Vatting process

Polycyclic Aromatic Carbonyl Dyes. StmcturaHy, these dyes contain one or more carbonyl groups linked by a quinonoid system. They tend to be relatively large molecules built up from smaller units, typically anthraquinones. Since they are appHed to the substrate (usually cellulose) by a vatting process, the polycycHc aromatic carbonyl dyes are often called the anthraquinonoid vat dyes. 

The rate of reduction of a vat dye depends partly on the intrinsic chemical properties of the dye and partly on the size and physical form of the dispersed particles undergoing this reaction. The physical factors are much less important than the chemical aspects [26]. The vatting process entails conversion of the insoluble keto form into the soluble sodium enolate (section 1.6.1). The reaction takes place in two stages at ambient temperature. Extremely rapid reduction to the hydroquinone is followed by slower dissolution in the alkaline solution. At higher temperatures, however, the dissolution rate approximates more closely to the rate of reduction. Temperature and dithionite concentration are the important variables and the rate of reduction is much less dependent on dye or alkali concentration. 

Vat dyes are insoluble in water and are applied to cellulosic fibres, usually with sodium dithionite under alkaline conditions, by a vatting process involving reduction to produce a... 

The precursors of the carbazoles are the anthrimides, in particular the 1,1 -dianthraquinonylamines (l,T-dianthrimides). These intermediates were originally used as vat dyes themselves, but very few give bright colours and the vatting process also brings about reduction to 1-aminoanthraquinone. Only one dianthrimide is currently active in the Colour Index [11] this grey vat dye is Cl Vat Black 28 (6.83). l,l -Dianthrimides are easily prepared by heating a 1-aminoanthraquinone with a 1-chloroanthraquinone in nitrobenzene or another solvent in the presence of sodium carbonate and a copper catalyst. 

Considerable interest has been shown in uses of vegetable food proteins in cheese-type products. Attempts have been made to coprecipitate casein and vegetable protein in the typical vat process for making cheeses (35). Rhee (36) has found that up to 50% peanut protein isolate and 25% soybean isolate can be effectively substituted for sodium caseinate in the preparation of imitation cheeses. 

Aniline et al. found SNB. in the blood of a 65-yr-old woman who occupied a second-floor apartment directly above a clandestine laboratory making SNB by an open-vat process. Pitts et al.52 reported... 

The highest level of NDMA (0.5 yg/ml) was found in a sample from a 36.5% aqueous solution of dimethylamine sulfate (DMAS). According to plant personnel, 117 liters of DMAS are used each day in the hide unhairing process. This would amount to less than 60 mg NDMA/day potential exposure from the contaminated DMAS. NDMA (0.0015 yg/ml) was also found in the re-lime pit (unhairing vat) process water. This process water contained 5.7 liters of DMAS in 8000 L of lime-saturated water. The other samples which contained NDMA (0.004 yg/ml and 0.006 yg/ml) were waste-water from the tannery outlet pipe collected at the local municipal waste-... 

In the vatting process the water-insoluble vat dye is reduced by sodium hydro-gensulfite (hydros) to the water-soluble phenate salt. This is less colored than the vat dye and has affinity for cotton. The cloth dyed with the phenate salt is placed in water, normally containing soap, and air is bubbled through the solution to regenerate the vat dye, which is trapped in the pores of the cotton (Scheme 2.4). The phenate salt may be stabilized by forming the sulfate ester. These stabilized, water-soluble salts of vat dyes, such as C.I. Solubilised Vat Blue 1 (5), are commercial products. 

The chemistry associated with the vatting process is illustrated in Fig. 13.24. For the reduction step, a mixture of sodium hydroxide (caustic) and sodium hydrosulfite (hydro, Na2S204) is used. Depending upon the amount of caustic and hydro employed one or both of the anthraquinone rings may undergo reduction. 

Although some liquid foods, such as beer and fruit juices, may be pasteurized after filling containers (with warm water or steam applied to raise the temperature appropriately), most are pasteurized in a vat process or a continuous-flow process and then packaged. The vat (or batch) process involves heating in a well-agitated tank for the required time... 

