KR100292546B1 - Preparation of leucoindigo in granule form and preparation method thereof - Google Patents

Abstract

The present invention relates to a leucoindigo preparation comprising Leucoindigo and an alkali metal hydroxide, a method for producing the Leucoindigo preparation and the use of the preparation for the dyeing of cellulose-containing fiber materials.

Description

Leucoindigo preparation in granule form and preparation method thereof

The present invention relates to a novel leucoindigo preparation in the form of granules consisting of leucoindigo and alkali metal hydroxides.

The invention also relates to a process for the preparation of a leucoindigo preparation and a method for dyeing a cellulose containing textile material using the leucoindigo preparation.

Indigo is a well known bat dye used for dyeing cellulose containing textile materials, in particular cotton warp yarns for blue denim products.

For dyeing, the water-insoluble indigo must first be converted into a water-soluble leuco form by reduction (batting), which is oxidized and then converted back into a pigment after being absorbed by the material to be dyed.

In a conventional dyeing process, indigo is batted by adding an inorganic reducing agent such as sodium dithionite and thiourea dioxide, or an organic reducing agent such as hydroxyacetone, to the alkaline medium upstream of the vessel of the salt bath. Part of the leucoindigo is oxidized when air passes and by contact with air on the surface of the dye bath and for this reason must be rearranged by addition of a small amount of reducing agent to the salt bath, so that an additional machine dependent part of the reducing agent is dyed. Consumed in the process.

One disadvantage in the batching of indigo using this reducing agent is because of the sulphate when using sodium dithionite (as measured in the wastewater of indigo dyehouse, the presence of about 3,500 to 5,000 mg / l sulphate), or hydroxyacetone In the case of using, due to the oxygen-consumable substance (as measured in the waste water of the Indigo dyehouse, the presence of oxygen-consuming substance of about 8,000mg / l COD), the amount of loading in the wastewater of the dyehouse is increased. In addition, a large amount of alkali must be added to the reduction using, for example, sodium dithionite.

Processes for preparing powdered solids as pasty preparations of leucoindigo containing sugars, for example compounds derived from molasses, mixed with polyhydroxy compounds such as glycerol, in particular alkali or zinc dust, as stabilizers are also known. (DE 200 914 degrees is 235 047). It is true that when these preparations are used for dyeing, the content of sulfates in the wastewater of the dyeing plant can be effectively lowered, but as a result TOC (total organic carbon content), COD (chemical oxygen demand) or BOD (biological oxygen demand) The dissolved organic hydroxy compound results in a very high loading in the wastewater, for example the COD of a 60% by weight leucoindigo product containing 25% molasses is about 8,000 mg / l.

FR-A-360 447 also describes a process for producing a solid white indigo preparation wherein a neutral solution of an alkali metal salt of leucoindigo is evaporated to dryness in a very thin layer. However, the product obtained in this way is not in the form of granules and is stabilized by mixing with undigested lime.

Finally, German patent application P 43 10 122.4 describes a dyeing process using indigo in the form of preliminary reduction, which is in the form of an alkaline aqueous solution obtained by catalytic hydrogenation. This method reduced the level of sulphate to the amount of hydrosulfite needed for air contact during the dyeing process while precluding the loading of organics into the wastewater. However, there is a disadvantage that the leucoindigo solution used is sensitive to oxidation reactions and must be handled under strict exclusion of oxygen.

It is an object of the present invention to provide a leucoindigo preparation which is advantageous for the dyeing process, excluding the above mentioned disadvantages.

The inventors have found that this object is achieved by the preparation of leucoindigo in granule form with leucoindigo and alkali metal hydroxide as essential components.

The inventors have also developed a process for the preparation of the leucoindigo preparation, which comprises the step of concentrated drying the alkaline aqueous solution of leucoindigo under conditions that exclude homogeneous mixed peroxygen.

Finally, the present invention provides a method of dyeing a cellulose-containing textile material using a leucoindigo preparation.

The leucoindigo preparation of the present invention contains leucoindigo which is an essential component and an alkali metal hydroxide in a molar ratio of 1: 1 to 1:10, preferably 1: 1 to 1: 2.

Therefore, leucoindigo exists as a monoalkali metal salt or a dialkali metal salt, depending on the content of the alkali metal hydroxide.

Examples of suitable alkali metal hydroxides are specifically potassium hydroxide, in particular sodium hydroxide.

The basic feature of the leucoindigo preparation of the present invention is granular. The granules are generally dominant with spherical particles having an average particle size of 0.1 to 2 mm, preferably 0.5 to 1.5 mm.

