Catalytic degradation of linear low-density polyethylene over HY-zeolite via pre-degradation method

Abstract

The catalytic degradation of linear low-density (lldPE) polyethylene over HY-zeolite catalyst was studied in a semi-batch reactor. One of the important problems encountered during catalytic pyrolysis of macromolecules is the contact with the catalyst, which is known to affect the product distribution and the quality of the coke formed. A pre-degradation procedure was introduced to achieve efficient contact between the LLDPE macromolecules and the catalyst. The influence of the pre-degradation to the reaction conditions including holding time, temperature, polymer to catalyst ratio and flow rate of carrier gas was examined. Moreover, the pre-degradation results were compared with the results obtained using normal mixing procedure. The results obtained showed that, pre-degradation promotes the liquid fraction by a factor of more than one-fold increase at the expense of the gas fraction and the coke yield. The optimal liquid fraction with pre-degradation was obtained at low reaction temperature and catalyst amount respectively, i.e. high polymer to catalyst ratio, making it economically viable method for the degradation of lldPE.

The Use of Heterogeneous Catalysis in the Chemical Valorization of Plastic Waste

“…[40,243,244] However, fixed bed reactors suffer from poor heat transfer which can result in reactor blockages and batch reactors require frequent material charging and restarting of the process. [153] These types of reactors are also limited in the amount of catalytic surface area available for reactants to access. [153] Furthermore, fixed bed reactors are difficult to implement in commercial applications due to poor heat transfer abilities and volume limitations.…”

“…[153] These types of reactors are also limited in the amount of catalytic surface area available for reactants to access. [153] Furthermore, fixed bed reactors are difficult to implement in commercial applications due to poor heat transfer abilities and volume limitations. Two-stage fixed bed reactors provide an opportunity for scale up; plastic waste is degraded in the first reactor-via thermal, noncatalytic pyrolysis-and the pyrolysis vapors are passed over a heated catalyst bed in the second stage.…”

“…[109] Fluidized-bed reactors (FBR) have better overall potential for scale-up than single-stage fixed-bed reactors because they can overcome operational problems such as heat transfer. [13,22,27,40,46,51,153,[250][251][252] FBRs allow for changes in fluidizing flow rate which can affect the product selectivity between light gas and gasoline range components -as well as between olefin and paraffin production -within the gaseous fraction. [80,105] Furthermore, FBRs allow for the recharging of materials and catalysts without halting the process.…”

“…[80,105] Furthermore, FBRs allow for the recharging of materials and catalysts without halting the process. [13,22,27,40,51,153,[250][251][252] However, FBRs have had defluidization problems caused by variable plastic particle sizes and the agglomeration of the sand with the molten plastic. [46] FBRs retain ash from the feedstock within the bed material, which can act as catalysts for the pyrolysis process, ultimately altering the product composition.…”

“…[109] Conical spouted bed reactors (CSBR) have been staked as an appropriate alternative for the conversion of plastic, largely because they avoid operational issues that stem from bed defluidization as a result of melted plastics. [13,51,149,153,167,253] CSBRs allow for vigorous contact between different phases and have a lower chance of particle agglomeration in bed materials. [13,51,149,153,253] CSBRs have short vapor residence times, as well as high heat and mass transfer rates between phases which allow for the conversion of polymers into waxes and fuels and prevents secondary reactions that lead to coke formation.…”