Phenol Production by Benzene Sulfonation Process

Phenol production process flowsheet by benzene sulfonation

Phenol Production  brief process description by the Benzene Sulfonation Process technology:

Benzene can be converted to phenol with the help of inorganic acids and salts and this process is oldest of all the process where phenol is produced by reactants such as cumene and toluene.

This process involves four major chemical reactions which are:

Sulfonation: Benzene is reacted with sulphuric acid to form benzene sulphonic acid at 150 to 170 deg centigrade

Neutralization: Benzene sulphonic acid is reacted with sodium sulfite to form sodium benzene sulphonate

Fusion: Sodium benzene sulphonate is fused with sodium hydroxide to form sodium phenoxide

Acidification: sulphuric acid and sodium phenoxide are reacted to produce crude phenol and sodium sulphite.

The above reaction step explains the requirement of the unit operation equipment in the process as

• Filtration: Pressure filter and centrifuge used in the separation of sodium sulphate and sodium sulphite
• Distillation: Separation of phenol from crude phenol
• Crystallization: Separation and recovery of sodium sulphite

Process description: This process is large-scale batch cycle operation due to slow reaction step at fusionator. Sodium benzene sulphonate is fed to cast iron make fusion pots which already contains molten caustic soda at a temperature of 300 deg centigrade, due to slow reaction with take about 5-6 hours of residence time the pot is fed at regular intervals where continuous loading and unloading of the pot occurs for continuity of the process, thus sodium phenoxide fraction which is obtained is fed to acidifier to produce crude phenol by reacting with sulphuric acid and sulphur dioxide. Vacuum distillation column is used to get phenol from crude phenol and remain salts are stripped in a steam stripper to remove phenol from them and aqueous salts. Crystallizers are used to increase the purity of the sodium sulphite; these crystals are separated from mother slurry by a continuous centrifugal separator, which is recycled to neutralizer.

Cholorobenzene and Caustic Process for Phenol Production

Phenol by Chlorobenzene-NaOH

Process Description of Chlorobenzene and Caustic process for phenol production:

For 1 ton of phenol production approximately the following raw materials are required as per the process described:
Benzene =        0.90 tons
Chlorine =        0.82 tons
NaOH   =         0.67 tons
HCl       =          0.51 tons
 The main reactions which take place for this process are:
1. Chlorination
    C6H6 + Cl2 ---> 85^oC , Fe- --> C6H5Cl (Chlorobenzene)
2. Causticization
    C6H5Cl +NaOH (aq)---> C6H5NaO
3. Hydrolysis
    C6H5NaO + HCl(aq) ---- > C6H5OH + NaCl(aq)

A Short Process Description for Phenol Production:

 

Benzene which is in dry state, reacted with chlorine at the presence of  the catalyst iron or anhydrous ferric chloride at about 85 deg centigrade temperature to form Chlorobenzene in a chlorination tower, unconverted benzene is recycled and monochlorobenzene is withdrawn all excess chlorine is used in neutralizer and about 10% solution of dilute caustic soda is mixed with Chlorobenzene which is reacted with caustic solution where chlorine present at the benzene ring is reacted with hydrogen and produce water vapors which are removed a tail gas. The resulting product diphenly oxide is pumped to the preheater and then passed to multi-tube reactor where causticization reaction occurs at the parameters 425 deg centigrade and 350 atm pressure, then the reacted mixture is passed to the neutralizer through the effluent heat exchangers.

Phenol is obtained from hydrolysis occurs at the neutralizer where reaction with concentrated hydrochloric acid take place to form phenol and sodium chloride.

Sodium chloride is formed as a side product, this salt is separated and send to electrolysis.
Upstream from the separator is sent to vacuum distillation column where phenol is stripped out. About 95% yield is obtained and diphenyl oxide is removed from the bottom of the column to recycle.