The oxidation stability of these particles is notable even in the absence of stabilizers. These particles are easy to handle and can be stored in air. However, for long term storage it is desirable to store in a sealed container.

A particular advantage of the leucoindigo preparation of the present invention is that it can be used directly for drying after the clarification treatment (after removal of the catalyst) of the aqueous solution obtained in the preparation of leucoindigo by catalytic hydrogenation.

Catalytic hydrogenation itself is generally known, for example, with an alkali indigo paste (typically 10-35% by weight of indigo, 2) using Raney nickel as the catalyst, under hydrogen pressure of 2-4 bar and at a temperature of 60-90 ° C. To 10% by weight sodium hydroxide).

It is common for the obtained leucoindigo solution to contain 10 to 35% by weight, preferably 15 to 30% by weight, particularly preferably 20 to 25% by weight of leucoindigo.

In the production process of the invention, it is advantageous for the leucoindigo solution to be concentrated to dryness in the absence of oxygen and then inactivated and homogeneously mixed with a protective gas such as nitrogen.

The production temperature required for drying is usually 50 to 80 ° C, or 70 to 120 ° C, depending on whether or not reduced pressure conditions are used.

During the drying process, the urine solution and the solid product must be mixed homogeneously.

Therefore, devices suitable for industrial use include, for example, rotary dryers, paddle dryers, and force wash contact dryers, preferably drying under reduced pressure (about 50 to 500 mbar). If necessary, the coarse grinding process may be further performed inside and outside the drying apparatus.

The process of the invention may also be carried out in a spray drying apparatus, such as a spray tower and in particular a spray fluidized bed, in which moisture vaporizes and collides with a hot inert gas, preferably nitrogen. The dried product here can be obtained directly to the desired particle size.

Before discharging the dried product, it is generally advantageous to cool to 20-40 ° C. to avoid reoxidation at high temperatures.

The process of the present invention provides a simple manner for the continuous production of leucoindigo preparations in granular form. Generally the unreduced indigo content of the dried product is only less than 8% by weight.

Advantageously, the leucoindigo preparation of the present invention is suitable for dyeing cellulose containing textile materials. The dyes obtained fully satisfy this requirement. In the dyeing process, the level of sulphate in the wastewater and the consumption of alkali metal hydroxides are drastically reduced, and only leucoindigo, which has been reclaimed by air contact in the dyeing process, must be reduced again.

Preparation of leucoindigo preparations according to the invention

Example 1

A solution of 20% by weight of leucoindigo, 5% by weight of sodium hydroxide and 75% by weight of water was concentrated to dryness at a speed of 55 rpm at a rate of 55 rpm at 30 mbar through a nitrogen inert rotary evaporator heated to an oil bath temperature of 130 ° C. It was then cabinetd at 40 ° C.

The granules were roughly ground so that the average particle diameter of the granules was 1 mm. Extraction with water using a Soxleth device showed a water insoluble content (byproduct and unreduced indigo) of 4.4% by weight.

Example 2

A solution of 20% by weight of leucoindigo, 5% by weight of sodium hydroxide and 75% by weight of water was continuously spray granulated in a nitrogen inert fluidized bed at a flow gas velocity of 1.2 msec ^-1 . The temperature of the inlet gas was 130 ° C. and the temperature of the outlet gas was 90 ° C., which was the same as the product temperature in the fluidized bed. The granules formed were discharged from the fluidized bed through a screw conveyor, filled into a nitrogen purge vessel and cooled to room temperature.

The useful particle's average particle diameter was about 1 mm. The water insoluble content was less than 5% by weight.

Claims (8)

A leucoindigo product in the form of granules containing leucoindigo and alkali metal hydroxide as essential components. 2. The leucoindigo preparation according to claim 1, wherein the molar ratio of leucoindigo to alkali metal hydroxide is from 1: 1 to 1:10. A method for producing the leucoindigo preparation according to claim 1, comprising concentrated drying of an alkaline aqueous solution of leucoindigo under conditions of homogeneous mixing and oxygen exclusion. The method of claim 3 wherein the process is performed in an inert atmosphere. The method of claim 3 wherein the process is performed under reduced pressure. The method of claim 3 wherein the process is carried out in an inert atmosphere under reduced pressure. 7. Process according to any one of claims 3 to 6, characterized in that it is carried out in a spray drying apparatus. A method of dyeing a cellulose-containing textile material using the leucoindigo preparation of claim 1.