Alternative Processing Sequence for Process Simplification, Cost Reduction, and Enhanced Light Olefin Recovery from Shale Gas

Natural gas liquids (NGLs) in shale gas are the predominant feedstock for light olefin production. Conventionally, NGLs are separated from CH4 and then fractionated into individual components before these components go through either steam cracking or catalytic dehydrogenation. In this work, we introduce an alternative processing sequence to intensify and simplify the conventional process. In the resulting processes, some of the front-end separations are delayed toward the end, which eliminates several repeated separations and associated equipment. Light hydrocarbons, such as CH4, serve as diluents to enhance the performance of steam cracker and catalytic dehydrogenation reactors. Modeling results for a 100 million standard cubic feet per day shale gas feed from the Bakken field show that the alternative processing sequence not only eliminates duplication of some process steps, leading to several process simplifications, reduced cost, and energy demand, but also increased olefin yield from the shale gas NGLs. The proposed concepts could be applied to many other reaction-separation networks, resulting in a more enriched flowsheet search space for investigation

Synthesis of Cu₂ZnSnS₄ Nanocrystal Ink and Its Use for Solar Cells

Synthesis of Cu2ZnSnS4 Nanocrystal Ink and Its Use for Solar Cell

Sun-to-Fuel Assessment of Routes for Fixing CO₂ as Liquid Fuel

This study presents a systems approach for comparing alternative routes for converting CO2 to liquid fuel using solar energy based on a novel metric of sun-to-fuel (STF) efficiency. The metric refers to the fraction of incident solar energy that is recovered in the liquid fuel. The STF efficiency analysis identifies energy and land use efficient routes that require immediate research and development effort to speed up their progress toward long-term cost-effectiveness. The analysis’ unique insights are particularly relevant for densely populated regions, having scarce per capita land availability relative to the per capita energy demands. With atmospheric CO2 as the renewable carbon source, we present a detailed case study comparing the currently known photosynthetic routes with a theoretical route based on direct extraction of CO2 from air and its subsequent thermochemical conversion to liquid fuel. The findings indicate that the latter route could be potentially more energy and thereby land use efficient than any of the currently known photosynthetic routes, therefore, warranting its inclusion in any transportation fuels research portfolio. An interesting finding of our study is that for the interim period while CO2 extraction is still uneconomical and CO2 sourced from power plants is instead used, the relative energy efficiency of different routes remains unchanged. This suggests that the results in general are independent of the concentration of the CO2 source

Earth Abundant Element Cu₂Zn(Sn_1−<i>x</i>Ge_<i>x</i>)S₄ Nanocrystals for Tunable Band Gap Solar Cells: 6.8% Efficient Device Fabrication

Cu2Zn(Sn1−xGex)S4 nanocrystals have been synthesized via batch reaction in oleylamine with no additional surfactants present. The nanocrystals are knife-coated on molybdenum substrates and then selenized to form a dense layer of Cu2Zn(Sn1−xGex)(S,Se)4, which is then used as the photoabsorbing layer in a thin film solar cell. The band gaps of the nanocrystals and the resulting solar cells are demonstrated to be controlled by adjusting the Ge/(Ge+Sn) ratio of the nanocrystal synthesis precursors. Solar cells fabricated from Cu2ZnGeS4 nanocrystal films yielded a power conversion efficiency of 0.51%. However, Cu2Zn(SnxGe1−x)S4 nanocrystals with a Ge/(Ge+Sn) ratio 0.7 yielded devices with an efficiency of 6.8% when synthesized to be Cu-poor and Zn-rich. This result opens the possibility of forming Ge gradients to direct minority carriers away from high recombination interfaces and significantly improve the device efficiency of CZTSSe-based solar cells

Earth Abundant Element Cu₂Zn(Sn_1−<i>x</i>Ge_<i>x</i>)S₄ Nanocrystals for Tunable Band Gap Solar Cells: 6.8% Efficient Device Fabrication

Cu2Zn(Sn1−xGex)S4 nanocrystals have been synthesized via batch reaction in oleylamine with no additional surfactants present. The nanocrystals are knife-coated on molybdenum substrates and then selenized to form a dense layer of Cu2Zn(Sn1−xGex)(S,Se)4, which is then used as the photoabsorbing layer in a thin film solar cell. The band gaps of the nanocrystals and the resulting solar cells are demonstrated to be controlled by adjusting the Ge/(Ge+Sn) ratio of the nanocrystal synthesis precursors. Solar cells fabricated from Cu2ZnGeS4 nanocrystal films yielded a power conversion efficiency of 0.51%. However, Cu2Zn(SnxGe1−x)S4 nanocrystals with a Ge/(Ge+Sn) ratio 0.7 yielded devices with an efficiency of 6.8% when synthesized to be Cu-poor and Zn-rich. This result opens the possibility of forming Ge gradients to direct minority carriers away from high recombination interfaces and significantly improve the device efficiency of CZTSSe-based solar cells

Earth Abundant Element Cu₂Zn(Sn_1−<i>x</i>Ge_<i>x</i>)S₄ Nanocrystals for Tunable Band Gap Solar Cells: 6.8% Efficient Device Fabrication

