Investment optimization model for freshwater acquisition and wastewater handling in shale gas production

Major challenges of water use in the drilling and fracturing process in shale gas production are large volumes required in a short‐period of time and the nonsteady nature of wastewater treatment. A new mixed‐integer linear programming (MILP) model for optimizing capital investment decisions for water use for shale gas production through a discrete‐time representation of the State‐Task Network is presented. The objective is to minimize the capital cost of impoundment, piping, and treatment facility, and operating cost including freshwater, pumping, and treatment. The goal is to determine the location and capacity of impoundment, the type of piping, treatment facility locations and removal capability, freshwater sources, as well as the frac schedule. In addition, the impact of several factors such as limiting truck hauling and increasing flowback volume on the solution is examined. A case study is optimized to illustrate the application of the proposed formulation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1770–1782, 2015     

Mono‐Estolide Synthesis from trans‐8‐Hydroxy‐Fatty Acids by Lipases in Solvent‐Free Media and Their Physical Properties

Pseudomonas aeruginosa 42A2 is known to produce two hydroxy‐fatty acids, 10(S)‐hydroxy‐8(E)‐octadecenoic and 7,10(S,S)‐dihydroxy‐8(E)‐octadecenoic acids, when cultivated in a mineral medium using oleic acid as a single carbon source. These compounds were purified, 91 and 96 % respectively, to produce two new families of estolides: trans‐8‐estolides and saturated estolides from the monohydroxylated monomer. trans‐8‐estolides were produced by three different lipases (Novozym 435, Lipozyme RM IM and Lipozyme TL IM) with reaction yields between 68.4 ± 2.1 and 94.7 ± 2.4 % in a solvent‐free medium at 80 °C in 168 h under vacuum. Novozym 435 was found to be the most efficient biocatalyst for both hydroxy‐fatty acids with reaction yields of 71.7 ± 2.3 and 94.7 ± 2.4 %, respectively. Moreover, saturated estolides were also produced from a saturated 10(S)‐hydroxy‐8(E)‐octadecenoic. These estolides were chemically and enzymatically synthesized with Novozym 435, under the previous described reaction conditions with yields of 60.7 ± 2.1 and 71.2 ± 2.3 % respectively. Finally, viscosity, glass transition temperature, decomposition temperatures and enthalpies were determined to characterize both types of estolides. Thermal applications for both types of polyesters were improved since glass transition temperatures were lowered and decomposition temperatures were increased, with respect to their corresponding substrates.     

Antecedents of construction project coalitions: a study of the Spanish construction industry

Research into the formation of alliances, relevant in the field of strategic management and especially, in the construction industry, is often explained in terms of interdependency and complementarities (exogenous factors). In contrast, the influence of a firm’s social relations networks (endogenous factors) has hardly been studied at all. Thus, a model is needed that includes both exogenous and endogenous factors as antecedents to the formation of strategic alliances in the construction industry. Cooperation in the construction sector is especially frequent, above all in public works programmes, as their scale requires coalitions of different‐sized firms. Accordingly, to explore how both exogenous and endogenous factors influence the formation of alliances, a social network analytical method—Multiple Regression Quadratic Assignment Procedure (MRQAP)—was applied to cooperative project coalitions in the Spanish public works construction sector from 2001–2007. Empirical findings confirm that construction companies form coalitions, principally on the basis of past alliances. Membership of business associations and groups is also a key factor, though the influence of geographic proximity is the most debatable result. In the construction industry, the formation of alliances is conditioned, among other factors, by previous social and economic relations that can generate the necessary information and trust for the selection of whichever partner is considered the most suitable for the development of the joint project.     

Hydrogenation of vegetable oil using highly dispersed Pt/γ-Al2O3 catalyst: Effects of key operating parameters and deactivation study

In the present work, Pt/γ-Al₂O₃ catalysts with high metal dispersion were prepared and characterized using chloroplatinic acid and platinum acetylacetonate as metal precursors. The activity and selectivity of the catalysts were evaluated in the hydrogenation of sunflower oil. A comprehensive analysis of the effects of key operational parameters on catalytic performance was carried out. The experimental variables were hydrogen pressure (275.8–551.6 kPa), temperature (160–200°C), and catalyst loading (0.005–0.015 kg Pt_exp/m³_oil). Platinum catalysts were active, with a double bond conversion of 28% at 2 h. The metal precursor affected catalyst selectivity. The catalyst prepared with chloroplatinic acid exhibited a lower formation of trans-isomers compared with Pt acetylacetonate. The γ-Al₂O₃ supported platinum catalyst with a metal loading of 0.51 wt.% and a metal dispersion of 98% maintained its initial catalyst activity and selectivity after 10 consecutive uses (1200 min accumulate operation time), without changes in its catalytic properties. The obtained results suggested that Pt catalysts are an attractive alternative to conventional nickel catalysts for the hydrogenation of vegetable oil.     

