Recovery of tertiary butyl hydroperoxide and tertiary butyl alcohol

Abstract: Propylene oxide (30) and tertiary butyl alcohol (40) are prepared by reacting propylene (12) and tertiary butyl hydroperoxide (16) in an epoxidation reaction zone (10) in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst (14) to provide an epoxidation reaction product (18) comprising unreacted propylene, unreacted tertiary butyl hydroperoxide, tertiary butyl alcohol, dissolved molybdenum catalyst and impurities, including aliphatic C₁-C₄ carboxylic acids. The epoxidation reaction product (18) is resolved in a distillation zone into a distillate propylene fraction (22), a distillate propylene oxide fraction (30), a distillate tertiary butyl alcohol fraction (40) and a heavy liquid distillation fraction (50) composed primarily of tertiary butyl hydroperoxide, tertiary butyl alcohol, the dissolved molybdenum catalyst, and impurities including lower aliphatic C₁ -C₄ carboxylic acids. The addition to said heavy liquid distillation fraction (50) of 5 to 10 wt.%, based on the weight of said heavy liquid distillation fraction, of a lower aliphatic alcohol (72) having 1 to 3 carbon atoms, avoids icing up of a falling film evaporator (60) when the heavy fraction (50) is resolved therein at a temperature of 20 to 150°C and a pressure of 1 to 200 mm Hg (0.133 to 26.7 KPa) into a liquid residue fraction (64) comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including substantially all of the molybdenum contained in said heavy liquid fraction (50), and an evaporated overhead fraction (62) comprising 80 to 95 wt.% of the charged heavy liquid distillation fraction, and containing substantially all of the lower aliphatic alcohol initially charged to said falling film evaporator (20) and also containing from 60 to 90 wt.% of tertiary butyl alcohol, 1 to 20 wt.% of tertiary butyl hydroperoxide and, correspondingly, 3 to 15 wt.% of impurities, including a portion of said aliphatic C₁ -C₄ carboxylic acid impurities, and separating said lower aliphatic alcohol from the other components of said evaporated overhead fraction and recycling said separated lower aliphatic alcohol (84, 88, 72) to said falling film evaporator (60) as at least a portion of the lower aliphatic alcohol (72).

Description: This invention relates to an improvement in a process for resolving the reaction mixture that is formed when preparing propylene oxide and tertiary butyl alcohol by reacting propylene with tertiary butyl hydroperoxide, in solution in tertiary butyl alcohol and in the presence of a soluble molybdenum catalyst. The above-mentioned reaction mixture will normally comprise unreacted propylene, propylene oxide, unreacted tertiary butyl hydroperoxide, the soluble molybdenum catalyst and impurities, including C₁ to C₄ aliphatic carboxylic acids. The reaction mixture is usually separated by distillation into a plurality of fractions, including a recycle propylene fraction, a propylene oxide product fraction, a tertiary butyl alcohol product fraction, and a heavy liquid distillation fraction. The latter heavy fraction will generally contain tertiary butyl alcohol, unreacted tertiary butyl hydroperoxide and impurities, including substantially all of the dissolved molybdenum catalyst and a portion of the aliphatic carboxylic acids impurities. In accordance with the present invention from 5 to 10 wt.% of an aliphatic alcohol having 1 to 3 carbon atoms is added to the heavy liquid distillation fraction. The resultant mixture is charged to a falling film evaporator and separated therein, under operating conditions including a temperature of 20 to 150°C and a pressure of 0.13 to 20.66 KPa, into an overhead vaporized fraction comprising substantially all of the aliphatic alcohol and from 80 to 95 wt.% of the heavy distillation fraction charged to the falling film evaporator. The overhead fraction will comprise from 5 to 10 wt.% of aliphatic alcohol, from 60 to 90 wt.% of tertiary butyl alcohol, from 1 to 20 wt.% of tertiary butyl hydroperoxide and from 3 to 15 wt.% of impurities, including at least some of the C₁-C₄ carboxylic acid impurities. The practice of the present invention will also provide a clear liquid residue fraction comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including substantially all of the molybdenum contained in the heavy liquid fraction. The overhead vaporized fraction is charged to a distillation zone and separated into a lighter aliphatic alcohol distillate fraction and a heavier distillation fraction containing the other components of the overhead vaporized fraction, including the tertiary butyl alcohol, the tertiary butyl hydroperoxide and the impurities. The aliphatic alcohol fraction may be recycled to the falling film evaporator as at least a portion of the lower aliphatic alcohol, component of the feed mixture, if desired. It is known to react propylene with tertiary butyl hydroperoxide in the presence of a soluble molybdenum catalyst to provide a reaction