Basics of Synthesizing Fuels and Other Products
For generations, crude oil, coal and natural gas have been the staple fuel sources and feedstocks for many products. The utilization of these fossil sources adds carbon dioxide to our atmosphere. This man made contribution to our atmosphere influences climate change and the rate of release of carbon dioxide from this source is increasing exponentially.
Fuels and products made from fossil sources can also be made from materials of biological origin. This is a vital key to the reduction of mankind's carbon dioxide contribution to our atmosphere. By converting organic material such as biomass, municipal solid waste and all other organic matter originating from the natural life cycle we eliminate the increase of carbon dioxide which would otherwise occur by burning or processing fossil fuels.
Carbon dioxide originating from biological matter is re-absorbed by the biosphere to produce more biomass by photosynthesis. As a result, there is no net increase in greenhouse gas. Many view this as natures way of using carbon dioxide and water to capture and store the energy of the sun.
How Biomass is Converted to Synthetic Products
By deconstructing the biomass organic molecules and re-arranging them we can produce ultra clean equivalents for the fuel and other commercial products in wide use.
Referring to the diagram below, when organic material is heated in the absence of oxygen it breaks down to make a gas - this is known as destructive distillation which has a long history of exploitation by mankind. If a bit of oxygen is added to the pyrolytic process , the some of the carbon and hydrogen in the organic matter react with the oxygen generating heat and various gases. This starts by the formation of hydrogen, carbon monoxide, carbon dioxide and water vapor and as more oxygen is added the carbon and hydrogen continue to oxidize until it is all converted to carbon dioxide and water. Complete combustion occurs when enough oxygen is added to oxidize all of the hydrogen and carbon.
Three types of thermal decomposition of organic matter are recognized as follow:
Pyrolysis which is the heating of the waste in the absence of air or oxygen to cause thermal decomposition of the organic fraction. In this process a wide range of organic molecules is produced as well as a significant residue of carbon and long chain hydrocarbons.
Gasification which is the thermal decomposition of the organic fraction using sufficient oxygen or air along with steam so as to render all hydrocarbon species into a combination of hydrogen, carbon monoxide and carbon dioxide. The relative concentration of these products varies in accordance with the amount of oxygen added and other process parameters.
Combustion which is the thermal decomposition of the organic fraction in excess oxygen or air resulting in the oxidation of the hydrocarbon species into water, carbon dioxide and other gases depending on what other elements are present in the hydrocarbons
Applied Gasification
In the gasification process, the aim is to produce a maximum amount of carbon monoxide and hydrogen and a minimum amount of water and carbon dioxide. The carbon monoxide and hydrogen are then cleaned and are passed through a synthesis stage where they react to form the basic organic molecule building block CH2 . Using the appropriate catalysts this building block can be combined in various ways to form chains and branches resulting in a mixture of various organic molecules corresponding to the desired product such as ultra clean Diesel fuel, gasoline, aviation fuel, methanol, polymers and so on.
The following diagram illustrates the possibilities possibilities of gasification to synthesis:
As can be seen in reading the diagram from left to right, waste and biomass goes into the process but no waste or non-commercial residue exits the process. This is in tune with the objective of protecting the ecology of our world and a desirable departure from the primitive practice of simply burying waste.
One of the more interesting products is hydrogen which is regarded by many to be the fuel of the future.