Carlos A. Henao

Surrogate-Based Process Synthesis

Abstract Superstructure optimization-based process synthesis is generally regarded as theoretically powerful; however, it has not been widely used in practice since it typically results in large-scale non-convex Mixed-Integer Non-Linear Programs (MINLP) which are very hard to solve effectively. To address this limitation, we propose a framework leading to substantially simpler formulations through the replacement of complex first-principle unit models by compact and yet accurate surrogate models. We show how all the relevant variable relationships established by a unit model, can be expressed in terms of a subset of the original model variables. We discuss how this subset of variables can be identified, and we present a method to develop high quality surrogate models through artificial neural networks. Finally, we propose a tailored surrogate model reformulation to incorporate binary variables that allow activation/deactivation of particular units within the superstructure model. An example is presented to illustrate the application of the proposed framework.

A superstructure-based framework for simultaneous process synthesis, heat integration, and utility plant design

Abstract We propose a superstructure optimization framework for process synthesis with simultaneous heat integration and utility plant design. Processing units in the chemical plant can be modeled using rigorous unit models or surrogate models generated from experimental results or off-line calculations. The utility plant subsystem includes multiple steam types with variable temperature and pressure. For the heat integration subsystem, we consider variable heat loads of process streams as well as variable intervals for the utilities. To enhance the solution of the resulting mixed-integer nonlinear programming models, we develop (1) new methods for the calculation of steam properties, (2) algorithms for variable bound calculation, and (3) systematic methods for the generation of redundant constraints. The applicability of our framework is illustrated through a biofuel case study which includes a novel non-enzymatic hydrolysis technology and new separation technologies, both of which are modeled based on experimental results.

Conversion of Glycerol to Liquid Fuels

Abstract A significant fraction of the total petroleum supply is used for transportation in the form of liquid hydrocarbons. This fact, along with the increasing demand for oil in developing countries has led to substantial research efforts in the area of renewable liquid fuels. One alternative is the conversion of vegetal oil and animal fat into bio-diesel. However, this comes with the production of significant amounts of glycerol, a byproduct that will become abundant if large scale bio-diesel production is implemented. In order to increase the total biomass to fuel efficiency during the production of bio-diesel and address the overproduction of glycerol, a novel integrated Glycerol Reforming (GR) + Fischer-Tropsch (FT) process is presented. The novelty of this process lies in the use of a Rhenium-based catalyst for the conversion of aqueous glycerol to synthesis gas (syngas). This step reduces significantly the cost of syngas production in traditional green FT processes. This work presents a preliminary process synthesis and an economic evaluation for a medium capacity GR-FT plant. The results show that the integrated process is economically attractive, and that there is room for further improvements trough the use of systematic process design and optimization methodologies.

A Novel Catalytic Strategy for the Production of Liquid Fuels from Ligno-cellulosic Biomass

Abstract Levulinic acid has recently been identified as a potential platform chemical that can be produced from agricultural waste and can lead to specialty chemicals, fuel additives and liquid fuels. Based on this versatile molecule, we have developed a catalytic cascade approach to convert solid cellulose into liquid hydrocarbon fuels for use in the transportation sector. Following a systems approach, a conceptual process synthesis effort was undertaken, leading to a novel process that combines the mentioned catalytic cascade with proper separation and recycle operations. A techno-economic analysis based on detailed simulation (accounting for experimental reaction conditions and yields) as well as detailed equipment sizing and costing was performed, followed by sensitivity analysis studies to identify the key economic parameters. Furthermore, to assess its economic attractiveness, the process was compared to a benchmark lignocellulosic bio-ethanol production facility. Finally, we considered two different types of biomass. Our studies indicate that the proposed strategy is economically attractive when biomass with high C 6 -sugar content is used.