(6iq) Optimization of 2-EH Product Purification Section Using Advanced Modelling Tools

Authors: 
AlGhamdi, A., SABIC
Research Interests: and Teaching Interests:

2-Ethyl Hexanol (2-EH) is produced in a SABIC affiliate, Saudi Arabia Fertilizer Corporation (SAFCO), using OXO technology from synthesis gas and propylene. In this process, the crude 2-EH alcohol product that comes out of the 2-EH reactor, contains lights (N-Butanol), heavies, intermediate product 2-Ethyl Hexanal(EHA), along with the 2-EH product, and water. This crude alcohol needs to be purified to get the pure (more than 99 wt%) 2-EH product. Also, N-Butanol shall be distilled out of crude alcohol completely as waste liquid fuel (WLF) and the intermediate product EHA shall be recovered and recycled back to the 2-EH reactor. Hence, the product purification section consists of series (4 columns) of distillation columns operated in vacuum to achieve the above objectives with minimum losses of 2-EH through WLF, highest purity of 2-EH and minimum EHA content in the 2-EH product.

In the product purification distillation column sequence, the first column separates the 2-EH product with heavies without any lights and with minimum EHA in ppm. Lights with EHA will be distilled of the first column, sent to lights column, where EHA is taken as bottom product and recycled, lights are taken as distillate. 2-EH product from the first column is sent to third column, where heavies are separated as bottoms, and pure 2-EH at (more than 99 wt%) is produced from the top and sent to the product tank. The above entire process objectives shall be achieved with minimum energy consumption and less product and intermediate product losses with light and heavy component streams.

In this Case Study, a thorough actual plant data analysis of the existing system has been carried out. It has been found that more than 5 MTPD of 2-EH is lost through WLF stream. Furthermore, considerable quantity of 2-EH product that is produced is always recycled back to reaction system. This higher recycle streams require high-energy requirement. Hence, an optimization of the system product purification system has been carried out, using Aspen Tech ® (steady state and dynamics). In the case study, a detailed model has been developed and validated with the PFD. Optimum conditions for the system have been found using the steady state model. A dynamic model has also been developed and analyzed for columns dynamics for various disturbances like feed disturbances. Based on these, fine-tuned the existing control philosophy of the system by incorporating cascade control. With the above model based study, convinced plant process and operational teams with the precise control settings for all the control parameters. The new settings have been implemented in the plant in stages starting from 2017 end till September 2018. The entire product refining system has been stabilized with the new conditions, and updated the DCS alarms and trip logics based on the dynamic model.