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Benavides P.T.,University of Illinois at Chicago | Benavides P.T.,Viswamitra Research Institute | Diwekar U.,University of Illinois at Chicago | Diwekar U.,Viswamitra Research Institute
Fuel | Year: 2012

The continuing depletion of fossil fuel reserves and the increasing environmental concerns has encouraged engineers and scientists to look for an alternative, clean, and renewable fuel that can reduce the negative environmental impact. Biodiesel has been considered as one of the best candidate of one of these renewable fuels. One of the pathways to biodiesel production is the transesterification reaction of triglycerides from vegetable oils and short-chain alcohols. A batch reactor is employed for the production of biodiesel. The flexibility of the batch process allows operating the reactor with different feed stocks and product specifications. This condition becomes challenging for the reactor modeling and control since uncertainty in the feed composition turns into time-dependent uncertainty and requires a batch-process based stochastic optimal control. In the first part of this work, the optimal control in this reactor involves optimization of the concentration of fatty acid methyl esters, well known as biodiesel, under the control of reactor temperature and the strategy applied to solve this problem is based on the maximum principle. The strategy increased the concentration by 8.46%. As far as the minimum time required to obtain the same base concentration, it reduced the reaction time by 69.5%. © 2011 Elsevier Ltd. All rights reserved.


Benavides P.T.,University of Illinois at Chicago | Benavides P.T.,Viswamitra Research Institute | Diwekar U.,University of Illinois at Chicago | Diwekar U.,Viswamitra Research Institute
Fuel | Year: 2012

The determination of time-varying profiles through dynamic optimization is an exclusive characteristic of optimal control problems; however, these types of problems become more challenging when variability and uncertainty in any parameter is included. In biodiesel production, there are inherent uncertainties arising due to variation in initial composition, operating parameters, and mechanical equipment design that can have a significant impact on the product quantity, quality and process economics. Thus, one of the most influential uncertainties in this process is the feed composition since the percentage and type of triglycerides in biodiesel composition varies considerable. In this work, the optimal control for biodiesel production in a batch reactor developed in Part 1 is extended to a problem when uncertainty in the feed composition is considerably. Under control of reactor temperature, we applied a numerical method, based on the Steepest Ascent of Hamiltonian to solve the stochastic optimal control problem that involved the application of Ito processes and the stochastic maximum principle. It has been found that the temperature profile obtained using deterministic optimal control is robust in the face of feed composition uncertainties also. © 2011 Elsevier Ltd. All rights reserved.


Benavides P.T.,University of Illinois at Chicago | Benavides P.T.,Viswamitra Research Institute | Diwekar U.,University of Illinois at Chicago | Diwekar U.,Viswamitra Research Institute
Fuel | Year: 2013

The optimal control problem encountered in biodiesel production can be formulated using various performance indices, namely, maximum concentration, minimum time, and maximum profit. The problems involve determining optimal temperature profile so as to maximize these performance indices. This paper presents the formulations of these optimal control problems and analyzes the solutions. Optimal control problems involve the solution of partial or second order differential equation depending on the method used, resulting in difficult tasks to solve due to their mathematical representation. This difficulty becomes more challenging when uncertainty in any parameter is considered. It has been shown that the application of maximum principle in optimal control problems provides the same results but its formulation avoids the solution of second order or partial differential equations. In this work, we use the maximum principle to solve the problems in the deterministic case. Further, we consider uncertainty in the feed composition and their effects on the optimal control solution. © 2012 Elsevier Ltd. All rights reserved.


Benavides P.T.,University of Illinois at Chicago | Benavides P.T.,Viswamitra Research Institute | Salazar J.,Viswamitra Research Institute | Diwekar U.,University of Illinois at Chicago | Diwekar U.,Viswamitra Research Institute
Environmental Progress and Sustainable Energy | Year: 2013

The Lawrence K. Cecil Award in Environmental Chemical Engineering recognizes an individual's outstanding chemical engineering contribution and achievement in the preservation or improvement of the environment. The recipient must be a member of AIChE, have 15 years of chemical engineering experience in the environmental field, and demonstrate leadership in research, teaching, engineering, or regulatory activities in either the public or private sector. The award is presented annually by the Environmental Division. This paper was prepared by the 2011 Cecil Award recipient based on work presented at the AIChE national meeting in Minneapolis. Continuing depletion of fossil fuel reserves and increasing environmental concerns have encouraged engineers and scientists to look for alternative, clean, and renewable fuels that can reduce fossil-fuels' negative environmental impact and secure the energy supplies. Biodiesel has been considered as one of the best candidates for these renewable fuels. For its production, transesterification reaction of triglycerides is recognized as a feasible pathway. This reaction can be carried out in continuous or batch reactors, however, most of the other unit operations, like decanters and distillation columns, are operated continuously. Most of the studies of biodiesel production have been done in continuous models. In this paper, we evaluate batch and continuous processing options for biodiesel production from the economical point of view. The economic feasibility of biodiesel as well the plants configuration not only depends on technical design aspects but also on other important factors such as seasonal variation of feedstock, transportation costs, and storage costs of material. Therefore, our comparison involves size of the market, transportation distance from supplier to producer facility, and feedstock availability of soybean oil by the allocation of supply of raw material. It was found that based on these aspects, batch processing shows interesting results and should be considered for production rather that continuous production as it is done today. Moreover, a sensitivity analysis provides more insights of the flexibility of batch processing when scheduling variation is considered. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 11-24, 2013 Copyright © 2012 American Institute of Chemical Engineers Environ Prog.

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