the solid catalyst.

FIELD OF THE INVENTION 
This invention relates to anthraquinone catalyzed chemical processes and 
especially to methods for manufacture of hydrogen peroxide, using 
anthraquinone as a catalyst. 
BACKGROUND OF THE INVENTION 
The photochemical reaction between alcohols and oxygen sensitized by 
quinone catalysts has been studied for a number of years. For example, 
Tickle and Wilkinson.sup.1 studied the photooxidation of isopropanol 
(2-propanol) using anthraquinone (AQ) as a catalyst. The overall 
stoichiometry of the reaction is 
##STR1## 
The mechanism is proposed to involve the photoreduction of AQ via its 
triplet State to form anthrahydroquinone which is converted back to the 
starting catalyst AQ with air or oxygen with the concurrent formation of 
HOOH. 
An analogous reaction involving the catalytic reduction of an alkyl 
anthraquinone by hydrogen is the basis of a current industrial synthesis 
of hydrogen peroxide (HOOH) via the reaction sequence 
##STR2## 
where R.sub.1 and R.sub.2 can be hydrogen or C.sub.1 -C.sub.20 alkyl 
groups 
Hydrogen peroxide is an important industrial chemical. It is widely used as 
a bleach, e.g. in the pulp and paper industry. It is also used extensively 
in the mining industry, e.g, for removing cyanide residues from gold 
mining operations. It is basically an environmentally acceptable chemical, 
unlike many competitive industrial bleaching compounds. Hydrogen peroxide 
is however a difficult material to transport safely. The locations where 
it is to be used industrially, e.g. mining sites and pulp mills, are often 
far removed from other chemical manufacturing and processing facilities. 
The production of the required hydrogen peroxide on site is accordingly 
desirable. 
AQ derivatives are widely used in industrial process for the production of 
hydrogen peroxide. The AQ derivative is hydrogenated to anthrahydroquinone 
(AHQ), which is subsequently oxygenated to AQ and hydrogen peroxide. 
Separation of the AQ from the product is complicated and costly. 
Liquid-liquid extraction, to take out the hydrogen peroxide product as an 
aqueous solution, is necessary. This is costly, and involves large volumes 
of recycle. Quantitative separation is not achieved. Only dilute solutions 
of hydrogen peroxide are obtained, unless subsequent distillation is 
undertaken. 
It is an object of the present invention to provide novel methods of 
conducting anthraquinone-catalyzed chemical processes, which overcome or 
at least reduce one or more of the aforementioned disadvantages. 
It is a further object to provide a novel process for production of 
hydrogen peroxide. 
SUMMARY OF THE INVENTION 
This invention provides methods by which an anthraquinone (AQ) moiety is 
immobilized on an inert, non-soluble carrier. The immobilized AQ maintains 
its chemical reactivity. It can be utilized for most of the chemical 
procedures in which AQ is used as a catalyst; it can be recycled, and it 
is easily separated from other reactants. 
Examples of processes where this novel, immobilized AQ can be used include: 
photochemical oxidation of alcohols, photochemical production of hydrogen 
peroxide, formation of hydrogen peroxide by chemical reduction of the AQ 
followed by air oxidation, and other radical reactions initiated by 
(photochemical) hydrogen abstraction. 
The immobilized AQ is able to undergo a multitude of reaction cycles 
retaining its activity and efficiency for a large number of turnovers; 
thus it can be regarded as a true (photo) catalyst. 
The process of the present invention very significantly reduces the 
problems of separation and recovery of the AQ catalyst and product, while 
maintaining the activity of the AQ moiety. 
The process of the present invention offers several advantages over the 
current methods involving the AQ-AHQ cycle. 
(a) The immobilization of AQ onto the solid supports prevents consumption 
or loss of this molecule during the process. It is easily retrieved when 
the reaction is stopped, and avoids contamination of the working solutions 
and effluents. 
(b) AQ immobilized on the totally inert inorganic supports has a special 
advantage over similar products where organic polymers are utilized as 
carriers. This is manifested, for example, in the photochemical process. 
AQ which was chemically attached to an organic polymer exhibited 
spectroscopic evidence for the reversible photochemical reduction and air 
oxidation as observed in organic AQ solution, However, the reactive 
intermediates attack the supporting polymer, consuming its available 
hydrogen atoms..sup.2 This is not the case with inert inorganic supports. 
(c) The ability of the immobilized AQ to function in aqueous and in polar 
and non polar organic solutions is of particular interest and 
significance. The common industrial process for hydrogen peroxide 
manufacture, "The AQ Process".sup.3, is complicated by changes in the 
reagent's solubility. AQ is soluble in organic non-polar solvents. The AQ 
is hydrogenated to form AHQ which is soluble in organic polar solvents. 