product comprising propylene oxide and tertiary butyl alcohol, see, for example US-A-3350422, --51635 and -3418340. It is also known to prepare soluble molybdenum catalysts to catalyze the reaction as disclosed, for example, in US-A-3480563, -4607113, -4626596, -4650886 and -4703027. US-A-3860662 is directed to an improvement in the basic process, relating to the recovery of alcohols from the reaction product, which product is stated to be of an acidic nature, wherein a basic material such as an alkali metal compound or alkaline earth metal compound is added to the reaction mixture. US-A-3947500 discloses a method for treating the reaction product formed by the reaction of an organic hydroperoxide with an olefin wherein an organic alcohol is formed as a by-product. It is stated that the alcohol tends to dehydrate and that to overcome this problem at least partially, the oxidation reaction product is treated with a compound of an alkali metal or an alkaline earth metal. The alkali metal or alkaline earth metal compound can be added to the epoxidation reactor or to the reaction product. US-A-3573226 discloses a method wherein a molybdenum-containing catalyst solution is prepared by incorporating metallic molybdenum into the distillate bottoms fraction of an epoxidation reaction product, followed by heating the resultant mixture in order to form a soluble molybdenum-containing reaction product which can be used to catalyze the epoxidation reaction. The molybdenum-catalyzed epoxidation of alpha olefins and alpha substituted olefins with hydroperoxides less stable than tertiary butyl hydroperoxide may be accomplished according to US-A-3862961, by employing a critical amount of a C₃ to C₉ secondary or tertiary monohydric alcohol, such as tertiary butyl alcohol, as stabilizing agent. Citric acid is used to minimize the iron-catalyzed decomposition of the organic hydroperoxide without adversely affecting the reaction between the hydroperoxide and the olefin in a similar oxirane producing process taught by US-A-3928393. The inventors of US-A-4217287 discovered that if barium oxide is present in the reaction mixture, the catalytic epoxidation of olefins with organic hydroperoxides can be successfully carried out with good selectivity to the epoxide, based on hydroperoxide converted, when a relatively low olefin to hydroperoxide mole ratio is used. The alphaolefinically unsaturated compound should be added incrementally to the organic hydroperoxide. US-A-3931076 is directed to a method for recovering molybdenum catalyst values from a peroxidation reaction product for recycle. Three techniques are disclosed. In accordance with the first embodiment, the residue fraction is calcined to provide molybdenum trioxide, which is then used to prepare a soluble molybdenum compound by reaction with aqueous ammonia. In a second embodiment, the molybdenum-containing fraction is treated with aqueous ammonia without calcining, to form an ammonium molybdate which is treated with a polyalcohol to give a molybdic ester. In a third embodiment, the molybdenum-containing fraction is treated with gaseous ammonia in order to form an ammonium molybdate precipitate, which can be recovered by filtration. US-A-3449217 is directed to a process for the recovery of tertiary butyl hydroperoxide from a mixture comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and organic acids and esters resulting from the liquid phase oxidation of isobutane by a process which minimizes hydroperoxide decomposition. This is done by accomplishing the distillation while the product has an effective pH of below 9. The reactor effluent is treated with a neutralizing agent, such as an alkali metal or an alkaline earth metal hydroxide. US-A-3819663 is directed to a method for treating a heavy distillation fraction of this nature in order to recover the molybdenum in the concentrated bottoms fraction for recycle to the epoxidation reaction zone as makeup catalyst. A wiped-film evaporation process is carried out at a temperature of 550 to 650°F (273 to 330°C) at atmospheric pressure to obtain a residual fraction for recycle as catalyst makeup, and a distillate fraction, comprising 85% or more of the heavy distillation fraction. The distillate fraction that is thus obtained can be used as a furnace fuel, or can be worked up for recovery of the individual components contained therein. US-A-3819663, however, does not contain any teaching as to how the individual components in the fraction would be obtained. The present invention provides a process for the preparation of propylene oxide and tertiary butyl alcohol wherein propylene and tertiary butyl hydroperoxide are reacted in an epoxidation reaction zone in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst to provide an epoxidation reaction product comprising unreacted propylene, unreacted tertiary butyl hydroperoxide, tertiary butyl alcohol, dissolved molybdenum catalyst and impurities, including aliphatic C₁-C₄ carboxylic acids, and wherein the epoxidation reaction product is resolved in a distillation zone into a distillate propylene fraction, a distillate propylene oxide fraction, a distillate tertiary butyl alcohol fraction and a heavy liquid distillate fraction composed primarily of tertiary butyl hydroperoxide, tertiary butyl alcohol, the dissolved molybdenum catalyst, and impurities including lower aliphatic C₁-C₄ carboxylic acids. According to the invention from 5 to 10 wt.