Indian Dyestuff Industry


Most of these industries are batch processes. These industries produce around 90,000 tons of dyes, out of which 10% is exported. Covering coastal areas of Maharashtra and Gujarat, these industries are located majorly in the belt of Ahmedabad to Chiplun. Coastal areas are preferred since these processes are water-intensive.


Other than water, the most common substance used in the dye industry is common salt. Why is this common salt a concern to us? Common salt if present in huge amounts in the effluent of these industries, can render good land to a barren one. Not to mention its corrosive power.

The E-factor of this industry is 50.

The total world market for dyes is a whooping 7 billion with a 2% growth rate. This growth rate is highly evident in populated nations like Asia. Dystar is one of the largest manufacturers of dyes.

Like any other industry, the dye industry faces issues like:

  • water pollution
  • air pollution
  • land pollution
  • waste management
  • health and safety

In places like Ankaleshwar, Mahad, Parshuram, some parts of Dombivali, air pollution in monsoon is highly visible. For a person with asthma, these places can prove fatal. It is not just India, but China too, both have profound demographics.

So, what is the world doing about this?

Read more about how companies like the ones below, are developing green technologies to tackle water abuse in this article.


Green chemistry and catalysis

Catalysis helps us:

  • reduce reaction time, which in turn saves energy
  • selectively carry out parallel reactions, which again saves time and money required for separation of the side-products. Some side-products are harmful and dangerous. So it also keeps us safe.
  • replace stoichiometric reagents with catalytic amounts of a substance, which helps us save resources and money. Some stoichiometric reagents are harmful and also create problems due to its existence. For example, aluminum chloride is a reagent used in Friedel–Crafts reaction, is a highly corrosive substance and also ends up acidifying the waste stream. Separation of AlCl3 is lengthy and expensive and it cannot be recycled due to its corrosive nature. A greener alternative for this can be explained with an example. Catalytically effective amount of a mixture of bismuth tri-halide and of perfluoroalkanesulfonic acid can be used for sulfonation reactions instead of AlCl3.

By and large, catalysts are a way to make a reaction go green. But, if one can find a way to turn a reaction greener without using a catalyst, even better. How can one do that? Alternative energy options such as microwave and ultrasound often can help us carry out reactions without using a catalyst or a solvent.

Ionic liquids are a fairly new class of catalysts. A part of the research community is cautious about using them as catalysts. Even though they are non-volatile unlike common solvents, they can be hazardous. From cradle to grave approach, that is from synthesis to its disposal, these can prove to be extremely harmful to us and the environment. Are they?

Read more:

Ionic liquids: green or not green?

Thermal Safety of Ionic Liquids

What the industry needs

What is needed for an industrial catalyst?

  1. High stability
  2. High selectivity
  3. Activity
  4. Ease of availability

I did not say high activity, since the kind of activity needed depends on the application. A highly active catalyst can affect the selectivity. Also, if the activity is lower than needed, it can be elevated using promoters.

A catalysts loses all this due to the following reasons:

  1. Poisoning
  2. Coking
  3. Decomposition

Catalysts if reusable, can undergo wear and tear due to the above mentioned reasons. Poisoning can occur due to impurities in the product streams, or the products itself can poison it. Sulfur is a notorious catalyst poison. It haunts the petroleum industry. It bonds to the active sites of the catalyst. Oxygen and water, are catalysts poisons for iron catalyst in ammonia synthesis.

Selective poisoning is deliberate poisoning of highly active catalysts that are so active that they catalyze undesired side reactions. Lindlar’s catalyst is one such example. Lindlar’s catalyst is a palladium catalyst poisoned with traces of lead and quinoline, that reduce its activity such that it can only reduce alkynes, not alkenes.

Coke is what gets deposited on a catalyst during oil refining. It deactivates it. The catalyst can be reactivated by burning it off.

Catalyst deactivation due to coke formation is an important technological and economic problem in petroleum refining and in the petrochemical industry. Remedies to catalyst deactivation are sought by a variety of strategies involving modification of catalyst surface composition such as the use of polymetallic catalysts and/or by manipulation of the reaction environment which often limits the yield due to thermodynamic constrains (i.e., high hydrogen pressures, etc.). In the limit, when the activity reaches unacceptable limits, regeneration by burning off carbon residues can usually be attained, Regeneration can take place in situ, as in fixed-bed reactors, or in an adjacent reactor to which the catalysts is transported to, such as in moving-bed reactors or in fluidized-bed reactors. In the first case intermittent operation is required, whereas in the second case the operation is continuous, but a second regeneration reactor is required. The choice of the proper process cycle is an economic optimization problem constrained by catalysts cost, operational and regenerational cost, and by the value of the final product [1–5]. Process optimization under catalyst decay is an engineering problem that requires a knowledge of the catalyst deactivation kinetic. – E. E. Wolf & F. Alfani, Catalysis Reviews: Science and Engineering, Volume 24, Issue 3, 1982

Decomposition of a catalyst occurs when it is exposed to temperatures it cannot handle. It renders it thermally, structurally and chemically unstable.


