Plastics & Microplastic Particles from Marcellus Shale Resources

Plastics & Microplastic Particles from Marcellus Shale Resources

Article by S. Tom Bond, Retired Chemistry Professor & Resident Farmer, Lewis County, WV
 
The unnatural world of today’s humans, discussed in my last article, involves use of starting materials which are degraded so they can not be reused.  These include both inorganic and organic materials.  They include something that is degrading the biological world that most of us have not heard of.  Today, in place of wood, which readily biodegrades, and metals, we use of materials made from hydrocarbons, which we call plastic, for many common items.
 
These plastics are expected to break up into small pieces as the result of the UV radiation in sunlight.  They don’t have chemistry susceptible to being broken down to molecular size as microbes do, but remain at a size barely visible and a little above for a very long time.  This removes any physical problems which would result from them being large chunks, sheets or fibers. but cause a particular set of problems on their own.
 
Before getting to the problems, lets say more about the chemistry of plastics.  Some of the many kinds by formula can be made from oil and coal, but the preferred “feedstock” is a derivative of natural gas.  As you probably know, natural gas is primarily methane, CH4.  What comes up the well in many places is called “wet gas” and includes other compounds, C2H6, ethane, C3H6, propane (yes, that propane), and butanes, C4H10.  These compounds are gases, which from butane in reverse order to methane can be liquefied by more and more pressure and cooling.  There may also be some pentane, C5H12 and larger, related compounds.  These are liquids, which may be considered as evaporated into the lighter gases, but are present in small quantities.  Compressing and cooling are used to separate these compounds.
 
Ethane and separately, propane, are put through a “catalytic cracker”  (“cracker” for short), to produce ethylene and propylene and hydrogen.  This leaves a more reactive “double bond,” in the carbon compounds, so the products can form a huge variety of different compounds when added to other simple molecules, like H2O, HCl, and styrene, which can then be converted to plastics, typically having very large molecules.  In bulk these molecules can be formed into three dimensional items, sheets and fibers.
 
This is why “wet” gas rather than dry gas is so eagerly sought.
 
Unfortunately, petroleum based plastics can not be decomposed by microbes, like biological molecules.  Many of them break down to small size pieces as a result of UV in sunlight, and, if on the surface, mix in and escape notice.  These little pieces are almost immortal, though.
 
The problem is they are ingested by small animals and disrupt their life cycle.  This happens in the sea with small animals which are the base of the food chain for larger fish and some larva of fish.  These creatures ingest the microplastic particles like their ordinary food, some of them in preference to their usual food.  They lack nourishment, and some are affected mechanically in their gut so they die.  The effect is to reduce the fish population, including food fish,  and some incorporation of the microplastic particles in fish  and animals higher up the chain.
 
The same thing happens on land with small creatures which live in the soil, but this does not seem to have the significance it does in the sea.  Plastics beyond the reach of sunlight in the soil are almost immortal.  Huge deposits, almost geological in extent, of our rejected materials are bing built in almost every county in the United States and other developed country, and also in less developed countries, because these materials are so cheap and handy.
 
This doesn’t exhaust the problems with plastics.  The old human habit of carelessly discarding used materials, which goes back beyond the stone age, means many of us even where proper disposal methods are available toss plastics by the roadside and in streams.  While the UV acts on this litter they uglify the roadsides and streams.  What goes into streams washes down stream, some producing greater litter when it catches in brush along the water, floating behind dams and the like, catching along shore when flood waters go down, and so forth.   Many beaches are notoriously trashy from plastic that washes in from the sea.
 
So what is the answer?  Public awareness and making the light strong materials we need from natural sources.  It is pretty hard to make a dent on the habits of some people.  Littering laws are in place, but law enforcement requires a designated officer to catch the individual.  Draconian punishments for the rare culprit caught don’t work.  It requires public education preferably at an early age, and advertising to remind adults people.  (Advertising  that , unfortunately, doesn’t make a profit.)
 
Polymers exist in nature, particularly fibers. These are mostly cellulose from plants, with some protein from animals like sheep.  These exclusively were used for textiles until the petroleum age.  Plants include other materials that could be modified to take the place of plastics, too.  Priority should be given to the chemistry needed to create the materials civilization  needs, and how to form these new materials into sheet and three dimensional products that are light, strong, take color well, and are biodegradable.
 
This will be a slow process, and it isn’t as urgent as stopping carbon dioxide pollution of the atmosphere.  However, the one most important ingredient to make the change we do have in abundance – people to train in chemistry.

Tagged as: cracking, ethane, marcellus shale, microplastics, NGL, plastics, polymerization