WO2017179026A1

WO2017179026A1 - Method and unit for reducing dioxane produced as a result of sulfonation of alcohol ether sulfates

Info

Publication number: WO2017179026A1
Application number: PCT/IB2017/052174
Authority: WO
Inventors: Giuseppe DI CARPEGNA; Luigi PERANI
Original assignee: Iit S.R.L.
Priority date: 2016-04-15
Filing date: 2017-04-14
Publication date: 2017-10-19
Also published as: ITUA20162646A1

Abstract

Method and unit for reducing dioxane produced as a result of sulfonation of alcohol ether sulfates, said reduction being carried out by at least one distillation step in at least one flash evaporator tank under vacuum. It involves supplying heat to the product being fed by: a. Adding live steam to the input product and subsequently releasing into the tank, b. Heating a mixture of input product with heat exchanger, c. Providing a neutralization step of reactants 21, in particular sulfonic acid, neutralizing agent and dilution water.

Description

TITLE: METHOD AND UNIT FOR REDUCING DIOXANE PRODUCED AS A RESULT OF SULFONATION OF ALCOHOL ETHER SULFATES

DESCRIPTION SCOPE OF THE INVENTION

The present invention relates to the field of sulfonation processes and in particular it relates to a method and relative unit for reducing dioxane, the by-product during the sulfonation of ethoxylated alcohol sulfates.

Dioxane is undesired in products for human use and its contents should be maintained below certain limits. Sulfonation plants are designed to minimize the formation of dioxane; nevertheless, the content thereof is usually higher than the desired limits. It is therefore necessary to reduce the content thereof.

The method involves reducing the content of dioxane by distillation of water and dioxane from the product itself.

PRIOR ART

In general, distillation is a technique used to separate two or more substances present in a mixture, which uses the difference in the boiling points of these substances (or in other words, their difference in volatility.

It is used to both separate complex mixtures (obtaining multiple mixtures in output, each having a different composition) and to purify individual substances (obtaining a stream in output containing the desired substance at a high purity and a waste stream containing impurities present in the feed).

Flash evaporation (or partial evaporation) consists of a partial evaporation (i.e. where only a portion of the liquid is evaporated) made by passing the liquid through a lamination valve (or another lamination device). If the feed consists of a multicomponent liquid mixture, the vapor phase in output from the equipment (called flash separator) will be richer with the more volatile component compared to the liquid phase.

DESCRIPTION AND ADVANTAGES OF THE INVENTION

One object of the present invention is to provide a method and a unit for reducing 1,4-dioxane produced as a result of sulfonation of alcohol ether sulfates with a simple, rational and rather cost-effective solution.

These and other objects are achieved with the features of the invention described in the independent claim 1. The dependent claims describe preferred and/or particularly advantageous aspects of the invention.

Advantages:

- It can produce a very efficient dioxane reduction,

- It is a very easy to use unit,

- It tolerates very easily high viscosities and operational errors,

- It is little prone to corrosion,

- It requires very simple and infrequent maintenance, - It easily tolerate an increase in the volume of the product that may cause problems in the vacuum group,

- It can be integrated into the neutralization unit with consequent saving on consumption.

Said objects and advantages are all achieved by the invention object of the present invention, which is characterized by the following claims.

BRIEF DESCRIPTION OF THE FIGURES

This and other features will become more apparent from the following description of some of the configurations, illustrated purely by way of example in the accompanying drawings.

- Figure 1 : shows a unit for reducing 1,4-dioxane without neutralization and heating with live steam,

- Figure 2: shows a unit for reducing 1,4-dioxane without neutralization and heating with hot fluid, preferably hot water in a heat exchanger,

Figure 3 : shows a unit for reducing 1,4-dioxane with neutralization and heating with hot fluid and heat exchanger.

DESCRIPTION OF THE INVENTION

The unit for reducing dioxane is described herein.

As said, 1,4-dioxane is formed as a by-product during the sulfonation of ethoxylated alcohols; it is highly flammable, irritating and harmful, and under normal conditions it occurs as a colorless, volatile liquid with a subtle smell of ether. 1,4-Dioxane has vapor pressure very close to that of water and the content of dioxane in alcohol ether sulfates is reduced by the product neutralized by the distillation of water and dioxane. The reduction to low enough levels takes place since the concentration of dioxane that is distilled in the vapor phase is sometimes higher than that of water; water remains in the liquid phase in the product.

The products from which dioxane is to be reduced, as said above, are alcohol ether sulfates and in particular sodium lauryl ether sulfate (hereinafter and in the figures also referred to as SLES); said products are unstable at relatively high temperatures and may decompose, thereby producing alcohol and sulfuric acid and thereby increasing the content of dioxane.

