Phenol Preparation Process and Propylene Recovery Therefrom

Europaisches Patentamt 0 361 755 J) European Patent Office © Publication number: A2 Office europeen des brevets

® EUROPEAN PATENT APPLICATION

0 Date of filing: 19.09.89

© Designated Contracting States: @ Inventor: Fukuhara, Hiroshi AT BE CH DE ES FR GB GR IT LI LU NL SE c/o MITSUI PETROCHEMICAL INDUSTRIES LIMITED 3, Chigusakaigan Ichihara-shi Chiba(JP) Inventor: Matsunaga, Fujihisa c/o MITSUI PETROCHEMICAL INDUSTRIES LIMITED 3, Chigusakaigan Ichihara-shi Chiba(JP)

© Phenol is produced by (a) reacting benzene with propylene to synthesize cumene, (b) oxidizing the cumene of step (a) into cumene hydroperoxide, (c) acid cleaving cumene hydroperoxide into phenol and acetone, (d) hydrogenating the acetone of step (c) into isopropanoi and (e) dehydrating the isopropanol of step (d) into propylene. The propylene from step (e) is useful by itself or is recycled from the step (e) to step (a) of the phenol producing process.

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Xerox Copy Centre 1 EP 0 361 755 A2 2

Phenol Preparation Process and Propylene Recovery Therefrom

BACKGROUND OF THE INVENTION duced is unbalanced relative to their commercial demands, one for less demand is produced largely in vain. This invention relates to the preparation of phe- As is known in the art, acetone is available in nol, and more particularly to a phenol preparing 5 surplus for these years. Thus the production of process which can recover propylene from the acetone by-product is now considered as a serious acetone by-product and recycle the recovered pro- drawback of the cumene process. Although ac- pylene as the starting material. etone has found the majority of its application as a It is well known in the art to react benzene with starting material for preparing methyl methacrylate, propylene to produce cumene, to oxidize cumene 70 the demand, for acetone is decreasing because of to produce cumene hydroperoxide, and to acid a switch of the starting material for preparing meth- cleavage cumene hydroperoxide into phenol and yl methacrylate to another. acetone. A conventional phenol preparing process Under the circumstances, there is a need for having these steps combined is generally known as the development of a phenol preparing process the cumene process. rs which is devoid of production of acetone and other It is also an old well-known technique to hy- by-products. Although several proposals have been drogenate acetone into isopropanol. This technique made, there is available no process capable of is still widely used at present for the assay of the preparing phenol in satisfactory yields. catalytic activity of a hydrogenating catalyst and In addition, impurities in propylene often cause other purposes. For example, the activity of Raney 20 a drawback during the preparing step of cumene nickel catalysts is often examined by comparing from benzene and propylene in the cumene pro- their acetone hydrogenating ability. Several ad- cess for the preparation of phenol. That is, pro- vanced processes have been proposed as dis- pylene for use in the cumene preparation is manu- closed in Japanese Patent Application Kokai Nos. factured generally using crude oil as the starting 12729/1987 and 77338/1987. 25 material. Crude oil, however, contains sulfur com- Nevertheless, insofar as the inventors know, it pounds and various heavy metals, and these impu- has never been proposed to produce isopropanol rities are sometimes carried in propylene as trace from the acetone by-product resulting from prep- contaminants, during its manufacturing process. For aration of phenol by the cumene process, and to example, carbonyl sulfide (COS) as a sulfur com- dehydrate the isopropanol into propylene. 30 pound or As as a heavy metal contaminant in There are known some analogous processes, propylene inhibits function of a catalyst (aluminum for example, to produce ethylene from ethanoi and chloride-HCI complex) for use in the cumene prep- to produce isobutylene from tert.-butanol. However, aration, thus disturbing normal progress of the these olefin producing processes cannot be applied cumene synthesis. Therefore, a strict purification of to the production of propylene from isopropanol for 35 . process is perproduced to avoid contamination the following reason. Since propylene is substan- propylene with these impurities. Types and quan- tially different in reactivity from ethylene or tity of these contaminants, however, vary depend- isobutylene, those skilled in the art cannot presume ing on not only the crude oil source but also the the dehydration of isopropanol from either the con- difference in the process conditions for the prep- ditions for synthesis of ethylene from ethanoi or the 40 aration of propylene from crude oil. Such irregular- conditions for synthesis of isobutylene from tert.