Major engineering problems in this process are:

HCl corrosion in Chlorobenzene plant section
High-pressure vessel design for causticization reactor
Phenol production by Benzene Sulfonation process
cumene peroxide process for phenol production

Cumene Peroxidation Process for Phenol Production

Reactions Involved in Cumene Peroxidation Process:

C₆H₅CH (CH₃) + O₂  →  C₆H₅C (CH₃)₂OOH
C₆H₅C (CH₃)₂OOH + H₂SO₄ ↔ C₆H₅OH + CH₃COCH₃
(Cumeneperoxide)                        (Phenol)        (Acetone)

Material Requirements:
The raw materials that are required for the manufacture of phenol involve the following materials.

• Cumene
• Air
• Sulfuric acid
• Sodium hydroxide

Final product: Phenol
Co-product: Acetone

A Short Process Description for Phenol Manufacturing:

The cumene peroxidation process for the manufacture of phenol involves the liquid phase air oxidation of cumene to cumene peroxide, which in turn is decomposed to phenol and acetone by the action of an acid.

The cumene (isopropylbenzene) may be manufactured by either liquid or vapor phase alkylation of benzene with propylene. In the liquid phase, the alkylation catalyst is usually sulfuric acid; in the vapor phase, it is phosphoric acid absorbed on a carrier. Purified cumene is mixed with purified recycled cumene and fed to the oxidation vessel along with a dilute soda ash solution, to maintain the pH between 6.0 and8.0, the mixture is contacted with air and held at 110 and 115°C until 20 to 25% of the cumene is converted to the cumene peroxide. Yields of cumene peroxide may be improved by operating at lower temperatures (100 to 110°C) and accepting lower conversions. In one modified process sequence of three to four reactors is operated at a successively lower temperature.

The crude mixture from the oxidizer is concentrated to about 80% cumene peroxide and fed to a reactor in which the cumene peroxide is cleaved to phenol and acetone. The reaction is usually carried out under conditions of mild temperature (70 to 80°C) and pressure and in the presence of a small amount of sulfuric acid. Numerous non-oxidizing inorganic acids, e.g. sulphuric dioxide are used. The cleavage mechanism is an example of a 1, 2 shift from carbon to oxygen.

Such 1, and 2 cleavages shouldn't occur during the oxidation stage because phenols are potent inhibitors of free radical oxidation. Therefore, it is essential that no acidic materials must interfere with the oxidation process.

The resulting product mixture consists following compositions of the products

COMPOUND (wt %)	%COMPOSITION
Phenol	14
Cumene	76
Acetone	8
Acetophenone	0.4
ά methyl styrene	1.6

Phenol by Cumene Process

The products are separated by distillation. Acetone is removed overhead in the first column and further purified by distillation. The bottoms from this column are then vacuum distilled to send unreacted cumene and by-product a methyl styrene overhead. If this impure cumene were recycled as such, the methyl styrene must be purified. This can be done by catalytic hydrogenation of the ά methyl styrene to cumene, by careful fractionation. In the latter case, methyl styrene is available as a by-product. The bottoms from the vacuum still are further distilled to separate acetophenone and cumene from phenol. Phenol is the overhead product obtained with a yield of 90 to 92%.

Other methods used for the production of phenol:

• Chlorobenzene Process
• Benzene Sulfonation process

Types Of Phenol Manufacturing Process

Phenol can be manufactured through five different processes. The processes are mentioned below.

• Cumene Peroxidation process
• Rasching process
• Toluene two-stage oxidation process
• Sulphonation process

1.Cumene Peroxidation process:

Benzene and purified propylene obtained from petroleum industry are mixed in liquid or vapour phase in presence of phosphoric acid on kieselguhr. As a result, cumene or isopropyl benzene is formed. The cumene thus formed is made into the form of an emulsion with dilute aqueous sodium carbonate solution, using sodium stearate as an emulsifier. The emulsion is then oxidized in an oxidizer with air under atmospheric pressure for 3 – 4 hours in presence of a catalyst, such as copper, cobalt or manganese salt.

The temperature and pH of the reaction are maintained between 160-260°c and 8.5-10.5 respectively. As a result of oxidation, cumene hydroperoxide is formed. The peroxide thus formed is then decomposed by 5-50%sulphuric acid in an acidifier at 45-65°c under pressure. As a result of decomposition, phenol (15%), acetone (9%), cumene (73%) are formed along with some α-methylstyrene and acetophenone. These separated by a separator. The cumene is recycled to be used again and phenol is either extracted or recovered by distillation. The yield is about 92%. Acetone is formed as a byproduct (0.6 lb. per lb of phenol).

2.Rasching process:

This process was developed in Germany in 1940. Benzene is first converted into Chlorobenzene by passing a mixture of benzene vapour, hydrochloric acid vapour and air under normal pressure at about 23°c in presence of a copper iron catalyst, supported on alumina. The reaction is exothermic in nature and so the temperature is maintained constant by external cooling. The conversion .the per pass is 10%

The Chlorobenzene after separation from unchanged reactants is hydrolyzed into phenol by heating with steam at about 400-500°c in presence of silica catalyst. The conversion is again about 10% per pass in this second step. Hydrogen chloride set free in the reaction is recovered and recycled. Crude phenol (97%) obtained according to the above reaction is purified by distillation under vacuum. The yield is about 75-85% of benzene. A small amount of HCl is sufficient to convert large amounts of benzene into phenol.

3.Toluene two-stage oxidation process:

Toluene in the liquid phase is oxidized with air in a reactor under 40-70 p.s.i in presence of a soluble cobalt catalyst maintained at 150°c. benzoic acid and water are thus formed. The reaction is exothermic and the temperature is maintained by external cooling. The crude molten benzoic acid at about 150-200°c is transferred from the reactor to distillation column, where separation of benzoic acid from unreacted toluene and produced water take place. The toluene is separated and recycled to the first oxidizing reactor. The pure benzoic acid is fed to a second reactor, where it is oxidized to phenol by air and steam under 20-25 p.s.i at 230°c in presence of cupric benzoate catalyst promoted with manganese. The reaction mass is periodically withdrawn from the second reactor into an extractor, where it is washed with water to remove unwanted tars and benzoic acid and steam are returned to the second reactor. The phenol, water and unreacted benzoic acid are conducted overhead to two distillation columns in series. In the first column, crude phenol is separated from overhead and unreacted benzoic acid is recycled to the second oxidizing reactor. Pure form phenol is obtained at the second distillation column as overhead product and supply's aromatics compounds and benzoic acid as a feed for crude phenol rectification column. The yield of phenol on benzoic acid is about 75- 80%.

4.Sulphonation process:

It is one of the oldest methods of manufacture of phenol. Benzene sulphonic acid is first prepared by passing vapour of benzene into concentrated sulphuric acid is about 150-170°c.the water formed during sulphonation process is distilled out because sulfuric acid gets diluted and conditions accelerate backward reaction to the process. Benzene sulphonic acid should be neutralized by reacting it with aqueous sodium sulphite to form the salt of benzene sulphonic acid. The sodium salt is filtered off and then fused with caustic in a cast iron vessel at about 340-380°c in the ratio (1:3) for about 5-6 hours. As a result, sodium phenate is formed. The melt is cooled, extracted with water and then acidified with sulphur dioxide. The latter is obtained as a result of neutralization of benzene sulphonic acid with sodium sulphite.the upper oily layer of crude phenol is distilled under vacuum to get pure phenol. The yield is about 80-90% of benzene. The lower layer contains sodium sulphite which is separated and used for the neutralization of benzene sulphonic acid.

S.No	Existing Methods	Raw Materials/ Catalyst	Yield	Products	Comments
1	Cumene peroxidation	Cumene, Air, H2SO4 and Emulsifying agents	92%	Phenol and acetone	Produces valuable co-product acetone
2	Toluene two-stage oxidation	Toluene, Air, Cobalt napthalate, Cupric benzoate catalyst	80%	Phenol and CO2	Low-cost operation by direct toluene application
3	Rasching phenol process	Benzene, Air, HCl	75%	Phenol and HCl as recycling	Feasible under large units
4	Chlorobenzene caustic hydrolysis	Benzene, Chlorine, NaOH, HCl	95%	Phenol, NaCl	Economically not feasible
5	Benzene sulfonate process	Benzene, H2SO4, NaOH	87%	Phenol, Na2SO3, Na2SO4	Operates on large batch cycles