SP4 - Oligomerization
Current technologies for ethylene oligomerization rely on the use of homogeneous organometallic catalysts. Environmental issues, among other reasons, prompts to the replacement of the homogeneous system by more friendly heterogeneous catalysts.
A large catalyst library (±100 samples) was tested from which the promising catalysts were selected and optimized. From this selection, several catalyst achieved the targeted productivity and lifetime. The productivity to liquid oligomers for an optimized Ni-Al-MCM-41 surpassed the initial target of 5 mmol/(kgcat•s) by ca. 24% in average during the 60 h run.
Identification of potential catalyst poisons that might be present in the ethylene stream leaving the OCM reactor and their impact on the catalytic performance was also a relevant aspect of the catalyst development. The most critical impurities were identified to be CO and CO2. In particular it was concluded from the poisoning studies that CO is a strong poison for the Ni-based oligomerization catalyst and must, thus, be eliminated from the stream entering the OLI reactor while CO2 concentration must be reduced to the minimum technically feasible levels.
In order to establish a correlation between catalyst properties and catalyst behavior, operando magnetic resonance (MR) spectroscopy was developed to follow OLI reaction over a reference Ni-containing heterogeneous catalyst, see Figure 6.
Using the optimized catalysts, an extensive experimental dataset was acquired which was used to develop a microkinetic model. This microkinetic model is capable to describe the effects of operating conditions and catalyst properties on ethylene oligomerization. Additionally, an industrial oligomerization reactor model based on these microkinetics was constructed and an industrial reactor was designed ‘in-silico’.
Finally, a pilot plant for ethylene oligomerization based on a fixed bed reactor was designed and assembled, see Figure 7. This pilot plant was used as demonstration unit to prove that the oligomerization step within OCMOL project was able to convert an ethylene-rich stream separated from OCM effluent into liquid fuels. The reactor model and pilot plant was used for predicting the optimal reaction operation in this pilot plant, including feedstock composition, temperature and pressure.
Selected Ni-SiO2-Al2O3 were formed and tested in the in the pilot plant. Reaction conditions were optimized in order to maximize the productivity lo liquid oligomers and lifetime.