Oxygen is blown in, and the AHQ is transformed back to AQ while releasing 
hydrogen peroxide. The hydrogen peroxide is collected by extraction with 
water. Special efforts are made to overcome the solubility problems and to 
minimize AQ losses. The immobilized AQ used in the process of the present 
invention can be integrated into the current process of HOOH manufacture. 
It bypasses these complications. It is active in aqueous as well as 
organic solutions. No losses of immobilized AQ to the solvents have been 
observed. 
This invention has the potential for producing hydrogen peroxide 
photochemically, using natural hydroxy compounds (alcohols, carbohydrates, 
polycarbohydrates) as hydrogen donors, thus enabling the preparation of 
this important chemical where light and the above-mentioned raw materials 
are abundant. Alternatively, these alcohols can be utilized to reduce the 
carbonyl functions of AQ in a catalyzed transfer hydrogenation 
reaction..sup.4

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention includes methods to activate silica or glass in the form of 
beads, loose powder, fibres, tubes,or plates by using silane coupling 
molecules, e.g., amino propyl trimethoxy silane (APTS), and a method to 
bind AQ thereto. Anthraquinone (in the form of AQ carboxylic acid 
chloride) is covalently bound to the free amino functions which have thus 
been attached to the silica/glass. The amount of AQ immobilized by this 
method relates to the accessible surface area of the silica/glass. High 
densities of amino groups can be obtained by proper choice of 
technique..sup.5 
Alternatively, an AQ (e.g., in the form of 2-isopropenyl or 
AQCH.dbd.CHCOOH) moiety can be copolymerized with, e.g., acrylic acid or 
any of its derivatives. This polymer is attached to the amine activated 
silica via its functional group--the carboxylic group--with the aid of 
coupling agents such as dicyclohexyl carbodiimide (DCC). This approach 
enables heavier loading of AQ on silica. Moreover, changing the co-monomer 
can provide AQ catalysts with varying affinity and effectivity towards 
solvents and substrates. 
In a similar process, the silica is functionalized with 
.beta.-(trimethoxysilicyl)propyl methacrylate followed by polymerization 
with a mixture of vinyl AQ and co-monomer. Anthraquinone-2-carboxylic acid 
chloride (AQCOC1) can be attached to cellulosefibres by a route which 
resembles its binding to silica. Other methods which are commonly used by 
the dyeing industry, can be utilized to affix AQ to cellulose fibres. 
In addition to anthraquinone-2-carboxylic acid derivatives, other suitable 
quinoid systems can be utilized to perform similar reactions. Among those 
are anthraquinone-2-sulfonic acid (AQ-2-SO.sub.3 H), 2,6- or 
1,5-disulfonic acid (AQ-2,6-diSO.sub.3 H; AQ-1,5-diSO.sub.3 H) and their 
derivatives and other members of the anthraquinone group substituted by 
electron-withdrawing moieties such as chlorine atoms, and also 
benzoquinone and benzanthrone..sup.6,7 
Several organic alcohols have displayed this hydrogen donor ability: 
primary alcohols (ethanol and n-butanol), secondary alcohols (isopropanol 
and sec-butanol), polyols (glycerol and the sugars sucrose and xylose). 
In one preferred method of application of our invention, the immobilized AQ 
is suspended in the (liquid) substrate. Air is blown through this 
suspension in order to stir it and to supply oxygen. Irradiation at 360 nm 
or shorter wave length induces photoreduction of the AQ to AHQ. In the 
presence of air or oxygen, this is subsequently oxygenated to yield 
hydrogen peroxide and the hydrogen-donating co-reagent is concurrently 
oxidized. For example, irradiation of immobilized AQ in isopropanol leads 
to the formation of hydrogen peroxide and acetone. The reaction can take 
place in a suspension of the pure co-reagent or in its aqueous solution. 
This process can also be performed in two distinct and separate stages. For 
example, the photochemical hydrogen abstraction can be performed (in the 
absence of oxygen) in a solution of hydrogen donor, e.g, isopropanol, 
which can be then removed from the reacting beads. Hydrogen peroxide can 
be harvested from the solid catalyst in a second medium, e.g., water after 
exposure to oxygen. This route of alternating reaction media has the 
advantage of collecting the hydrogen peroxide in a pre-selected medium, 
free from starting materials. 
