Multiobjective optimization of product and process networks: General modeling framework,efficient global optimization algorithm,and case studies on bioconversion

A comprehensive optimization model that can determine the most cost‐effective and environmentally sustainable production pathways in an integrated processing network is needed, especially in the bioconversion space. We develop the most comprehensive bioconversion network to date with 193 technologies and 129 materials/compounds for fuels production. We consider the tradeoff between scaling capital and operating expenditures (CAPEX and OPEX) as well as life cycle environmental impacts. Additionally, we develop a general network‐based modeling framework with nonconvex terms for CAPEX. To globally optimize the nonlinear program with high computational efficiency, we develop a specialized branch‐and‐refine algorithm based on successive piecewise linear approximations. Two case studies are considered. The optimal pathways have profits from ?$12.9 to $99.2M/yr, and emit 791 ton CO₂‐eq/yr to 31,571 ton CO₂‐eq/yr. Utilized technologies vary from corn‐based fermentation to pyrolysis. The proposed algorithm reduces computational time by up to three orders of magnitude compared to general‐purpose global optimizers. © 2014 American Institute of Chemical Engineers AIChE J, 61: 530–554, 2015     

Cogasification of blended coal‐biomass in an air/steam BFB gasifier: Experimental investigation and model validation

A series of cogasification experiments were performed at a 100 kW bubbling fluidized bed (BFB) gasifier to gasify the blended pellets made from two types of coals and woody biomass, with biomass‐to‐fuel mass ratios of 0–30%. In the cogasification, a mixture of air and steam was fed from the BFB gasifier bottom as gasification agent and the blended biomass‐coal pellets were fed into the bed layer. Impacts of biomass mass fraction in the binary pellets and gasification operation temperature on producer gas composition were experimentally investigated. The experimental results have been used to validate a mathematical model developed in this study. From both experimental observation and model prediction, it was found that adding biomass into coal has overall negative impact on producer gas quality in terms of combustible substance contents, and the extents of the blending effect were different among fuel types which have different properties. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1639–1647, 2015     

Delignification of intact biomass and cellulosic coproduct of acid‐catalyzed hydrolysis

The kinetics of acid‐catalyzed hemicellulose removal and also alkaline delignification of oat hull biomass were investigated. All three operational parameters namely, catalyst concentration (0.10–0.55 N H₂SO₄), temperature (110–130°C), and residence time (up to 150 min) affected the efficiency of hemicellulose removal, with 100% of hemicellulose removed by appropriate selection of process parameters. Analysis of delignification kinetics (in the temperature range of 30–100°C) indicated that it can be expressed very well by a two‐phase model for the crude biomass and also for the hemicellulose‐prehydrolyzed material. The application of acid‐catalyzed prehydrolysis improved the capacity of lignin dissolution especially at lower temperatures (30 and 65°C) and accelerated the dissolution of lignin. This acceleration of delignification by prehydrolysis was possible at all levels of temperature in the bulk phase; however, results were more significant at the lower temperatures in the terminal phase. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1783–1791, 2015     

Mechanistic insights into the structure‐dependent selectivity of catalytic furfural conversion on platinum catalysts

The effects of surface structures on the selectivity of catalytic furfural conversion over platinum (Pt) catalysts in the presence of hydrogen have been studied using first principles density functional theory (DFT) calculations and microkinetic modeling. Three Pt model surface structures, that is, flat Pt(111), stepped Pt(211), and Pt₅₅ cluster are chosen to represent the terrace, step, and corner sites of Pt nanoparticle. DFT results show that the dominant reaction route (hydrogenation or decarbonylation) in furfural conversion depends strongly on the structures (or reactive sites). Using the size‐dependent site distribution rule, our microkinetic modeling results indicate the decarbonylation route prevails over smaller Pt particles less than 1.4 nm while the hydrogenation is the dominant reaction route over larger Pt catalyst particles at T = 473 K and = 93 kPa. This is in good agreement with the reported experimental observations. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3812–3824, 2015     

Lignocellulosic Biofuels: Phase Separation during Catalytic Hydrodeoxygenation of Liquid Phase Pyrolysis Oil

This paper contributes to the understanding of liquid phase pyrolysis (LPP) oil upgrading. The subject of discussion is hydrodeoxygenation (HDO). A three-stage hydrotreatment of liquid phase pyrolysis oil is described. It was found that during the initial heating stage conditions no HDO oil was produced. The HDO oil was formed during the main heating stage. During the initial heating stage, the oxygen content and the average molecular weight remained relatively constant. In the main heating stage the oxygen content decreased from 40 wt.% to 24 wt.% and the average molecular weight also decreases from 630 to 570 g/mol. Finally in the isothermal stage HDO oil was formed, indicated by a drop in oxygen content.     

