Study On The Separation Process Of Butanol From Mixtures Containing Low-carbon Primary Alcolhols And N-alkanes:Experiments And Simulation

Fischer-Tropsch synthesis products contained n-alkanes and primary alcohols of different carbon-chain length.However,there was azeotropy between n-alkane and primary alcohol.It was complicated to separate alkanes and alcohols.Amoung the mixtures of low boiling point chemicals of the Fischer-Tropsch synthesis products(the mixture of low carbon n-alkanes and primary alcohols),methanol,ethanol and propanol could be separated from the mixture of alkanes and alcohols by extraction with water.Butanol was hardly separated from the mixture by the method because it was not readily soluble in water.The mixture consisted of hexane,heptane,octane,nonane,ethanol,propanol,butanol and pentanol was selected in this paper.The separation process of 20kt/y n-butanol from the mixture was researched in this paper by experiments and simulation.The simulated data of butanol-octane system using different thermodynamic models were compared to the experimental data,the results showed that the Wilson model was suitable for the fractional separation process of the mixture.The results of the simulation using Wilson showed that a clear division between different alcohols could be achieved and each stream contained one primary alcohol and two n-alkanes.The mixture containing butanol-octane-nonane was researched to separate the butanol from the mixture.Ethanol aqueous solution was selected as extractant to separate butanol from butanol-octane-nonane mixture.Liquid-liquid equilibrium(LLE)data for the quaternary systems of ethanol + butanol + octane + water and ethanol + butanol +nonane + water were obtained at 298.15 K under atmospheric pressure in this thesis.The non-random two liquid(NRTL)equation was used to correlate the LLE data,and the two quaternary systems were used to regress the interaction parameters of the model.Both the obtained interaction parameters and the original default parameters in Aspen Plus of NRTL model were used to predict the LLE of the quinary system ethanol +butanol + octane + nonane + water and were compared to the experimental data and the results showed that the calculated values using the regressed parameters rather than the default parameters in Aspen Plus coincided with the experimental data well,an indication that the NRTL model and the interaction parameters obtained from quaternary systems could be used to predict the LLE data of quinary system.The LLE data of the quinary system were also characterized by the distribution coefficient and the selectivity.It was shown that both the distribution coefficients increased with the increase of ethanol/(ethanol + water)mass ratio while the selectivity of butanol against alkanes increased first and then decreased with the increase of ethanol/(ethanol + water)mass ratio.When the ethanol/(ethanol + water)mass ratio reached 0.40,the selectivity reached the highest value of 691.Therefore,the ethanol aqueous solution which contained about 40 wt%ethanol was suitable for separating butanol from the butanol-octane-nonane mixture.A separation process was developed in the thesis.The obtained interaction parameters of NRTL model of the quinary system ethanol + butanol + octane + nonane+ water were used to simulate the extraction unit while the simulation and optimization of other units were performed on the basis of other references.20kt/y butnaol was achieved by the separation process with the mass flow rate of 2.74t/hr,the mass fraction of 99.83%and the recovery rate of 99.45%.Heat exchanger network analysis and optimization was performed which finally saved 10.29%energy.