One can also obtain high yields of hydrogen peroxide by continuous 
irradiation in the presence of air. This process is believed to take place 
via the excited triplet state of the anthraquinone moiety and these 
excited states are known to be quenched by oxygen. It appears that the 
rate of photoreduction on these highly active catalysts can compete 
effectively with quenching by oxygen. 
In the non-photochemical route, the immobilized AQ is converted to AHQ with 
the aid of soluble reducing agents such as sodium borohydride or sodium 
dithionite or hydrogenation using homogeneous catalysts which are known to 
reduce carbonyl functions such as ruthenium triphenylphosphine 
complexes..sup.8 
The basic reactions and structures can be represented as follows: 
##STR3## 
SPECIFIC DESCRIPTION OF THE MOST PREFERRED EMBODIMENTS 
Example 1 
Activation of Silica-Gel Beads 
Aminopropyl trimethoxysilane (APTS, 2 g) was added to 100 ml of water. 
Acetic acid was added dropwise to pH 4. After brief stirring, 20 g of 
silica gel beads (60-120 mesh, BDH) were added. After one hour the aqueous 
solution was decanted. The silica was washed with water and ethanol, and 
air dried overnight. These activated beads were further reacted with AQ 
derivatives (see examples below) and have over 0.11 mmol free amine/g as 
evidenced by the amount of binding. 
Higher densities of amino groups can be obtained by refluxing silica with 
APTS in toluene..sup.5 
Example 2 
Activation of Glass Fibres 
Pyrex glass fibres (5 g) were treated with sodium hydroxide (20% solution) 
for ca. 30 min. at room temperature. The base was rinsed and the fibres 
washed thoroughly with water, dilute hydrochloric acid, and ethanol, and 
then air dried. The fibres were than treated with an aqueous APTS mixture 
as described in Example 1. 
Example 3 
Binding of AQCOC1 to Fumed Silica 
Fumed silica (Cab-o-Sil M5, Cabot Corp., 5 g, activated with APTS, as 
described in Example 1 and dry tetrahydrofuran (THF, 50 mL) was stirred in 
a flask. AQCOC1 (220 mg) in 10 mL of THF was added dropwise. After 30 
min., ca. 0.5 mL of pyridine was added and the mixture stirred for an 
additional 1 hour. The modified silica was filtered, thoroughly washed 
with ethanol, and then dried. The washings contained about 50 mg of 
AQCOOEt and AQCOOH (as determined by UV adsorption at 324 nm) indicating 
that ca. 0.126 mmol/g of AQ was immobilized on the surface of the silica. 
Example 4 
Binding of AQCOC1 to Silica Gel 
Silica gel 60 (5 g, 230-400 mesh, EM Science, APTS activated as in 1) was 
reacted with 165 mg AQCOC1 as in Example 3. Analysis of the washing shows 
that 159 mg (0.11 mmol/g) AQ were bound to the silica beads. 
Example 5 
Binding of AQCOC1 to Pyrex Glass Fibres 
Pyrex glass fibres activated with APTS (5 g) were reacted with AQCOC1 (55 
mg) by procedure of Example 3. Analysis of the washings determined that 35 
mg (0.026 mmol/g) of AQ was bound. 
Example 6 
BiO glass 1500 (porous glass for chromatography, Bio-Rad) was reacted with 
AQCOC1 by the procedure of Example 3. Bound AQ 0.045 mmol/g. 
Example 7 
Binding of AQCOC1 to Cellulose 
Cellulose pulp (2 g) was stirred in water for 24 hours. The water was 
removed and the pulp soaked in dry methanol. Methanol was drained off and 
a new portion was added. This was repeated four times, followed by similar 
cycles using dry THF. Finally, 10 mg of AQCOC1 was added. After 5 hours a 
few drops of pyridine was added and the mixture was stirred overnight. 
Analysis of the washings indicates that 0.01 mmol of AQ was bound to the 
pulp. 
Example 8 
Binding of AQCOOH to Silica Gel 
To 5 g of aminopropyl-functionalized silica gel (Aldrich, .about.9% 
functionalized) in 75 mL dry THF, were added 1.26 g AQ-COOH and 1.2 g DCC. 
The mixture was stirred overnight and then filtered, washed with acetone, 
methanol, water and acetone, and then dried. Analysis of the washings 
showed that 1.18 g (0.94 mmol/g) AQ were bound to the silica. 
Example 9 
Binding of AQ-2-SO.sub.3 H to Silica 
AQ-2-SO.sub.3 Na (Aldrich) was converted to AQ-2-CO.sub.2 C1 with the aid 
of thionyl chloride..sup.9 The chloride (0.3 g, 1 mmol) was reacted with 4 
g of aminopropyl-functionalized silica in THF. After 1 h, pyridine (0.5 
mL) was added. The mixture was stirred for 12 h, filtered, washed with 
EtoH, and then dried. Examination of the washings showed that the binding 
was nearly complete, i.e., 0.25 mmol/g). 