- ity burdens the propylene purification process with butanol. exceptionally complex and severe steps. As to the reuse of the acetone which is by- In consequence, a process for the preparation produced in the cumene process, for example, by of propylene with highly stable purity containing no its conversion into propylene, no useful proposals 45 such impurities has been expected to be estab- have been made. lished, for the purpose of reducing the extreme The phenol preparing process generally known burden of steps in the propylene purification pro- as the cumene process is characterized by the cess. production of acetone by-product, which is ad- vantageous from some aspects, but disadvanta- 50 geous from other aspects. More particularly, it is an SUMMARY OF THE INVENTION advantage in that simultaneous production of two products in a single preparation unit is more effi- cient than individual production in separate units. In Therefore, an object of the invention is to pro- turn, if the proportion of phenol and acetone pro- vide a novel and improved process for preparing 3 =P 0 361 755 A2 phenol in commercially satisfactory yields without nol can be produced from benzene, oxygen, and producing by-products. hydrogen using a hydrocarbon having 3 carbon The outstanding problem of the cumene pro- atoms as an interlocking element. cess is the production of large amounts of acetone by-product, but not the low percent yield of phenol ; produced. To overcome the problem, the inventors DETAILED DESCRIPTION OF THE INVENTION have developed a process capable of converting the acetone by-product into propylene, that is, a process capable of obtaining propylene upon prep- In the practice of the invention, steps (a), (b), aration of phenol. By incorporating this process into 10 and (c) may be in accord with the conventional the phenol preparing process, the inventors have well-known cumene process. reached a process for preparing phenol without One typical example of the cumene process producing acetone by-product. will be described. Moreover, the propylene preparation obtained by dehydrating isopropanol which has been con- 75 verted from acetone by means of hydrogenation (a) Step of reacting benzene with propylene to does not contain any of the above-cited sulfur synthesize cumene compounds and heavy metals. Purity of the propylene, therefore, is high enough to be used as the Benzene is reacted with propylene in the pres- raw material for cumene synthesis. Such a high 20 ence of a catalyst such as aluminum chloride com- purity renders possible reduction of the burden of plex. The aluminum chloride complex is prepared steps in the propylene purification process to a by causing aluminum chloride to absorb gaseous high degree and, in consequence, sharp industrial hydrogen chloride in a solvent such as cumene. rationalization of the cumene preparation process. The molar ratio of benzene to propylene is The above and other objects can be achieved 25 preferably in the range of from 1/1 to 10/1, more according to the present invention by cooperatively preferably from 1.2/1 to 6/1. The catalyst or alu- combining the following steps. minum chloride complex is preferably present in an According to a first aspect of the invention, amount of about 0.01 to 5% by weight, more there is provided a process for preparing phenol, preferably about 0.1 to 1% by weight of aluminum comprising the steps of: 30 chloride based on the reactants. For this reaction, (a) reacting benzene with propylene to syn- hydrogen chloride gas may be co-present in the thesize cumene, reaction system in order to stabilize the complex (b) oxidizing the cumene of step (a) to con- catalyst. vert it into cumene hydroperoxide, The alkylation to produce cumene preferably (c) acid cleaving cumene hydroperoxide into 35 takes place at a temperature of from 30 to 200° C, phenol and acetone, more preferably 60 to 160°C under a pressure of (d) hydrogenating the acetone of step (c) to from atmospheric pressure to 15 kg-f/cm2. The convert it into isopropanol, reaction may be carried out in a batchwise, con- (e) dehydrating the isopropanol of step (d) tinuous, or semi-batchwise manner. into propylene, and 40 The alkylation partially yields higher alkylated (f) recycling the propylene of step (e) to step by-products in addition to the end product or (a). cumene. The reaction mixture resulting from al- According to a second aspect of the invention, kylation is thus subject to distillation to separate there is provided a process for recovering pro- the mixture into unreacted benzene, cumene, and pylene from the acetone by-product produced 45 higher alkylated products. The unreacted benzene upon preparation of phenol, comprising the steps and higher alkylated products are recycled to the of: alkylation step and subjected to alkylation again. (a) reacting benzene with propylene to synthesize cumene, (b) oxidizing the cumene of step (a) to con- so (b) Step of oxidizing the cumene of step (a) into vert it into cumene hydroperoxide, cumene hydroperoxide (c) agid cleaving cumene hydroperoxide into phenol and acetone, Oxidation of cumene is carried out at a tem- ' (d) hydrogenating the acetone of step (c) to perature of about 60 to 1 50 C, preferably about 90 convert it into isopropanol, and 55 to 130° C under a pressure of about 1 to 10 kg- (e) dehydrating the isopropanol of step (d) f/cm2 using molecular oxygen. The molecular oxy- into propylene. gen used herein may be oxygen, air, or a mixture According to the process of the invention, phe- of oxygen diluted with an inert gas.

