WO2014195746A1

WO2014195746A1 - Process for the preparation of phenol/acetone from cumene

Info

Publication number: WO2014195746A1
Application number: PCT/IB2013/001190
Authority: WO
Inventors: Wilson Martins; Marcelo FERREIRA BORGES; Aimar DOMINGUES; Guilherme TORRES BARRETO
Original assignee: Rhodia Poliamida e Especialidades Ltda
Current assignee: Rhodia Poliamida e Especialidades Ltda
Priority date: 2013-06-07
Filing date: 2013-06-07
Publication date: 2014-12-11
Anticipated expiration: 2015-12-07

Abstract

The present invention relates to a process for the preparation of phenol/acetone mixture from cumene. The invention thus aims a process for the production of phenol/acetone mixture from cumene, via cumene hydroperoxide (CHP), which comprises the following steps: a. oxidation of cumene with a gas containing oxygen to produce CHP, b. concentration of the solution containing CHP obtained from step a. by evaporation, to at least 70 percent by weight; c. production of phenol/acetone mixture by acid cleavage of CHP solution obtained from step b., in which step b. is carried out in a multiple effect evaporation system comprising at least 2 effects.

Description

PROCESS FOR THE PREPARATION OF PHENOL/ACETONE FROM CUMENE

Field of the invention

The present invention relates to a process for the preparation of phenol/acetone mixture from cumene.

Background of the invention

It is well known that phenol can be produced from cumene.

The common production process takes place in two phases. In the first phase, the cumene is oxidized to cumene hydroperoxide (CHP), with conversions which range from 20- 30 percent by weight, and in the second phase the CHP is acid cleaved into phenol and acetone with an acid, generally sulfuric acid. Between the first and second phase, there is generally a concentration step in which the CHP is concentrated to 70-95 percent by weight.

The first step of oxidation of cumene with air fed from compressors is an exothermic reaction which occurs in an alkaline environment, for instance with soda, so as to avoid the anticipated cleavage into phenol and acetone. During this oxidation step, various byproducts are formed such as dimethylphenylcarbinol (DMPC), alpha methyl styrene (AMS) and acetophenone.

The mixture of CHP and unreacted cumene is then washed and sent to the concentration section, in this step, cumene is vaporized, condensed and recycled to the beginning of the process.

The concentrated cumene hydroperoxide (CHP) is then sent to the cleavage section, where under low pH conditions the CHP is broken into phenol and acetone, this reaction is extremely exothermic, making it dangerous due to the possibility of runoff.

Phenol with acetone and the byproducts generated in the process are sent to separation sections of the plant where phenol and acetone are purified through distillation processes.

In the phenol plants, CHP is usually concentrated in a classical evaporation system like a distillation column in which the cumene is the light key component and CHP is the heavy key component. An external source of heat, generally steam, is thus necessary to maintain the column at a sufficient temperature.

In the process described in R.J Schmidt; Industrial catalytic processes - phenol production - Applied Catalysis A: General, 280 (2005), p. 89 - 103, a pre-flash drum is present, where the effluent of the oxidizer is concentrated by two heat streams; one is residual heat from the oxidizer and the other very low pressure steam. The outlet of the pre flash drum is then evaporated with very low pressure steam and fed into a concentration column. The outlet on the top of the column is cumene to be recycled in the oxidizing section and the bottom outlet is concentrated CHP to the cleavage section. Both stages of concentration operate under the same vacuum which is generated by ejectors.

The main drawbacks of this process are the following:

The high energy consumption due to the addition of a large quantity of vapor to the system in order to heat the different equipments;

The insecurity of the process during the concentration step, because of the instability of CHP at elevated temperature;

Product losses due to CHP degradation.

Concerning safety considerations, they are linked to concentration and temperature of CHP streams. Indeed, it is not recommended that CHP at concentrations higher than 30% is held at temperatures above 100°C both for safety reasons in case of a runoff reaction of cleavage and for CHP degradation reasons that could present significant losses to the plant.

The objective of the invention is thus to provide a new process for producing phenol/acetone mixture from cumene via CHP, which is safer, more productive and less energy-consuming. The Applicant has now found a process for the production of phenol/acetone from cumene which is improved compared to the processes known in the state of the art. This new process, as far as the concentration phase is concerned, improves selectivity to CHP, saves energy and allows a better control of the temperature in favour of the safety.