Distillation step provided by the present invention claimed is carried out at moderate temperatures while operating at low pressure, i.e. under vacuum.

By evaporating, water produces a drop in the product temperature to values corresponding to the vapor pressure of water at the pressure existing in the distillation tank. The amount of water evaporated is therefore a function of the heat contained in the incoming product (i.e. of its flow and temperature) and of the working pressure in the distillation tank.

The concentration of dioxane in the distilled product is according to Henry's law, i.e. it is a function of the concentration of dioxane in the distilled vapors, and therefore it is the lower the greater the amount of water that is distilled.

The distillation method and unit provide for:

- treating the product to be distilled in a flash evaporation tank under vacuum,

- distributing the product on the top of a vertical wall within said flash evaporation tank so as to form a layer of small thickness,

- dropping the product by gravity along said wall so as to promote the venting of the vapors.

The above product can come either from neutralization unit or from storage. Since the temperature of the product is kept relatively low to prevent decomposition, the amount of heat contained therein is therefore limited and insufficient to evaporate sufficient water to reduce the content of dioxane below the required limit.

The invention may further involve providing heat to the product; in this way, the amount of vapor that separates from the product in the flash tank can be increased to reduce the residual concentration of dioxane in the product below the required limit.

The feeding of said heat takes place in such a way as not to cause overheating which could damage the product.

The product arrives to the flash tank at a lower temperature than the boiling temperature at atmospheric pressure. In this way, evaporation takes place only within the flash tank where the pressure is less than the atmospheric pressure present in the supply lines.

FIRST EMBODIMENT

With particular reference to figure 1, reference numeral 1 indicates as a whole a unit for reducing 1,4-dioxane without neutralization and heating with live steam.

Reference numeral 2 indicates the flash tank or evaporator with the feeding conduit which feeds the product, specifically line 3, in direct or indirect connection with at least one mixing means 4 configured to mix product 5, SLES in the present case, and steam 6.

According to a first reduction method implemented by the invention, it is contemplated to provide heat by adding the live steam 6 directly to product 5 entering the flash evaporator 2.

By mixing with product 5, the live steam 6 extracts part of dioxane. After that, all this steam is released in 7 within the flash evaporator 2. The amount of steam that is released in the flash is calculated to reduce the content of dioxane below the required limit.

SECOND EMBODIMENT

With particular reference to figure 2, reference numeral 10 indicates as a whole a unit for reducing 1,4-dioxane without neutralization and heating of the product with hot water.

In this way, a second reduction method of the invention contemplates to provide heat through a heat exchanger, indicated with reference numeral 11. Again with reference to the figure 2, part of the product discharged from the bottom of the flash evaporator 2 is recirculated through a recirculation pump 12 and mixed back with product 5 fed to the reduction unit 10, i.e. the product in input to evaporator 2 itself.

The recirculated product has a low temperature and this lowers the temperature of the mixture created by mixer 13.

The passage of the mixture through the heat exchanger 11 or through the inlet 14 and outlet 15 line in connection with tank 2 allows the latter to be heated, providing it with sufficient heat to evaporate the amount of water in said flash evaporation tank 2 needed to reduce the content of dioxane in the product below the required limit.

THIRD EMBODIMENT

With particular reference to figure 3, reference numeral 20 indicates as a whole a unit for reducing 1,4-dioxane with neutralization.

In addition, it is also contemplated in this case the optional heating of the incoming product with hot water and heat exchanger 11 as already described for the example above.

In this way, a third reduction method of the present invention contemplates to implement the evaporation following a neutralization step of reactants 21, especially sulfonic acid, neutralizing agent and dilution water.

The term "neutralization" means the progress of an acid- base reaction up to its equivalence point. The heat generated by the neutralization reaction causes the evaporation of part of the dilution water in the flash tank 2.

The flash tank 2, in the specific example, is now incorporated into a traditional neutralization circuit and replacing the cooling exchanger.

Normally, the direct reaction heat of reactants 21 causes very high temperature rises; in order to keep the temperature rise within acceptable limits and not to cause the decomposition of the product, the method contemplates to recycle, by recirculating pump 23, part of the product that is cooled and discharged from bottom 22 of the flash tank 2. In this case, the part of product enters back into a neutralization mixer 24 along with reactants 21.

In all three examples described above, the product with low concentration of dioxane is discharged from the bottom of the flash tank, line 22 and extraction pump indicated with reference numeral 8.

Depending on the selected process, part of the product is recirculated and mixed with the feed to the flash evaporation tank, while the amount equivalent to the production is sent to further processing or storage.