Deactivation mechanisms: A) Coke formation, B) Poisoning, C) Sintering of the active metal particles, and D) Sintering and solid-solid phase transitions of the washcoat and encapsulation of active metal particles (cf. Suhonen 2002).

(Image: Oulu University Library)

Although regenerating a catalyst brings it back to life, but in due course it keeps losing its activity bit by bit if not entirely, which is when it is eventually replaced. A catalyst, like diamond, is not forever. The worth of the catalyst can be found by knowing its TOF and TON.

TOF is its turn over frequency and TON is its turn over number.

TOF is the amount of reactions per unit time occurring at the reaction center.

TON is TOF upto the death of the catalyst, which can be shown numerically as follows:

TON = TOF * lifetime of the catalyst

What is a catalyst?

There, in your mouth, there is a catalyst at work, that accelerates the rate of digestion of the food you eat. It has a pretty name called ‘ptyalin‘. Without it, the starch in your food would take, I don’t know how long, to get hydrolyzed to glucose. This catalyst resides in the human saliva.  It is one of the many different enzymes that are present in our bodies. Enzymes are nature’s catalysts.

Coming to industrial catalysts, a catalyst increases (accelerates) the rate of reaction without affecting the equilibrium. It does take part in the reaction, it forms some kind of a complex with the reactants, but is regenerated again.


(Image: Industrial Catalysis: A Practical Approach, Second Edition. Jens Hagen)

You can read Industrial Catalysis: A Practical Approach, Second Edition, by Jens Hagen. Excellent book.

The books says that there is still no fundamental theory of catalysis. To date there has been no standard book that deals equally with hetero and homo catalysis, as well as industrial aspects thereof.

The book also says that apart from accelerating reactions, catalysts have another important property, they can influence the selectivity of chemical reactions. How? We’ll see that in other posts.

In general, catalysts are used for industrial synthesis, in biological applications and environmental protection. Industrial applications include the chemical industry (dyes and pigments, agrochem, pharmaceuticals, fine chemicals etc.) and the petroleum industry.

Talking about money, market of heterogeneous catalysts is 80 percent while that for homogeneous catalysts is 20 percent. Why? Well, as the definition of heterogeneous catalysts goes, they can be easily separated from the reaction mixture.

Read more:

Science: Explaining Nature’s Catalysts


Chemical treatment of wastewater


“Pollution is nothing but the resources we are not harvesting. We allow them to disperse because we’ve been ignorant of their value.” – R. Buckminster Fuller

Chemicals are used during wastewater treatment in an array of processes to expedite disinfection. These chemical processes, which induce chemical reactions, are called chemical unit processes, and are used alongside biological and physical cleaning processes to achieve various water standards. There are several distinct chemical unit processes, including chemical coagulation, chemical precipitation, chemical oxidation and advanced oxidation, ion exchange, and chemical neutralization and stabilization, which can be applied to wastewater during cleaning.

Wastewater Chemical Treatment

Chemical Precipitation

Chemical precipitation is the most common method for removing dissolved metals from wastewater solution containing toxic metals. To convert the dissolved metals into solid particle form, a precipitation reagent is added to the mixture. A chemical reaction, triggered by the reagent, causes the dissolved metals to form solid particles. Filtration can then be used to remove the particles from the mixture. How well the process works is dependent upon the kind of metal present, the concentration of the metal, and the kind of reagent used. In hydroxide precipitation, a commonly used chemical precipitation process, calcium or sodium hydroxide is used as the reagent to create solid metal hydroxides. However, it can be difficult to create hydroxides from dissolved metal particles in wastewater because many wastewater solutions contain mixed metals.

Chemical Coagulation

This chemical process involves destabilizing wastewater particles so that they aggregate during chemical flocculation. Fine solid particles dispersed in wastewater carry negative electric surface charges (in their normal stable state), which prevent them from forming larger groups and settling. Chemical coagulation destabilizes these particles by introducing positively charged coagulants that then reduce the negative particles’ charge. Once the charge is reduced, the particles freely form larger groups. Next, an anionic flocculant is introduced to the mixture. Because the flocculant reacts against the positively charged mixture, it either neutralizes the particle groups or creates bridges between them to bind the particles into larger groups. After larger particle groups are formed, sedimentation can be used to remove the particles from the mixture.

e.g. Alum and ferric (or ferrous) sulphate are examples of inorganic coagulants.

