WO1991009043A1

WO1991009043A1 - Process for continuously bleaching liquids with ozone

Info

Publication number: WO1991009043A1
Application number: PCT/EP1990/002080
Authority: WO
Inventors: Paul Schulz; Stefanie MÜLLER; Stefan Hammelstein; Keith Neary
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1989-12-11
Filing date: 1990-12-03
Publication date: 1991-06-27
Also published as: EP0505464A1; DE3940827A1

Abstract

In a process for continuously bleaching viscous liquids, a thin film of the liquid is brought into contact with gaseous ozone. The process is particularly suitable for bleaching alkylglycosides.

Description

"Process for the continuous bleaching of liquids with ozone"

The present invention relates to a continuous process for bleaching viscous liquid products with gaseous ozone.

Chemical-technical products are often more or less strongly colored due to production, although the corresponding substances are colorless in their purest form. The colored impurities often interfere with the application or further processing of the technical products, so that they are generally cleaned, or at least optically brightened, by a bleaching process, often directly after their production. Such bleaching processes are normally based on chemical changes, which should preferably be irreversible. In order to make the bleaching result permanent, the bleaching reagent should not only attack the colored by-products themselves, but also the precursors of these substances, which are usually also present in the technical products and can form colored contaminants again during storage and thus the Influence color stability of the bleached product. In particular, oxidation and reduction reactions can be considered as chemical reactions which can usually be used for bleaching.

The usual reductive bleaching agents are sulfites, hydrogen sulfites and SO2 _. Dithionites, boranates and hydrogen in the presence of hydrogenation catalysts. Bleaches which have an oxidative effect are usually used which release active oxygen or active chlorine. Examples of such bleaching agents are hydrogen peroxide, alkali peroxides, perborates, persulfates, percarbonates, and hypochlorites, which are normally used in the form of aqueous solutions, and chlorine dioxide, elemental chlorine, elemental oxygen and ozone, which are used either as aqueous solutions or in gaseous form. The applicability of chemical bleaching processes is limited in practice by the relative sensitivity of the product and the by-product to be removed to the bleaching agent used and by the formation of ecotoxicologically questionable by-products, so that one goal in the development of new bleaching processes is to minimize the by-product proportion reaction conditions that are as mild and gentle as possible on the product, that is, low temperatures and short contact with the bleach, should be.

The products to be bleached are usually in a more or less easily mobile form in order to facilitate the reaction with the bleaching agent. Liquids to be bleached are used either as such or diluted as solutions. Solids to be bleached, for example cellulose, are usually reacted as slurries or pastes with the bleaching agents present in liquid or gaseous form. Gaseous bleaching agents, for example chlorine, oxygen or ozone, have the inherent disadvantage compared to liquid bleaching agents which can easily be mixed with the product to be bleached, that they penetrate into the liquid product before the actual bleaching reaction or on the The surface of suspended solids with sufficiently fast kinetics must adsorb, which can only be facilitated by ^" more or less complex mixing techniques, for example using packed columns or bubble columns, only in the case of relatively low-viscosity liquids, which should not or only slightly foam can.

The requirement for low reaction temperatures and short contact times with the bleaching agent is particularly difficult to meet in the bleaching of highly viscous liquids, since the bleaching agent is transported slowly into the liquid and within the liquid to the colored bodies to be bleached. So far, these difficulties have been countered by lowering the viscosity of the liquid product to be bleached, for example by diluting with an inert solvent, by using a relatively large excess of bleach or by increasing the activity of the bleach, for example by increasing the reaction temperature. However, these solutions pose new problems because they remove solvents subsequently, for example by Make distillation necessary, favor the decomposition of the bleaching agent due to the high reaction temperature or cause side reactions and therefore by-products or impurities, for example due to attack on the product, to occur to a significant extent by an excess of bleaching agent.

Surprisingly, it has now been found that highly viscous chemical-technical liquid products can be effectively bleached by ozone by eliminating the aforementioned difficulties if gaseous ozone is continuously passed along a flowing thin layer of the liquid to be bleached. Since the thin layer of liquid is preferably on a smooth surface, liquids with a pronounced foaming power can also be bleached.