Cu2Zn(Sn1−xGex)S4 nanocrystals have been synthesized via batch reaction in oleylamine with no additional surfactants present. The nanocrystals are knife-coated on molybdenum substrates and then selenized to form a dense layer of Cu2Zn(Sn1−xGex)(S,Se)4, which is then used as the photoabsorbing layer in a thin film solar cell. The band gaps of the nanocrystals and the resulting solar cells are demonstrated to be controlled by adjusting the Ge/(Ge+Sn) ratio of the nanocrystal synthesis precursors. Solar cells fabricated from Cu2ZnGeS4 nanocrystal films yielded a power conversion efficiency of 0.51%. However, Cu2Zn(SnxGe1−x)S4 nanocrystals with a Ge/(Ge+Sn) ratio 0.7 yielded devices with an efficiency of 6.8% when synthesized to be Cu-poor and Zn-rich. This result opens the possibility of forming Ge gradients to direct minority carriers away from high recombination interfaces and significantly improve the device efficiency of CZTSSe-based solar cells

Estimation of Liquid Fuel Yields from Biomass

We have estimated sun-to-fuel yields for the cases when dedicated fuel crops are grown and harvested to produce liquid fuel. The stand-alone biomass to liquid fuel processes, that use biomass as the main source of energy, are estimated to produce one-and-one-half to three times less sun-to-fuel yield than the augmented processes. In an augmented process, solar energy from a fraction of the available land area is used to produce other forms of energy such as H2, heat etc., which are then used to increase biomass carbon recovery in the conversion process. However, even at the highest biomass growth rate of 6.25 kg/m2·y considered in this study, the much improved augmented processes are estimated to have sun-to-fuel yield of about 2%. We also propose a novel stand-alone H2Bioil-B process, where a portion of the biomass is gasified to provide H2 for the fast-hydropyrolysis/hydrodeoxygenation of the remaining biomass. This process is estimated to be able to produce 125−146 ethanol gallon equivalents (ege)/ton of biomass of high energy density oil but needs experimental development. The augmented version of fast-hydropyrolysis/hydrodeoxygenation, where H2 is generated from a nonbiomass energy source, is estimated to provide liquid fuel yields as high as 215 ege/ton of biomass. These estimated yields provide reasonable targets for the development of efficient biomass conversion processes to provide liquid fuel for a sustainable transport sector

Identifying Heat-Integrated Energy-Efficient Multicomponent Distillation Configurations

We present a tractable nonlinear programming (NLP) formulation that models a given multi-component distillation configuration and searches for its global minimum heat duty. The novelty in the current model is that it can explore feasible heat integrations with a pre-specified desired minimum approach temperature between various condensers and reboilers while simultaneously optimizing the operating conditions within the configuration. We do not use cumbersome thermodynamic models for the equilibrium temperature calculation of a saturated multicomponent mixture. Instead, we propose a modified version of the well-known Antoine equation that reduces the calculation of the temperature at a given pressure to a simple function of component mole fractions and relative volatilities while retaining the fidelity of more complex models. We explore possible heat integrations by creating a heat exchange network between column condensers, reboilers, and side draw product locations. Considering these integrations along with the heat duty minimization is essential because it is often possible to alter the operating conditions of the columns and reduce energy consumption by admitting more heat integration possibilities. Finally, we demonstrate the power of our framework in identifying optimal configurations that yield large energy savings for several four- and five-component zeotropic distillation systems

Sulfide Nanocrystal Inks for Dense Cu(In_1−<i>x</i>Ga_x)(S_1−<i>y</i>Se_<i>y</i>)₂ Absorber Films and Their Photovoltaic Performance

Recent developments in the colloidal synthesis of high quality nanocrystals have opened up new routes for the fabrication of low-cost efficient photovoltaic devices. Previously, we demonstrated the utility of CuInSe2 nanocrystals in the fabrication of CuInSe2 thin film solar cells. In those devices, sintering the nanocrystal film yields a relatively dense CuInSe2 film with some void space inclusions. Here, we present a general approach toward eliminating void space in sintered nanocrystal films by utilizing reactions that yield a controlled volume expansion of the film. This is demonstrated by first synthesizing a nanocrystal ink composed of Cu(In1−xGax)S2 (CIGS). After nanocrystal film formation, the nanocrystals are exposed to selenium vapor during which most of the sulfur is replaced by selenium. Full replacement produces a ∼14.6% volume expansion and reproducibly leads to good dense device-quality CIGSSe absorber films with reduced inclusion of void space. Solar cells made using the CIGSSe absorber films fabricated by this method showed a power conversion efficiency of 4.76% (5.55% based on the active nonshadowed area) under standard AM1.5 illumination

Carbon Impurity Minimization of Solution-Processed, Thin-Film Photovoltaics via Ligand Engineering of CuInS₂ Nanoparticles

Colloidal semiconductor nanoparticles (NPs) have long been used as a reliable method for depositing thin films of semiconductor materials for applications, such as photovoltaics via solution-processed means. Traditional methods for synthesizing colloidal NPs often utilize heavy, long-chain organic species to serve as surface ligands, which, during the fabrication of selenized chalcogenide films, leaves behind an undesirable carbonaceous residue in the film. In an effort to minimize these residues, this work looks at using N-methyl-2-pyrrolidone (NMP) as an alternative to the traditional species used as surface ligands. In addition to serving as a primary ligand, NMP also serves as the reaction medium and coating solvent for fabricating CuInS2 (CIS) NPs and thin-film solar cells. Through the use of the NMP-based synthesis, a substantial reduction in the number of carbonaceous residues was observed in selenized films. Additionally, the resulting fine-grain layer at the bottom of the film was observed to exhibit a larger average grain size and increased chalcopyrite character over those of traditionally prepared films, presumably as a result of the reduced carbon content. As a result, a gallium-free CuIn(S,Se)2 device was shown to achieve power-conversion efficiencies of over 11% as well as possessing exceptional carrier generation capabilities with a short-circuit current density (JSC) of 41.6 mA/cm2, which is among the highest for the CIGSSe family of devices fabricated from solution-processed methods