The Research On Vapor-Liquid Equilibrium For Ethylene Absorption System

The mass fraction of C2H4in the refinery dry gas is very high, which is between14%-22%. However, the gas is burned as fuel gas in most of refineries in our country. The separation and recovery of ethylene has remarkable significance on energy-saving and CO2emission reduction. This paper studied vapor-liquid equilibrium for ethylene absorption on physical method.First, the method excess Gibbs energy was used to evaluate absorbing performance of solvents in this paper. Twenty ethylene and solvents (alcohols, ethers, aromatics) binary system were selected approximately. Their activity coefficients and the maximal excess Gibbs energies were calculated using the software ASPEN PLUS and UNIFAC model (activity coefficient model). The results showed that GEmax of C2H4+aromatics binary system are smaller than others.The VLE data of C2H4and some solvents were collected. The rule that solvents’formula structure could affect their absorbing performance was found in the solvents comparison. In the same temperature and pressure, the more symmetric formula structure is, the higher solubility is. Mesitylene, which formula is C9H12and methyl groups distributed in the aromatic ring symmetrically, was selected to be C2H4absorbent by the method of excess Gibbs energy.Then, the paper put forward two point improvements on the high-pressure VLE apparatus. Experiments show that the improvements are effective. Vapor-Liquid Equilibrium data for ethylene and mesitylene were measured at temperature range from253.15K to333.15K and pressures range from0.5MPa to3.0MPa with the improved high pressure VLE apparatus. The VLE data were correlated with the Peng-Robinson equations of state. The binary interaction parameter kij is also obtained. The experimental data passed the thermodynamics consistency test. The results showed that PR equation of state can better describe the vapor-liquid behaviors of the C2H4+C9H12binary system.VLE experimental data of C2H4+C9H12binary system showed that, on one hand, the solubility of ethylene in the mesitylene was very high in a wide temperature range. Solubility is greatly affected by temperature. It shows that absorbing performance of mesitylene was better than toluene for C2H4while comparing with the VLE data for C2H4+C7H8binary system. So, mesitylene has considerable potential as a new ethylene absorbent and is worthy of research. This study support advanced process application development with VLE data and model foundation. On the other hand, the experimental results show the GEmax criterion, which is used to evaluate solvents, is correct.