Chemical Engineering Around the House

     When I was thinking about writing this article, I was standing in my kitchen looking for a snack.  On the counter I noticed a water bottle that my wife had washed that evening.  After rinsing it with hot water, she placed on the cap back onto the bottle.  The appearance of the bottle reminded me of an important lesson that chemical engineers have learned over the years.  I read many reports of large chemical processing vessels collapsing after being cleaned with steam.  Usually, the cause of the incident was that the operator sealed the vessel too soon after cleaning.  If all of the steam has not yet condensed and the vessel is sealed, the pressure inside the vessel will decrease (below atmospheric pressure) as the steam condenses.  Essentially, a vacuum is formed as the volume of the water vapor decreases.  The same mechanism is what caused the plastic bottle to "suck in".  As the water cooled and condensed, the pressure inside the bottle decreased and atmospheric pressure pushed the sides of the bottle inward.  A simple, yet important lesson for engineers.  Many tanks and process vessels have been destroyed by this action.  You can see the bottle on the left and you can imagine the price to be paid for destroying a full sized process vessel (such as the one shown below).

     Another item caught my eye in the kitchen that evening.  A simple plastic soda bottle.  Many people don't realize that these bottle are made of polyester!  Yes, the same material that the famed leisure suit was fabricated from.   Polyester is manufactured in large scale chemical plants just like most chemicals.   At the end of the process, the plastic is cut into tiny chips as shown on the right.  These plastic chips are then sold to companies that use a process called injection molding to make bottle preforms.  The preforms are then packaged and sold to bottlers of the end products whether it be soda or something else.  The bottler uses a technique called blow molding to inject hot gas into the preform and "blow" it out the final size.  Below, I've shown a couple of preforms and the final bottle size that we're all familiar with.

     Finally, I noticed the water filter on our kitchen sink.   This filter contains one of the oldest filtration medias known to chemical engineers....activated carbon.  Via a process called adsorption, small particles adhere to the activated carbon as the fluid passes through the filter.   Chemical engineers have long used activated carbon to purify liquids and gases.   Perhaps the most common application in use today in the chemical industry is the use of carbon to remove tiny particles from gas streams before they are released to the atmosphere.  Without the activated carbon, these particles could make the surrounding area a very unpleasant place to live or work.  Below, I've shown our small carbon filter and an industrial size vessel filled with activated carbon.

     Showing people that chemical engineering touches their lives everyday is easy.  From plastic bottles to activated carbon filter, you can find many more examples.  It's also important to note that chemical engineers can also learned some things from the home as is evident with the collapsing water bottle.  Maybe the industrial world and world that we call "home" aren't so different after all.

By: Christopher Haslego, Owner and Chief Webmaster (read the author's Profile)
chris.haslego@cheresources.com