METHODOLOGY
A) Pyrolysis
Pyrolysis is generally defined as the controlled heating of a material in the absence of oxygen. In plastics Pyrolysis, the macromolecular structures of polymers are broken down into smaller molecules or oligomersand sometimes monomer units.
B) Thermal Pyrolysis of Polyolefin
The non-catalytic or thermal Pyrolysis of polyolefin is a high energy, endothermic process requiring temperatures of at least 350–500 °C.
MAIN DEVICES USED IN THE PROCESS
A) Condenser
It cools the entire heated vapour coming out of the reactor. It has an inlet and an outlet for cold water to run through its outer area. This is used for cooling of the vapour. The gaseous hydrocarbons at a temperature of about 350°C are condensed to about 30 – 35°C.
B) Reactor
It is a stainless steel tube of length 300mm, internal diameter 225mm, outer diameter 230mm sealed at one end and an outlet tube at the other end. The reactor is placed under the LPG burner for external heating with the raw material inside. The reactor is made with the following: stainless steel, mild steel and clay for lagging. The reactor is heated to a temperature of about 450°C and more.
C) Process Description
Thermal cracking process without catalyst was used in converting waste plastic into liquid fuel. Two types of waste plastic are selected for this particular experiment. By weight 50% of each Low density polyethylene and polypropylene was selected for the experiment. Bothwaste plastic are solid hard form. Collected waste plastic was cleaned using liquid soap and water. During waste plastics are cleaned is cerates waste water. This waste water is purified for reuse using waste watertreatment process. Washed waste plastics are cut into 3-5 cm size to fit into the reactor conservatively. For experimental purpose we used 600gm sample 300gm of PP and 300gm of LDPE. A vertical steel reactor used for thermal cracking and temperature used ranges from100° C to 400° C. When temperature is increased to 270° C liquid slurry turns into vapour and the vapour then passes through a condenser unit. At the end we collect liquid fuel. Between 100º C and 250º C around 20 -30% of the fuelis collected and then when raised to 325º C the next 40% is collected and finally when held at 400º C the yield is fully completed. During the thermal cracking process plastic portions are not broken down immediately because plastics have short chain hydrocarbon to long chain hydrocarbon. 1st stage of heat applied breaks down only the short chain hydrocarbon. When temperature profile is increased the plastic carboncarbon bond breakdown slowly.
As thetemperature is increased the long chains are breakdown step by step. During in this thermal cracking process some light gas such as methane, ethane, propane andbutane are produced.
METHOD AND METHODOLOGY
Following two major methods are used to converting plastic wastes into useful products such as a fuels
A.Thermal pyrolysis
B.Catalytic pyrolysis
A.Thermal pyrolysis The non-catalytic or thermal pyrolysis of plastic is a high energy, endothermic process requiring temperatures of at least 350°
C–500° C. Thermal cracking or Pyrolysis, involves he degradation of the polymeric materials by heating in the absence of oxygen [1]. The process is usually conducted at temperatures between 350° C and 500° C and results in the formation of a carbonized char (solid residues) and a volatile
B.Catalytic pyrolysis Addition of catalyst enhances the conversion and fuel quality. As compared to the purely thermal pyrolysis, the addition of catalyst in pyrolysis. Significantly lowers pyrolysis temperatures and time.
A significant reduction in the degradation temperature and reaction time [1] under catalytic conditions results in an increase in the conversion rates for a wide range of polymers at much lower temperatures than with thermal pyrolysis. Narrows and provides better control over the hydrocarbon products distribution in Low density polyethylene (LDPE), High density polyethylene (HDPE), polypropylene [5] and polystyrene pyrolysis. While thermal pyrolysis, results in a broad range of hydrocarbons ranging from C5 to C28, the selectivity of products in the gasoline range (C5, C12) are much more enhanced by the presence of catalysts. Again, oils obtained by catalytic pyrolysis contain less olefins and more branched hydrocarbon and aromatic content. Increases the gaseous product yields.
Under similar temperatures and reaction times, a much higher gaseous product yield is observed in the presence of a catalyst for plastic wastes [3].In this papers going use catalytic pyrolysis method to convert waste plastic into bio fuel . mainly two catalyst are used such as dry ash powder and dry wood powder. Dry ash powder mainly consists of carbon content that accelerate the chemical reaction and dry powder helps to catch the fire easily and enhance the conversion of plastic waste into bio fuel compounds.