![Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/110819/TOC-Subject-Sample-2021-Physical-Sciences.jpg"})
ABSTRACT
Montan wax extraction which is considered to be an application of solid–liquid extraction (leaching) was systematically studied. Different mass transfer models for Montan wax extraction of brown coal–toluene system are established to simulate and analyse the extraction process with fixed-bed extractors and stirred extractors. Empirical correlations are applied to determine the mass transfer coefficients and the axial diffusion coefficient
. A method (denoted as Opt-empirical method) to estimate the effective diffusion coefficient
is proposed for the Montan wax extraction, which is validated by using sets of experimental data in percolation columns and stirred extractors.
Nomenclature
| = | specific surface area of a solid particle (1/m) | |
| B, | = | phase ratio ( |
| = | concentration of solute in fluid phase (in terms of mass of solute per unit volume unit) (kg/m3) | |
| = | concentration of saturated solubility (kg/m3) | |
| = | concentration of solute in solid particle at the position r = R (kg/m3) | |
| = | initial concentration of solute in brown coal (Montan wax content in brown coal) (kg/m3) | |
| = | concentration of solute in solid phase (in terms of mass of solute per unit volume of solid matrix) (kg/m3) | |
| = | concentration of solute at equilibrium conditions, that concentration of solute on particle surface is in equilibrium with average concentration of solute in solid phase (kg/m3) | |
| = | maxium concentration of solute at equilibrium conditions (kg/m3) | |
| = | mean particle diameter (mm) | |
| = | impeller diameter (m) | |
| = | vessel diameter (m) | |
| = | effective diffusion coefficient (mFootnote2/s) | |
| = | binary diffusion coefficient of solute A (Montan wax) in solvent B (toluene) (mFootnote2/s) | |
| = | axial dispersion coefficient (mFootnote2/s) | |
| F, | = | flow rate of solvent (cm3/min) |
| = | external mass transfer coefficient/film mass transfer coefficient (m/s) | |
| K, | = | equilibrium coefficient parameter (—) |
| L, | = | length of packed bed, |
| M, | = | whole amount of solid substrate loaded into the extraction container (g) |
| = | parameter in Freundlich equilibrium dependent on solvent and the matrix of raw materials and operation conditions (normally greater than 1) (—) | |
| N, | = | impeller speed (min–1) |
| = | radius of the extraction container (m) | |
| = | Reynolds number based on particle diameter, | |
| = | Reynolds number based on impeller diameter, | |
| = | Renolds number based on vessel diameter, | |
| = | Schmidt number | |
| = | Sherwood number based on vessel diameter, | |
| = | interstitial solvent velocity, | |
| = | superficial solvent velocity (m/s) | |
| = | simulated yield of Montan wax at | |
| = | yield of Montan wax from experiments data at |
Greek Letters
| = | packed-bed porosity (—) | |
| = | porosity of the solid particle (—) | |
| = | density of the liquid (kg/m3) | |
| = | bulk density (kg/m3) | |
| = | particle density (kg/m3) | |
| = | viscosity (pa s) |
Funding
The authors gratefully acknowledge China Scholarship Council for their financial support and the support of the Growth Core “ibi – Innovative Brown Coal Integration in Central Germany” funded by the German Federal Ministry of Education and Research.