KR19990069816A - Desalination method of phenol tar - Google Patents

Abstract

The present invention relates to tar, which is a batch or continuous process that mixes salt containing tar and dilute aqueous orthophosphoric acid and precipitates it into two phases, the organic phase and the aqueous phase containing most of the salt, and then removes the aqueous phase from the organic phase. The desalination method of the present invention. This method is used to remove salts from tar in high proportions and to reduce contamination and corrosion of devices behind the process stream.

Description

Desalination method of phenol tar

The present invention generally relates to a process for preparing phenol from isopropylbenzene (cumene), in particular for recovering the main products from tar by-products of this process.

In the production of phenol and acetone by the oxidation of cumene, the most serious disadvantage is that tar is produced by this process. Tar may be produced in a high proportion of about 10 to 20% by weight of the resulting phenol. Tar is typically about 4 to 15 weight percent phenol, about 20 to 25 weight percent cumylphenol (CP), about 20 to 35 weight percent alpha-methylstyrene dimer (AMS dimer), about 3 to 10 weight Complex mixture containing% acetophenone (SP) and dimethylbenzyl alcohol (DMBA), about 0.2 weight% water, and about 0.1 to 3 weight% inorganic salts and unidentified high molecular weight compounds.

Given the level of phenol production worldwide, the treatment and disposal of tar by-products from phenol products is a major economic and environmental challenge for phenol producers. As the improvement of the phenol process is realized, it is increasingly difficult to recover the main product from tar. Due to the inorganic salts present in the tar, the removal method becomes more complicated. These salts include the sulphates and phenates of iron and sodium as well as the sodium salts of organic acids resulting from the oxidation of isopropylbenzene, ie acid-mediated cleavage of cumene hydroperoxide followed by the neutralization of acid by-products.

The pH of phenol tars ranges from weakly acidic to strongly alkaline, ie 6.5 to 11.

The viscosity of the tar is 60 centipoise (cp) to 2300 centipoise depending on the performance of the process and the speed of performance.

Inorganic salts in tar, such as sodium sulfate, destroy the devices used to recover the main product from tar. The salt crystallizes causing clogging of pipes, heat exchangers and column reboilers. In addition, in order to prevent corrosion of the device due to salt decomposition, it is necessary to limit the choice of materials used in the construction of the device, such as using corrosion resistant alloys and containers with inner coatings, especially when performing at high temperatures.

The salt can also inhibit the action of the hydrogenation catalyst and other catalysts used in the recovery process.

In order to reduce reactor corrosion and prolong reactor life, it is necessary to preliminarily de-salt tar before thermal destruction.

Because of this problem, very little useful components could be recovered from the tar, and phenol tar was mostly burned as fuel oil. Even in the case of burning or incineration of phenol tar as fuel oil, the presence of salts leads to corrosion of the device, air pollution from certain substances, and the formation of an envelope in the burner, which results in a loss of burner efficiency.

One of the widely used methods for removing salts, known to those skilled in the art, is to wash tar with dilute sulfuric acid. The washing process is carried out in two stages. In the first step the tar is acidified with dilute sulfuric acid and in the second step it is washed with water to remove the acid and soluble degradation products.

In another method, tar is treated two or three times using 10% sulfuric acid at about half the volume of tar. After the acid is added, the acid / tar mixture is stirred at about 50-60 ° C. for about 1 hour. After settling, the bottom layer containing the remaining acid and soluble salts is separated from the top tar layer. By this method, about 80% of the salt can be removed together with the ash remaining in the tar at about 15 to 70 mg / kg (0.0015 to 0.007) by weight.

Another method uses 10% H ₂ SO ₄ , but in this method only 10% of the tar volume.

In another method, phenol tar is desalted by a batch process, in which 2 to 20% by weight of the total tar weight is washed in multiple steps with 3 to 30% by weight aqueous sulfuric acid solution. The batch is stirred at a temperature of about 50 to about 150 ° C. to keep the pH below 7. After settling for 2 hours, the tar is separated from the wash solution. At 20 ° C. the salt crystallizes from the aqueous layer. After the salt is removed, the aqueous layer is reused to wash the tar in the next batch. The tar after separation has an ash content of 0.15% by weight and a moisture content of 1.8% by weight. The pH of the extracted water is 5.2 and the pH of the salt solution is about 4-7.