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In order for the oxidation to take place smooth- preferably 0.1 to 2% by weight based on the ly, an alkaline compound is preferably co-present reaction mixture concentrate. in the reaction system to adjust the pH of the Also, step (c) uses a solvent as reaction me- system to an appropriate level, preferably in the dium. Examples of the solvent include aromatic range of pH 8.5 to 10.5. Examples of the alkaline 5 hydrocarbons such as benzene, toluene, xylene, compound include sodium carbonate, potassium and cumene; aliphatic hydrocarbons such as hex- carbonate, sodium hydroxide, and potassium hy- ane, heptane, cyclohexane, and methylcyclohex- droxide, all in the produce of aqueous solution. The ane; alcohols such as methanol, ethanoi, propanol, pH of the reaction system is adjusted throughout and butanol; the oxidation process by adding the alkaline com- 10 ketones such as acetone, methyl ethyl ketone, pound in small increments to the system. and methyl isobutyl ketone; and ethers such as The reaction time for oxidation is not particu- diisopropyl ether and dibutyl ether. Acetone is the larly limited and may be selected so as to achieve most preferred reaction medium because it is pro- a maximum selectivity of the end product or duced by the acid decomposition of cumene cumene hydroperoxide. 15 hydroperoxide. The amount of the solvent used is An initiator is preferably added to the reaction preferably about 1 to 20 times, more preferably system to smoothly start oxidation. Examples of about 2 to 10 times the weight of the reaction the initiator includes azo compounds such as a,a - mixture concentrate undergoing acid cleavage. azobisisobutyronitrile and a,a -azobiscyclohexyl- The acid cleavage may be carried out in either nitrile. The cumene hydroperoxide resulting from 20 a continuous or semi-batchwise manner. Batchwise oxidation of cumene is also a preferred initiator. operation is less desirable because a high con- The initiator is preferably added to the system in centration cumene hydroperoxide solution can an amount of from about 0.1 to 5% by weight, come in contact with the acid catalyst, giving rise more preferably from about 0.5 to 2% by weight to too rapid cleavage. based on the reactants. 25 At the end of acid cleavage, the reaction mix- The oxidation may be carried out in a batch- ture is subject to concentration to recover the ac- wise, continuous, or semi-batchwise manner. etone. Part of the recovered acetone is used as the reaction medium for acid cleavage again while the remaining acetone corresponding to the amount (c) Step of acid cleaving cumene hydroperoxide 30 produced by acid cleavage of cumene hydroperox- into phenol and acetone ide is delivered to subsequent step (d) for hydrogenating acetone into isopropanol. The concentrate The cumene' hydroperoxide is often present in which has been stripped of acetone is subject to a concentration of about 20 to 30% by weight in precision distillation for recovering the end product the oily phase of the reaction mixture resulting 35 or phenol. from step (b). The reaction mixture of (b) should preferably be concentrated, as by distillation, so as to increase the cumene hydroperoxide concentra- (d) Step of hydrogenating the acetone of step (c) tion to 60 to 85% by weight before the mixture is into isopropanol subject to acid cleavage. Such concentration may 40 be carried out at a temperature of up to 150°C, Catalysts, often Raney nickel catalysts are preferably up to 120° C, and more preferably up to used in the step of hydrogenating acetone into 100°C. Concentration at too higher temperatures isopropanol. Also useful are nickel, copper-chro- would undesirably cause thermal cleavage of mium, Raney nickel-copper, copper-zinc and plati- cumene hydroperoxide resulting in a low yield of 45 num group catalysts known as hydrogenating cata- the end product or phenol. As long as effective lysts, for example, platinum, palladium, ruthenium, concentration is achieved, the temperature is pref- rhodium, and similar metals on active carbon, alu- erably as low as possible for safe handling of minum and other carriers. Preferred catalyst is • peroxide. Raney nickel. The reaction temperature may range ° An acidic compound is used as the catalyst in 50 from room temperature to 200 C. For a commer- the cleavage of step (c). The catalysts used herein cially acceptable reaction rate, the reaction tem- include strong acids such as sulfuric acid, perch- perature may range from 60 to 150° C, more pref- loric acid, and hydrofluoric acid. Also included are erably from 60 to 140° C. heteropoly-acids such as phosphotungstic acid and Hydrogenation may be carried out by either phosphomolybdic acid. Solid acids such as ion- 55 liquid or gas phase reaction. Thus the pressure exchange resins and silica-alumina may also be may range from atmospheric pressure to 80 kg- used. The catalyst is preferably added in an f/cm2, more preferably from 5 to 50 kg-f/cm2. Hy- amount of about 0.01 to 5% by weight, more drogen gas is used relative to the acetone reactant

