The present invention relates to an acid catalysed process for producing an organic peroxide. Several organic peroxide production processes are acid catalysed and require the use of large amounts of strong acid. The preferred acid to be used is sulfuric acid. The use of large amounts of sulfuric acid leads to the formation of large amounts of sulfate-containing waste streams.

It is an object of the present invention to reduce these sulfate-containing waste streams.

Recycling of streams in a process to produce organic peroxides from alcohols or ketones is known from CN 101857563 and CN 108658824. CN101857563 and CN 108658824 disclose a process to prepare tertbutyl hydroperoxide by reacting tert butanol and hydrogen peroxide in the presence of sulfuric acid in which part of the mother liquor is recycled to be reused as solvent for newly added reactants. To avoid an indefinite dilution of the process streams the mother liquor is only recycled partly. Because only part of the mother liquor is recycled into the process only part of the sulfuric acid and unreacted hydrogen peroxide and tert butanol are reused. Effectively, the majority of the sulfuric acid employed will end up as a waste stream in the process as disclosed.

This object to further reduce sulfate-containing waste streams has been met by the process of the present invention, which includes steps for the purification, concentration, and re-use of the sulfuric acid stream originating from an organic peroxide production process.

The sulfuric acid stream contains peroxide: hydrogen peroxide, residues of the organic peroxide that was produced, or a combination thereof. It will also contain other organic species. In order to be re-used, it is essential that the sulfuric acid is purified from organic residues. It is also essential to concentrate the sulfuric acid to a concentration that is required for its re-use. Furthermore, peroxide residues have to be removed from the stream, because not all process steps in which the purified and recycled stream will be used allow the presence of peroxide residues.

The organic peroxide production process according to the present invention comprises the following steps:

a. reacting an alcohol or ketone with hydrogen peroxide, thereby forming a reaction mixture comprising:

- an organic phase comprising an organic peroxide and

- an aqueous phase comprising (i) at least 5 wt% H2SO4 and (ii) H2O2 and/or organic peroxide residues,

b. separating the aqueous phase from the organic phase,

c. optionally adding H2O2 to and/or removing any residual organic compounds from said aqueous phase,

d. obtaining an aqueous phase comprising 5-60 wt% H2SO4 and 0.3-35 wt% H2O2, and

e. heating the aqueous phase of step d. at a temperature in the range 20-

300°C, at a pressure of 0.001 to 1 bar, thereby decomposing at least part of the H2O2, removing part of the water, and increasing the H2SO4 concentration of the aqueous mixture by at least 7 weight percentage points to a concentration in the range 12-95 wt%.

Quite unexpectedly, the sulfuric acid containing stream can be concentrated by a simple step, above step e), in which water is evaporated. As known by those skilled in the art, when reacting an alcohol or ketone with a hydrogen peroxide in the presence of sulfuric acid, the formation of acetone peroxides cannot be prevented. Acetone peroxides bear the risk of solidifying in a water evaporation step such as above step e), and acetone peroxide crystals are known to be friction sensitive explosives. However, in the process of the invention the acetone peroxide buildup and formation of colored products is unexpectedly suppressed by the combination of steps c), d) and e) of the process of the invention and the amount of acetone peroxide remains below the level at which it can create safety problems It should be noted that US 4,168,274 and GB1501356 disclose a process that involves the recycling of a sulfuric acid waste stream in which a concentration step of the sulfuric acid solution is present. However, these documents relate to the preparation of a peracid by reacting an organic acid with hydrogen peroxide in the presence of sulfuric acid. When preparing peracids by reacting acids with hydrogen peroxide, contrary to when reacting alcohols or ketones with hydrogen peroxide, as a person skilled in the art is aware, acetone peroxides will not be formed.

The aqueous phase resulting from step e. can be used for any purpose for which it is suitable, such as the production of phosphoric acid from phosphate rock, the production of ammonium sulfate from coking plants, the production of aluminium sulfate from bauxite, the manufacture of dyestuff solutions, the production of hydrogen via the sulfur-iodine cycle (Bunsen reaction), as industrial cleaning solution, or as electrolyte in e.g. lead-acid batteries.

In a preferred embodiment, at least part of the aqueous phase resulting from step e. is re-used in an organic peroxide production process. This can be the same process, for the same organic peroxide, as it resulted from, but may also be a process for the production of another organic peroxide.

The advantage of the present process is that it does not require the addition of contaminating materials, such as metals, which makes the recycled sulfuric acid suitable for re-use in a peroxide production process.