%, based on the weight of said heavy liquid distillation fraction, of a lower aliphatic alcohol having 1 to 3 carbon atoms, is added to said heavy liquid distillation fraction, the resulting mixture is resolved in a falling film evaporator at a temperature of 20 to 150°C and a pressure of 1 to 200 mm Hg (0.133 to 26.7 KPa) into a liquid residue fraction comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including substantially all of the molybdenum contained in said heavy liquid fraction, and an evaporated overhead fraction comprising 80 to 95 wt.% of the charged heavy liquid distillation fraction, and containing substantially all of the lower aliphatic alcohol initially charged to said falling film evaporator and also containing from 60 to 90 wt.% of tertiary butyl alcohol, 1 to 20 wt.% of tertiary butyl hydroperoxide and, correspondingly, 3 to 15 wt.% of impurities, including a portion of said aliphatic C₁-C₄ carboxylic acid impurities. Said lower aliphatic alcohol is separated from the other components of said evaporated overhead fraction and recycled to said falling film evaporator as at least a portion of the lower aliphatic alcohol. According to one embodiment, the evaporated overhead fraction has an acid number of not more than 12 and is recycled to said epoxidation reaction zone. According to another embodiment, the evaporated overhead fraction has an acid number of more than 12, is charged to a neutralization zone and treated therein with 1/2 to 1 equivalent of calcium oxide and/or calcium hydroxide per equivalent of said aliphatic C₁-C₄ carboxylic acid impurities contained therein, to provide a slurry of precipitated solids including calcium salts of said C₁-C₄ carboxylic acid impurities. This slurry is charged to a separation zone and separated therein to provide a solids fraction comprising calcium salts of said lower aliphatic carboxylic acids and a substantially solids-free filtrate having an acid number of less than 12 and comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and a reduced quantity of said carboxylic acid impurities, and said filtrate is recycled to said epoxidation reaction zone. It has been surprisingly discovered, in accordance with the present invention, that when the heavy distillation fraction is subjected to vacuum evaporation in the manner described in admixture with 5 to 10 wt.% of an aliphatic alcohol having 1 to 3 carbon atoms under the described evaporation conditions, the normally expected icing of the condenser surfaces will be substantially inhibited. When propylene is reacted with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in an epoxidation reaction zone in the presence of a soluble molybdenum catalyst, an epoxidation reaction mixture is formed which will contain not only unreacted feed components and the desired propylene oxide and tertiary butyl alcohol, but also impurities including the dissolved molybdenum catalyst, oxygen-containing impurities, such as ditertiary butyl peroxide, aliphatic C₁ to C₄ carboxylic acids such as formic acid, acetic acid, isobutyric acid, etc., alcohols such as methanol, isopropyl alcohol, tertiary butyl alcohol, etc., esters such as methyl formate, methyl acetate, methyl isobutyrate, etc., ketones such as acetone, etc., aldehydes such as isobutyraldehyde, etc., and hydrocarbon impurities resulting from undesired side reactions of the propylene, such as hydrocarbons containing 6 or more carbon atoms. Although most of the impurities are originally present in the epoxidation reaction mixture in trace amounts, as the epoxidation reaction mixture is resolved by distillation into a propylene recycle fraction, a propylene oxide product fraction and a tertiary butyl alcohol product fraction, all of which are distillate fractions, the impurities are progressively concentrated in a heavier distillation fraction, such as a distillation fraction having the composition generally set forth in Table I. This fraction is hereafter sometimes referred to, especially in the Working Examples, as the "catalyst bottoms". In accordance with the present invention, the heavy liquid distillation fraction is mixed with 5 to 10 wt.% based on the weight of the heavy liquid distillation fraction, of an aliphatic alcohol having 1 to 3 carbon atoms to provide a charge mixture, and the charge mixture is used as a charge stock for a falling film evaporator which is operated at a temperature of 20 to 150°C and a pressure of 0.13 to 26.66 KPa (1 to 200 mm Hg). The charge mixture is resolved in the falling film evaporator into an overhead fraction comprising substantially all of the aliphatic alcohol and from 80 to 95 wt.