4 7 IP 0 361 755 A2 5 n a molar ratio of from 1/2 to 10/1 , preferably from used as the catalyst. Among these catalysts, most 1/1 to 5/1. preferred are 7-alumina and titanium oxide. The hydrogenation, may be carried out in the Dehydration of isopropanol may be carried out Dresence or absence of a reaction medium. Exam- in either gas or liquid phase. The reaction tempera- solvent used herein include alcohols 5 ture preferably ranges from about 100 to 450° C, Dies of the ° such as methanol, ethanoi, propanol, and butanol. more preferably from about 200 to 350 C, most phosphoric acid, hydrochloric ber and the like. acid, and nitric acid, halo peroxides such as perch- loric acid, perbromic acid, and periodic acid, heteropolyacids such as phosphomolybdic acid, 50 (f) Step of recycling the propylene of step (e) to silicomolybdic acid, phosphotungstic acid, and step (a) silicotungstic acid. Other useful catalysts are solid acidic materials, for example, ordinary solid acids In a preferred embodiment, the propylene-con- such as silica, silica-alumina, alumina and 7-alu- taining gas product discharged from the reactor of mina and metal oxides such as titanium oxide, zinc 55 step (e) is once collected in a gas holder and oxide, and zirconium oxide. Various zeolites which thereafter pressurized by a booster pump into a now draw attention as shape selective catalysts pressurized gas having a propylene content of 80 and zeolites modified with metal ions may also be to 99.9%, more preferably 99.5 to 99.9% and a

5 9 EP 0 361 755 A2 10 pressure of 10 to 20 kg-f/cm2 before it is recycled A 500-ml stainless steel autoclave equipped to step (a), that is, alkylation step. In an alternative with an air blowing tube, alkali feed port, sampling embodiment, the propylene-containing gas product nozzle, thermometer sheath, reflux condenser, and is directly passed through a dry ice trap to collect intensive stirrer was charged with 120 grams of the liquefied product, which is transferred to a 5 cumene, 30 grams of 5% sodium carbonate aque- pressure vessel where the temperature is raised to ous solution, and 0.5 grams of a,a - restore the liquefied product to a gaseous state for azobisisobutyronitrile initiator. The air in the auto- recycling to the alkylation step. clave was purged with nitrogen and the initial pressure was set at 5 kg-f/cm2 with nitrogen before io heating was started with stirring. When the interior EXAMPLE temperature reached 110°C, air blowing was started. At the same time as the start of air blowing, the Examples of the invention are given below by revolution of the stirrer was increased to ensure way of illustration and not by way of limitation. 15 sufficient gas-liquid contact. Cumene was oxidized by blowing air at a rate of 30 l/hr. While the oxidation reaction continued, the reaction mixture Example 1 was sampled out at intervals through the sampling nozzle to examine the pH of the reaction mixture. 20 Small portions of 5% sodium carbonate aqueous Alkylation of benzene with propylene solution were pumped to the reactor through the alkali feed port so as to maintain the reaction A 1 -liter glass autoclave equipped with a mixture at pH 9 to 10. Teflon-coated agitating blade and a thermometer The reaction was terminated when 10 hours sheath was charged with 78 grams of benzene and 25 had passed since the start of air blowing. The aluminum chloride complex. The amount of alu- reaction mixture was taken out of the autoclave and minum chloride complex charged was 0.08 grams separated into oily and aqueous phases. The oily calculated as aluminum chloride, which corre- phase was subjected to liquid chromatography to sponded to a molar ratio of aluminum chloride determine the content of cumene hydroperoxide, complex to propylene of 1/1000. The autoclave was 30 finding that the oily phase contained 26% by immersed in an oil bath and the interior of the weight of cumene hydroperoxide. autoclave was maintained at a temperature of 100° C with thorough stirring. To the autoclave, 25.2 grams of propylene in Acid cleavage of cumene hydroperoxide gaseous state was admitted in increments. That is, 35 the propylene was supplied over a period of about The oily phase resulting from oxidation of 90 minutes while the interior pressure of the auto- cumene was concentrated at a temperature of clave was maintained at 3 kg-f/cm2. The reaction 100°C and a vacuum of 160 mmHg, distilling off was terminated at the end of propylene supply, and the unreacted cumene. The concentrating operation the reaction mixture was taken out of the autoclave. 40 was stopped when the oily phase was concentrated The reaction mixture was analyzed by gas by a factor of about 3. The oily phase then con- chromatography to find that it contained 25.1% by tained about 78% by weight of cumene weight of cumene, 13.3% by weight of meta- hydroperoxide. diisopropylbenzene, 7.4% by weight of para- A 500-ml four-necked flask equipped with a diisopropylbenzene, and 7.9% by weight of 45 stirrer, dropping funnel, thermometer sheath, and triisopropylbenzene. The total yield of cumene, reflux condenser was charged with 150 ml of ac- diisopropylbenzenes, and triisopropylbenzene was etone and 2 grams of cone, sulfuric acid. The 99% based on the weight of the propylene feed. dropping funnel was charged with 100 grams of the The reaction mixture was separated by distilla- cumene hydroperoxide concentrate. The flask was tion into unreacted benzene, cumene, higher so set in a water bath at a temperature of 80 °C to isopropylated products. The higher iropropylated cause the acetone to continuously reflux with stir- products were fed back to the initial or alkylation ring the flask contents. step for transalkylation to convert them into Under acetone reflux, the cumene hydroperox- cumene. ide concentrate was added dropwise to the flask 55 from the funnel. The rate of addition of the concentrate was adjusted while observing the amount Oxidation of cumene of refluxing acetone. After the entire amount of the cumene hydroperoxide concentrate was added, the