Example 10 
Binding of AQ-2,6-diSO.sub.3 H to Silica 
AQ-2,6-diSO.sub.3 Na was converted to AQ-2,6-diSO.sub.2 Cl..sup. 9 To a 
stirred suspension of aminopropyl-functionalized silica (3 g) in THF, was 
added 0.33 g (0.15 mmol) of the dichloride. After 1 h, pyridine (0.5 mL) 
was added and the mixture was stirred for an additional 12 h. Silica 
particles were filtered, washed with acetone, then with dilute Na.sub.2 
CO.sub.3, acetone and dried. Analysis of the washings showed that the 
whole amount was practically bound, i.e, loading of 0.25 mmol/g. 
Example 11 
Irradiation of Silica-AQ with Alcohols and Water Alcohol Mixtures 
The irradiation experiments were performed in a Pyrex tub-shaped reactor 
equipped with a fitted glass at the bottom, an inlet side-arm and a tap. 
Air or nitrogen was supplied through the side-arm and the fritt, stirring 
the reaction mixture and forming either an oxidative or inert atmosphere. 
Alternatively, these gases were supplied via the top forcing the liquid out 
while maintaining the desired atmosphere. A condenser at the top prevented 
loss of volatiles. This reactor was placed in a Rayonette irradiation well 
apparatus 16 360-nm lamps. Air was bubbled via the fitted glass and 
coolant was circulated in the condenser. 
Irradiation experiments were carried out for 1-2 h. The amount of H.sub.2 
O.sub.2 produced was determined by an iodometric method for the organic 
reaction mixtures. The aqueous solutions were analyzed via titanate 
formation..sup.10 Several experimental examples are summarized in Table 1. 
TABLE 1 
__________________________________________________________________________ 
HYDROGEN PEROXIDE FORMATION BY IRRADIATION OF 
IMMOBILIZED AQ WITH ALCOHOLIC HYDROGEN DONORS 
Catalyst Irradiation 
H.sub.2 O.sub.2 mol 
H.sub.2 O.sub.2 / 
(mg) Substrate (h) (mmol) 
mol AQ 
__________________________________________________________________________ 
(a) 120.sup.a 
iPrOH 1 0.32 33 
(b) 100.sup.a 
iPrOH (40% in H.sub.2 O) 
1 0.14 17 
(c) 100.sup.a 
iPrOH (20% in H.sub.2 O) 
1 0.1 12 
(d) 120.sup.a 
iPrOH 2 0.47 60 
(e) 100.sup.a 
nBuOH 1 0.3 37 
(f) 100.sup.a 
2-BuOH 1 0.19 24 
(g) 100.sup.a 
Ethanol 1 0.38 47 
(h) 100.sup.a 
nBuOH (20% in H.sub.2 O) 
1 0.05 6 
(i) 100.sup.a 
2-BuOH (20% in H.sub.2 O) 
1 0.01 1 
(i) 100.sup.a 
Ethanol (20% in H.sub.2 O) 
1 0.02 2.5 
(k) 100.sup.a 
Glycerin (20% in H.sub.2 O) 
1 0.03 3.6 
(l) 100.sup.a 
Sucrose (20% in H.sub.2 O) 
1 0.02 2.4 
(m) 655.sup.a 
iPrOH 1 0.02 40 
(n) 655.sup.b 
H.sub.2 O 1 &gt;0.004 
(o) 100.sup.d 
xylose (5% in H.sub.2 O) 
1 0.0053 
2 
(p) 100.sup.c 
sucrose (5% in H.sub.2 O) 
1 0.253 11 
(q) 100.sup.c 
iPrOH (40% in H.sub.2 O) 
1 2.464 110 
(r) 500.sup.c 
xylose (5% in H.sub.2 O) 
1 0.3 2.4 
__________________________________________________________________________ 
.sup.a Cabo-sil M5: AQ content, 0.08 mmol/g, as made in Example 3. 
.sup.b Cellulose pulp: AQ content, 0.005 mmol/g, as made in Example 2. 
.sup.c Aminopropyl silica (Aldrich) AQ (as AQSO.sub.2 NH--) content 0.25 
mmol/g as made in Example 9. 
.sup.d Aminopropyl silica (Aldrich) AQ content 0.94 mmol/g as made in 
Example 8. 