These conventional methods have a number of disadvantages:

1) The cost of the material is extra because of the considerable amount of sulfuric acid consumed.

2) The use of sulfuric acid will corrode the device a lot, so it is necessary to use a corrosion resistant alloy or to coat the inside.

3) Multistage cleaning creates a significant amount of hazardous waste that needs to be treated to minimize environmental degradation.

4) Multistage washing consumes two to three times the volume of tar treated.

5) After the major components have been recovered, residual acid remains in the tar causing corrosion problems during subsequent tar treatment and waste disposal.

6) If salts crystallize, they must be neutralized before disposal of the concentrated acid salt waste.

The present invention is capable of removing salts at high rates and reducing contamination and corrosion of the device, without the use of sulfuric acid, which is expensive and can corrode the device, and without the environmentally and economically disadvantageous multistage cleaning, It is intended to provide a method for desalting tar.

Tar is mixed with an aqueous solution of dilute orthophosphoric acid as extractant, the mixture is stirred, the mixture is separated into two phases, an organic phase and an aqueous phase, and the aqueous phase is removed from the organic phase conventionally. It turns out that technical problems can be minimized even if they cannot be completely avoided. By using the process of the present invention at least 90% by weight of salt is removed from the tar. In a preferred embodiment, at least 94% by weight of salt is removed and in more preferred embodiments at least 96% by weight of salt is removed.

The process of the invention can be carried out batchwise or continuously. If the process is carried out batchwise, the tar and dilute orthophosphoric acid aqueous solutions are most conveniently mixed with stirring by any means of agitation available. In order to mix the two phases well, it is preferred to continue mixing for at least 10 minutes, more preferably at least 30 minutes, even more preferably at least 60 minutes. If mixing is continued for more than two hours in a batch process, the desalting process is economically inefficient. In a continuous mode, the mixing is most conveniently carried out by flowing a dilute aqueous solution of orthophosphoric acid in the reverse direction of the flow of tar. Mixing is preferably carried out in a vertical column, where the aqueous phase enters the bottom of the column, enters the top of the tar column to be desalted, is removed from the bottom of the desalted tar column, and the aqueous phase containing the salt Is removed from the top. This column may have a baffle, tray or packing to better mix the phases. The most important in successfully carrying out the process of the present invention is the addition of phosphoric acid such that at least a substantial amount of the salts present and produced are transferred from the salt-containing tar to the aqueous phase, followed by sufficient contact between the salt-containing tar and the aqueous phase. will be.

Separation of the two phases occurs rapidly after the agitation is stopped. Sedimentation preferably takes place within 2 hours, more preferably within 1.5 hours, even more preferably within 0.5 hours.

The process is useful for desalting tars containing any level of salt, but tars containing up to about 8 wt%, more preferably up to about 5 wt%, even more preferably up to about 3 wt% salt It has been found to be preferred for desalting. The process is also effective for removing salts from tars containing small amounts of salt on the order of 0.01% by weight. However, it is usually economically more efficient to use this process if the tar contains at least 0.1% by weight of salt.

The amount of orthophosphoric acid in the dilute aqueous solution depends on the pH of the tar, the phase ratio, the salt content of the tar to be desalted, the apparatus performing the process and the manner in which the process is carried out, but the orthophosphoric acid content of the aqueous solution is about 0.01 to about 3 weights. %, More preferably about 0.02% to about 2%, even more preferably about 0.03% to about 1% by weight. The pH of tar is as low as 6, and as high as 14 when containing free caustic. The pH of tar is more typically about 7 to about 10.

The temperature at which desalination occurs is not critical as long as the tar can flow. Of course, at elevated temperatures, the viscosity of the tar decreases, leading to better mixing of the two phases and faster desalination. Therefore, it is preferable to perform the process at a temperature where the temperature of tar is at least 15 ° C, more preferably at least 50 ° C, even more preferably at least 90 ° C. Because desalting occurs between the two liquids, the process is carried out at a temperature lower than the boiling point of the aqueous solution or tar (whichever is lower). The process can be carried out under pressure above or below atmospheric pressure.