The optimum pH for alum treatment is 6 to 7 while that for Iron(III)sulfate is 6 to11. Therefore if the pH of wastewater is say 8, we have to use the latter one or neutralize the wastewater to get the pH to 6 or 7 and then use alum, whatever works.

Chemical Oxidation and Advanced Oxidation

With the introduction of an oxidizing agent during chemical oxidation, electrons move from the oxidant to the pollutants in wastewater. The pollutants then undergo structural modification, becoming less destructive compounds. Alkaline chlorination uses chlorine as an oxidant against cyanide. However, alkaline chlorination as a chemical oxidation process can lead to the creation of toxic chlorinated compounds, and additional steps may be required. Advanced oxidation can help remove any organic compounds that are produced as a byproduct of chemical oxidation, through processes such as steam stripping, air stripping, or activated carbon adsorption.

Ion Exchange

When water is too hard, it is difficult to use to clean and often leaves a grey residue. (This is why clothing washed in hard water often retains a dingy tint.)  An  ion exchange process can be used to soften the water. Calcium and magnesium are common ions that lead to water hardness. To soften the water, positively charged sodium ions are introduced in the form of dissolved sodium chloride salt, or brine. Hard calcium and magnesium ions exchange places with sodium ions, and free sodium ions are simply released in the water. However, after softening a large amount of water, the softening solution may fill with excess calcium and magnesium ions, requiring the solution be recharged with sodium ions.

Chemical Stabilization

This process works in a similar fashion as chemical oxidation. Sludge is treated with a large amount of a given oxidant, such as chlorine. The introduction of the oxidant slows down the rate of biological growth within the sludge, and also helps deodorize the mixture. The water is then removed from the sludge. Hydrogen peroxide can also be used as an oxidant, and may be a more cost-effective choice.

Reference: Thomasnet

Biological treatment of wastewater


“Don’t forget that the flavors of wine and cheese depend upon the types of infecting microorganisms.” – Martin H. Fischer

Biological treatment aka secondary treatment:

In wastewater treatment, the treatment process that follows primary treatment. It is used to remove the remaining organic solids that have not been removed in primary treatment together with the 90% or more of the dissolved organics. Aerobic biological treatment is commonly used. Secondary treatment may also incorporate nitrification and biological phosphorus removal.

Reference: Dictionary of waste and water management, Elsevier

Secondary treatment, usually biological, tries to remove the remaining dissolved or colloidal organic matter. Generally, the biodegradation of the pollutants is allowed to take place in a location where plenty of air can be supplied to the microorganisms. This promotes formation of the less offensive, oxidized products. Engineers try to design the capacity of the treatment units so that enough of the impurities will be removed to prevent significant oxygen demand in the receiving water after discharge.

There are two major types of biological treatment processes:

  1. attached growth
  2. suspended growth

In an attached growth process, the microorganisms grow on a surface, such as rock or plastic. Examples include open trickling filters, where the water is distributed over rocks and trickles down to underdrains, with air being supplied through vent pipes; enclosed biotowers, which are similar, but more likely to use shaped, plastic media instead of rocks; and so-called rotating biological contacters, or RBC’s, which consist of large, partially submerged discs which rotate continuously, so that the microorganisms growing on the disc’s surface are repeatedly being exposed alternately to the wastewater and to the air. The most common type of suspended growth process is the so-called activated sludge system. This type of system consists of two parts, an aeration tank and a settling tank, or clarifier. The aeration tank contains a “sludge” which is what could be best described as a “mixed microbial culture”, containing mostly bacteria, as well as protozoa, fungi, algae, etc. This sludge is constantly mixed and aerated either by compressed air bubblers located along the bottom, or by mechanical aerators on the surface. The wastewater to be treated enters the tank and mixes with the culture, which uses the organic compounds for growth– producing more microorganisms– and for respiration, which results mostly in the formation of carbon dioxide and water. The process can also be set up to provide biological removal of the nutrients nitrogen and phosphorus. Refer to Figure 1 for a simplified process flow sheet.


Reference: Handbook of Waste water treatment technologies by Nicholas Cherimisinoff

Some people are rather skeptical when it comes to biological treatment. Here’s why:

  • Slow rate of treatment
  • Large volumes require more floor area
  • Often needs engineered microorganisms which translates into shelling out a lot of money

Read more: