A "Wastes-Treat-Wastes" Technology: Role and Potential of Spent Fluid Catalytic Cracking Catalysts Assisted Pyrolysis of Discarded Car Tires

Abstract

Spent fluid catalytic cracking catalysts (FCC catalysts) produced by the petrochemical industry are considered to be environmentally hazardous waste, and precious metals and heavy metals deposited on the surface make them difficult to treat. Even so, these catalysts retain some of their activity. The pyrolysis of waste tires is considered to be one of the most effective ways to solve the fossil fuel resource crisis, and this study attempts to catalyze the pyrolysis of waste tires using spent catalysts to increase the value of both types of waste. FCC catalysts reduced the activation energy (E) of waste tire pyrolysis. When the catalyst dosage was 30 wt.%, the E of tread rubber decreased from 238.87 kJ/mol to 181.24 kJ/mol, which was a 19.94% reduction. The E of the inner liner decreased from 288.03 kJ/mol to 209.12 kJ/mol, a 27.4% reduction. The spent catalyst was more effective in reducing the E and solid yield of the inner liner made of synthetic rubber. It should be emphasized that an appropriate increase in the heating rate can fully exert the selectivity of the catalyst. The catalyst could also be effectively used twice, and the optimum ratio of catalyst/waste tires was about 1/4.5. Compared with specially prepared catalysts, it is more cost-effective to use such wastes as a catalyst for waste tire pyrolysis.

Keywords: pyrolysis; spent catalyst; thermogravimetry; waste tires.

Figure 1

(a) TG and DTG curves of inner liner using spent catalysts (4.65 mg) or not; (b) Conversion rate and reaction rate curves of inner liner using spent catalysts or not; (c) TG and DTG curves of tread rubber using spent catalysts or not; (d) Conversion rate and reaction rate curves of tread rubber using spent catalysts (4.42 mg) or not. (β = 25 ^oC min, Temperature range: 40–600 ^oC, Shielding gas and Rate: N2, 40 mL min⁻¹ Purge gas and Rate: N₂, 50 mL min⁻¹, Crucible: AL₂O₃).

Figure 1

(a) TG and DTG curves of inner liner using spent catalysts (4.65 mg) or not; (b) Conversion rate and reaction rate curves of inner liner using spent catalysts or not; (c) TG and DTG curves of tread rubber using spent catalysts or not; (d) Conversion rate and reaction rate curves of tread rubber using spent catalysts (4.42 mg) or not. (β = 25 ^oC min, Temperature range: 40–600 ^oC, Shielding gas and Rate: N2, 40 mL min⁻¹ Purge gas and Rate: N₂, 50 mL min⁻¹, Crucible: AL₂O₃).

Figure 2

Schematic diagram of zeolite function.

Figure 3

(a) Comparison of activation energy of tread rubber; (b) Comparison of activation energy of inner liner.

Figure 4

Activation energy of inner liner at different catalysts (20 wt.%) usage times.

Figure 5

(a) Activation energy fitting results of tread rubber at different catalyst dosages; (b) Activation energy fitting results of inner liner at different catalyst dosages.