The advantages of this process are:

1) When a weak acidic aqueous solution of orthophosphoric acid is used, desalination of phenol tar having any composition occurs without forming an emulsion which significantly shortens the phase sedimentation time (less than 2 hours) according to the desalination method.

2) The use of less aggressive extractants compared to sulfuric acid significantly extends the life of the device.

3) Because desalting is carried out in a single step by treating only with extractant without further washing with water, there is no problem associated with purifying flue fumes during burning of tar due to trace acid in the treated tar. Consumption is significantly reduced.

4) In practice, using a weak aqueous solution of orthophosphoric acid as an extractant does not create difficulties associated with the utilization and biopurification of wastewater, since small amounts of phosphate are a nutrient medium for biological systems.

5) By using a continuous countercurrent desalting process both the concentration and amount of extractant is reduced.

The commercial use of the processes presented herein will be apparent from the following examples which illustrate the invention but do not in any way limit the scope of the invention.

Example 1

A phenol tar stream having a salt content of 0.846% by weight, a pH of the water extract of 8.6 and a viscosity of 2240 cps at 20 ° C. was stirred with a 0.30% by weight aqueous solution of orthophosphoric acid in a batch mixer. The total standing ratio of tar / extractant at this time was 1 / 1.5, the mixing temperature was 90 ° C, the treatment time was 30 minutes, and the settling time was 1.5 hours. The salt content remaining after sedimentation was 0.008% by weight and the water content was 4.8% by weight.

Example 2

A phenol tar stream having a salt content of 0.116% by weight, a pH of the water extract of 8.7 and a viscosity of 59 cps at 20 ° C. was stirred with a 0.25% by weight aqueous solution of orthophosphoric acid in a batch mixer. The mixing time was 30 minutes and the settling time was 30 minutes. The remaining salt content was 0.003% by weight. The removal rate of salt was 97.4% and the water content of tar was 4.2% by weight.

Example 3

A phenol tar stream having a salt content of 2.4 wt%, a viscosity at 20 ° C. of 2240 cps and a pH of 10.85 of the water extract was treated in a countercurrent extractor with 0.05 wt% aqueous solution of orthophosphoric acid. The total standing ratio at 90 ° C. was then 1: 0.5. The salt content in the purified product was 0.07% by weight, the salt removal rate was 97% and the water content in the treated tar was 2.5% by weight.

The process of the present invention uses an aqueous solution of orthophosphoric acid rather than sulfuric acid and does not need to go through a multi-step water washing step, significantly extending the life of the device compared to the conventional method, and reducing the cost and causing no environmental problems.

Claims (14)

(a) tar containing salt is mixed with dilute aqueous solution of orthophosphoric acid, (b) a mixture of tar and acid is stirred, (c) the mixture is separated into two phases, an aqueous phase and an organic phase, and (d) water A method for removing salt from tar, comprising removing at least 90% by weight of salt from tar by removing the appearance. The method of claim 1, The tar is a tar byproduct produced during the preparation of phenol from cumene. The method of claim 2, Method that is a batch process. The method of claim 3, wherein The mixture is stirred for at least 10 minutes. The method of claim 3, wherein Method of separating the mixture by sedimentation. The method of claim 5, How sedimentation occurs within 2 hours. The method of claim 2, The process is a continuous process. The method of claim 7, wherein Method performed in vertical column. The method of claim 8, Dilute aqueous solution of orthophosphoric acid enters the bottom of the column, tar containing salt enters the top of the column, organic phase exits from the bottom of the column, and aqueous phase exits from the top of the column. The method of claim 1, The tar contains up to about 8% salt by weight. The method of claim 1, The tar contains at least 0.01% by weight salt. The method of claim 1, The orthophosphoric acid content of the diluted aqueous solution of orthophosphoric acid is from about 0.01% to about 3% by weight. The method of claim 1, The temperature of tar is 10 degreeC or more. The method of claim 1, The pH of tar containing salts is 6 or more.