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Thermal - you heat large hydrocarbons at high temperatures (sometimes high pressures as well) until they break apart.
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Steam - high temperature steam (1500 degrees Fahrenheit / 816 degrees Celsius) is used to break ethane, butane and naphtha into ethylene and benzene, which are used to manufacture chemicals.
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Visbreaking - residual from the distillation tower is heated (900 degrees Fahrenheit / 482 degrees Celsius, 755 Kelvin), cooled with gas oil and rapidly burned (flashed) in a distillation tower. This process reduces the viscosity of heavy weight oils and produces tar.
Hydro-carbon fuels have a major problem. Most hydro-carbon fuels have a negative effect on the environment. By using petrol or diesel we produce carbon dioxide CO2 and H2O, as long as the fuel is completely combusted, i.e. there is an excess of oxygen, however if there should be a lack of oxygen where the combustion I taking place carbon monoxide, CO, is produced. Carbon monoxide is exceptionally poisonous to humans and other animals. As for CO2 it is known to be one of the green house gases. The green house gases have been linked to climate change and as a result are considered bad for the environment. Also a small amount of Hydrocarbons or volatile organic compounds (VOCs) - produced mostly from unburned fuel that evaporates and Nitrogen oxides (NO and NO2, together called NOx) - contributes to smog and acid rain, and also causes irritation to human mucus membrane.
A simple way to reduce the effects of exhaust emissions on the environment is to use a catalytic converter. This ingenious little device is located between the engine and the end of the exhaust pipe, as shown in the diagram.
The converter it’s self is made up of three main section, however to fully understand how it works we must first understand how it is controlled. Between the converter and the engine is a sensor which monitors the amount of oxygen in the exhaust stream. The sensor then tells the on board computer whether or not to increase or decrease the amount of oxygen entering the engine. Then within the converter itself the catalysts get to work, there are normally two different types of catalyst, a reduction catalyst and an oxididtion catalyst. Both are made up of ceramic honeycomb structures, coated with a metal catalyst, usually platinum, rhodium and/or palladium. This allows the maximum surface area of the catalyst to be exposed to the exhaust stream whilst minimizing the amount of catalyst required. Below is a diagram of the inside of a catalytic converter.
The reduction catalyst uses platinum and rhodium to reduce NOx emissions. This works by separating any nitrogen oxides into nitrogen and oxygen. As shown in the equation bellow:
2NO => N2 + O2 or 2NO2 => N2 + 2O2
The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. As shown in the equation below:
2CO + O2 => 2CO2
There are many alternatives to hydro-carbon fuels; however, each alternative has its own problems. Electric cars are slow to recharge and therefore are not useful for long journeys. Proton exchange membrane fuel cells are a reasonable alternative, they are almost like batteries that recharge themselves whilst power is drawn from them. This is very good idea, however it requires a mixture of oxygen and hydrogen to make water and hydrogen is exceptionally dangerous, especially when stored.
The other main alternative is hydrogen power. Hydrogen can be produced from water by using the process of electrolysis. The big problem with this is that the hydrogen can not be produced as quickly as a vehicle might need it.
Probably the best alternative is to use vegetable oil. The vegetable oil when mixed with distilled alcohol (can be made from same crop) is a great alternative to diesel. It works perfectly in diesel engines and will not run out (as long as we produce vegetables). As a result of this it is my astute opinion that vegetable oil is the fuel of the future.
It is therefore my conclusion that modern society in its current form could not survive with out hydro-carbon fuels and that transport particularly will not change unless some one can find a way to eliminate or at least limit the problems with one of the alternatives.
