Christos T. Maravelias

Nonenzymatic Sugar Production from Biomass Using Biomass-Derived γ-Valerolactone

Renewable Breakdown Routine In order to transform cellulose-containing biomass into liquid fuels such as ethanol, it is first necessary to break down the cellulose into its constituent sugars. Efforts toward this end have focused on chemical protocols using concentrated acid or ionic liquid solvents, and on biochemical protocols using cellulase enzymes. Luterbacher et al. (p. 277) now show that γ-valerolactone, a small molecule solvent that can itself be sourced renewably from biomass, promotes efficient and selective thermal breakdown of cellulose in the presence of dilute aqueous acid. A solvent sourced from biomass may offer a cost-effective means of breaking down cellulose for biofuels production. Widespread production of biomass-derived fuels and chemicals will require cost-effective processes for breaking down cellulose and hemicellulose into their constituent sugars. Here, we report laboratory-scale production of soluble carbohydrates from corn stover, hardwood, and softwood at high yields (70 to 90%) in a solvent mixture of biomass-derived γ-valerolactone (GVL), water, and dilute acid (0.05 weight percent H2SO4). GVL promotes thermocatalytic saccharification through complete solubilization of the biomass, including the lignin fraction. The carbohydrates can be recovered and concentrated (up to 127 grams per liter) by extraction from GVL into an aqueous phase by addition of NaCl or liquid CO2. This strategy is well suited for catalytic upgrading to furans or fermentative upgrading to ethanol at high titers and near theoretical yield. We estimate through preliminary techno-economic modeling that the overall process could be cost-competitive for ethanol production, with biomass pretreatment followed by enzymatic hydrolysis.

INTEGRATION OF PRODUCTION PLANNING AND SCHEDULING: OVERVIEW CHALLENGES AND OPPORTUNITIES

We review the integration of medium-term production planning and short-term scheduling. We begin with an overview of supply chain management and the associated planning problems. Next, we formally define the production planning problem and explain why integration with scheduling leads to better solutions. We present the major modeling approaches for the integration of scheduling and planning decisions, and discuss the major solution strategies. We close with an account of the challenges and opportunities in this area.

Scope for industrial applications of production scheduling models and solution methods

Abstract This paper gives a review on existing scheduling methodologies developed for process industries. Above all, the aim of the paper is to focus on the industrial aspects of scheduling and discuss the main characteristics, including strengths and weaknesses of the presented approaches. It is claimed that optimization tools of today can effectively support the plant level production. However there is still clear potential for improvements, especially in transferring academic results into industry. For instance, usability, interfacing and integration are some aspects discussed in the paper. After the introduction and problem classification, the paper discusses some lessons learned from industry, provides an overview of models and methods and concludes with general guidelines and examples on the modeling and solution of industrial problems.

Production of renewable jet fuel range alkanes and commodity chemicals from integrated catalytic processing of biomass

This article presents results from experimental studies and techno-economic analysis of a catalytic process for the conversion of whole biomass into drop-in aviation fuels with maximal carbon yields. The combined research areas highlighted include biomass pretreatment, carbohydrate hydrolysis and dehydration, and catalytic upgrading of platform chemicals. The technology centers on first producing furfural and levulinic acid from five- and six-carbon sugars present in hardwoods and subsequently upgrading these two platforms into a mixture of branched, linear, and cyclic alkanes of molecular weight ranges appropriate for use in the aviation sector. Maximum selectivities observed in laboratory studies suggest that, with efficient interstage separations and product recovery, hemicellulose sugars can be incorporated into aviation fuels at roughly 80% carbon yield, while carbon yields to aviation fuels from cellulose-based sugars are on the order of 50%. The use of lignocellulose-derived feedstocks rather than commercially sourced model compounds in process integration provided important insights into the effects of impurity carryover and additionally highlights the need for stable catalytic materials for aqueous phase processing, efficient interstage separations, and intensified processing strategies. In its current state, the proposed technology is expected to deliver jet fuel-range liquid hydrocarbons for a minimum selling price of

A hybrid MILP/CP decomposition approach for the continuous time scheduling of multipurpose batch plants

4.75 per gallon assuming nth commercial plant that produces 38 million gallons liquid fuels per year with a net present value of the 20 year biorefinery set to zero. Future improvements in this technology, including replacing precious metal catalysts by base metal catalysts and improving the recyclability of water streams, can reduce this cost to

A general framework for the assessment of solar fuel technologies

2.88 per gallon.

