Screw kiln reactors

As an example, catalytic cracking of pme LDPE was carried out in the screw kiln reactor over mesoporous Al-MCM-41 (plastic/catalyst mass ratio of 50) at T1/T2 = 400/450°C, respectively. The reported yields of hydrocarbons within the gasoline range (C5-C12) amounts to 80% with a high content of C7-C8 hydrocarbons, stemming likely from the occurrence of secondary catalytic oligomerization reactions affecting to the initially formed C3 and C4 fractions. 

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J. Aguado, D. P. Serrano, J. M. Escola, and E. Garagorri, Catalytic conversion of low-density polyethylene using a continuous screw kiln reactor, Catal. Today, 75, 257-262 (2002). 

Figure 3.14 Screw kiln reactor for the conversion of plastic and plastic-oil mixtures [87] (a) scheme (b) photograph of a laboratory reactor. (Reproduced by permission from Elsevier)...

The high influence of cracking catalyst on PE conversion was confirmed by Aguado et al. [11] in a continuous screw kiln reactor. The application of a sophisticated laboratory Al-MCM-41 cracking catalyst and process temperature of 400-450°C led to 85-87% yield of gas and gasoline fractions (C1-C12). Besides olefins and n- and iso-paraffins some quantity of aromatics, 5 wt% was determined in the process products. In the same reactor system with a noncatalytic process the gas yield was halved while similarly as in case of the fluid reactor system yields of gas oil and heavy waxes fraction (C13-C55) attained values of 62% (compared with 4 wt% in catalytic process) [12]. 

Figure 5.13 The selectivity of carbon atom number obtained in the thermal and catalytic degradation of LDPE in two-screw kiln reactor. (Reproduced with permission from Elsevier)...

Serrano et al. [11] studied the use of a laboratory-scale screw kiln reactor to transform low-density polyethylene (LDPE) into petrochemical feedstock. In this process, pyrolysis was carried out at reaction temperatures of 400-550°C and screw speeds of 3-20 rpm (Figure 19.6). In this process the plastic feed is initially heated in a feed hopper until the feed is melted. The melted plastic is then fed into the screw conveyor where it is depolymerized into gas, liquid and solid. The hopper is equipped with a stirrer to mix the feed plastic. Nitrogen is also used to provide an inert medium for pyrolysis. 

In order to determine the performance of the screw kiln reactor Serrano et al. [11] carried out several experiments looking at the effect of screw speed and reaction temperature. The output was calculated as the sum of the gaseous, liquid and solid products exiting from the reactor (Table 19.8). 

D. P. Serrano et al., Conversion of low density polyethylene into petrochemical feedstocks using a continuous screw kiln reactor. Journal of Analytical and Applied Pyrolysis, 58, 789-801 (2001). 

Day, M., Shen, Z., Cooney, I.D. Pyrolysis of auto shredder residue experiments with a laboratory screw kiln reactor. J. Anal. Appl. Pyrolysis 51, 181-200 (1999)... 

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