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•eaction was continued for a further 30 minutes. At was calculated on the basis of tnese analytical tie end of reaction, the reaction mixture was ana- results, finding that isopropanol was produced in a yzed by liquid chromatography, finding that little yield of 99.8%. cumene hydroperoxide was left, that is, a conversion of approximately 100%. It was found that 5 chenol was produced in an amount corresponding Dehydration of isopropanol :o 95% of the converted cumene hydroperoxide. Powder sodium carbonate was added to the A vertical stainless steel reactor tube having an -eaction mixture to neutralize the sulfuric acid cata- inner diameter of 1 inch (25.4 mm) and a length of yst. The solids were removed from the neutralized 10 500 mm was loaded at an intermediate with 20 ml -eaction mixture by filtration and the filtrate was of commercially available gamma-alumina finely di- concentrated to recover acetone. The amount of vided to a size of 8 to 14 mesh. The air in the acetone recovered contained the acetone charge reactor was purged with nitrogen and the reactor dIus 28.5 grams of acetone resulting from acid was then heated under a nitrogen pressure of 10 cleavage of cumene hydroperoxide. 15 kg-f/cm2. When the reactor interior temperature reached 320° C, isopropanol was fed to the reactor from its Hydrogenation of acetone top at a flow rate of 40 ml/hr. The reaction was continued for 8 hours while the reaction pressure A vertical stainless steel reactor tube having an 20 was maintained at 10 kg-f/cm2. inner diameter of 1 inch (25.4 mm) and a length of A liquid product predominantly comprising wa- 500 mm was loaded at an intermediate with 100 ter and a gas product predominantly comprising grams (48 ml) of lumpy Raney nickel alloy (R-20L propylene were produced with the progress of re- manufactured by Nikko Rika K.K.). The reaction action in an amount of 9.5 g/hr. and 12.2 l/hr., tube was filled with water and then 20% caustic 25 respectively. The liquid and gas products were soda aqueous solution was slowly pumped into the analyzed by gas chromatography, finding the reac- tube to develop the Raney nickel catalyst. The tion result that the isopropanol conversion was reactor interior temperature rose because the cata- 99.6%, and the propylene yield was 99.3%. The lyst development produced exothermic heat. The gas product contained propylene in a purity of flow rate of the caustic soda solution was controlled 30 99.9%. such that the reactor interior temperature did not The resulting gas product, that is, propylene exceed 60 ° C. After 0.5 liters of the caustic soda was ready for recycle to the benzene alkylation solution was pumped, the feed was replaced by step without special purification. water to rinse the reactor filling. Rinsing was continued until the water outflow from the reactor be- 35 came neutral. At the end of rinsing, the pump feed Alkylation using the gas product from isopropanol was replaced by isopropanol to fill the reactor dehydration therewith. Heating of the reactor was started. When the interior temperature reached 100° C, A 1 -liter glass autoclave equipped with a reaction was commenced by feeding acetone and 40 Teflon-coated agitating blade and a thermometer hydrogen into the reactor from its top at a flow rate sheath was charged with 78 grams of benzene and of 59.0 g/hr. and 40.2 l/hr., respectively. The reac- aluminum chloride complex. The amount of alu- tor was maintained at a pressure of 20 kg-f/cm2. minum chloride complex charged was 0.08 grams The reaction mixture exiting the reactor at the calculated as aluminum chloride, which corre- bottom was separated into the reaction liquid and 45 sponded to a molar ratio of aluminum chloride hydrogen gas by means of a gas-liquid separator. complex to propylene of 1/1000. The autoclave was The reaction liquid and hydrogen gas were dis- immersed in an oil bath and the interior of the charged at a flow rate of 60.0 g/hr. and 1 5.3 l/hr., autoclave was maintained at a temperature of respectively. 100° C with thorough stirring. The reaction was continued for 9 hours while so To the autoclave, the gas product resulting acetone and hydrogen were continuously fed. At from the previous dehydration of isopropanol this point, the reaction liquid and hydrogen gas (which was collected by liquefying in a dry ice trap) were respectively analyzed by gas chromatog- was admitted in increments while the interior pres- raphy. It was found that 0.2% by weight of acetone sure of the a.utoclave was maintained at 3 kg-f/cm2. remained in the reaction liquid and the remaining 55 The gas product was supplied over a period of component consisted solely of isopropanol. Analy- about 90 minutes in an amount corresponding to sis of the gas discharge showed the absence of 25.2 grams of propylene. The reaction was then methane, ethane and propane. Reaction efficacy terminated. The reaction mixture was taken out of