Brief description of the invention

The invention thus aims a process for the production of phenol/acetone mixture from cumene, via cumene hydroperoxide (CHP), which comprises the following steps:

a. oxidation of cumene with a gas containing oxygen to produce CHP,

b. concentration of the solution containing CHP obtained from step a. by evaporation, to at least 70 percent by weight;

c. production of phenol/acetone mixture by acid cleavage of CHP solution obtained from step b., in which step b. is carried out in a multiple effect evaporation system comprising at least 2 effects.

The main advantage of the multiple effect evaporation system according to the invention is to achieve steam economy, increase process safety and reduce product loss due to CHP degradation. Indeed, the process according to the invention allows having a low delta of temperature between the vapor and the liquid during concentration step. Indeed, the heat transfer coefficient of such equipment is improved compared to previous technologies. The risks linked to anticipated cleavage are also reduced due to the type of equipment that the multiple effect evaporation system allows to be used (falling film evaporators for example). Moreover, the highest temperature achieved in the multiple effect system happens at the first stage, in this stage the CHP concentration is still low and close to the oxidizer outlet concentration.

Definitions

A multiple-effect evaporation system is an apparatus for efficiently using the heat from steam to evaporate a product. In a multiple-effect evaporation system, cumene is evaporated in a sequence of vessels (at least 2), each held at a lower pressure than the last. Because the boiling temperature of cumene decreases as pressure decreases, the vapor boiled off in one vessel can be used to heat the next, and only the first vessel (at the highest pressure) can require an external source of heat.

The number of "effects" means the number of steps in which the evaporation occurs at different pressures. There can be more than one evaporator in the same effect, in series or in parallel.

By "a lower pressure than the last", it should be understood in the sense of the present invention that the pressure drop through the whole train (evaporation system) should be from 70 to 97%. For example, if the train has two effects, this reduction of from 70 to 97% represents the drop from the first to the second effect, if the train has 5 effects, this reduction would be almost equally divided, that is to say a reduction of the pressure of from 17% to 25% on each effect. Detailed description of the invention

Step a. oxidation of cumene with a gas containing oxygen to produce CHP

The reagents, cumene and a gas containing oxygen, preferably air, are fed to the reactor preferably in continuous and are recycled continuously to the reactor. A gas phase, consisting substantially of residual air and vapours, is discharged from the head of the reactor together with the reaction product, a mixture consisting essentially of CHP and non-reacted cumene, in addition to possible by-products.

The oxidation reaction of the cumene takes place at a temperature ranging from 50 to 150 °C and at a pressure ranging from 0.1 to 0.8 MPa.

The oxidation reaction of cumene is preferably carried out in the presence of a basic compound. Examples of basic compounds are amines, hydroxides and carbonates of alkaline metals such as lithium, sodium, potassium, or alkaline-earth metals such as calcium and magnesium, used alone or mixed with each other. The hydroxides and carbonates can generally be fed as aqueous solutions/dispersions with such flow-rates that the amount of base metal ranges from 0.1 to 10, preferably from 0.5 to 8, equivalent grams per ton of cumene fed. The same concentration is valid for the amines.

The oxidation reactor is advantageously cooled to maintain the temperature at the set value, as the oxidation reaction is exothermic. As an alternative, the vapours of cumene can be continuously removed from the reactor to avoid the increase of temperature in the oxidation reactor.

Step a. can be followed by a washing step of the CHP solution, which generally consists of adding water or another polar solvent, decanting and isolating the organic layer containing CHP to send it to step b..

Step b. concentration of the solution containing CHP obtained from step a. by evaporation

The stream of CHP solution issued from step a. is generally in a concentration by weight between 10 and 40 % of CHP, more generally between 20 and 30% of CHP. The remaining is essentially cumene and some by-products like DiMethylPhenyl Carbinol, Alpha Methyl Styrene and Acetophenone.

The concentration of the stream of CHP solution from step a., to a value higher than 70 percent by weight of CHP, advantageously between 70 and 95% by weight, takes place by evaporation in specific equipment being a multiple effect evaporation system comprising at least 2 effects.

The principle of the multiple effect evaporation system according to the present invention is that the cumene present in the CHP solution is gradually evaporated in a sequence of vessels so as to reach the desired concentration of CHP at the end of step b..

The first effect is fed with the CHP solution issued from step a. and heated to a temperature between 90 and 130°C, preferably between 90 and 100°C and at a pressure sufficient to evaporate a certain mass of cumene, preferably between 40 and 60% by weight of cumene. The stream of CHP solution issued from the first effect (preferably at a concentration by weight between 35 and 40 %) is then fed to the second effect. The steam of cumene issued from the first effect is condensed in the second effect and thus heat the second effect to pursue the evaporation of cumene. The pressure in the second effect is set at a value lower than in the first effect but sufficient to evaporate another certain mass of cumene, preferably between 40 and 60% by weight of cumene.