A stochastic programming approach for clinical trial planning in new drug development

A hybrid Mixed-Integer Linear Programming (MILP)/Constraint Programming (CP) decomposition algorithm is proposed for the short-term scheduling of batch plants that rely on the State Task Network (STN) representation. The decisions about the type and number of tasks performed, as well as the assignment of units to tasks are made by the MILP master problem (MP). The CP subproblem checks the feasibility of a specific assignment and generates integer cuts for the master problem. A graph-theoretic preprocessing that determines time windows for the tasks and equipment units is also performed to enhance the performance of the algorithm. To exclude as many infeasible configurations as possible, three classes of integer cuts are generated. Various objective functions such as the minimization of assignment cost, the minimization of makespan for fixed demand and the maximization of profit for a fixed time horizon can be accommodated. Variable batch-sizes and durations, different storage policies, and resource constraints are taken into account. The proposed framework is very general and can be used for the solution of almost all batch scheduling problems. Numerical results show that for some classes of problems, the proposed algorithm can be two to three orders of magnitude faster than standalone MILP and CP models.

A strategy for the simultaneous catalytic conversion of hemicellulose and cellulose from lignocellulosic biomass to liquid transportation fuels

The conversion of carbon dioxide and water into fuels in a solar refinery presents a potential solution for reducing greenhouse gas emissions, while providing a sustainable source of fuels and chemicals. Towards realizing such a solar refinery, there are many technological advances that must be met in terms of capturing and sourcing the feedstocks (namely CO2, H2O, and solar energy) and in catalytically converting CO2 and H2O. In the first part of this paper, we review the state-of-the-art in solar energy collection and conversion to solar utilities (heat, electricity, and as a photon source for photo-chemical reactions), CO2 capture and separation technology, and non-biological methods for converting CO2 and H2O to fuels. The two principal methods for CO2 conversion include (1) catalytic conversion using solar-derived hydrogen and (2) direct reduction of CO2 using H2O and solar energy. Both hydrogen production and direct CO2 reduction can be performed electro-catalytically, photo-electrochemically, photo-catalytically, and thermochemically. All four of these methods are discussed. In the second part of this paper, we utilize process modeling to assess the energy efficiency and economic feasibility of a generic solar refinery. The analysis demonstrates that the realization of a solar refinery is contingent upon significant technological improvements in all areas described above (solar energy capture and conversion, CO2 capture, and catalytic conversion processes).

A decomposition framework for the scheduling of single- and multi-stage processes

The paper presents a multi-stage stochastic programming formulation for the planning of clinical trials in the pharmaceutical research and development (R&D) pipeline. Scenarios are used to account for the endogenous uncertainty in clinical trial outcomes. Given a portfolio of potential drugs and limited resources, the model determines the trials to be performed in each planning period and scenario. To reduce the size of the formulation we employ a reduced set of scenarios without compromising the quality of uncertainty representation. Furthermore, we present a number of ideas that allow us to reduce the number of non-anticipativity constraints necessary to model indistinguishable scenarios. The proposed approach is the first stochastic programming formulation to address this problem.

Large-scale bi-level strain design approaches and mixed-integer programming solution techniques.

We develop and evaluate an integrated catalytic conversion strategy, which utilizes both the hemicellulose and cellulose fractions of lignocellulosic biomass to produce liquid hydrocarbon fuels (butene oligomers). In this strategy, the cellulose and hemicellulose fractions are simultaneously converted to levulinic acid (LA), using LA-derived γ-valerolactone (GVL) as a solvent. The LA is then converted to GVL, which is subsequently converted to butene, and then to butene oligomers. To generate the integrated strategy, we develop separation subsystems to achieve experimentally optimized feed concentrations for the catalytic conversion steps. Importantly, to minimize the utility requirements of the overall process, we perform heat integration, which allows us to satisfy all heating requirements from combustion of biomass residues, which are also used to produce steam for electricity generation. In addition, we develop an alternative design in which there is no electricity generation, study alternative feedstocks, and perform sensitivity analyses. Our technoeconomic analysis shows that the integrated strategy using hybrid poplar feedstock leads to a minimum selling price of