Optimization models for shale gas water management

There are four key aspects for water use in hydraulic fracturing, including source water acquisition, wastewater production, reuse and recycle, and subsequent transportation, storage, and disposal. Water use life cycle is optimized for wellpads through a discrete‐time two‐stage stochastic mixed‐integer linear programming model under uncertain availability of water. The objective is to minimize expected transportation, treatment, storage, and disposal cost while accounting for the revenue from gas production. Assuming freshwater sources, river withdrawal data, location of wellpads, and treatment facilities are given, the goal is to determine an optimal fracturing schedule in coordination with water transportation, and its treatment and reuse. The proposed models consider a long‐time horizon and multiple scenarios from historical data. Two examples representative of the Marcellus Shale play are presented to illustrate the effectiveness of the formulation, and to identify optimization opportunities that can improve both the environmental impact and economical use of water. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3490–3501, 2014     

Optimal maintenance scheduling of a gas engine power plant using generalized disjunctive programming

A new continuous‐time model for long‐term scheduling of a gas engine power plant with parallel units is presented. Gas engines are shut down according to a regular maintenance plan that limits the number of hours spent online. To minimize salary expenditure with skilled labor, a single maintenance team is considered which is unavailable during certain periods of time. Other challenging constraints involve constant minimum and variable maximum power demands. The objective is to maximize the revenue from electricity sales assuming seasonal variations in electricity pricing by reducing idle times and shutdowns in high‐tariff periods. By first developing a generalized disjunctive programming model and then applying both big‐M and hull reformulation techniques, we reduce the burden of finding the appropriate set of mixed‐integer linear constraints. Through the solution of a real‐life problem, we show that the proposed formulations are very efficient computationally, while gaining valuable insights about the system. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2083–2097, 2014     

Acid Value,Polar Compounds and Polymers as Determinants of the Efficient Conversion of Waste Frying Oils to Biodiesel

The cost of starting materials for the production of biodiesel is typically 75 % of the final retail price. Oils previously used for frying, waste frying oils (WFO), are a very suitable resource. Repetitive use of oil for frying foods involves high temperature, moisture and aeration for extended periods. The most important deterioration processes triggered by these conditions are hydrolysis and oxidation. In this study, 24 WFO samples of different origins were analyzed and classified as potential starting materials for biodiesel production using three quality parameters representing the main factors that affect the conversion of WFO. These parameters were: acid value, content of polar compounds and content of polymers, which varied in the ranges from 0.2 to 7.6, 14.9 to 43.2 and 0.9 to 15.2 %, respectively. Ester content obtained using conventional transesterification (TE) for WFO conversion decreased with increased levels of WFO deterioration determined by any of the three parameters noted above. TE products obtained had ester content between 81.4 and 95.7 %. Total ester content of a WFO sample with relatively low %AV could be increased to 96.5 % using a two-stage base catalysis TE. Finally, conversion of WFO samples resulted in ester contents of 89.0 and 91.3 %, respectively, when transesterified by conventional TE. After blending up to 10 % with refined oil, the ester content achieved was near 96.5 %. Thus, the blending represents an alternative for obtaining a product with suitable ester content.     

Shale gas pad development planning under price uncertainty

In this article, we study shale gas pad development under natural gas price uncertainty. We optimize the sequence of operations, gas curtailment, and storage on a single pad to maximize the net present value. The optimization problem is formulated as an mixed-integer linear programming model, which is similar to the one proposed by Ondeck et al. We investigate how natural gas price uncertainty affects the operation strategy in the pad development. Both two-stage and multistage stochastic programming are used as the mathematical framework to hedge against uncertainty. Our case study shows that there is value of using stochastic programming when the price variance is high. However, when the variance of the price is low, solving the stochastic programming problems does not create additional value compared with solving the deterministic problem.     

New Formulation of a Methylseleno-Aspirin Analog with Anticancer Activity Towards Colon Cancer

Aspirin (ASA) has attracted wide interest of numerous scientists worldwide thanks to its chemopreventive and chemotherapeutic effects, particularly in colorectal cancer (CRC). Incorporation of selenium (Se) atom into ASA has greatly increased their anti-tumoral efficacy in CRC compared with the organic counterparts without the Se functionality, such as the promising antitumoral methylseleno-ASA analog (1a). Nevertheless, the efficacy of compound 1a in cancer cells is compromised due to its poor solubility and volatile nature. Thus, 1a has been formulated with native α-, β- and γ-cyclodextrin (CD), a modified β-CD (hydroxypropyl β-CD, HP-β-CD) and Pluronic F127, all of them non-toxic, biodegradable and FDA approved. Water solubility of 1a is enhanced with β- and HP- β-CDs and Pluronic F127. Compound 1a forms inclusion complexes with the CDs and was incorporated in the hydrophobic core of the F127 micelles. Herein, we evaluated the cytotoxic potential of 1a, alone or formulated with β- and HP- β-CDs or Pluronic F127, against CRC cells. Remarkably, 1a formulations demonstrated more sustained antitumoral activity toward CRC cells. Hence, β-CD, HP-β-CD and Pluronic F127 might be excellent vehicles to improve pharmacological properties of organoselenium compounds with solubility issues and volatile nature.     

Study of the refractory used in a submerged arc furnace in the copper-making industry

A cost driver in the copper-making industry is the periodical relining of the furnaces because of wear. This paper presents thermochemical calculations (using the FactSage^™ database) focused on the evaluation of the slag-refractory chemical interaction in a submerged arc furnace (SAF) used for slag-cleaning operations. This evaluation was made under different conditions: slag-refractory volume ratio, oxygen partial pressure, and different types of slag. The new phases formed as a consequence of the slag-refractory chemical interaction were identified and quantified. To support the theoretical calculations based on thermochemistry, a postmortem study was carried out on a SAF used at the Atlantic Copper Smelter (Spain) after a 6-year campaign (4.5 mill. t. slag processed). Refractory samples were taken from different locations on the wall and analyzed using a scanning electron microscope equipped with an Energy Dispersive Spectroscopy system.