A preferred embodiment of the process according to the invention consists in conveying or allowing the liquid to be bleached to flow continuously or, where appropriate, using gravity, in the form of a thin film on the inner wall of a preferably vertically arranged tubular reaction chamber, and in the meantime with the gaseous ozone, which preferably moves in countercurrent to the liquid. The low layer thickness of the liquid phase, which is preferably 0.05 mm to 2 mm, promotes both the ozone uptake and its distribution in the liquid.

To generate a largely uniform liquid film on the inside of the reaction chamber, it can be useful to use rollers, blades or wipers rotating around the central axis of the chamber, as are customary in thin-film evaporators. Such rotor elements can consist, for example, of elastically pressed blades or rigid elements with constant wall distances. The layer thickness and the flow speed of the liquid phase can be regulated as required by the type and arrangement of the rotor elements used and their speed of rotation.

In the process according to the invention, ozone is preferably in, for example, a carrier gas which is largely inert under the reaction conditions Oxygen, nitrogen or air, diluted form used, the concentration of the ozone in the mixture with the carrier gas is preferably 1-10 vol .-%. The process according to the invention preferably works with a gaseous phase under normal pressure, slight overpressures being able to occur in the reaction chamber, for example due to the fact that the gaseous phase is passed through a downstream ozone destruction system after flowing through the reaction chamber. The linear gas flow rates in the reaction chamber are preferably 0.1 m / s or less.

The contact time of the gaseous ozone with the liquid to be bleached can be influenced by the flow rate of both the liquid phase and the gaseous phase. It is preferably between 0.1 and 10 minutes.

In order to set the desired reaction temperature, which in the bleaching process according to the invention is preferably between 10 ° C. and 60 ° C., but depending on the product to be bleached, this range may also lie outside the heating chamber on the outside of the reaction chamber Cooling facilities are located; the outside of the reaction chamber is preferably wholly or partially shaped as a hollow body through which a heatable and / or coolable liquid medium is passed.

If the bleaching result is not satisfactory after the bleaching process described so far, the bleached product can be subjected again to the bleaching process according to the invention. This can be done either by recycling the bleached liquid product several times into the reaction chamber that has already passed through, or by using one or more further reaction chambers connected downstream, so that the total contact time with the ozone increases accordingly.

The bleaching process according to the invention is in principle suitable for all flowable or pumpable liquid products. It is irrelevant whether the products themselves are highly viscous liquids or from solutions, emulsions or suspensions of chemical-technical products in an inert Solvents, especially water, exist. If they do not already arise during the manufacture of the chemical-technical product to be bleached, such solutions can be produced, for example, by the process described in the ^' European patent application EP 365 831. The process according to the invention can preferably be used for bleaching those products which have viscosities between 100 mPa-s and 1 000 000 mPa-s at 20 ° C.

The pH of the liquid products to be bleached should preferably be neutral or acidic before entering the reaction chamber, so that the spontaneous ozone decomposition accelerated under alkaline conditions and thus the ozone consumption is minimized. If the product to be bleached has an alkaline pH, this can be reduced by adding acids that are compatible with the product, which may include, for example, acetic acid or hydrochloric acid.

The relatively highly viscous liquid products which can be bleached by the process according to the invention include, in particular, aqueous solutions of alkylglycosides of the formula (I),

H- (Glyk) _n -0R (I)

in the glyc is a glycose unit, n is a number between 1 and 10, which can also be broken as an analytically determined arithmetic size, and R is an aliphatic radical with 1 to 30 carbon atoms. The. The preparation of such alkyl glycosides is described, for example, in US Pat. Nos. 3,219,656, 3,547,828, 3,839,318, European Patent Applications EP 92355, EP 165721, EP 301 298 and EP 377 883. The alkyl glycosides are normally obtained in the form of more or less strongly colored aqueous solutions and, as described in the documents mentioned, have hitherto been bleached in a batch process, for example by adding aqueous H2 O 2 solutions and heating to, for example, 100 ° C., which has the disadvantages of the additional dilution , the occurrence of by-products resulting from oxidative product degradation, for example aliphatic carboxylic acids, and the compulsion to destroy excess oxidizing agent present in the product. These disadvantages are overcome by the bleaching process according to the invention, which provides practically oxidizer-free products which are largely free from impurities caused by oxidative product degradation and which have hook and loop numbers of about 5 to about 50.