Which available method of application is suitable for the designed component (vat process, barrel process, brush plating, chemical reduction, etc.) ... 

Photopolymer vat processes involve selective curing of predeposited photopolymers using some type of light source. Stereolithography, the first patented and commercialized AM process, works by scanning a laser across the surface of a vat of photopolymer. A platform is raised to just one layer thickness below the surface of the liquid. The laser scans the first cross-sectional layer, attaching the layer to the platform. The platform is lowered within the vat one layer thickness... 

ZnS204. Made SO2 on aqueous suspension of Zn dust. Used in bleaches and the vat dyeing process. 

The type of floe requited depends on the separation process which foUows, eg, rotary vacuum filtration requites evenly sized, smaU, strong floes that capture ultrafines to prevent cloth blinding and cloudy filtrates. The floes should not be subject to sedimentation in the vat or breakage by the agitator. 

Percolation Leaching. Ground material coarse enough to permit circulation of a solution through a bed of particles can be leached by percolation of the solvent through the material placed ia a tank or vat. The process usually takes several days. 

From an appHcations point of view, the sulfur dyes are between vat, direct, and fiber-reactive dyes. They give good to moderate lightfastness and good wetfastness at low cost and rapid processing (see Dyes, application and evaluation). 

The manufacturing process of anthraquinone vat dyes is more compHcated, and, in the extreme case of Cl Vat Blue 64 [15935-52-1] (12) (Cl 66730), requites 11 steps starting from phthaUc anhydride. 

Dihydroxyanthraquinone. This anthraquinone, also known as quinizarin [81-64-1] (29), is of great importance in manufacturing disperse, acid, and vat dyes. It is manufactured by condensation of phthalic anhydride (27) with 4-chlorophenol [106-48-9] (28) in oleum in the presence of boric acid or boron trifluoride (40,41). Improved processes for reducing waste acid have been reported (42), and yield is around 80% on the basis of 4-chlorophenol. 

Diaminoanthraquinone is an important intermediate for vat dyes and disperse dyes, and is prepared by oxidizing leuco-l,4-diaminoanthraquinone with nitrobenzene in the presence of piperidine. An improved process has been reported (45). 

Cl Vat YeUow 12 is prepared by condensing l-anaino-5-ben2oylaininoanthraquinone [117-06-6] (161) with oxalyl chloride in nitroben2ene. Cl Vat YeUow 33 is prepared by condensation of two moles of 1-aminoanthraquinone with one mole of 4V -a2obis(4-biphenylcarbonyl chloride). Cl Vat Red 21 is prepared from 1,4-diaminoanthraquinone (33) and l-nitroanthraquinone-2-carboxyhc acid (58) by the foUowing process ... 

Anthraquinone dyes have been produced for many decades and have covered a wide range of dye classes. In spite of the complexity of production and relatively high costs, they have played an important role in the areas where excellent properties ate requited, because they have excellent lightfastness and leveling properties with brUhant shades that ate not attainable with other chtomophotes. However, recent increases in environmental costs have become a serious problem, and future prospects for the anthraquinone dye industry ate not optimistic. Some traditional manufacturers have stopped the production of a certain dye class or dye intermediates that were especially burdened by environmental costs, eg, vat dyes and their intermediates derived from anthraquinone-l-sulfonic acid and 1,5-disulfonic acid. However, several manufacturers have succeeded in process improvement and continue production, even expanding their capacity. In the forthcoming century the woddwide framework of production will change drastically. 

Most vat dyes are based on the quinone stmcture and are solubilized by reduction with alkaline reducing agents such as sodium dithionite. Conversion back to the insoluble pigment is achieved by oxidation. The dyes are appHed by either exhaust or continuous dyeing techniques. In both cases the process is comprised of five stages preparation of the dispersion, reduction, dye exhaustion, oxidation, and soaping. 

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