Gasification of Waste Tyres: Thermodynamic Attainable Region Approach

2021 ◽  
Vol 1045 ◽  
pp. 179-185
Author(s):  
Athi Enkosi Mavukwana ◽  
Celestin Sempuga
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Effect Of Temperature ◽  
Syngas Production ◽  
Attainable Region ◽  
Waste Tyres ◽  
Graphical Technique ◽  
Region Approach ◽  
Minimum Gibbs Free Energy

The innovative G-H graphical technique, a plot of Enthalpy vs Gibbs free energy was utilized to obtain a thermodynamically attainable region (AR) for the gasification of waste tyres. The AR is used to examine the interaction between the competing reactions in a gasifier and used to identify optimal targets for the conversion of waste tyres. The objective is to investigate the effect of temperature on the product selectivity. a temperature range of 25-1500°C at 1 bar was used for the analysis. The results show that at temperatures from 200°C to 600°C methane and carbon dioxide are dominant products at minimum Gibbs free energy. However, as the temperature increases, methane production decreases and hydrogen production become more favourable. Between 600°C and 700°C, carbon dioxide and hydrogen are dominant products. The AR results show that the products of gasification (CO and H2) are preferred products at minimum Gibbs free energy only at temperatures from 800°C to 1500°C, when both water and oxygen are used as oxidants. Therefore, syngas production from tyres is only feasible at high temperatures. Temperatures above 1000°C are recommended to prevent the formation of intermediate radicals.

Chemical equilibrium and chemical kinetics

2018 ◽  
Author(s):  
Dennis Sherwood ◽  
Paul Dalby
Keyword(s):  
Free Energy ◽  
Equilibrium Constant ◽  
Gibbs Free Energy ◽  
Chemical Kinetics ◽  
Chemical Equilibrium ◽  
First Principles ◽  
Effect Of Temperature ◽  
Total System ◽  
Free Energies

Building on the previous chapter, this chapter examines gas phase chemical equilibrium, and the equilibrium constant. This chapter takes a rigorous, yet very clear, ‘first principles’ approach, expressing the total Gibbs free energy of a reaction mixture at any time as the sum of the instantaneous Gibbs free energies of each component, as expressed in terms of the extent-of-reaction. The equilibrium reaction mixture is then defined as the point at which the total system Gibbs free energy is a minimum, from which concepts such as the equilibrium constant emerge. The chapter also explores the temperature dependence of equilibrium, this being one example of Le Chatelier’s principle. Finally, the chapter links thermodynamics to chemical kinetics by showing how the equilibrium constant is the ratio of the forward and backward rate constants. We also introduce the Arrhenius equation, closing with a discussion of the overall effect of temperature on chemical equilibrium.

Chemical Tension in VLS Nanostructure Growth Process: From Nanohillocks to Nanowires

2007 ◽  
Vol 1017 ◽  
Author(s):  
Na Li ◽  
Teh Y. Tan ◽  
Ulrich Gösele
Keyword(s):  
Free Energy ◽  
Energy Release ◽  
Gibbs Free Energy ◽  
Thermodynamic Limit ◽  
Equilibrium Model ◽  
Growth Process ◽  
Energy State ◽  
Crystal Layer ◽  
Global Equilibrium ◽  
Minimum Gibbs Free Energy

AbstractABSTRACTWe formulate a global equilibrium model to describe the growth of 1-d nanostructures in the VLS process by including also the chemical tension in addition to the physical tensions. The chemical tension derives from the Gibbs free energy release due to the growth of a crystal layer. The system global equilibrium is attained via the balance of the static physical tensions and the dynamic chemical tension, which allows the system to reach the minimum Gibbs free energy state. The model predicts, and provides conditions for the growth of nanowires of all sizes exceeding a lower thermodynamic limit. The model also predicts the conditions distinguishing the growth of nanaohillocks from nanowires.

scholarly journals The effect of temperature on the okra drying process: kinetic study and physical properties of powders

2021 ◽  
pp. 649-660
Author(s):  
Francislaine Suelia dos Santos ◽  
Rossana Maria Feitosa de Figueirêdo ◽  
Alexandre José de Melo Queiroz ◽  
Ana Raquel Carmo de Lima ◽  
Thalis Leandro Bezerra de Lima
Keyword(s):  
Free Energy ◽  
Physical Properties ◽  
Gibbs Free Energy ◽  
Effective Diffusion ◽  
Effective Diffusivity ◽  
Effect Of Temperature ◽  
Drying Temperature ◽  
Drying Kinetic ◽  
Drying Models ◽  
The One