In a more preferred embodiment, at least part of the aqueous phase resulting from step e. is re-cycled to step a.

The aqueous phase that is treated in steps c., d., and e. can result from one specific organic peroxide production process, but may also be a mixture of the aqueous phases resulting from two or more different organic peroxide production processes.

Increasing the H2SO4 concentration in step e. by heating the aqueous phase is not so straightforward as it may seem. The H2C>2 that is present in said phase will decompose, which can result in significant oxygen gas formation and, consequently, pressure build-up. Furthermore, this oxygen, together with volatile organics, can form a flammable and potentially explosive mixture.

The alcohol that is employed in step a) in embodiments is chosen from the group consisting of tert-butyl alcohol, tert-amyl alcohol, 1 ,1 ,3,3-tetramethylbutanol, 2,5- dimethyl-2,5-hexanediol, 2-methyl-2,4-pentanediol, 2,5-dimethyl-2,5-dihydroxy- hexyne-3, 1 ,3-bis(isopropanol)benzene, and 1 ,4-bis(isopropanol)benzene

The ketone that is employed in step a) in embodiments is chosen from group consisting of acetone, acetyl acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone, methyl hexyl ketone, methyl heptyl ketone, diethyl ketone, ethyl propyl ketone, ethyl amyl ketone, methyl octyl ketone, methyl nonyl ketone, cyclopentanone, cyclohexanone, 2-methylcyclohexanone, 3,3,5- trimethyl cyclohexanone

The reaction of step a) is done in the presence of H2SO4.

Suitable organic peroxides that can be produced according to the process of the present invention are dialkyl peroxides, cyclic ketone peroxides, trioxepanes, and aliphatic hydroperoxides.

Specific examples of dialkyl peroxides are 2,2-di(tert-butylperoxy)butane, dicumyl peroxide, di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert- butylperoxy)hexane, di-tert-butylperoxide, di-tert-amylperoxide, 2,5-dimethyl- 2,5-di(tert-butylperoxy)hexyne-3, and tert-butyl cumyl peroxide.

Preferred dialkyl peroxides are 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5- dimethyl-2,5-di(tert-butylperoxy)hexyne-3, di-tert-amylperoxide, and di-tert- butylperoxide. The production of these peroxides requires relatively concentrated sulfuric acid solutions (30 wt% or higher).

The term“cyclic ketone peroxides” includes dimeric cyclic ketone peroxides and trimeric cyclic ketone peroxides. These peroxides have the following structures: wherein R ¹ -R ⁶ are independently selected from the group consisting of hydrogen, C1 -C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7-C20 alkaryl, which groups may include linear or branched alkyl moieties; and each of R ¹ -R ⁶ may optionally be substituted with one or more groups selected from hydroxy, alkoxy, linear or branched alkyl, aryloxy, ester, carboxy, nitrile, and amido.

Preferred cyclic ketone peroxides are 3,6,9-triethyl-3,6,9-trimethyl-1 ,4,7- triperoxonane (3MEK-cp) and mixtures comprising 3MEK-cp and at least one peroxide satisfying formula

wherein R ¹ through R ³ are independently selected from alkyl and alkoxyalkyl groups, said groups having 2 to 5 carbon atoms, the total number of carbon plus oxygen atoms of R ¹ +R ² +R ³ is in the range 7-15. The term alkoxyalkyl group refers to a group with the formula -CnH2n-0-CmH2m+i , wherein both n and m are at least 1 .

Trioxepanes have the formula

wherein R ¹ , R ² , and R ³ are independently selected from hydrogen and a substituted or unsubstituted hydrocarbyl group, and optionally two of the group of R ¹ , R ² , and R ³ are linked to form a ring structure. Preferably, R ¹ , R ² , and R ³ are independently selected from the group consisting of hydrogen and substituted or unsubstituted C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 aralkyl, and C7- C20 alkaryl, which groups may include linear or branched alkyl moieties, while two of R ¹ , R ² , and R ³ may be connected to form a (substituted) cycloalkyl ring; the optional one or more substituents on each of R ¹ -R ³ being selected from the group consisting of hydroxy, alkoxy, linear or branched alk(en)yl, aryloxy, halogen, carboxylic acid, ester, carboxy, nitrile, and amido.

