Waste Management – SWM Rules, EWM Rules, etc

What is Pyrolysis?

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Pyrolysis

Mains level : Not Much

Plastic from used personal protective equipment (PPE) can be transformed into renewable liquid fuels using chemical a process called pyrolysis, says a new study.

Try this PYQ:

Q.In the context of which one of the following are the terms ‘pyrolysis and plasma gasification’ mentioned? (CSP 2019)

(a) Extraction of rare earth elements

(b) Natural gas extraction technologies

(c) Hydrogen fuel-based automobiles

(d) Waste-to-energy technologies

What is Pyrolysis?

  • Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere.
  • It involves a change in chemical composition. The word is coined from the Greek-derived elements pyro “fire” and lysis “separating”.
  • It is most commonly used in the treatment of organic materials. It is one of the processes involved in charring wood.
  • It is considered as the first step in the processes of gasification or combustion.

How does it work?

  • In general, pyrolysis of organic substances produces volatile products and leaves a solid residue enriched in carbon, char.
  • Extreme pyrolysis, which leaves mostly carbon as the residue, is called carbonization.
  • The process is used heavily in the chemical industry, for example, to produce ethylene, many forms of carbon, and other chemicals from petroleum, coal, and even wood, to produce coke from coal.

Applications

  • Aspirational applications of pyrolysis would convert biomass into syngas and biochar, waste plastics back into usable oil, or waste into safely disposable substances.

Limitations and Concerns

  • The technology requires drying of soil prior to treatment.
  • Limited performance data are available for systems treating hazardous wastes containing polychlorinated biphenyls (PCBs), dioxins, and other organics.
  • There is concern that systems that destroy chlorinated organic molecules by heat have the potential to create products of incomplete combustion, including dioxins and furans.
  • These compounds are extremely toxic in the parts per trillion range.
  • The molten salt is usually recycled in the reactor chamber. However, depending on the waste treated (especially inorganics) and the amount of ash, spent molten salt may be hazardous and require special care in disposal.
  • Pyrolysis is not effective in either destroying or physically separating inorganics from the contaminated medium.
  • Volatile metals may be removed as a result of the higher temperatures associated with the process, but they are not destroyed.
  • When the off-gases are cooled, liquids condense, producing an oil/tar residue and contaminated water.
  • These oils and tars may be hazardous wastes, requiring proper treatment, storage, and disposal.
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