This study aimed to evaluate the effect of drying temperature (50, 60, 70 and 80 °C) on okra dehydration by comparing its powder’s physical properties obtained from a sample produced by a lyophilization process. Ten drying models were adjusted to the experimental data of the drying kinetics. As a result, effective diffusivity and activation energy were determined in addition to thermodynamic parameters: entropy, enthalpy and Gibbs free energy. A physical characterization, as well as the pigments and colorimetry analyses of the aforementioned powders were made, by comparing them with samples produced by lyophilization. The powders were characterized for hygroscopicity, solubility, wettability, apparent and compacted density, fluidity and cohesiveness, pigments, colorimetric, morphological analysis (SEM) and X-ray diffraction. Midilli model was the one that best adjusted to the drying kinetic curves. There was a booster in the effective diffusion coefficient with the increase of temperature. Enthalpy and entropy were reduced with the increase of both drying temperature and Gibbs free energy. The powders presented high luminosity, and the lyophilized powder had higher pigments retention and greater solubility. All powders presented poor fluidity and intermediate cohesiveness, with amorphous, irregular and asymmetric particles. Thus, from the present study it was possible to evaluate the best drying method, the one that should be applied for the drying of okra, considering the costs involved, its quality and the final application of the product, meeting the specific needs of each consumer

Thermodynamic Interpretation of Carbonation Process of Portland Cement Hydration Products

2013 ◽  
Vol 753-755 ◽  
pp. 543-557
Author(s):  
Yan Jun Liu ◽  
Bo Tian Chen ◽  
Yong Chao Zheng
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Cement Paste ◽  
Cement Hydration ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Equilibrium Pressure ◽  
Carbonation Process

Cement hydration products carbonation is not only blamed for the carbonation-induced hardened cement paste or concrete cracking, also attributed to the pore water PH-value decrease, which causes the reinforcement corrosion under the existence of water and oxygen due to removal of oxide film passivating rebar surface, in hardened cement paste and concrete. Based on chemical thermodynamics, this paper presents the susceptibility of different cement hydration products to carbonation through calculating their Standard Gibbs Free Energy respectively, Gibbs free energy under temperature variation and the minimum equilibrium pressure of carbon dioxide triggering the carbonation process. The calculated results show that, under standard state (25°C, 100kpa), the minimum equilibrium pressure of carbon dioxide triggering carbonation process is significantly variable for different types of cement hydration products. For example, mono-sulfate sulfoferrite hydrates (3CaOFe2O3CaSO412H2O) is the most susceptible to carbonation, followed by mono-sulfate aluminate hydrates (3CaOAl2O3CaSO412H2O), while multi-sulfate sulfoaluminate hydrates (3CaOAl2O33CaSO432H2O) is the least vulnerable to carbonation, followed by silicate hydrates (5CaO6SiO25.5H2O). The findings in this paper are significant in understanding thermodynamic mechanism of cement hydrates carbonation and seeking the solution to prevent cement hydrates from carbonation-induced deterioration.

scholarly journals LFER and the Effect of Temperature on Oxyanion Adsorption by Goethite

2019 ◽  
Vol 98 ◽  
pp. 10001 ◽  
Author(s):  
Anna Dabizha ◽  
Nataliya Vlasova ◽  
Michael Kersten
Keyword(s):  
Free Energy ◽  
Linear Relationship ◽  
Gibbs Free Energy ◽  
Surface Complexation ◽  
Equilibrium Adsorption ◽  
Effect Of Temperature ◽  
Complexation Reaction ◽  
Temperature Dependent ◽  
Deprotonation Reaction ◽  
Oxyanion Adsorption

A linear relationship between the Gibbs free energy, ΔGr,H+, of the aqueous complex deprotonation reaction, and the Gibbs free energy, ΔGr,ads, of bidentate surface complexation reaction of oxyanions was derived from modelling of temperature dependent batch equilibrium adsorption experiments. As exemplified in this study, this relationship may be exploited to predict temperature-dependent adsorption behavior of oxyanions not yet known such as pertechnetate.

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