% of the heavy liquid residue fraction. The clear liquid residue fraction that is obtained from the falling film evaporator by the process of the present invention is a liquid fraction that can be handled with comparative ease, insofar as its disposal is concerned. Typically, this residual fraction will be sold to a company that reclaims metals from hydrocarbon fractions in order that the molybdenum contained therein may be recovered for re-use. The evaporated overhead fraction obtained in the falling film evaporator will typically contain substantially all of the aliphatic alcohol contained in the charge mixture, and from 60 to 90 wt.% of tertiary butyl alcohol, 1 to 20 wt.% of tertiary butyl hydroperoxide and, correspondingly, from 3 to 15 wt.% of impurities. Among the impurities that will typically be present are formic acid, acetic acid and isobutyric acid. In accordance with the present invention, the evaporated overhead fraction from the falling film evaporator is charged to a distillation zone where the aliphatic alcohol is separated from the other components of the evaporated overhead fraction for removal from the system, as desired, or for recycle for admixture with the heavy distillation fraction to form a portion of the charge mixture for the falling film evaporator. If the evaporated overhead fraction (i.e. a molybdenum-free distillate fraction from which the aliphatic alcohol has been removed) has an acid number of less than 12, which corresponds to a C₁-C₄ carboxylic acid content of 1 wt.% or less, it may be recycled, if desired, to the epoxidation reaction zone. If the evaporated overhead fraction is a more heavily contaminated fraction, however, such as a fraction that contains a greater concentration of C₁-C₄ carboxylic acids, and is nevertheless recycled to the epoxidation reaction zone, the epoxidation reaction may be adversely affected. The presence of excess quantities of carboxylic acids tends to decrease propylene selectivity to propylene oxide, because the increased acidity of the reaction mixture tends to promote side reactions of the propylene oxide with alcohols such as tertiary butyl alcohol that are present in the epoxidation reaction mixture. Also, the selectivity of TBHP to PO is reduced. In this situation, the more heavily contaminated molybdenum-free distillate fraction may be treated so as to remove an amount of acidic impurities sufficient to permit recycle to the epoxidation reaction zone. Thus, the more heavily contaminated lighter evaporated condensate fraction can be treated with calcium oxide and/or hydroxide in the manner disclosed and claimed in P23399 copending European Application 90308546.2. When this is to be done, the more heavily contaminated lighter evaporated condensate fraction can be charged to a neutralization zone and treated with 1/2 to 1 equivalents of calcium oxide and/or calcium hydroxide, based on the carboxylic acid content of the condensate fraction, to form a slurry of partially precipitated carboxylic acid impurities. The precipitate may be separated from the treated product by any suitable means such as centrifugation, filtration, etc., to provide a filtrate that is suitable for recycle to the epoxidation reaction zone. The single figure is a schematic drawing of a preferred reaction and purification sequence that may be used in the practice of the present invention. The Figure is a schematic flowsheet illustrating a preferred method of practicing the process of the present invention. Propylene is charged to an epoxidation reaction zone 10 by a line 12, together with a soluble molybdenum catalyst charged by a line 14 and a solution of tertiary butyl hydroperoxide and tertiary butyl alcohol charged by a line 16. The epoxidation reaction is an epoxidation reaction of the type disclosed in US-A-3351653 as further elaborated upon, for example, in GB-A-1298253, wherein propylene is reacted with tertiary butyl hydroperoxide at a reaction temperature of 82 to 149°C (180 to 300°F) and a pressure of 2.17 to 6.99 MPa (300 to 1000 psig) and, more preferably, a temperature of 104 to 138°C (220 to 280°F) and a pressure of 3.55 to 5.62 MPa (500 to 800 psig). The soluble molybdenum catalyst charged to the epoxidation reaction zone by the line 14 may be an epoxidation catalyst of the type known in the art, such as the above-mentioned US-A-3351653 or GB-A-1298253, or by US-A-4626596, -4650886, -4654427 or -4758681, which are directed to molybdenum/alkanol complexes such as solutions of molybdenum compounds in ethylene glycol which contain a high concentration of molybdenum and are particularly useful as catalysts in the epoxidation reaction, e.g. at a temperature of 50 to 180°C and a propylene to tertiary butyl hydroperoxide ratio from 0.9:1 to 3.0:1. Suitably, the tertiary butyl hydroperoxide that is charged to the epoxidation reaction zone 10 by way of line 16 is a 40 to 75 wt.% solution of tertiary butyl hydroperoxide in tertiary butyl alcohol. The catalyst is charged to the epoxidation reaction zone 10 by the charge line 14 in an amount such as to provide from 50 to 1000 ppm of molybdenum, based on the total of the reactants charged and, more preferably, from 200 to 600 ppm. The reaction is preferably conducted at superatmospheric pressure, such as a pressure of 300 to 1000 psig (2.17 to 6.99 MPa). When the reaction is conducted on a continuous basis, as illustrated in the drawing, the feed materials are charged to the epoxidation reaction zone 10 through the lines 12, 14 and 16 at rates sufficient to maintain the desired concentration of reactants, and an equivalent volume of epoxidation reaction mixture is withdrawn from the epoxidation reaction zone 10 by way of a discharge line 18. The reaction mixture discharged by the line 18 will normally comprise unreacted propylene, a minor amount of unreacted tertiary butyl hydroperoxide, propylene oxide, tertiary butyl alcohol, including tertiary butyl alcohol formed by the reaction of the tertiary butyl hydroperoxide with propylene, the molybdenum catalyst and impurities such as propane, propionaldehyde, acetone, methanol, isopropanol, water, acetaldehyde, methyl formate, acetic acid, formic acid, isobutyric acid, hydrocarbons containing 6 or more carbon atoms and high boiling residue components. The reaction product 18 is charged to an epoxidation reaction product distillation zone 20 where it is separated by distillation into desired fractions in accordance with methods known to those skilled in the art, for example, by the distillation sequence disclosed in GB-A-1298253. One of the distillate products recovered in the zone 20 is a propylene fraction which is discharged by a line 22, controlled by a valve 24, and provided with a branch line 26, controlled by a valve 28, in order to permit the recycle of unreacted propylene to the epoxidation reaction zone 10 through the propylene charge line 12. Another distillate fraction obtained is a propylene oxide product fraction 30, which is discharged by the line 30. The propylene oxide fraction may be purified in a propylene oxide purification zone (not shown) by known techniques, for example, those disclosed in US-A-3715284, -3909366, -3881996, -3607669, -3843488 or -4140588. Another product recovered from the distillation zone 20 is a tertiary butyl alcohol distillate product 40, which may be further purified, if desired, to remove oxygenated impurities by catalytic treatment as disclosed, for example, in US-A-4704482, -4705903 or -4742149. A heavy distillation fraction 50, usually a bottoms fraction, is also discharged from the distillation zone 20. As described in US-A-3819663 and -4455283, the heavy distillation fraction will contain substantially all the molybdenum catalyst initially charged to the epoxidation reaction zone 10 by way of the line 14. The heavy distillation fraction 50 will contain other products, such as tertiary butyl hydroperoxide, tertiary butyl alcohol, and impurities including oxygenates lighter than tertiary butyl alcohol, such as acetaldehyde, acetone, isopropyl alcohol, etc., oxygenates heavier than tertiary butyl alcohol but lighter than tertiary butyl hydroperoxide, and residue components heavier than tertiary butyl hydroperoxide, such as propylene glycol tertiary butyl ethers, hydrocarbons containing 6 or more crbon atoms, etc. As indicated, the heavy distillation fraction 50 will also contain carboxylic acids such as formic acid, acetic acid and isobutyric acid. In accordance with the present invention, 5 to 10 wt.% based on the weight of the heavy liquid distillation fraction, of an aliphatic alcohol having 1 to 3 carbon atoms, such as methanol, ethanol, n-propanol, or isopropanol and preferably n-propanol, is charged by way of a charge line 72 controlled by a valve 73 to the line 50 leading to a falling film evaporator 60. Also in accordance with the present invention, the falling film evaporator 60, which is preferably a wiped film evaporator, is operated at a temperature of 20 to 150°C and a pressure of 0.13 to 26.66 KPa (1 to 200 mm Hg). The average residence time of the charge mixture in the falling film evaporator 60 is such that from 80 to 95 wt.% of the material charged by way of the line 50 is taken overhead as a distillation fraction by way of the line 62; the remaining 5 to 20 wt.% of the material charged by way of the line 50 being discharged from the falling film evaporator 60 by way of a bottoms discharge line 64. The fraction 64 will contain substantially all of the molybdenum initially discharged from the epoxidation reaction zone 10. It has been surprisingly discovered, in accordance with the present invention, that when the charge mixture 50 is subjected to falling film evaporation in the manner described and under the conditions described, the small amount of lower alcohol added (5 to 10%) prevents icing of TBA on the condenser walls. The vaporized fraction discharged from the wiped film evaporator by the line 62 will contain substantially all the propanol charged to the wiped film evaporator 60 through the line 50 and will also comprise 60 to 90 wt.% of tertiary butyl alcohol, 1 to 20 wt.% of tertiary butyl hydroperoxide and from 3 to 15 wt.% of impurities. In accordance with the present invention, the vaporized fraction 62 from the falling film evaporator 60 is charged to a distillation zone 80, where it is separated into a molybdenum-free distillate fraction discharged by a line 84 controlled by a value 86 for discharge from the system or for recycle through a branch line 88 controlled by a valve 89 leading to the propanol charge line 72. The heavy distillation fraction (e.g. bottoms fraction 82) is substantially free from propanol and comprises the tertiary butyl alcohol, tertiary butyl hydroperoxide and other impurities charged to distillation column 80 by line 62. If the molybdenum-free distillate fraction discharged from the distillation zone 80 by the line 82 has an acid number of 12 or less (i.e. contains 1 wt.% or less of C₁-C₄ aliphatic carboxylic acids) it may be routed to the tertiary butyl hydroperoxide charge line 16 by a tertiary butyl hydroperoxide recycle line 66, controlled by a valve 68. As indicated above, if the acid number of the molybdenum-free distillate fraction 82 is more than 12 and it is recycled to epoxidation reaction zone 10, the selectivity of the propylene to propylene oxide and TBHP to propylene oxide may be adversely affected. In this situation, the molybdenum-free distillate fraction 82 may be discarded from the system by a branch line 202 controlled by a valve 203. In accordance with a preferred embodiment of the present invention, however, the molybdenum-free distillate fraction 82 is routed by a branch line 204, controlled by a valve 205, to a neutralization zone 208 in order to reduce the acid number to an acceptable level of 12 or less. In accordance with this embodiment, the molybdenum-free distillate fraction 82 is treated in the manner described and claimed in European Application No. 90308546.2. Thus, an autoclave 208 equipped with suitable agitation means such as an impeller 207 may be provided. The fraction 204 is continuously cahrged through valve 205 to the autoclave 208, together with 1/2 to 1 equivalents of powdered calcium oxide and/or calcium hydroxide, based on the carboxylic acids contained in the fraction 204, the calcium oxide and/or calcium hydroxide being continuously charged to the autoclave 208 by way of a charge line 206. Appropriate neutralization conditions are established in the autoclave 208, such as a temperature of 70 to 100°C, a residence time of 1/4 to 5 hours, and an appropriate pressure, such as atmospheric pressure. As a consequence, the calcium oxide and/or calcium hydroxide will partially react with the carboxylic acids present in the autoclave 208 to form a precipitate. The resultant slurry is discharged from the autoclave 208 by an autoclave discharge line 210 leading to a separation zone 220 (e.g. a centrifugation zone, a filtration zone, etc.) where the slurry is separated into a solids fraction comprising calcium salts of precipitated carboxylic acids, which is discharged by a line 222, and a filtrate fraction comprising a partially purified stream of tertiary butyl alcohol and tertiary butyl hydroperoxide, having an acid number of 12 or less, which is discharged by a discharge line 224 leading to a holding tank 230. If desired, the partially purified filtrate 224, comprising tertiary butyl alcohol and tertiary butyl hydroperoxide, may be discharged from the holding tank 230 by a line 232 controlled by a value 234 for recycle to the epoxidation reaction zone 10, by way of tertiary butyl hydroperoxide recycle line 66. If desired, the filtrate 224 may be discharged from the holding tank 230 by a line 236, controlled by a valve 238, for another purpose, for example, for use as a boiler fuel The invention will be further illustrated by the following specific Examples. EXAMPLES Tables II to VIII set out the Conditions and Results. Run No. 1 is a controlled evaporation conducted in a standard rotary evaporator with the feed and conditions as described in Table II. Note in this control run there was extensive freezing and crystallization of the largely TBA overhead. Pure TBA freezes at about 25°C. This can present serious problems on a commercial scale. In Runs No. 2 to 5, n-propanol was added to the feed (epoxidation catalyst bottoms), and at the 5% level or greater (4.26%) there was no freezing in the condenser coils or neck of the receiver flask. This addition of n-propanol did not appear to affect adversely other material balances, such as the TBHP balance, the molybdenum balance, or acid balance as measured by acid number. In summary, the addition of n-propanol to the epoxidation catalyst bottoms before final evaporation and catalyst concentration will prevent freezing in the condensers (heat exchangers) which could seriously upset a commercial operation.

Claims: A process for the preparation of propylene oxide (30) and tertiary butyl alcohol (40) wherein propylene (12) and tertiary butyl hydroperoxide (16) are reacted in an epoxidation reaction zone (10) in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst (14) to provide an epoxidation reaction product (18) comprising unreacted propylene, unreacted tertiary butyl hydroperoxide, tertiary butyl alcohol, dissolved molybdenum catalyst and impurities, including aliphatic C₁-C₄ carboxylic acids, and wherein the epoxidation reaction product (18) is resolved in a distillation zone into a distillate propylene fraction (22), a distillate propylene oxide fraction (30), a distillate tertiary butyl alcohol fraction (40) and a heavy liquid distillation fraction (50) composed primarily of tertiary butyl hydroperoxide, tertiary butyl alcohol, the dissolved molybdenum catalyst, and impurities including lower aliphatic C₁-C₄ carboxylic acids, characterized by adding to said heavy liquid distillation fraction (50) from 5 to 10 wt.%, based on the weight of said heavy liquid distillation fraction, of a lower aliphatic alcohol (72) having 1 to 3 carbon atoms, resolving the resulting mixture in a falling film evaporator (60) at a temperature of 20 to 150°C. and a pressure of 1 to 200 mm Hg. (0.133 to 26.7 Kpa) into a liquid residue fraction (64) comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including substantially all of the molybdenum contained in said heavy liquid fraction (50), and an evaporated overhead fraction (62) comprising 80 to 95 wt.% of the charged heavy liquid distillation fraction, and containing substantially all of the lower aliphatic alcohol initially charged to said falling film evaporator (20) and also containing from 60 to 90 wt.% of tertiary butyl alcohol, 1 to 20 wt.% of tertiary butyl hydroperoxide and, correspondingly, 3 to 15 wt.% of impurities, including a portion of said aliphatic C₁-C₄ carboxylic acid impurities, and separating said lower aliphatic alcohol from the other components of said evaporated overhead fraction and recycling said separated lower aliphatic alcohol (84,88,72) to said falling film evaporator (60) as at least a portion of the lower aliphatic alcohol (72). A process according to claim 1 characterized in that the falling film evaporator (60) is a wiped film evaporator. A process according to claim 1 characterized in that the lower aliphatic alcohol is propanol. A process according to any one of claims 1 to 3 characterized in that the evaporated overhead fraction (62) has an acid number of not more than 12 and is recycled (68,16) to said epoxidation reaction zone (10). A process according to any one of claims 1 to 3 characterized in that the evaporated overhead fraction (62) has an acid number of more than 12, is charged to a neutralization zone (208) and treated therein with 1/2 to 1 equivalent of calcium oxide and/or calcium hydroxide (206) per equivalent of said aliphatic C₁-C₄ carboxylic acid impurities contained therein to provide a slurry of precipitated solids (210) including calcium salts of said C₁-C₄ carboxylic acid impurities, which slurry is charged to a separation zone (220) and separated therein to provide a solids fraction (222) comprising calcium salts of said lower aliphatic carboxylic acids and a substantially solids-free filtrate (224) having an acid number of less than 12 and comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and a reduced quantity of said carboxylic acid impurities, and said filtrate (224) is recycled (232,66,16) to said epoxidation reaction zone (10).

Inventors: KEATING KENNETH PATRICK, MARQUIS EDWARD THOMAS SR, MEYER ROBERT ALLEN, SANDERSON JOHN RONALD, KEATING, KENNETH PATRICK, MARQUIS, EDWARD THOMAS, SR., MEYER, ROBERT ALLEN, SANDERSON, JOHN RONALD
Applicants: TEXACO CHEMICAL, TEXACO CHEMICAL COMPANY
Application year: 1990
Main classification: C07D301
IPC codes: C07C407, B01J27, C07C31, C07C27, C07D303, C07C29, C07D301, C07B61