The vapor phase with a high content of dioxane separated from the product leaves the flash tank 2 from the top, line 9, and goes to the vacuum system, generated by a vacuum pump 30. The vacuum in the flash tank also removes non-condensable gases, with the advantage that the product with low dioxane extracted by pump 8 is therefore degassed and does not require a dedicated air removal unit for this operation.

From the flash evaporation tank 2, the steam is sent to a heat exchanger 35 where it is condensed.

The condensate flows by gravity into a bottom tank 36 where it accumulates. The condensate, rich in dioxane, is extracted from the bottom and sent to final treatment.

The inert gases are extracted by a vacuum pump and released to the atmosphere.

In all the examples described so far, reference was made to a single stage reduction unit for reducing 1,4-dioxane, however other variants may be contemplated without departing from the scope of protection of the invention. For example, a variant of the process contemplates to evaporate a same amount of water evaporated in two stages, with the advantage of producing a greater reduction in the content of dioxane in the final product.

Therefore, an object of the invention is also a nit for reducing dioxane comprising two evaporation stages, both with a flash tank operating under vacuum.

In the case just described, the method contemplates to feed the product in output from the first stage into the second stage.

The product in output from the first stage is cold and does not contain heat to evaporate water, in this case it is contemplated to provide heat again using the methods already described for the single-stage case, in particular:

a. Adding live steam to the input product and subsequently releasing into the tank,

b. Heating a mixture of input product with heat exchanger.

The vacuum system generates vacuum in both flash tanks.

Claims

1. Method for reducing dioxane produced as a result of sulfonation of alcohol ether sulfates, said reduction being performed by means of at least one distillation step into at least one vacuum flash evaporator tank, the method characterized in that it provides for supplying heat to the product or reactants (21) fed to said tank in order to carry out an evaporation in the tank; said heat being supplied according to at least one of the following manners:

b. By passing the input product through a heat exchanger and subsequently releasing into the tank itself,

c. By at least one neutralization step of reactants (21) and subsequently releasing into the tank.

2. Method according to claim 1, characterized in that the product or reactants are fed to the tank at atmospheric pressure.

3. Method according to claim 1, characterized in that the heat supplied to the product or to the reactants being fed raises their temperature to a value below the boiling temperature at atmospheric pressure.

4. Method according to any one of the preceding claims, characterized in that steps b) and c) provide for using part of the product that is cooled and discharged from the bottom, recirculating it to mixing means.

5. Method according to any one of the preceding claims, characterized in that it provides for two evaporation stages, both with vacuum flash tank; and wherein it is provided for feeding the product in output from the first stage to the second stage; said step further provides for supplying heat according to steps a) and/or b).

6. Method according to any one of the preceding claims, wherein it is provided for delivering the steam produced by the flash evaporation tank (2) to a heat exchanger (35) where it is condensed; the condensate, rich in dioxane, is extracted and delivered to final treatment.

7. Unit (1) for reducing 1,4 dioxane from alcohol ether sulfates according to the method of the preceding claims, characterized in that it comprises at least one flash evaporator or tank (2), provided with conduit, feeding line (3) with which the product to be treated is fed, in a direct or indirect connection with at least one mixing means (4), wherein said mixing means (4) is configured to mix the product (5) and the steam (6) with each other.

8. Unit (10) for reducing 1,4 dioxane from alcohol ether sulfates according to claim 7, characterized in that it comprises at least one flash evaporator or tank (2), provided with conduit, feeding line (15) with which the product to be treated is fed, in a direct or indirect connection with at least one mixing means (13), wherein said mixing means (13) is configured to mix the product (5) fed to the reduction unit and part of the product that is discharged from the tank (2) with each other; wherein said mixture passes through at least one heat exchanger.

. Unit (20) for reducing 1,4 dioxane from alcohol ether sulfates according to claim 8, characterized in that it comprises at least one flash evaporator or tank (2), provided with conduit, feeding line (15) with which the product to be treated is fed, in a direct or indirect connection with at least one mixing means (24), wherein said mixing means (24) is configured to mix the reactants (21) fed to the reduction unit and part of the product that is discharged from the tank (2) with each other; wherein said tank (2) is built in a neutralization circuit.

0. Unit for reducing 1,4 dioxane from alcohol ether sulfates according to claim 7 or 8 or 9, characterized in that it comprises two evaporation stages, both with flash tank operating under vacuum and wherein the product of the first stage is fed to the second stage and means for supplying heat also to said second stage.

1. Unit for reducing according to any one of claims 7 to 10, wherein the product to be treated comes from a neutralization unit or from storage.