Preferably, R ¹ and R ³ are selected from lower alkyl groups, more preferably C1-C6 alkyl groups, such as methyl, ethyl, and isopropyl, methyl and ethyl being most preferred. R ² is preferably selected from hydrogen, methyl, ethyl, iso-propyl, iso- butyl, tert-butyl, amyl, iso-amyl, cyclohexyl, phenyl, CH3C(0)CH2-, C2H ₅ 0C(0)CH2-, HOC(CH ₃ )2CH2-, and

wherein R ⁴ is independently selected from any of the group of compounds given for R ^{1 3} . Another preferred trioxepane is:

Specific examples of aliphatic hydroperoxides are tert-butyl hydroperoxide, tert- amyl hydroperoxide, hexyleneglycol hydroperoxide, 2,5-dimethyl-2,5- dihydroperoxy hexane, 2,5-dimethyl-2,5-dihydroperoxy-3-hexyne, and 1 , 1 ,3,3- tetramethylbutyl hydroperoxide, and 1 ,1 -dimethylbutyl hydroperoxide.

If a mono-alcohol is used in step a. of the process, a dialkyl peroxide or a hydroperoxide results, depending on the amount of hydrogen peroxide and the sulfuric acid concentration. For dialkylperoxide production, an aqueous sulfuric acid solution with a concentration of at least 30 wt% is generally required; for hydroperoxides, a concentration between 10 and 30 wt% is generally used. Examples of suitable mono-alcohols are tert-butyl alcohol, tert-amyl alcohol, and 1 ,1 ,3,3-tetramethylbutanol.

If a di-alcohol is used in step a. of the process, a di-hydroperoxide results, which can be further reacted with a mono-alcohol, also in the presence of sulfuric acid, towards a bis-dialkyl peroxide. Aqueous sulfuric acid solutions with a concentration of at least 10 wt% are preferably used in the latter reaction.

Examples of di-alcohols are 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-2,5- dihydroxy-hexyne-3, 1 ,3-bis(isopropanol)benzene, and 1 ,4- bis(isopropanol)benzene.

In order to obtain a dimeric or trimeric cyclic ketone peroxide, a ketone is reacted with hydrogen peroxide in the presence of a 20-75 wt% aqueous sulfuric acid solution and an inert diluent (phlegmatizer). Examples of suitable ketones are linear, branched or cyclic C3-C13 ketones, most preferably C3-C7 ketones. Examples of suitable ketones are acetone, acetyl acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone, methyl hexyl ketone, methyl heptyl ketone, diethyl ketone, ethyl propyl ketone, ethyl amyl ketone, methyl octyl ketone, methyl nonyl ketone, cyclopentanone, cyclohexanone, 2- methylcyclohexanone, 3,3,5-trimethyl cyclohexanone, and mixtures thereof.

Trioxepanes are obtained by reacting a glycol (dialcohol) with hydrogen peroxide in the presence of 20-60 wt% aqueous sulfuric acid solution, in order to form a glycol hydroperoxide. The glycol hydroperoxide is subsequently reacted with a ketone or aldehyde, again in the presence sulfuric acid (10-60 wt% aqueous solution), to form the trioxepan. This process is described in WO 2006/066984. A suitable example of a glycol is 2-methyl-2,4-pentanediol.

The formed organic peroxide will be present in the organic layer of the resulting bi-phasic reaction mixture and can be isolated by conventional techniques, such as gravity, a liquid/liquid separator, a centrifuge, or a continuous (plate) separator (step b.). The organic peroxide is generally washed with water or an alkaline aqueous solution.

The aqueous phase will contain (i) H2SO4 and (ii) H2O2 and/or remaining organic peroxide. It may also contain additional organics. These organics in preferred embodiments need to be substantially removed and/or destroyed, in order to prevent them from blackening the aqueous mixture or to build up to an undesired level.

In preferred embodiments these organics are more completely removed and/or destroyed by (vacuum) distillation (step e.) or by adding an (additional) amount of hydrogen peroxide to the aqueous mixture (step c.).

The aqueous phase of step d. preferably contains at least 5 wt%, preferably at least 10 wt%, more preferably at least 20 wt%, and most preferably at least 30 wt% H2SO4. It preferably contains not more than 60 wt % H2SO4.

In addition to H2SO4, other acids may be present in the aqueous phase.

The aqueous phase of step d. comprises 0.3-35 wt%, preferably 0.5-35 wt%, more preferably 1 -35 wt%, even more preferably 2-35 wt%, and most preferably 2-25 wt% H2O2.

