Super critical fluid dyeing

Supercritical FluidA supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist.. In addition, close t

Evaporate Curve

Gas

Super Cretical Fluid Dyeing Machine

Prepared By : Mazadul Hasan sheshir ID: 2010000400008

13th Batch (session 2009-2013) Department : Wet Processing Technology Email: mazadulhasan@yahoo.com

Blog : www Textilelab.blogspot.com (visit)

Southeast University

Department Of Textile Engineering I/A 251,252 Tejgaon Dhaka Bangladesh

Prepared By :

Total Textile Process at a Glance

The textile industry is believed to be one of the biggest consumers of water In conventional textile dyeing, large amounts of water are used both in terms of intake of fresh water and disposal of wastewater On average, an estimated 100–150 litres of water is needed to process 1 kg of textile material, with some 28 billion kilos of textiles being dyed annually Water is used as a solvent in many pretreatment and finishing processes, such as washing, scouring, bleaching and dyeing

Hence, the elimination of process-water and chemicals would be a real breakthrough

for the textile dyeing industry, and it seems this has now come to fruition , with the

launch of the world’s first ever industrial dyeing machines that uses super carbon dioxide (CO2) as a replacement for water The manufacturer behind thissystem is the Dutch company, DyeCooTextile Systems BV Years of extensiveresearch and development has goneinto producing the novel, completelywater-free dyeing process which hasconsiderable lower operational costscompared to conventional dyeingprocesses.

‘The principle of dyeing with CO2 was invented in Germany twenty-five years ago Developing a well functioning machine, however, turned out to be too expensive.’ DyeCoo Textile Systems’ parent company, Feyecon, began tackling this issue ten years ago in partnership with the Delft University of Technology and Stork This ultimately resulted in DyeCoo (which was formed in 2008), which literally means dyeing with CO2

Different between conventional & supercritical CO2 dyeing

Supercritical Fluid

A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist It can effuse(spill,shed) through solids like a gas, and dissolve materials like a liquid

In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned" Supercritical fluids are suitable as a substitute for organicsolvents in a range of industrial and laboratory processes Carbon dioxide and water are the most commonly used supercritical fluids, being used for decaffeination and power generation, respectively.

Properties

Solvent

Molecular weight

Critical temperature

Critical pressure

Critical density

Carbon dioxide (CO2) 44.01 304.1 7.38 (72.8) 0.469 Water (H2O) (acc

shows density, diffusivity and viscosity for typical liquids, gases and supercritical fluids

Comparison of Gases, Supercritical Fluids and Liquids

Density (kg/m3)

Viscosity (

µPa∙s)

Diffusivity (mm²/s)

Supercritical Fluids

100–1000 50–100 0.01–0.1

Liquids 1000 500–1000 0.001

In addition, there are:

• No surface tension in a supercritical fluid

•No liquid/gas phase boundary

• By changing the pressure and temperature of the fluid, can be "tuned" to be more

liquid- or more gas

• Soluble in material in the fluid

• Solubility in a supercritical fluid tends to increase with density of the fluid (at

constant temperature)

•Density increases with pressure, solubility tends to increase with pressure

•Relationship with temperature is a little more complicated

• At constant density, solubility will increase with temperature

All supercritical fluids are completely miscible with each other so for a mixture a single phase can be guaranteed if the critical point of the mixture is exceeded The critical point of a binary mixture can be estimated

as the arithmetic mean of the critical temperatures and pressures of the two components,

Tc(mix) = (mole fraction A) x TcA + (mole fraction B) x TcB.

For greater accuracy, the critical point can be calculated using equations of state, such as the Peng Robinson, or group contribution methods Other properties, such as density, can also be calculated using equations of state.

Supercritical Carbon Dioxide(CO2)

Carbon dioxide is a readily available, cheap, recyclable and is toxic and flammable Above the temperature of 31.6 oC and pressure of 73 atm carbon dioxide exhibits physical properties, which are intermediate between those of gases and liquids

non-These conditions are called supercritical conditions and are readily achievable using commercially available equipment Supercritical carbon dioxide is able to dissolve a range of chemical substances including organic substrates, catalysts, and light gases Its main advantage however comes from the fact that this solvent can be easily turned into a gas by simply releasing the pressure leaving no solvent residues and requiring

no evaporation or separation

Benefits

• Applied a clean solvent

• Improved control and fine-tuning of process

• Developed a remarkably selective synthetic process

• Minimised waste & Increased atom utilization

• Minimised handling and purification procedures

Supercritical Carbon Dioxide(CO2)

Supercritical Carbon Dioxide(CO2)