And so on, the third effect (if any), is fed with the stream of CHP solution issued from the second effect and the steam of cumene issued from the second effect is used to heat the third effect. The pressure in the third effect is set at a value lower than in the second effect. The sequence is repeated until the desired concentration of CHP is obtained.

Advantageously, the pressure drop through the whole train of evaporators in step b. is from 70 to 97%. The pressure drop on each effect depends on the total number of effects in step b.. For example, for 2 effects, the pressure drop of from 70 to 97% is carried out between the first and the second effect. For 5 effects, the pressure drop of from 70 to 97% is divided by 5, thus giving a pressure drop of from 17% to 25% on each effect.

The equipment used for the multiple effect evaporation system is advantageously a falling film evaporator, with or without liquid recirculation or any type of design that makes possible the small difference of temperature between the vapor and the liquid. While in theory, evaporators may be built with an arbitrarily large number of stages (effects), evaporators with more than 10 stages are rarely practical. Advantageously, the number of effects is between 2 and 5, preferably 4.

According to a first embodiment, there are at least 2 effects in the system and the first effect is fed with the solution of CHP issued from the outlet of the oxidation reactor of step a. In this case, an external source of heat is necessary to heat the first effect. It is generally steam. In this embodiment, the source of heat could also be a condensate or a hot stream from the process.

According to a second embodiment, there are at least 2 effects in the system and the first effect is carried out directly in the oxidation reactor of step a. and the steam of cumene generated in the oxidation is used to heat the second effect. In this case, there is no need for an external source of heat as the oxidation reaction is exothermic and the evaporation of cumene in this step allows the withdrawal of calories so as to maintain the temperature at the desired value.

According to a preferred embodiment, the first effect is fed with the solution of CHP issued from step a. at a concentration by weight of around 25-30%, the first effect is heated by means of an external vapor source (steam under pressure of 0.1- 0.5 MPa), at a temperature of 90-100°C under a pressure of around 10-15 kPa so as to obtain a solution of CHP at a concentration by weight of 35-40% of CHP which is fed to the second effect. The second effect is heated via condensation of the cumene evaporated in the first effect. The temperature of the second effect is around 70-80°C and the pressure is around 0.5-1 kPa.

The cumene vapor issued from the last effect can be distilled in a distillation column to recover CHP evaporated at the bottom of the column that can be joined to the concentrated CHP solution before being sent to cleavage step. The cumene recovered at the top of the column is advantageously recycled at the oxidation stage.

The concentrated CHP concentrated solution thus produced can be stored before being sent to the acid cleavage reaction. Step c. production of phenol/acetone mixture by acid cleavage of CHP obtained from step b.,

The acid cleaved reaction takes place in the presence of an acid and eventually further acetone. The acid is preferably an inorganic acid such as sulfuric, phosphoric or nitric acid. The acetone, which is also a by-product of the acid cleaved reaction, is used with diluents function whereas the acid is the catalyst which favours the acid cleavage, extremely exothermic, of the CHP to phenol and acetone. The acid is advantageously fed into the reactor in a single step.

The concentration of acid in the reaction medium ranges from 80 to 250 ppm, preferably from 110 to 180 ppm, and is more preferably 150 ppm.

As the acid cleaved reaction of CHP is extremely exothermic, the reaction heat should be rapidly disposed of. For this reason, the reaction system can comprise exchangers to cool the system.

Description of the drawings

FIG.l is a schematic view of a specific embodiment of step b. of the invention.

In this specific embodiment, the first effect 3 is fed with the dilute solution 2 of CHP and cumene (issued from step a. - not shown). An external source of steam 1 at 2.5 bars is used as driving force in the first evaporator 3. The stream of CHP solution 4 leaves the first effect 3 and is fed into the second effect 7. The driving force for the evaporation on the second effect is the vapor 5 generated in the first effect, this means that a solution of cumene 5 evaporated on the first effect 3 is being condensed on the second effect 7. The steam condensed at the first effect 3 is withdrawn to utilities via 6.

The vapor 9 of the second effect goes through a distillation column 11 of a few stages to recover a small quantity of evaporated CHP at the bottom of the column 12, which is joined to the stream of concentrated CHP 8 before being sent to cleavage step (not shown). The cumene stream 14 issued from top of the distillation column 11 is joined to the cumene stream 10 which was condensed on the second effect to be recycled.