In order to decompose at least part of the H2O2, remove part of the water, and raise the H2SO4 concentration by at least 7 weight percentage points to a concentration in the range 12-95 wt%, preferably 50-95 wt%, more preferably 70- 95 wt%, and most preferably 75-85 wt%, the aqueous mixture is heated to a temperature in the range 20-300°C, preferably 30-250°C, even more preferably 50-200°C, and most preferably 100-200°C, at a pressure of 0.001 -1 bar, preferably 0.01 -1 bar (step e.).

It should be noted that the temperature of the aqueous phase formed in step b. is generally in the range 0-20°C, preferably 0-10°C, as peroxide production processes are often performed at low temperatures. It is not desired to concentrate to >96 wt% H2SO4, as that requires distillation of S03 and its subsequent dissolution.

The heating is preferably conducted in one or more distillation and/or heating steps.

The heating step in a preferred embodiment involves stripping of volatile organic components at temperatures below the decomposition temperature of H2O2. Suitable temperatures are in the range 30-120°C. The pressure can be atmospheric but is preferably lower, in order to avoid an explosive atmosphere during the process.

If the hydrogen peroxide concentration of the aqueous mixture is relatively high (about 2 wt% or more), its decomposition will result in a substantial oxygen stream. Distillation at atmospheric pressure is then preferred in view of safety concerns.

If the peroxide concentration is lower, or gets lower during the process, distillation at reduced pressure should be considered. It is also possible to first apply atmospheric distillation, followed by distillation at reduced pressure.

The aqueous distillate that is removed during step e. is condensed in a condenser and subsequently collected in a vessel.

Due to the decomposition of hydrogen peroxide, the distillate will contain significant amounts of oxygen. The oxygen will not condense in the condenser and in order to ensure safe processing it is required to keep the oxygen concentration of the distillate below the flashpoint. Preferably, the oxygen concentration in the gas phase is kept below 30 vol%, preferably below 8 vol%. This can be achieved by introducing nitrogen or air into the system, thereby diluting the oxygen. More preferably, a nitrogen or air stream is added to the distillate before entering the condenser, or while present in the condenser.

Step e. can be conducted batch-wise, semi-continuously or continuously. In a batch process with higher volumes, the temperature should be carefully controlled to prevent dangerous situations. Furthermore, in batch processes most gas is formed at the beginning of the process, which may lead to the establishment of very concentrated oxygen streams. With concentrated oxygen streams, it is difficult to control the nitrogen stream such that the mixture stays below the flashpoint. In (semi)continuous operation, however, the rate of oxygen and CO2 formation will be more to almost completely constant and the oxygen concentration will be much easier to control. In semi-continuous mode, a first portion of the aqueous phase is heated to boiling temperature in a batch reactor; then the remaining portion of the aqueous phase containing H2S04 and H202 is dosed to said batch reactor and (part of) the concentrated acid is taken out intermittently. In this way, the rate of oxygen formation and organics stripping is also more efficient and better controllable. Continuous operation or semi- continuous operation is preferred. In a specific embodiment, the process relates to the production of 2,5-di-tert- butylperoxy-2,5-dimethylhexane or 2,5-di-tert-butylperoxy-2,5-di(tert- butylperoxy)hexyne-3. These peroxides are conventionally prepared in two steps. In the first step, 2,5-dimethyl-2,5-hexanediol, resp. 2,5-dimethyl-2,5-dihydroxy- hexyne-3, is reacted with hydrogen peroxide, in the presence of sulfuric acid, towards 2,5-dihydroperoxy-2,5-dimethylhexane, resp. 2,5-dihydroperoxy-2,5- dimethylhexyne-3. An excess of hydrogen peroxide in a high concentration (e.g. a 70 wt% aqueous solution) is generally required, including a relatively large amount of highly concentrated sulfuric acid (e.g. a 70-95 wt% aqueous solution). The dihydroperoxide can be isolated from the aqueous effluent by filtration or centrifugation and contains significant amounts of sulfuric acid, hydrogen peroxide, a little diol, and various organic byproducts.

The dihydroperoxide is then reacted with tert-butanol, again catalyzed by highly concentrated sulfuric acid (e.g. 60-90 wt% aqueous solution), to form the desired peroxide. The aqueous effluent from this step, which may also be obtained by gravity separation or centrifugation, will contain sulfuric acid and organic byproducts. The combined aqueous effluents comprise about 10-50 wt% hteSC and about 5- 20 wt% H2O2. Organics can be removed from the resulting aqueous phase by stripping with an air stream, followed by a distillation to destroy most of the H2O2, and increase the H2SO4 concentration. A further distillation at reduced pressure may be performed thereafter to further increase the H2SO4 concentration.

