Optimization of the Design of High-Purity P-cresol Production Process

P-cresol Production

Cresol is mainly used in the synthesis of pharmaceuticals, pesticides, spices, etc., is an important raw material for fine chemicals. With the expansion of the use of p-cresol in the field of medicine and spices, the market demand for cresol product quality is higher and higher, many countries generally require p-cresol purity ≥ 99% (freezing point ≥ 34 ℃).

The main synthetic methods of p-cresol are toluene sulfonation alkali melting method, phenol methylation method, isopropyl toluene method, p-toluidine method, etc., but the purity of p-cresol obtained has not been high, because the production of p-cresol in the production of cresol at the same time produce p-cresol, o-cresol, m-cresol three isomers. Industrial production of p-cresol is commonly used toluene sulfonation alkali fusion method, using sulfuric acid as sulfonating agent sulfonation will produce a lot of waste acid pollution, and p-cresol purity is low, equipment corrosion is serious, “three wastes” emissions, high production costs.

In this project, a cresol production plant in China is modified to use SO3 as sulfonating agent instead of sulfuric acid, which not only eliminates the large amount of waste acid produced by sulfuric acid sulfonation, but also eliminates the waste water discharge by using closed-circuit system for all wastewater in the production process, and increases the purity of cresol from 90%~94% to 99% by melting and crystallization process.

The production process before modification (using sulfuric acid as sulfonating agent).

Toluene is sulfonated with sulfuric acid at 110~130℃ to produce toluene sulfonic acid, which is then neutralized and reacted with molten sodium hydroxide at 340~365℃ to produce sodium cresol, which is then acidified to produce crude cresol.

modified production process (with SO3 as a sulfonating agent)

The toluene sulfonation alkali-melting process is used to produce sulfur trioxide from sulfur, which is continuously sulfonated with toluene to produce toluene sulfonic acid, then neutralized with sodium sulfite and lye to produce sodium toluene sulfonate. The solid sodium toluene sulfonate and caustic soda react with alkali to obtain sodium phenol, which is then digested, filtered and reacted with SO2 gas to obtain crude cresol, crude cresol is then distilled to obtain p-cresol, o-cresol, phenol and mixed phenolic products.

The p-cresol obtained after distillation is separated by melt crystallization process to obtain high purity (purity ≥99%) if the p-cresol does not reach the required purity. The crude sodium sulfite generated in the reaction is dissolved in water, decolorized, evaporated, crystallized, centrifuged, air-dried, and made into industrial secondary products (content ≥ 93%) as a by-product of sodium sulfite for sale.

Process flow and operation scheme

Sulfur Trioxide Generation Section

The solid sulfur enters the rapid sulfur melting tank to melt the sulfur, which is heated by a steam snake tube with 0.6 MPa to melt the solid sulfur into liquid sulfur, which then overflows into the refined sulfur tank. It is fed into the converter. The reformer is equipped with 5 catalyst layers. The conversion rate of sulfur dioxide to sulfur trioxide is over 97% through the action of 5 catalyst stages.

Sulfonation reaction section

The raw toluene is fed into the dispense tank by a toluene pump. After the catalyst is added to the dispense tank, it is pumped to the solution cooler by a solution pump and mixed with the recovered toluene pumped to the solution cooler in a certain ratio before entering the solution cooler. The mixed solution is cooled to 5°C by the glycol carrier coolant and enters the sulfonation reactor to react with the SO3 gas from the SO3 generation section.

The reaction generated toluene sulfonic acid flows to the aging device, and the exhaust gas (containing SO3, toluene sulfonic acid, toluene and other components) from the sulfonation reactor and the top of the aging device is defoamed by the defoamer and enters the tower from the lower part of the absorption tower, and is treated by C absorbent, B absorbent and A absorbent from the bottom to the top, and the content of the components in the gas meets the environmental protection requirements, and escapes from the top of the tower into the atmosphere. Absorbent A, absorber B, absorber C, respectively, in the upper, middle and lower absorption tower after the pump into the tower after recycling. Light components from the top of the tower through the condenser, condensate into the reflux tank, recovery of toluene storage tank, and then the recovery of liquid pumped into the recovery of toluene buffer tank for recovery.

alkali melting, digestion, sodium refining section

When the temperature is raised to about 340℃, after a certain time, part of the reaction gas is separated in the separator after cooling by the cooler, the separation liquid and the discharge liquid of the alkali melting kettle are put into the digestion tank, stirring is turned on, and then the water is added to the digestion reaction. The cooling water is pumped to the cooler by circulating pump for cooling, and the cooling water is pumped to the digestion tank by water transfer pump for application. The digesting liquid is pumped into the crystallization tank by the digesting liquid submerged pump respectively, stirring is started, and the cooling water is passed through the jacket for cooling and crystallization, when the sodium p-methyl phenol is completely separated out, the material is put into the centrifuge for centrifugation. Filtrate were put into the filtrate storage tank by the filtrate pump to the sodium phenol storage tank, and then by the sodium phenol delivery system.

Pumped to a large storage tank for phenol sodium, which is pumped to a storage tank for phenol sodium in the neutralization and acidification chemical section. The filter cake sodium sulfite is removed from the sodium sulfite refining section.