7 13 EP 0 361 755 A2 14 the autoclave and analyzed by gas chromatog- convert it into isopropanol, and raphy to find that it contained 25.1% by weight of (e) dehydrating the isopropanol of step (d) cumene. 13.3% by weight of meta-diisopropylben- into propylene. zene, 7.4% by weight of para-diisopropylbenzene, 2. A process according to claim 1 wherein said and 7.9% by weight of triisopropylbenzene. The 5 steps (a), (b), and (c) are included in the cumene total yield of cumene, diisopropylbenzene, and process for the synthesis of phenol and acetone. triisopropylbenzene was 99% based on the weight 3. A process according to claim 1 or 2 wherein of the propylene feed. step (d) is carried out in the presence of a hy- It is thus demonstrated that phenol can be drogenation catalyst at a temperature of from room produced from benzene as a primary reactant and w temperature to 200° C. oxygen and hydrogen as secondary reactants with- 4. A process according to claim 1, 2 or 3 out producing acetone by-product by combining a wherein step (e) is carried out in the presence of series of steps of: an acidic compound at a temperature of 100 to (a) reacting benzene with propylene to syn- 450 °C. thesize cumene, '5 5. A process according to any one of the (b) oxidizing the cumene of step (a) into preceding claims which also comprises the step of: cumene hydroperoxide, (f) regarding the propylene of step (e) to step (a). (c) acid cleaving cumene hydroperoxide into 6. A process according to claim 5 wherein step phenol and acetone, (f) includes pressurizing the propylene of step (e) (d) hydrogenating the acetone of step (c) 20 for recycling to step (a). into isopropanol, (e) dehydrating the isopropanol of step (d) into propylene, and (f) recycling the propylene of step (e) to step (a). 25 According to the present invention, phenol can be effectively produced from benzene via a hydrocarbon having 3 carbon atoms as an intermediate by combining the above-defined steps (a) to (f), eliminating a need for paying attention to the com- 30 mercial demand for acetone which is otherwise produced as a by-product in the prior art cumene process. Propylene can be produced from the acetone by-product produced upon preparation of phenol 35 by combining the above-defined steps (a) to (e). Thus prepared propylene is useful by itself for any other uses. Although some preferred embodiments have been described, many modifications and variations 40 may be made thereto in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifi- cally described. 45

Claims

1. A process for preparing phenol, comprising 50 the steps of: (a) reacting benzene with propylene to synthesize cumene, (b) oxidizing the cumene of step (a) to convert it into cumene hydroperoxide, 55 (c) acid cleaving cumene hydroperoxide into phenol and acetone, (d) hydrogenating the acetone of step (c) to