Patrick L. Mills

A citrus waste-based biorefinery as a source of renewable energy: technical advances and analysis of engineering challenges

An assessment of recent technical advances on pretreatment processes and its effects on enzymatic hydrolysis as the main steps of a proposed citrus processing waste (CPW) biorefinery is presented. Engineering challenges and relevant gaps in scientific and technical information for reliable design, modeling and scale up of a CPW biorefinery are also discussed. Some integrated physico-chemical pretreatments are proposed for testing for CPW, including high speed knife-grinding and simultaneous caustic addition. These new proposed processes and the effect of parameters such as particle size, surface area and morphology, pore volume and chemical composition of the diverse fractions resulting from pretreatment and enzymatic hydrolysis need to be evaluated and compared for pretreated and untreated samples of grapefruit processing waste. This assessment suggests the potential for filling the data gaps, and preliminary results demonstrate that the reduction of particle size and the increased surface area for the CPW will result in higher reaction rates and monosaccharide yields for the pretreated waste material.

Challenges in Reaction Engineering Practice of Heterogeneous Catalytic Systems

Abstract The Topsoe Catalysis Forum was created as a framework for an open exchange of views on catalysis in fields of interest to Haldor Topsoe. The forum scope included a discussion of new catalytic reactions and new principles of catalysis in an attempt to jointly look beyond the horizon ( Topsoe catalysis forum, 2013 ). The 2013 meeting was dedicated to Modeling and Simulation of Heterogeneous Catalytic Processes and provided an opportunity to review and discuss the current state of the art in the engineering practice of heterogeneous catalytic systems ( Topsoe catalysis forum, 2013 ). The primary objective of this chapter is to capture key elements of our conference presentation ( Dudukovic, 2013 ) that were focused on multiscale reaction engineering concepts and to what extent these have been applied in the commercial implementation of multiphase heterogeneous catalytic reacting systems. Of particular interest is to identify common approaches and tools used in practice, and to examine their effectiveness in the scale-up and development of more efficient, environmentally friendly catalytic processes. Current practice is limited by the availability of experimental tools to increase the reliability of scale-up, and by the lack of more robust models for analysis and optimization of reactor systems for existing processes or the design of new reactor systems for implementation of new catalytic chemistries. From an economic perspective, the pursuit of short-term financial objectives favors the use of existing reactors with minimal modifications with performance analysis based upon simplified approaches. A longer-term perspective on the development and implementation of more advanced experimental techniques and modeling approaches for reactor analysis that are applicable to commercial reactor conditions would accelerate the development of new process technologies and result in reduced risk with associated lower costs.

Molecular and biochemical characterization of recombinant cel12B, cel8C, and peh28 overexpressed in Escherichia coli and their potential in biofuel production

BackgroundThe high crystallinity of cellulosic biomass myofibrils as well as the complexity of their intermolecular structure is a significant impediment for biofuel production. Cloning of celB-, celC-encoded cellulases (cel12B and cel8C) and peh-encoded polygalacturonase (peh28) from Pectobacterium carotovorum subsp. carotovorum (Pcc) was carried out in our previous study using Escherichia coli as a host vector. The current study partially characterizes the enzymes’ molecular structures as well as their catalytic performance on different substrates which can be used to improve their potential for lignocellulosic biomass conversion.Resultsβ-Jelly roll topology, (α/α)6 antiparallel helices and right-handed β-helices were the folds identified for cel12B, cel8C, and peh28, respectively, in their corresponding protein model structures. Purifications of 17.4-, 6.2-, and 6.0-fold, compared to crude extract, were achieved for cel12B and cel8C, and peh28, respectively, using specific membrane ultrafiltrations and size-exclusion chromatography. Avicel and carboxymethyl cellulose (CMC) were substrates for cel12B, whereas for cel8C catalytic activity was only shown on CMC. The enzymes displayed significant synergy on CMC but not on Avicel when tested for 3xa0h at 45xa0°C. No observed β-glucosidase activities were identified for cel8C and cel12B when tested on p-nitrophenyl-β-d-glucopyranoside. Activity stimulation of 130% was observed when a recombinant β-glucosidase from Pcc was added to cel8C and cel12B as tested for 3xa0h at 45xa0°C. Optimum temperature and pH of 45xa0°C and 5.4, respectively, were identified for all three enzymes using various substrates. Catalytic efficiencies (kcat/Km) were calculated for cel12B and cel8C on CMC as 0.141 and 2.45xa0ml/mg/s respectively, at 45xa0°C and pH 5.0 and for peh28 on polygalacturonic acid as 4.87xa0ml/mg/s, at 40xa0°C and pH 5.0. Glucose and cellobiose were the end-products identified for cel8C, cel12B, and β-glucosidase acting together on Avicel or CMC, while galacturonic acid and other minor co-products were identified for peh28 action on pectin.ConclusionsThis study provides some insight into which parameters should be optimized when application of cel8C, cel12B, and peh28 to biomass conversion is the goal.