George Manos

A review on thermal and catalytic pyrolysis of plastic solid waste (PSW)

Plastic plays an important role in our daily lives due to its versatility, light weight and low production cost. Plastics became essential in many sectors such as construction, medical, engineering applications, automotive, aerospace, etc. In addition, economic growth and development also increased our demand and dependency on plastics which leads to its accumulation in landfills imposing risk on human health, animals and cause environmental pollution problems such as ground water contamination, sanitary related issues, etc. Hence, a sustainable and an efficient plastic waste treatment is essential to avoid such issues. Pyrolysis is a thermo-chemical plastic waste treatment technique which can solve such pollution problems, as well as, recover valuable energy and products such as oil and gas. Pyrolysis of plastic solid waste (PSW) has gained importance due to having better advantages towards environmental pollution and reduction of carbon footprint of plastic products by minimizing the emissions of carbon monoxide and carbon dioxide compared to combustion and gasification. This paper presents the existing techniques of pyrolysis, the parameters which affect the products yield and selectivity and identify major research gaps in this technology. The influence of different catalysts on the process as well as review and comparative assessment of pyrolysis with other thermal and catalytic plastic treatment methods, is also presented.

Statistical mechanical lattice model of the dual-peak electrocaloric effect in ferroelectric relaxors and the role of pressure

Despite considerable effort, the microscopic origin of the electrocaloric (EC) effect in ferroelectric relaxors is still intensely discussed. Ferroelectric relaxors typically display a dual-peak EC effect, whose origin is uncertain. Here we present an exact statistical mechanical matrix treatment of a lattice model of polar nanoregions forming in a neutral background and use this approach to study the characteristics of the EC effect in ferroelectric relaxors under varying electric field and pressure. The dual peaks seen in the EC properties of ferroelectric relaxors are due to the formation and ordering of polar nanoregions. The model predicts significant enhancement of the EC temperature rise with pressure which may have some contribution to the giant EC effect.

Microscopic interpretation of sign reversal in the electrocaloric effect in a ferroelectric PbMg1/3Nb2/3O3-30PbTiO3 single crystal

With increasing temperature, PbMg1/3Nb2/3O3-30PbTiO3 (PMN-30PT) crystals change from pseudo-rhombohedral to tetragonal to cubic phases. In addition to the usual positive electrocaloric effect (ECE), a negative ECE, whose origin is uncertain, is observed. Here, these two types of the ECE contributions in PbMg1/3Nb2/3O3-30PbTiO3 crystals are modelled theoretically using a one dimensional statistical mechanical lattice model, which is solved by an exact matrix method. The quasi one-dimensional model reproduces the trends in the experimental behaviour and attributes the electrocaloric sign reversal to free energy changes induced by the electric field.

Exact statistical mechanical one-dimensional lattice model of alkane binary mixture adsorption in zeolites and comparision with Monte-Carlo simulations

Adsorption isotherms obtained by Monte-Carlo simulation for ethane–methane mixtures in the zeolite silicalite show a highly unusual structure with a shoulder at low coverage and adsorption preference reversal at high pressures whose interpretation is uncertain. To understand this behaviour an exact calculation of the statistical mechanics of a lattice model of alkane mixture adsorption in zeolites has been undertaken. The lattice model reproduces all of the novel features of the Monte-Carlo isotherms, allowing us to infer that these unusual characteristics arise from a combination of molecular reorientation of ethane molecules, and displacement of ethane by methane at higher pressures.

Microscopic theory of the electrocaloric effect in the paraelectric phase of potassium dihydrogen phosphate

Here we present a microscopic theory of the electrocaloric effect in potassium dihydrogen phosphate, KH2PO4, based on Slater’s lattice model. The model reproduces the essential features of the experimentally observed behavior and also gives a remarkably accurate description of the electric field dependence of the electrocaloric effect. The basic principle of the theory also gives guidelines for a theoretical analysis of other dielectrics and for the further development of materials with an enhanced electrocaloric effect.

Plastic catalytic pyrolysis to fuels as tertiary polymer recycling method: Effect of process conditions

This paper presents results regarding the effect of various process conditions on the performance of a zeolite catalyst in pyrolysis of high density polyethylene. The results show that polymer catalytic degradation can be operated at relatively low catalyst content reducing the cost of a potential industrial process. As the polymer to catalyst mass ratio increases, the system becomes less active, but high temperatures compensate for this activity loss resulting in high conversion values at usual batch times and even higher yields of liquid products due to less overcracking. The results also show that high flow rate of carrier gas causes evaporation of liquid products falsifying results, as it was obvious from liquid yield results at different reaction times as well as the corresponding boiling point distributions. Furthermore, results are presented regarding temperature effects on liquid selectivity. Similar values resulted from different final reactor temperatures, which are attributed to the batch operation of the experimental equipment. Since polymer and catalyst both undergo the same temperature profile, which is the same up to a specific time independent of the final temperature. Obviously, this common temperature step determines the selectivity to specific products. However, selectivity to specific products is affected by the temperature, as shown in the corresponding boiling point distributions, with higher temperatures showing an increased selectivity to middle boiling point components (C8-C9) and lower temperatures increased selectivity to heavy components (C14-C18).

Exact statistical mechanical treatment of benzene adsorption in a zeolite twin-pore one-dimensional lattice model

Abstract An exact matrix calculation of the statistical mechanics of a lattice model of benzene adsorption in silicalite modelled as two types of quasi one-dimensional pores is presented. The calculation reproduces the experimentally observed two steps in the level of adsorption with rising pressure and also satisfactorily gives the essential features of the loading dependence of the heat of adsorption.

Comparative study of Monte Carlo simulations and exact statistical mechanical lattice model of commensurate transitions of alkanes adsorbed in zeolites

A study of commensurate transitions in a lattice model of adsorbed straight chain alkanes (ethane, hexane and heptane) in the zeolite Silicilate is presented, and a comparison made of the calculated isotherms with those from experiments and Monte Carlo simulations. The unusual isotherm shapes predicted by the model are in broad agreement with those from Monte Carlo simulations and experiments; thereby supporting the interpretation of such inflections in isotherms first put forward by Smit and Maesen.

Exact matrix treatment of an osmotic ensemble model of adsorption and pressure induced structural transitions in metal organic frameworks

Here we present an exactly treated quasi-one dimensional statistical mechanical osmotic ensemble model of pressure and adsorption induced breathing structural transformations of metal-organic frameworks (MOFs). The treatment uses a transfer matrix method. The model successfully reproduces the gas and pressure induced structural changes which are observed experimentally in MOFs. The model treatment presented here is a significant step towards analytical statistical mechanical treatments of flexible metal-organic frameworks.

Deactivation Studies During Catalytic Cracking of C8 Aliphatic Hydrocarbons over Ultrastable Y-Zeolite. Conversion and Product Yield Profiles with Time Onstream

The deactivation of an ultrastable Y-zeolite during cracking of n-octane, isooctane and 1-octene was studied in a fixed-bed reactor. The relative reactivities of the three reactants in increasing order were n-octane < isooctane < 1-octene. At high residence times, complete conversion was achieved followed by a relatively slow decline that, in fact, presented a falsified deactivation picture. On the other hand, a surprising olefin yield increase with time onstream was observed, i.e., isobutene during isooctane cracking and octene isomers in the case of 1-octene. The isobutene yield increase was assigned to preferential deactivation of strong acid sites that allowed primary products to desorb into the gas phase, increasing their apparent yield rather than undergo secondary reactions. Similarly, 1-octene isomers showed a yield increase with time onstream due to stronger deactivation of cracking reactions than isomerization.