The resulting purified and concentrated H2SO4 can be used in various processes. In a preferred embodiment, it is re-used in the first and/or second step of this peroxide production process.

In another specific embodiment, the process relates to the production of di-tert- butyl peroxide or di-tert-amyl peroxide. According to this embodiment, tert-butyl alcohol or tert-amyl alcohol is reacted with hydrogen peroxide in the presence of a 30-78 wt% aqueous sulfuric acid solution, to form di-tert-butyl peroxide or di- tert-amyl peroxide, respectively.

The organic and aqueous phases can be separated by gravity, centrifugation, a liquid/liquid separator, or a continuous (plate) separator.

The aqueous phase contains 5-70 wt% H2SO4, 0.1 -10 wt% tert-butanol or tert- amyl alcohol, and 0.1 -5 wt% organic peroxide.

Hydrogen peroxide is then dosed to the aqueous phase, resulting in an aqueous phase with a hydrogen peroxide concentration of 0.3-20 wt%, preferably 0.3-10 wt%, and most preferably 0.3-5 wt%. This mixture is then preferably stirred at a temperature in the range 50-250°C, more preferably 80-220°C, most preferably 100-210°C, optionally under reduced pressure, in order to destroy and/or remove organic residues and increase the sulfuric acid concentration.

In another embodiment, the process relates to the production of hydroperoxides. According to this embodiment, a tertiary alcohol or a substituted alkene is reacted with hydrogen peroxide in the presence of sulfuric acid (5-95 wt% aqueous solution) to form tert-alkyl hydroperoxides. The organic and aqueous phases can be separated by gravity, centrifugation, a liquid/liquid separator, or a continuous (plate) separator.

The aqueous phase contains 5-60 wt% H2SO4, 1 -25 wt% H2O2, 0.1 -20 wt% tertiary alcohol, and 0.1 -5 wt% organic peroxides.

Hydrogen peroxide is then optionally dosed to the aqueous phase, which is then preferably stirred at a temperature in the range 50-250°C, more preferably 80-

220°C, most preferably 100-210°C, optionally under reduced pressure, in order to destroy and/or remove organic residues and increase the sulfuric acid concentration.

In another embodiment, the process relates to the production of trimeric cyclic ketone peroxides. According to this embodiment, a ketone is reacted with hydrogen peroxide in the presence of 20-95 wt% aqueous sulfuric acid solution, to form trimeric cyclic ketone peroxides.

The organic and aqueous phases can be separated by gravity, centrifugation, a liquid/liquid separator, or a continuous (plate) separator.

The aqueous phase contains 20-70 wt% H2SO4, 1 -25% H2O2, 0.1 -20 wt% ketones, and 0.1 -10 wt% organic peroxides. Hydrogen peroxide optionally is then dosed to the aqueous phase, which is then preferably stirred at a temperature in the range 50-250°C, more preferably 80- 220°C, most preferably 100-210°C, optionally under reduced pressure, in order to destroy and/or remove organic residues and increase the sulfuric acid concentration.

In another embodiment, the process relates to the production of trioxepanes. According to this embodiment, a ketone is reacted with a hydroxyl hydroperoxide in the presence of 20-95 wt% aqueous sulfuric acid solution, to form trioxepanes.

The organic and aqueous phases can be separated by gravity, centrifugation, a liquid/liquid separator, or a continuous (plate) separator.

The aqueous phase contains 10-70% wt% H2SO4, 0.1 -20 wt% ketones, and 0.1 - 20 wt% organic peroxides Hydrogen peroxide is then optionally dosed to the aqueous phase, which is then preferably stirred at a temperature in the range 50-250°C, more preferably 80- 220°C, most preferably 100-210°C, optionally under reduced pressure, in order to destroy and/or remove organic residues and increase the sulfuric acid concentration.

EXAMPLES

Example 1

An aqueous 70 wt% hydrogen peroxide solution (121 .6 g) was added to a jacketed reactor. The reactor was cooled to 5°C. An aqueous 78 wt% sulfuric acid solution (157.5 g) was then dosed to the reactor within 20 minutes, while the temperature of the mixture was controlled below 10°C. After addition of the sulfuric acid, the mixture was cooled to 5°C. Solid 2, 5-dimethyl-2, 5-dihydroxy hexane (36.6 grams, 0.25 moles) was added to the mixture at such a rate that the temperature stayed below 10°C.

