Research on finding a process to recover oil to use as fuel from waste plastic began in the mid 1980s.
Initially, a Zeolite Catalytic process was developed, converting plastic waste to liquid fuel under high pressure hydrogen. Unfortunately, the cost of production was found to be very high, and it could not be competitive against traditionally refined fuel from crude petroleum.
Subsequently, BP scientists developed a non-catalytic chemical extraction process, followed by fractionation. In the process, plastic waste in small pellet form (under 20mm) was heated and cracked in a reactor vessel, without air, to produce acceptable liquid fuel; which could be further processed to make gasoline or diesel suitable for automotive use.
In the process, pellets of waste plastic are fed in an air-free environment. The pellets are liquefied with no possibility of coking. Subsequently, the liquid product is refined by chemical extraction and fractionation to produce gasoline and diesel. Most kinds of plastic waste can be used for this process. This includes Polyethylene plastics (PE), coming from used food bags, and the coverings of industrial and engineering products prior to packing. Also Polypropylene plastics (PP) which are woven into bags for packing cement, fertilizer, food grains and other bulk products.
Similarly polystyrene which is used for fish, fruit and vegetable packing, and as candy boxes etc and polystyrene paper used in foam packing as insulation and for lining delicate equipment prior to packing into other containers.
Municipal waste collection can provide a readymade major source for these materials and is increasing day to day; it is conservatively estimated that even in developing countries, the amount of waste plastic amounts to as much as 12-15% of average municipal waste collections.
The refining of plastic waste, uses infrared energy to break up the various plastics into their hydrocarbon components. The gas that is produced in this process, is removed, dried and subsequently can be used as gaseous fuel.
Liquified plastic is then treated with a mixture of chemical additives to remove unwanted elements. The treated liquid is then fractionated to produce all three types of liquid fuel. These are:
a) Light Liquid Oil; that is identical to gasoline b) Medium Liquid Oil; which is the same as diesel. c) Heavy Liquid Oil; which is the same as the Bunker C fuel used in ships, locomotives and steam boilers
The fractionated end product can be varied according to market demand.
Instead of all three products, one may have any two products or only any one product, as desired. This inherent flexibility of the process is an added advantage for the refiner.
The dry gas, separated earlier, can be used as a fuel for gas engine or for firing the boiler. As the process is based on infra red ray for heating, “non PVC” plastics are preferred.
If there is PVC in the waste plastic; then it needs additional chemicals and the end liquid fuel output is reduced. Furthermore, in the heating of PVC, Hydrochloric acid is formed, and needs to be neutralised by adding Sodium Hydroxide; which naturally increases operating costs so the profit and yield is also lower. Ideally it is preferable to limit PVC content to below three percent for good results; however up to a maximum of ten percent PVC can be tolerated.
This is an interesting and quite viable proposition for Bangladesh. Empty plastic bottles and various types and sizes of containers are being trashed or resold. These can provide the needed raw material. Potential investors, looking for new products to be manufactured, should go for this local possibility of producing much needed liquid fuel; all of which is now imported.
Our entrepreneurs should invest in this valuable by product; from waste plastic sheets and other packaging wastes. This is freely available in Bangladesh, and a processing plant is justified; since the market for the products are expanding day by day in Bangladesh. Such investment would create jobs and energy and would be a boon for the country!