The system requires a vacuum system 17 and a chiller (16-18-19) to cool the condenser 15 at high vacuum conditions. Experimental part

With reference to Figure 1, the first effect (being a falling film evaporator without liquid recirculation) is fed with a solution of CHP and cumene, with CHP at 29% by weight concentration. Steam at 2.5 bars (0.25 MPa) is used as driving force in the first evaporator. The stream of CHP solution leaves the first effect at 39% by weight of CHP and is fed into the second effect (being a falling film evaporator without liquid recirculation). The driving force for the evaporation on the second effect is the vapor generated in the first effect, this means that a solution of cumene evaporated on the first effect is being condensed on . the second effect.

The vapor of the second effect goes through a distillation column of a few stages to recover a small quantity of CHP evaporated, the bottom of the column is joined to the concentrated CHP, the top of the column is joined to the condensed cumene on the second effect to be recycled.

The first effect should operate at an absolute pressure of 105mmHg (14 kPa) and the second effect at an absolute pressure of 5mmHg (0.7 kPa).

The system includes a vacuum system and a chiller to cool the condenser at high vacuum conditions.

Table 1 shows the operation conditions of each effect.

Table 1 : Operation conditions

Table 2 shows the temperatures of the effects and the column condenser.

Table 2: Temperatures

T 1st effect 92 °C

T 2nd effect 65 °C

T Condenser Column 13 °C

Minimum Delta T * 6 °C *Delta T is the difference in temperature between the bulk of the liquid being evaporated and the vapor being condensed.

STEAM ECONOMY

The steam economy for this process is estimated to be around 65% compared to regular technology. By "regular technology", it should be understood that that the evaporation of cumene is carried out in a simple distillation column (5 theoric plates) operating at a temperature of 92°C (heated by an external source of steam) and a pressure of 19 kPa until CHP solution recovered at the bottom of the column be at a concentration by weight between 70 and 95%, then sending the concentrated solution to the cleavage reaction. The cumene evaporated is condensed at 16°C and 1.3kPa in the top condenser of the column and recycled to the process at a concentration between 80 and 95%.

The numbers are shown in Table 3:

Table 3: Steam consumption reduction

SAFETY AND CHP LOSS

To guarantee safety and prevent loss of CHP, the temperature of the first effect was limited to less than 100°C. The design of the falling film evaporators also predicts low residence time which reduces the possibility of CHP degradation and reaction runoff.

Claims

1. A process for the production of phenol/acetone mixture from cumene, via cumene hydroperoxide (CHP), which comprises the following steps:

a. oxidation of cumene with a gas containing oxygen to produce CHP,

c. production of phenol/acetone mixture by acid cleavage of CHP solution obtained from step b.,

wherein step b. is carried out in a multiple effect evaporation system comprising at least 2 effects.

2. The process according to claim 1, wherein the first effect is heated to a temperature between 90 and 130°C and at a pressure sufficient to evaporate between 40 and 60% by weight of cumene.

3. The process according to claim 1 or 2, wherein the first effect is heated to a temperature between 90 and 100°C and at a pressure sufficient to evaporate between 40 and 60% by weight of cumene.

4. The process according to anyone of claim 1 to 3, wherein CHP solution issued from the first effect is at a concentration by weight between 35 and 40%.

5. The process according to anyone of claim 1 to 4, wherein CHP solution issued from the first effect is then fed to the second effect and the steam of cumene issued from the first effect is condensed in the second effect thus heating the second effect to pursue the evaporation of cumene.

6. The process according to anyone of claim 1 to 5, wherein the pressure in the second effect is set at a value lower than in the first effect but sufficient to evaporate between 40 and 60% by weight of cumene.

7. The process according to anyone of claim 1 to 6, wherein the equipment used for the multiple effect evaporation system is a falling film evaporator, with or without liquid recirculation.

8. The process according to anyone of claim 1 to 7, wherein the number of effects is between 2 and 5.

9. The process according to anyone of claim 1 to 8, wherein an external source of heat is used to heat the first effect.

10. The process according to anyone of claim 1 to 8, wherein the first effect is carried out directly in the oxidation reactor of step a. and the steam of cumene generated in the oxidation is used to heat the second effect.

11. The process according to anyone of claim 1 to 10, wherein the cumene vapor issued from the last effect is distilled in a distillation column to recover evaporated CHP at the bottom of the column.

12. The process according to claim 11, wherein the cumene recovered at the top of the distillation column is recycled at the oxidation stage.

13. The process according to anyone of claim 1 to 12, wherein the acid cleaved reaction takes place in the presence of an inorganic acid chosen between sulfuric, phosphoric or nitric acid.

The process according to anyone of claim 1 to 13, wherein step a. of oxidation of cumene is carried out in the presence of a basic compound.