After the addition of the 2, 5-dimethyl-2, 5-dihydroxy hexane, the temperature was raised to 25°C and kept at this temperature for one hour. The temperature was subsequently reduced to 5°C and 200 mL water was added. After 2 minutes of agitation, the reaction mixture was filtered and washed with cold water. Solid 2,5- dimethyl-2, 5-dihydroperoxyhexane was obtained in a yield of 78%. The 471 g aqueous phase containing 26% H2SO4 was combined with the acid layer of the next step. Tert-butanol (88 wt% in water, 143 grams, 1 7 moles) was added (20 min) dropwise into a stirred solution of sulfuric acid (78 wt %, 104.7 grams, 0.83 moles) in a jacketed reactor held at 15°C 2, 5-Dimethylhexane-2, 5-dihydroperoxide obtained in the previous step (54 g, 0 20 moles) was added in 20 min., after which the temperature was raised to 40°C and kept at this temperature for up to four hours.

The reaction resulted in a two-layer mixture; the layers of which were separated by draining off the aqueous layer. The organic layer contained 2,5-dimethyl-2,5- di-tert-butylperoxyhexane in a yield of 70%.

The aqueous layer was diluted with 150 g water and tert-butanol was removed by distillation at 100 mbar. The resulting 276 g aqueous phase containing 30 wt% HteSCHwas combined with the aqueous phase of the first step, thereby forming a waterphase containing 27 wt% H2SO4 and 9 wt% H2O2.

Said waterphase was dosed just below the top of a glass vigreux column that was mounted on a three-necked glass vessel. The vessel was stirred and the temperature was maintained at 135-140°C by heating with an external oil bath at atmospheric pressure. The vigreux column was connected to a condenser (at 20°C) and a vessel to collect the condensate. Air was fed to the condenser in order to dilute the oxygen content in the gas phase to 25 vol%. The waterphase was dosed to the vigreux column at a rate of 5 gram per minute, resulting in the formation of a condensate at a rate of 2.65 gram per minute. No solids (any compound such as di acetone peroxide) were observed in the equipment, the acid or the distillate. At steady state, 2.35 gram per minute colourless concentrated acid was pumped out of the three-necked vessel. The concentrated acid had a H2SO4 content of 58.3% and a H2O2 content of 1 .8%.

In a 2 ^nd concentration step, the concentrated acid of the previous step was dosed to a three-necked glass vessel. The vessel was stirred and the temperature was maintained at about 162°C by heating with an external oil bath and was connected to a vacuum system at 70-120 mbar pressure. The three-necked glass vessel was connected to a condenser and a vessel to collect the condensate. The concentrated acid was dosed at a rate of 2 gram per minute and 0.6 gram per minute condensate was obtained. At steady state, 1.4 gram per minute colourless concentrated acid was pumped out of the three-necked vessel. No solids (any compound such as di acetone peroxide) were observed in the equipment, the acid or the distillate. The concentrated acid had a H2SO4 content of 83 wt% and a H2O2 content of <0.5%. The acid was diluted with water to 78 wt% and could be re-used to make 2, 5-dimethylhexane-2, 5-dihydroperoxide as explained above.

Example 2

To a 2.5 liter reactor - equipped with 3 baffles, a turbine impeller, a thermometer and a cooling mantle - were added 900 gram 70 wt% H2SO4 and 600 gram 30 wt% H2O2. Tert-butyl alcohol (700 gram) was dosed within 1 hour, thereby keeping the temperature in the range 35-40°C. The mixture was heated to 45°C and stirred for 1 hour at this temperature. After that, the mixture was cooled to 30°C and allowed to separate. The 1.520 g waterlayer had a sulfuric acid concentration of 41 wt%. The organic layer was washed with a bicarbonate solution and contained 668 g of di-tert-butylperoxide with a purity of 99.4% in a yield of 96%.

H2O2 (102 g, 30 wt%) was added to the waterlayer. The resulting mixture was dosed (rate: 500 ml/hour) to a 100 ml heated vessel that was operated at 93°C and 100-150 mbar. Water vapor was sent to a condenser. The acid flowing out of the vessel was sent to a multi compartment evaporator, in which the temperature was increased to 157°C at a pressure of 100-150 mbar. The colourless acid coming from the last compartment was cooled to room temperature and had a H2SO4 content of 74 wt%. No solids (any compound such as di acetone peroxide) were observed in the equipment, the acid or the distillate.

After dilution with water to 70 wt% H2SO4, the acid could be used again in the preparation of di-tert-butylperoxide according to the above procedure.