Gorka Elordi

Characterization of the Liquid Obtained in Tyre Pyrolysis in a Conical Spouted Bed Reactor

Used tyres pose a serious environmental problem and pyrolysis is considered one of the more feasible solutions that may be economically profitable on a large scale. In this study the pyrolysis of tyres has been carried out in a conical spouted bed reactor at 500 °C and the liquid product has been characterized taking into account composition, heat value and simulated distillation. The tyre mass feed in each run was 2 g and the bed was made up of 15 g of sand. Pyrolysis of scrap tyre at the 500 °C gives way to a yield of 3.1% of gases, 37.6% of liquid fraction (C5-C10 range hydrocarbons), 25.6% of tar (C11+) and 33.7% of char. The liquid fraction is of suitable quality for its use as fuel but the char requires activation for its upgrading.

Imaging the Profiles of Deactivating Species on the Catalyst used for the Cracking of Waste Polyethylene by Combined Microscopies

The catalytic cracking of high-density polyethylene (HDPE) is an attractive process to valorize wastes throughout the production of the original monomers or fuels. The cracking catalyst based on zeolites is able to drive the scission of the polymeric chain, while controlling the final selectivity of monomers or fuels. The disadvantage of using a cracking catalyst is the deactivation caused by coke fouling, which hinders the cracking of heavy hydrocarbons and reduces the lifetime of the catalyst. Amongst the reactor designs able to directly feed solid HDPE without clogging problems, fluidizedand spouted-bed reactors are the most promising. 4] In such reactors, the mechanism of cracking of HDPE involves several steps: 1) the polymer is fed into the reactor as a solid and melts, coating the surface of the catalytic particles; 2) the melted plastic is cracked through a thermal mechanism involving radicals, and forms waxes; 3) the waxes diffuse through the macropores and the mesopores of the catalyst and eventually reach the acid sites were they react through carbocation chemistry, most probably through protonated cyclopropanes; 4) the cracked products can diffuse through the micropores of the catalyst, reacting to form lighter products or reacting to form coke. The formation of coke on zeolites during the cracking of heavy hydrocarbons involves steps at multiple scales: at the nanoscale, the acid sites catalyze reactions of condensation, cyclization, and hydrogen transfer to form aromatics with lower H/C ratio values; at the microscale, coke molecules can flow, be trapped, and grow in the mesoand macropores of the catalyst leading to site blockage. In a previous work, we demonstrated that the coke deposited on an MFI catalyst during the cracking of HDPE grows in the interior and the exterior of the zeolite crystals simultaneously. The external coke grows faster than the internal coke and it is directly responsible for the final collapse of the activity of the catalyst. Despite the vast bibliography dealing with the mechanisms of creation and growth of the internal coke, the same pathways corresponding to the external coke remain much less studied. In this sense, a fundamental question in the cracking of HDPE is to understand the impact and composition of external coke, and the location (profiles) within the catalytic particle. This issue is critical for understanding the deactivation and future strategies for preparation and regeneration of the catalyst. Visualizing the way a catalyst is prepared, activated, used, or deactivated is a critical topic for rationally designing a catalyst with enhanced properties. The most advanced methods for imaging (that are non-invasive and can analyze by an operando approach) are tomographic energy dispersive diffraction (TEDDI), UV/vis spectroscopy, magnetic resonance imaging (MRI), 12] and fluorescence microscopy, with great potential for elucidating the mechanisms of preparation and deactivation at the level of the individual zeolite crystal, in a time-resolved manner. FTIR and Raman imaging are amongst the simpler imaging methodologies, with the reported successes in the steps of preparation, 15] or the deactivation of the dehydrogenation catalyst, or the hydrotreating catalyst. These methodologies are inevitably intrusive and require dissection of the catalytic particle. However, they require a less expensive infrastructure and, especially, enable the characterization of macroscopic external coke presumably formed in the cracking of HDPE. In this work, we have imaged the external (macroscopic) coke deposited on catalytic particles containing MFI (HZSM-5) zeolite during the cracking of HDPE in a spouted bed (pilot plant) reactor. Summarized in Figure 1 are the steps followed in the study. The catalytic particles consisted of zeolite crystals agglomerated into an inert matrix of bentonite and a-Al2O3. In this way the zeolite is dispersed and the catalyst has better flu-

Pathways of coke formation on an MFI catalyst during the cracking of waste polyolefins

A study has been carried out on the deposition kinetics of carbonaceous-species on an acid catalyst (containing an MFI zeolite) in the cracking of high-density polyethylene and polypropylene. The initiation of coke deposition occurs on the acid sites, followed by aromatic and aliphatic growth in the micro- and mesopores, respectively.

Catalytic Pyrolysis of High Density Polyethylene on a HZSM-5 Zeolite Catalyst in a Conical Spouted Bed Reactor

HDPE has been pyrolysed at 450 °C and 500 °C using HZSM-5 zeolite as a catalyst. Batch runs have been carried out at atmospheric pressure in a conical spouted bed reactor. Product analysis has been carried out by means of a GC, connected on-line with a thermostated line. The degradation rate of the plastic is slightly faster at 500 °C than at 450 °C and much faster than thermal pyrolysis in both cases. Products have been grouped into five lumps: the lump of light olefins, C2-C4; light alkanes, C1-C4; the gasoline fraction, C5-C11 compounds; C11+ hydrocarbons; and the coke deposited on the catalyst. An HZSM-5 catalyst is appropriate to obtain light olefins; about 55 wt% in both cases. The yield of gasoline fraction is also considerable and although its composition is not suitable for commercial gasoline, is interesting for its use in petrochemistry. The catalyst deactivation rate is low.