Method and Apparatus for the Pyrolysis of Polymers

Abstract

A plastic pyrolysis plant, and a method of performing plastic pyrolysis, utilises a reactor ( 14 ) adapted to crack the polymeric material feedstock ( 1 ) in an environment without oxygen to convert the polymeric material into a hydrocarbon vapour and a solid carbon product called coke, wherein the reactor ( 14 ) cracks the polymeric material; and an extruder ( 2 ) to melt, heat and pump the plastic feed to the reactor ( 14 ). The extruder defines inlet ports for additives in solid, liquid or gaseous form, and at least one vent ( 5 ) for extracting any contamination vapours that may form, such that the extruder ( 2 ) is configured to remove contamination from the polymeric material feedstock ( 1 ). A contamination removal additive ( 3 ) may be introduced, through a first inlet of the extruder ( 2 ), that is mixed with the polymer feedstock ( 1 ) and that reacts to form a halide with any halogen atoms in the polymer feedstock; and which then breaks down as the temperature increases within the extruder, so as to release through a vent ( 5 ) the halogen as the hydrogen halide vapour. A fluid such as steam may be introduced into the extruder ( 2 ) at an inlet downstream of the first inlet, to assist the breakdown and release of hydrogen halide vapour through the vent ( 5 ).

1 . A polymer pyrolysis plant that comprises a reactor adapted to crack the polymeric material feedstock in an environment without oxygen to convert the polymeric material into a hydrocarbon vapour and a solid carbon product called coke, wherein the reactor cracks the polymeric material; and an extruder to melt, heat and pump the plastic feed to the reactor; wherein the extruder defines inlet ports for additives in solid, liquid or gaseous form, and at least one vent for extracting any contamination vapours that may form, such that the extruder is configured to remove contamination from the polymeric material feedstock, wherein the plant is arranged to introduce a stripping fluid into the extruder at a first inlet upstream of the vent, so the stripping fluid drives contamination out through the vent. 
     
     
         2 . A plant as claimed in  claim 1  wherein the plant is arranged to introduce, through a second inlet of the extruder that is upstream of the first inlet, a contamination removal additive that is mixed with the polymer feedstock and that reacts to form a halide with any halogen atoms in the polymer feedstock; and which then breaks down as the temperature increases within the extruder, so as to release through a vent the halogen as the hydrogen halide vapour. 
     
     
         3 . (canceled) 
     
     
         4 . A plant as claimed in  claim 2  wherein the removal additive is an oxide or hydroxide that forms a chloride that is at least 50% dissociated into an oxide or hydroxide and acid at 375° C. in the presence of the stripping fluid. 
     
     
         5 . A plant as claimed in  claim 1  wherein the removal additive is one or more of activated aluminium oxide (Al 2 O 3 ), FCC catalyst, and magnesium oxide or hydroxide (MgO or Mg(OH) 2 ). 
     
     
         6 . A plant as claimed in  claim 1  arranged to introduce into the extruder a catalyst, to be thereby mixed into the polymer feedstock before it reaches the reactor. 
     
     
         7 . A plant as claimed in  claim 1  comprising at least one caustic or water scrubber/separator to treat hydrocarbon products produced by the reactor. 
     
     
         8 . A plant as claimed in  claim 1  wherein the catalyst in the reactor comprises an FCC catalyst or equilibrium catalyst. 
     
     
         9 . A method of performing plastic pyrolysis using a reactor adapted to crack the polymeric material feedstock in an environment without oxygen to convert the polymeric material into a hydrocarbon vapour and a solid carbon product called coke, wherein the reactor cracks the polymeric material; wherein the polymeric material is fed into the reactor by using an extruder to melt, heat and pump the plastic feed to the reactor; wherein the method comprises introducing a wherein the method comprises introducing a stripping fluid into the extruder at a first inlet upstream of the vent, so the stripping fluid drives contamination out through the vent. 
     
     
         10 . (canceled) 
     
     
         11 . A method as claimed in  claim 9  wherein the removal additive is an oxide or hydroxide that forms a chloride that is at least 50% dissociated into an oxide or hydroxide and acid at 375° C. in the presence of the stripping fluid. 
     
     
         12 . A method as claimed in  claim 9  wherein the removal additive is one or more of activated aluminium oxide (Al 2 O 3 ), FCC catalyst, and magnesium oxide or hydroxide (MgO or Mg(OH) 2 ). 
     
     
         13 . A method of performing plastic pyrolysis using a reactor adapted to crack the polymeric material feedstock in an environment without oxygen to convert the polymeric material into a hydrocarbon vapour, wherein the reactor cracks the polymeric material; wherein the hydrocarbon vapour is processed to form at least one liquid hydrocarbon phase and a syngas phase; and wherein at least the C2 to C4 products of the syngas are separated so they can be transported to be fed downstream of the pyrolysis section of a steam cracker or downstream of a Fischer-Tropsch synthesis or a methanol-to-olefins reactor or another similar process reactor, in order for them to be separated into individual components. 
     
     
         14 . A method as claimed in  claim 13  wherein at least the C2 to C4 products of the syngas are separated by cooling, compression, pressure reduction, or absorption, or by a combination of cooling, compression and absorption, or by pressure swing adsorption. 
     
     
         15 . A method as claimed in  claim 14  wherein the syngas stream is treated to absorb mainly the C3 and C4 hydrocarbons and also some of the C2 and C5 hydrocarbons into a hydrocarbon liquid, to form monomer rich liquid (MRL). 
     
     
         16 . A method as claimed in  claim 15  wherein MRL is formed by pressurising the syngas to a pressure of 10 to 25 bar (g) and cooled to a temperature of 0 to 20° C., and contacted with the hydrocarbon liquid. 
     
     
         17 . A method as claimed in  claim 15  wherein the hydrocarbon liquid is naphtha. 
     
     
         18 . A method as claimed in  claim 9  wherein a catalyst is used to increase the propylene to ethylene ratio. 
     
     
         19 . A method as claimed in  claim 13  wherein a catalyst is used to increase the propylene to ethylene ratio. 
     
     
         20 . A plant as claimed in  claim 6  wherein the extruder has a third inlet downstream of the vent, and the catalyst is introduced through the third inlet. 
     
     
         21 . A method as claimed in  claim 9  also comprising introducing a contaminant removal additive through a first inlet port of the extruder that reacts to form a halide with any halogen atoms in the polymer feedstock; and which then breaks down as the temperature increases within the extruder, so as to release through a vent of the extruder the halogen as the hydrogen halide vapour.