Abstract
The separation and recycling of effective resources in Fischer-Tropsch wax residue (FTWR) are urgent because of the environmental hazards and energy waste they bring. In this study, organic solvents are used to separate recyclable resources from FTWR efficiently, achieving the goals of “Energy Recycle” and “Fisher-Tropsch Wax Residue Treatment”. The response surface methodology (RSM) response surface analysis model accurately evaluates the relationship among temperature, residence time, liquid–solid ratio, and desorption rate and obtains the best process parameters. The results show that the product yield can reach 82.28% under the conditions of 80 °C, 4 h, and the liquid–solid ratio of 24.4 mL/g. Through the kinetic analysis of the desorption process of FTWR, the results show that the desorption process conforms to the pseudo second-order kinetic model and the internal diffusion model. The thermodynamic function results showed that there were not only van der Waals forces in the desorption process, but other strong interaction forces such as hydrogen bonds. In addition, Langmuir, Freundlich, and BET equations are used to describe the desorption equilibrium. Scanning electron microscopy (SEM) were used to analyze the pore structure of FTWR during desorption. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Gas chromatography-mass spectrometer (GC-MS) analysis confirmed that the desorption product’s main component was hydrocarbons (50.38 wt%). Furthermore, naphthenic (22.95 wt%), primary alcohol (11.62 wt%), esters (8.7 wt%), and aromatic hydrocarbons (6.35 wt%) compounds were found and can be further purified and applied to other industrial fields. This study shows that using petroleum ether to separate and recover clean resources from Fischer-Tropsch wax residue is feasible and efficient and has potential industrial application prospects.
Highlights
The increasing demand for energy and the limited resources of fossil fuels have forced humans to look for renewable energy alternatives to fossil fuels [1,2]
The first stage was related to surface diffusion, namely waste Fischer-Tropsch catalyst (WFTC), the Fischer-Tropsch wax (FTW) adsorbed on the surface layer was desorbed in the solvent; the second stage was the intra-particle diffusion process, that is, the FTW deposited in the spent catalyst pores was desorbed by the solvent; the third stage was the dynamic equilibrium process of adsorption and desorption, at this time the inside of the particle diffusion becomes very weak
The wax from Fischer-Tropsch wax residue (FTWR) was obtained by solvent extraction with petroleum ether
Summary
The increasing demand for energy and the limited resources of fossil fuels have forced humans to look for renewable energy alternatives to fossil fuels [1,2]. Many studies have investigated solvent desorption to recover oily wastes containing sludge, but few have reported the recycling of FTW resources in FTWR. The current resource recovery method for wax-based solid waste is mainly pyrolysis, which converts wax into pyrolysis gas and condenses and recovers it. The presence of the Fischer-Tropsch catalyst in FTWR affect the quality of the finished wax recovered by pyrolysis. The carbon number of the finished wax and the recovery rate were poor This will inevitably waste a part of wax resources. The desorption process of the wax in the three-way environment of Fischer-Tropsch wax, solvent and catalyst was verified and analyzed through isotherm analysis and kinetic fitting, and the desorption mechanism was proposed. This work was devoted to finding the best extraction process and elucidating the reaction mechanism through systematic experimental and theoretical methods
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