Building with Bioplastics - Part 5

August 1, 2012 – Vol.17 No. 20

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 5.

Which plants for feedstock?

by Bruce Mulliken, Green Energy News

Plants grow by taking carbon dioxide out of the air and use that carbon and oxygen, along with hydrogen and oxygen from water, to build themselves, as it were. Plants can be harvested, then mechanically and chemically processed to make new carbon, hydrogen and oxygen-based compounds. Those compounds can then be used to make bioplastics. Those bioplastics, in turn, can be used to manufacture super durable products that can remain in service for a decade or much more, all the while keeping that carbon from the atmosphere, locked away, sequestered, and not doing any harm, like warming the world’s atmosphere.

Bioplastics, and end products made with them, can be used as carbon sinks that can also be a profitable industry.

But which plants, which plant feedstocks, would be used to bioplastics and where will those plants come from?

Braskem, for example, the largest thermoplastic resin producer in the Americas, makes its “green” polyethylene from ethanol that’s produced from sugarcane. Ethylene is only one chemical step away from ethanol. The company is based in Brazil which is also the world’s largest sugarcane producer. (The U.S. is number 5.)

If ethanol is a core component of one type of bioplastics – bio-polyethylene – then any plant used to make ethanol should also be able to make the it. However, there more varieties of bioplastics than bio-polyethylene and each, depending on the manufacturer, may use a different route from plant to bioplastic. The point is, there is a wide variety of plant sources that could be used to make bioplastics, but it would be up each producer to decide which plant is best for their technology.

Yet, in general some thoughts on which plants to use might be taken into consideration:

--- Avoid the use of food-based plant feedstocks. When the build-out of the ethanol industry was underway to provide enough ethanol to add 10 percent to the U.S. gasoline supply, there was much discussion about using food for fuels. To avoid a repeat and time wasted in this debate, food directly used for bioplastics should be avoided;

--- Use waste plant material such as agricultural waste. There’s no shortage of agricultural waste, including food plant waste, as well as urban tree and woody yard residue. In one study (albeit from 2000 and thus 12 years old) showed that in 2000 just over 12 million tons of timber was harvested from National Forests compared with 14.5 million tons of urban tree waste and woody yard residues generated. And that’s just one study on two sources of waste plant material;

--- Use fast growing plants. Think grasses. The faster a plant grows the more carbon is pulled from the air, the more frequent the harvesting can be, and the sooner that carbon can be sequestered in bioplastic. Trees are slow growers and often not harvested for decades. Grasses grow rabidly and are harvested often weekly. Other plants might be somewhere in between, like vines. If this method of bioplastics for sequestration is employed on a wide scale scientists will have to determine which plants will be the most productive in pulling carbon from the air while being the best for bioplastics;

--- Use plants that don’t require a lot of water. As the current, widespread drought shows, there may be off years in which to harvest feedstocks, including from waste, for bioplastics. However, carbon dioxide emissions won’t stop just because there’s a drought. Some plants are more drought tolerant than others and could be taken into consideration in a choosing feedstock;

--- Use plants that require the least amount of processing. The long chain of growing, harvesting, and processing plants into bioplastics will likely generate some carbon dioxide effectively reducing the amount of carbon dioxide sequestered. Some plants are easier to grow than others, requiring less care and feeding. Some plants and plant waste might have a shorter route from harvesting to processing into bioplastics. It seems likely that the shorter the route, the lower the carbon dioxide emissions. Easy to grow, easy to process should be the mantra here;

--- Use plants that grow near sources of high levels of carbon dioxide. Elevated levels of carbon dioxide encourages plant growth. Carbon dioxide concentrations are not uniform throughout the Earth’s atmosphere. Carbon dioxide doesn’t disperse uniformly the moment it’s emitted. Some places will have heavier concentrations than others. Where there’s high concentrations of carbon-emitting homes, cars and large industry there’s likely to be larger concentrations of carbon dioxide. So, why not grow plants in these areas specifically for bioplastic feedstock? The high levels of carbon dioxide would encourage plant growth while at the same time greater levels of carbon dioxide would be removed and sequestered.

One place to grow plants specifically for bioplastic feedstock might be on the shoulders and median strips on highways. Carbon dioxide levels are high there because of the traffic. In areas where grass is grown it also has to be cut and maintained. Why not grow a bioplastic feedstock on this property?

There’s a side benefit to utilizing this space. The land abutting highways is usually owned by the local community, county or the state. Those who manage the land also have to pay to keep it maintained. Feedstocks for bioplastics grown on this land could be sold to producers and thus be a source of revenue for the state or local government;

--- Finallly one thing to keep remembering: Sequestering carbon from plants in plastic is meant to be a profit-making industry not just a good deed.

Links.

Braskem (U.S. site)

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 2.
Residential bioplastic building materials when managed and recycled could sequester carbon dioxide for centuries.

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 3.
Building big things for significant carbon sequestration.

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 4.
Renewable energy plays a significant role.

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 5.
Which plants for feedstock?

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 6.
Man-made systems to capture carbon dioxide for plastics and other chemicals.

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 7.
The need for a regulated industry.

BUILDING WITH BIOPLASTICS:
ATMOSPHERIC CARBON STORAGE IN CONSTRUCTION MATERIALS - PART 8.
New technologies to convert plant material into chemicals for bioplastics and series wrap-up.

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