After the alkali is finished, the submerged pump pumps it into the filter to filter out a few impurities and put it into the liquid storage tank, then the submerged pump pumps it into the evaporator crystallizer and starts stirring. Steam is passed through the coils in the crystallizer for heating, and the water evaporates to the condensate cooler for cooling, and then is put into the storage tank for recycling. The crystallization liquid is put into the centrifuge to separate, and the filtrate is put into the liquid storage tank for application.

Spray drying, airflow drying section

The sodium toluene sulfonate obtained from the neutralization reaction is spray dried and then sent to the alkali melting and digestion section. Air flow drying is to filter the filter cake obtained after the digestion reaction and then dry it in an air flow dryer to obtain the by-product sodium sulfite (content ≥ 93%).

Neutralization, acidification, distillation section

The reused sodium sulfite solution, liquid alkali and toluenesulfonic acid are measured and added into the neutralization kettle, stirring is started, and the jacket is heated by steam to control the temperature. When the neutralization is finished, the sodium toluene sulfonate solution is put into the sodium toluene sulfonate storage tank and pumped into the sodium toluene sulfonate storage tank, then pumped into the spray drying system. Neutralization process of SO2 gas defoamer after defoamer to cooler cooling, into the acidification tower and alkali melting, digestion section of the sodium phenol solution (sodium phenol pumped to the cooler and then into the acidification tower) mixed cycle absorption.

Absorption liquid into the sodium phenol storage tank, after stratification of the acidic phenol into the acidic phenol underground storage tank by the acidic phenol submerged pump into the acidic phenol sink, the sinking liquid sodium inflow into the lower liquid storage tank, and then put into the lower liquid underground storage tank by the submerged pump respectively into the neutralization kettle. The upper liquid acidic phenol flows into acidic phenol storage tank, then into acidic phenol neutralization tank to neutralize with quantitative solid soda ash, then into alkaline phenol sink by alkaline phenol submerged pump, the lower liquid sodium sulfite goes to the lower liquid storage tank, the upper liquid alkaline phenol flows into alkaline phenol storage tank, then into distillation section by alkaline phenol pump.

The alkaline phenol is pumped to the raw material tank, then pumped to the preheater by the raw material pump after metering to enter the dewatering tower, the bottom of the dewatering tower is heated by the dewatering tower reboiler, part of the water in the mixed phenol is evaporated from the top of the tower and condensed by the condenser of the dewatering tower into the water storage tank, the water pump is pumped to the neutralization, acid chemical section of the sodium phenol storage tank. The mixed phenol at the bottom of the tower is pumped to the decoking tower by the material pump, the bottom of the decoking tower is heated by the decoking tower reboiler, and the mixed phenol at the top of the tower is condensed by the condenser of the decoking tower and goes to the intermediate tank. At the bottom of the reconstituted fraction goes to the stripper tower, heated respectively by the stripper tower reboiler, a small amount of mixed phenol is condensed by the stripper tower condenser and then returned to the raw material tank for use, the reconstituted fraction at the bottom of the stripper tower reboiler is pumped into the reconstituted fraction tank by the reconstituted fraction pump.

The mixed phenol in the intermediate tank is pumped to the preheater by the material pump after metering into the neighbor-pair separation tower, the bottom of the neighbor-pair separation tower is heated by the neighbor-pair separation tower reboiler, the bottom of the cresol into the intermediate tank, the top of the neighbor-pair phenol, the phenol by the neighbor-pair separation tower condenser condensation after metering to the preheater into the phenol-o-phenol tower. The bottom of phenol-cresol tower is heated by the reboiler of phenol-cresol tower, the top of the tower is measured into the phenol product tank after the condensation of phenol-cresol tower, the finished product is sold by the phenol pump; the bottom of the tower into the o-phenol product tank respectively, the finished product is sold by the o-phenol pump.

The middle tank of p-cresol by the material pump after measuring hit to the p-cresol tower, p-phenol tower bottom by p-phenol tower reboiler heating, tower top p-cresol by the p-cresol tower condenser condensation measured into the p-cresol product tank, by the p-cresol product pump hit sold; tower bottom recombination into the recombination tank by the recombination pump hit sold. All towers are operated under negative vacuum pressure.

Main Equipment Determination

(1) Alkali Melting Kettle

Operating pressure: atmospheric pressure, operating temperature: 330℃, design pressure:Normal pressure, design temperature: 350℃, medium: sodium toluene sulfonate, sodium hydroxide. Equipment material: cast steel.

(2) Sulfur incinerator

The sulfur incinerator is a horizontal steel cylinder lined with thermal and refractory bricks, and the sulfur is sprayed into the furnace by a spray gun. The sulfur is sprayed into the furnace by the spray gun. The furnace is equipped with several retaining walls to make the sulfur combustion complete. Materials: shell, Q235-A; lining, inner ring of refractory bricks, outer ring of heat preservation bricks.

(3)Transformer

The main material of the converter is carbon steel with internal column support and a fan-shaped castor plate. The catalyst section is lined with refractory bricks to protect the shell on the one hand and reduce heat loss on the other. Materials: shell, Q235-A; lining, refractory bricks; column, heat-resistant cast iron; castor plate, heat-resistant cast iron.

(4) Absorption tower

The absorption tower is a vertical cylinder with a steel shell lined with acid-proof concrete and a wire mesh defroster on the upper part of the tower, equipped with a manhole for easy installation and maintenance of the wire mesh. Equipment materials: shell, Q235-A; lining, acid-resistant concrete; acid separation device, cast iron parts; beams, high-alumina acid-resistant ceramic.

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