Phase diagram

Figure: CO2 pressure-temperature & density-pressure phase diagram

Investigation of Dye-Fiber Reactions in SC-CO2

Chemistry of Dyes

•Reactive dyes for cotton, rayon, silk, and wool form stable chemical links with textile materials

to produce colored fabrics with excellent overall fastness, other dyestuffs only form loose bonds with fibers (VS-dye)

•Acetate, nylon, and polyester fibers colored with dispersed dyes retain their color even after repeated exposure to sunlight and washing (ES-dye)

Conventional aqueous-based dye-fiber reaction

Investigation of Dye-Fiber Reactions in SC-CO2

Dye-Fiber Reaction in SC CO2

Sulfonyl-azo-dyes

Dyeing Procedure

Dyeing Procedure

1 Add fiber and dye to vessel

2 Pressurize system (with CO2) up to 800 psi and stir at approximately 850 rpm

3 Heat to required temperature (100 -180 ºC)

4 Pressurize to 3500 psi; hold for 2 hours

5 Release pressure, remove fabric

Dyeing Procedure

CO2 Dyeing System

(1) Gas cylinder of CO2,

(2) High pressure pump,

(3) Autoclave reactor vessel with stirrer, V = 1000 ml,

(4) Circulation pump- acquisition in future

(5) Electrical heating jacket

1

4 5

Dyeing Procedure

High Pressure Batch Reactor

Testing Dye-Fiber Reaction

Dyeing Procedure

• Measure color strength (K/S) of each dyed fiber

•Wash fiber with acetone (remove surface dye)

• Conduct soxhlet extraction using ethyl acetate (to remove unreacted dye)

• Compare effect of vinylsulfone reactive group on dye fixation

Results

Dyeing Procedure

Comparison of Dyed Fabrics

Dyeing Procedure

Initial Conclusions

•Color depth improved with increasing temperature

•Strong evidence for dye-fiber bond formation using vinylsulfone-based dye on nylon and wool

•ES-dyeing on wool fibers showed extremely low color yields after extraction (no reaction)

•94% fixation at 180 oC/ 3500 psi on wool

Dyeing Procedure

Dyeing polyester with disperse dyes in supercritical CO2

Supercritical fluids are highly compressed gases which possess valuable properties of both a liquid and gas Any gas above its critical temperature retains the free mobility of the gaseous state but with increasing

pressure its density will increase towards that of a liquid The properties which are intermediate between gases and liquids are controlled by pressure.

Other attributes of carbon dioxide are

•It is virtually an inexhaustible resource (atmosphere, combustion processes, and natural geologic deposits)

•It is not only biodegradable as a nutrient promoting the growth of plants, but is an essential element of natural processes

•It does not affect the edibility of foodstuffs and will only have toxic effects at extremely high concentrations

•It has no disposal problems It is recovered from the process in the form of an uncontaminated gas and can be reused

•It is easy to handle and combustible

•It has a critical point within the range which is readily manageable by technical means (31C and

73 bar)

•It is non-toxic, non-hazardous and low cost

•It is nonflammable and non-corrosive

Both economic and ecological

Having a low critical temperature

Disadvantage

Investment

Solve colorants

Time of process

Dyeing Procedure

Supercritical CO2dyeings were performed using an SFE 400 supplied by SUPELCO, equipped with

a 50 cm3 internal volume vessel The operating pressure could be set up to 6000 psi, managed

in 100 psi increments The oven temperature range (30±2000C) was controlled at 100C increments The polyester fabrics (1 g) were suspended on a stainless steel net inside the vessel and the solid, pure dye was placed on the bottom of the vessel A ratio of 1.5% dye omf was used When the system reached the desired temperature and pressure, the liquid was let into the vessel After 30 min under constant conditions, the system was expanded to atmospheric pressure and the dry samples were removed Dyeings in aqueous medium were produced also

in which polyester samples were dyed in a thermostatted bath (Linitest) using a 40:1 liquor ratio, at 1200C for 1 h (1.5% omf pure dye, 0.25% omf Na2SO4, 0.5% omfDispersogen-A, 40% omfLenol-O); Dispersogen-A and Lenol-O were Hoechst auxiliary products 2.4

Dyeing of polyester

Dyeing Procedure

“When carbon dioxide is heated to above 31°C and pressurised to above 74 bar, it becomes supercritical, a state of matter that can be seen as an expanded liquid, or a heavily compressed gas In short, above the critical point, carbon dioxide has properties of both a liquid and a gas In this way supercritical CO2, has liquid-like densities, which is advantageous for dissolving hydrophobic dyes, and gas-like low viscosities and diffusion properties, which can lead to shorter dyeing times compared to water Compared to water dyeing, the extraction of spinning oils, the dyeing and the removal of excess dye can all be carried out in one plant in the carbon dioxide dyeing process which involves only changing the temperature and pressure conditions; drying is not required because at the end of the process CO2 is released in the gaseous state The CO2 can be recycled easily, up to 90% after precipitation of the extracted matter in a separator.” To read more about supercritical fluid dyeing technology