生物质原料供应链技术经济研究进展

生物质原料供应链是生物质资源转化的基础保障，是未来实现大规模生物质能源开发利用的关键所在。本文对生物质供应链相关技术问题进行了分析，分别介绍了生物质原料收获与收集、储存与预处理、运输等技术现状与存在的问题。同时，对供应链的技术经济性进行了综述，对比阐述了国内外采用的研究方法，通过建立定量化的数学模型来优化供应链的技术经济指标是当前研究的主要方式。国内外研究结果显示，生物质原料的收购价格、收集半径和收购模式是影响生物质供应链成本的关键因素。我国由于户均耕地占有面积小，生物质原料分散，生物质供应链是一个复杂的系统工程。在此基础上，进一步对生物质供应链的发展提出了展望，为生物质资源供应链的研究与发展提供参考和借鉴。     

Hydrogen Production by the Thermophilic Bacterium Thermotoga neapolitana

As the only fuel that is not chemically bound to carbon, hydrogen has gained interest as an energy carrier to face the current environmental issues of greenhouse gas emissions and to substitute the depleting non-renewable reserves. In the last years, there has been a significant increase in the number of publications about the bacterium Thermotoga neapolitana that is responsible for production yields of H₂ that are among the highest achievements reported in the literature. Here we present an extensive overview of the most recent studies on this hyperthermophilic bacterium together with a critical discussion of the potential of fermentative production by this bacterium. The review article is organized into sections focused on biochemical, microbiological and technical issues, including the effect of substrate, reactor type, gas sparging, temperature, pH, hydraulic retention time and organic loading parameters on rate and yield of gas production.     

Impact of human activity on NO soil fluxes

Changes in land use driven by the increasing demand of food are affecting the fluxes of trace gases to the atmosphere. The more important human activities that affect NO soil fluxes are: deforestation, intensification of agricultural practices, and biomass burning. In this review emphasis is given to identifying the physicochemical and biological processes involved in the changes, and no attempt to quantify their contribution to global or regional NO budgets is made.Conversion of tropical forest to pasture is occurring very rapidly. An increase of the NO emission is observed immediately after deforestation (1–5 years) followed by a significant decrease (below forest levels) in old pastures and secondary successional forests. It seems that deforested tropical areas produce, in the long term, less NO than primary forests. The observed changes are not completely understood, but are most likely driven by the availability of exchangeable nitrogen and the bacteria' population.Soil plowing and fertilization are important factors that affect NO fluxes in agricultural soils. Plowing increases soil porosity and aeration, as well increasing the surface area that is exposed to the atmosphere. These physical changes increase the production of soil nitrate, and the escape efficiency of NO from the soil, enhancing NO fluxes. The emission of NO from fertilized soils depends on many variables: type of fertilizer (i.e. ammonium, nitrate), the structure of the soil microbial community (e.g., populations of nitrifiers and denitrifiers), meteorogical conditions (e.g. soil moisture and temperature), and soil management (e.g. plowing). A combination of these factors should explain the large range reported for the fraction of N-fertilizer that is emitted as NO to the atmosphere. Measurements made in diverse ecosystems show that vegetation burning enhances NO soil emissions. However, it seems that different processes, which are not well understood, occur at the various sites; e.g., in the tropical savannah, enhanced emissions, from dry soils, are observed immediately after burning, whereas in Californian chaparral burned dry soils emit on average less than the unburned plots, and the fluxes only increase after soil wetting. Changes in the physical conditions of the soil surface and N availability are the most likely factors that explain the increased fluxes.