Examples

example 1

A 50 weight percent aqueous crude alkyl glycoside solution made from glucose and essentially

According to the method described in European patent application EP 301 298, which has a viscosity at 20 ° C. of 5000 mPa-s (Brookfield, spindle No. 5, 10 revolutions per minute), a pH of 5.5 and had a Velcro number of 200, would be by a thin-film system (Buss-SMS T 100, ratio height ^' to diameter 7: 1, inner surface 0.3 m ^) with centrifugal ^' pressed wiper blades (linear wiper speed 3.75 m / s) directed. The throughput of the liquid phase through the reaction chamber was 60 kg / m ^ • h, the residence time of the liquid phase in the reaction chamber was about 2 minutes. A gas stream consisting of air containing 2.5% by volume of ozone was directed against the liquid in such an amount that about 1.5 g of ozone accounted for 1 kg of liquid phase. The reaction temperature was kept at about 40 ° C. by heating the reaction chamber over the double tube jacket (heating liquid water with a temperature of approximately 50 ° C.). After bleaching and vacuum degassing, the product had a color number according to Klett ^a ) of 30.

Example 2

Analogous to Example 1, the same alkylglycoside solution was bleached using the same apparatus. With otherwise identical procedural

^a ) determined in 5% by weight solution in water / isopropanol (1: 1), layer thickness 1 cm, using a blue filter (spectral range 400 to 465 nm) The throughput of the liquid phase through the reaction chamber was 33 kg / m ^{2 •} h, the residence time of the liquid product in the reaction chamber was 4 minutes. The reaction temperature was kept at 30 ° C., the bleached product had a Velcro ³ ) below 20.

Claims

1. A process for the continuous bleaching of pumpable liquids, characterized in that the liquid is brought into contact with gaseous ozone in the form of a thin film.

2. The method according to claim 1, characterized in that the reaction temperature is 10 ° C - 60 ° C.

3. The method according to any one of claims 1 or 2, characterized in that the liquid before bleaching at 20 ° C has a viscosity of ^' 100 mPa-s to 1 000 000 mPa-s.

4. The method according to any one of claims 1 to 3, characterized in that the layer thickness of the thin film of the liquid to be bleached is 0.05 mm to 2 mm.

5. The method according to any one of claims 1 to 4, characterized in that ozone in a mixture with a gas which is largely inert under the reaction conditions, in particular air, nitrogen or oxygen, is used and the gas mixture is 1% by volume to 10 vol .-% consists of ozone.

6. The method according to any one of claims 1 to 5, characterized in that the liquid to be bleached is in contact with the gaseous ozone in the reaction chamber for 0.1 to 10 minutes.

7. Procedure according to one of the. Claims 1 to 6, characterized in that the liquid to be bleached is conveyed continuously, possibly using gravity, in the form of a thin film on the inner wall of a preferably vertically arranged tubular reaction chamber and in the meantime with the gaseous ozone which is present preferably moved in countercurrent to the liquid, is brought into contact.

8. The method according to any one of claims 1 to 7, characterized in that the liquid to be bleached essentially from alkyl glycosides of the general formula (I),

H- (Glyk) _n -0R (I)

in the glyc a glycose unit, n a number from the range from 1 to

10, and R is an aliphatic radical having 1 to 30 carbon atoms, and optionally an inert solvent, preferably water.

9. alkyl glycosides of the general formula (I),

H- (Glyk) _n -0R (I)

in the glyc is a glycose unit, n is a number from the range from 1 to 10, and R is an aliphatic radical having 1 to 30 C atoms, characterized in that they have been bleached by a process according to claim 8 and a color number according to Velcro from 5 to 50.