Dyeing with CO2

Dyeing Procedure

Fastness assessment

1 Wet fastness was determined according to UNI 7638 (ISO 105-C 01/03/04)

2 For the determination of fastness to artificial light, a Xenotest Hanau 150S (Heraeus)

3 apparatus was employed, equipped with a 1500 W xenon arc lamp,

4 according to UNI 7639 (ISO 105-B02)

Dyeing Procedure

Dyeing Conditions

Extraction vessel: 40 Liter

Fiber: 4 PET Packages

Dye: C.1 Disperse Blue 79 Pressure: 4200 psi

Temperature: 120ºC

CO2 Recirculation: 5 Kgs/min

Dye time: 40 minutes

The results show that the concentration of dye absorbed by the fibre increased initially on increasing the pressure to 3500 psi, but was practically constant between 3500 and 4000 psi Similar results were obtained when the study was carried out at 100 and 1200C The data reported in

Fig 1 Variations in dye uptake (Df) by the fibre as a function of pressure at constant temp(800C).

Results

Table 1 Variation in dye uptake by the fibre as a function of pressure at constant temp (1000C)

Fiber from the dyed packages was woven into a “sock” and evaluated for uniformity

1.In conventional method of dyeing textiles undergo multiple processes.

2 In these processes water, dyes, and other auxiliaries are used to enhance the efficiency of dyeing process.

3 After dyeing a subsequent drying process with high energy consumption is necessary

4.The cost of waste water treatment and of arranging water of acceptable

quality is becoming serious concerns Either the water available is too hard or not available in sufficient amount or therefore dyeing plants cannot be set up at some places.

5.By using scCO2 dyeing machine we can overcome all these problems of

conventional machine.

Problems with Conventional Water-Dyeing Machine

Problems

1 Elimination of usage of water, water treatment and water pollution

2 Elimination of a drying step, thus reduces energy cost

3 Elimination of auxiliaries, such as, dispersing agent, leveling agent

4 Rapid diffusion and potential for high degree of dye exhaustions

5 Dyeing occurs with high degree of levelness

6 No after treatment is required

7 Time required for dyeing is very less

8 Gives good rubbing fastness

9 Dyeing houses may be started on sites where there is water scarcity

10 No air pollution due to recycling of CO2 is accomplished

11 Economical and environmentally friendly

Advantages of scCO2 Dyeing Machine

1 Initial investment is high.

2 High pressure and high temperature are required for dye solubility during the

process.

3 It is a batch process So processing of long length fabric (continuous) is not

possible.

4 During polyester dyeing, the trimer is produced This is removed using aqueous

cleaning waterless scCO2 as a problem to eliminate.

5 There is little data available about dyestuff solubility in scCO2.

6 At present, scCO2 dyeing is confined to synthetic fibers.

Disadvantages/Limitations

Benefits of scCO2 M/C over Conventional M/C: An Overall Comparison

Conventional Water-Dyeing Dyeing in Supercritical CO2

High volume of water required Completely avoids the use of water

Produces huge effluent No waste water at all

Wastage of valuable dyestuffs Unreacted dye remains as powder

Requires huge chemicals and auxiliaries No need for dispersing and leveling agents

High energy requirements Requires only 20% energy of conventional

dyeingDyeing, washing and drying times are 3-4

hours per batch

Only 2 to 2.5 hours per batch

Drying is required after dyeing process Not required as CO2 is released in gaseous

stateAfter treatment is a compulsory step No after treatment is required

Water treatment (ETP) and recycling is

difficult and costly

CO2 can be easily recycled upto 95%

Dyeing factory need to establish where

water is sufficiently available

Dyeing factory can be established where water is not available

Overall cost comparing to scCO2 is high Machine cost is high

The machine is not suitable for dyeing natural (hydrophilic) fibers in its current

arrangement For natural fibers the diffusion of scCO2 is hampered by its inability to break the hydrogen bonds present in many natural fibers, including cotton, wool and silk A further problem is that reactive dyes, direct dyes and acid dyes which are

suitable for dyeing of natural fibers are insoluble in scCO2 and also dye may be

damaged at such high pressure and temperature However, Investigators are trying to find out a solution for dyeing natural fibers in scCO2 Some possible approaches are chemically treating/modifying the fiber before dyeing or using improved dyestuffs, such as, disperse reactive dye.

Challenges