Example 12 
Alternating Cycles of Photoreduction and Oxygenation 
The reaction vessel was charged with 200 mg of silica AQ (0.02 mmol/g), 10 
mL of iPrOH, and a constant stream of nitrogen was passed through the 
fritt. The reactor was irradiated for 5 min. Alcohol was forced out from 
the reactor with the aid of nitrogen. Water (5 mL) was introduced and air 
was bubbled for 3 min. The aqueous solution was filtered and kept. The 
reaction vessel was flushed with nitrogen and the iPrOH solution was 
re-introduced and irradiated. After five alternating cycles the aqueous 
solution contained 0.014 mmol of hydrogen peroxide, i.e, production of 3.5 
mol H.sub.2 O.sub.2 /mol AQ. 
Example 13 
Preparation of Hydrogen Peroxide Via Sodium Borohydride Reduction 
Silica AQ (2 g, 60-120 .about.0.06 mmll/g AQ) as prepared in Example 5 was 
suspended in ethanol (in the reactor described above) with the aid of a 
fine stream of nitrogen. Sodium borohydride (0.145 g) was added and the 
mixture reacted for 30 min. The solvent was filtered off and washed with 
ethanol under a nitrogen atmosphere. Finally, ethanol was added to the 
particles and air blown for .about.5 min. The solution was collected and 
the hydrogen peroxide determined to be 0.34 mg. Similar results were 
obtained using sodium dithionite as the reducing agent. 
Example 14 
Photooxidation of Glycerine 
Aqueous glycerine (10 mL, 20% glycerine) was irradiated with 120 mg silica 
AQ (0.08 mmll/g) for 5 h with air blowing through the mixture. GC analysis 
determined formation of dihydroxy acetone (0.85 mmol, 17 mol/mol AQ/h). 
Example 15 
Irradiation of Toluene 
Toluene (10 mL) and silica AQ (120 mg, 0.08 mmol AQ/g) were irradiated as 
above (5h). GC analysis demonstrated the formation of benzaldehyde (44 mg, 
0.36 mmol, 4.5 mol/mol AQ) as well as benzoic acid. Analysis of the 
toluene by the iodometric method showed that 0.4 mmol (5 mol/mol AQ) of 
peroxide was formed. 
Example 16 
Preparation of Acrylic Acid 2-Isopropenyl Anthraquinone Copolymer 
2-isopropenyl AQ (0.3 g), 1.2 g acrylic acid (Aldrich, containing 
inhibitors (200 ppm MEHQ) and 40 mg AIBN were placed in a heavy-walled 
glass tube. Oxygen was removed by three freeze/thaw cycles. The tube was 
sealed and heated to 80.degree. C. for 1 h. The polymer thus obtained was 
dissolved in dioxane. TLC (20% AcOEt in hexane) shows disappearance of 
free isopropenyl AQ. 
Example 17 
Binding of Poly(acrylic) 2-Isopropenyl AQ to Silica APTS 
Silica 60 APTS (2 g) was added to 20 mL dry dioxane solution containing 0.5 
g of polymer. Dicyclohexyl carbodiimide (DCC) 85 mg was added and the 
mixture was stirred overnight, then filtered and washed with dioxane 
ethanol, acetone and dried. Irradiation of 20% aqueous isopropanol for 1 h 
as in Example 9 yielded 0.08 mmol H.sub.2 O.sub.2 in the effluent from the 
catalyst. 
Example 18 
Solar Irradiation 
The procedure of Example 11a was repeated except that the reactor was 
placed in bright summer sunlight for 5 h. The yield of hydrogen peroxide 
was 0.28 mmol. 
Example 19 
Preparation of Methyl Methacrylate-acrylic Acid 2-Isopropenyl Anthraquinone 
Terpolymer 
2-isopropenyl AQ (0.3 g), 0.5 g acrylic acid and 0.7 g methyl acrylate 
(Aldrich) containing inhibitor (200 ppm methyl hydroquinone, MeHQ) and 40 
mg 2,2'-azobis-isobutyronitrile (AIBN) were placed in a heavy-walled glass 
tube. Oxygen was removed by three freeze/thaw cycles. The tube was sealed 
and heated to 80.degree. C. for 1 h. The polymer thus obtained was 
dissolved in dioxane. TLC (20% AcOEt in hexane) shows disappearance of 
free isopropenyl AQ. 
A 1% solution of the polymer in dioxane was sprayed on filter paper 
(Whatman #1) and dried. The filter paper was cut into small square pieces 
(ca. 5.times.5 mm). The impregnated paper pieces were suspended in the 20% 
iPrOH water mixture and irradiated as in Example 11 for 1 h. Hydrogen 
peroxide (0.07 mmol) was produced. 
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