A novel single particle study of steam gasification kinetics of a coal-derived char at high temperatures and pressures

A novel single particle experiment was developed to allow for detailed char gasification measurements in pure steam at temperatures from 1000 °C to 1400  °C and pressures from 1  bar to 15  bar. A coal-derived activated carbon was thoroughly characterized with respect to its composition, physical structure, and reactivity revealing properties consistent with chars reported in the literature. The single particle approach allowed for the boundary and initial conditions to be well known and for the mass of the particle to be accurately measured before and after testing to provide high-quality conversion data. The resulting conversion data were analyzed using the random pore model and the shrinking core model, of which the random pore model provided the best fit. Apparent activation energies were calculated using the random pore model which provided values ranging from 57.1 kJ/mol to 129 kJ/mol which are nominally half of the magnitude of the values reported in the literature under kinetically controlled conditions, thus demonstrating that regime II conditions were present. Additionally, the activation energies decreased with increasing temperature further demonstrating the presence of regime II conditions. The calculated reaction order ranged from 0 to 0.5 and decreased with increasing pressure agreeing well with literature values and trends.     

An economic and environmental comparison of a biochemical and a thermochemical lignocellulosic ethanol conversion processes

With the world’s focus on rapidly deploying second generation biofuels technologies, there exists today a good deal of interest in how yields, economics, and environmental impacts of the various conversion processes of lignocellulosic biomass to transportation fuels compare. Although there is a good deal of information regarding these conversion processes, this information is typically very difficult to use on a comparison basis because different underlying assumptions, such as feedstock costs, plant size, co-product credits or assumed state of technology, have been utilized. In this study, a rigorous comparison of different biomass to transportation fuels conversion processes was performed with standard underlying economic and environmental assumptions so that exact comparisons can be made. This study looked at promising second-generation conversion processes utilizing biochemical and thermochemical gasification technologies on both a current and an achievable state of technology in 2012. The fundamental finding of this study is that although the biochemical and thermochemical processes to ethanol analyzed have their individual strengths and weaknesses, the two processes have very comparable yields, economics, and environmental impacts. Hence, this study concludes that based on this analysis there is not a distinct economic or environmental impact difference between biochemical and thermochemical gasification processes for second generation ethanol production.     

Corn stover availability for biomass conversion: situation analysis

As biorefining conversion technologies become commercial, feedstock availability, supply system logistics, and biomass material attributes are emerging as major barriers to the availability of corn stover for biorefining. While systems do exist to supply corn stover as feedstock to biorefining facilities, stover material attributes affecting physical deconstruction, such as densification and post-harvest material stability, challenge the cost-effectiveness of present-day feedstock logistics systems. In addition, the material characteristics of corn stover create barriers with any supply system design in terms of equipment capacity/efficiency, dry matter loss, and capital use efficiency. However, analysis of a conventional large square bale corn stover feedstock supply system concludes that (1) where other agronomic factors are not limiting, corn stover can be accessed and supplied to a biorefinery using existing bale-based technologies, (2) technologies and new supply system designs are necessary to overcome biomass bulk density and moisture material property challenges, and (3) major opportunities to improve conventional bale biomass feedstock supply systems include improvements in equipment efficiency and capacity and reducing biomass losses in harvesting, collection, and storage. Finally, the backbone of an effective stover supply system design is the optimization of intended and minimization of unintended material property changes as the corn stover passes through the individual supply system processes from the field to the biorefinery conversion processes.

Pyrolytic hydrolysis of polycarbonate in the presence of earth-alkali oxides and hydroxides

The rise in the use of polycarbonate (PC) calls for the development of after-use treatments. In this work, we describe a process for obtaining bisphenol A (BPA), phenol and isopropenyl phenol (IPP) from PC by hydrolysis at temperatures between 300 and 500 °C. The experiments were carried out in a steam atmosphere in the presence of MgO, CaO, Mg(OH)₂ or Ca(OH)₂ as catalysts, respectively. The results were compared with the hydrolysis of PC in the absence of any catalysts. All of these catalysts accelerated the hydrolysis of PC drastically, with MgO and Mg(OH)₂ being more effective than their Ca counterparts. The differences between oxides and hydroxides were negligible indicating the same mechanism for both, oxides and hydroxides. BPA was the main product at 300 °C, with a yield of 78% obtained in the presence of MgO. At 500 °C, BPA was mainly degraded to phenol and isopropenyl phenol (IPP). It can be shown that a combined process involving PC hydrolysis at 300 °C and BPA fission at 500 °C leads to high yields of phenol and IPP and the drastic decrease of residue.     

Optimization of Oxygen Parameters for Determination of Carbon and Nitrogen in Biochar Materials

Recently, there has been increased focus on biochar materials due to their ability to sequester carbon for long-term in soil. In the production of biochar or charcoal, plant biomass is heated in a low or no oxygen environment. This process results in a product with unique characteristics. But there is limited research on the standardization of methods for determining total carbon (C) and nitrogen (N) in the biochar materials whose properties vary by feedstock type and pyrolytic conditions. The objective of this study was to determine the oxygen dosing time (OT) and dose (OD) for total organic carbon (TC) and nitrogen (TN) analysis in biochar materials by dry combustion method (using Vario Max CNS analyzer). Central composite rotatable design was used to determine the effect of five levels of oxygen dosing time (OT) and dosing level (OD) on measurement of total carbon and total nitrogen in four types of plant originated biochars. OT and OD level interaction had significant impact on the measurement of TC and TN in all types of biochar materials. Optimum levels of OT and OD were determined as 103 to 110 sec and 180 to 232 ml/min, respectively.     

Selective production of benzene and naphthalene from poly(butylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) by pyrolysis in the presence of calcium hydroxide

Poly(butylene terephthalate) (PBT) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) were pyrolysed in a fixed bed reactor in the presence of calcium hydroxide (Ca(OH)₂) in order to obtain benzene and naphthalene, respectively. In these experiments different ratios of polymer and Ca(OH)₂ were used. Also the temperature was varied in a range between 600 °C and 800 °C. It was found that the highest yield of benzene (67%) was obtained at a temperature of 700 °C and a molar Ca(OH)₂/PBT ratio of 10. The amount of carbon, fixed in the reactor residue after the experiment, was reduced from 56% for pure PBT to 38% under these conditions. Aromatic byproducts were reduced, as well, while the amount of 1,3-butadiene increased. Tetrahydrofuran was just formed under the influence of Ca(OH)₂.For PEN, the optimal conditions were found at a temperature of 600 °C and a molar Ca(OH)₂/PEN ratio of 5. A naphthalene yield of 80% from PEN was obtained. The rise of the naphthalene yield was caused by a more effective decomposition of the polyester by Ca(OH)₂, which led to the reduction of carbon in the reactor residue after the experiment from 59% for pure PEN to 10% under optimised conditions. The part of aromatic byproducts changed just slightly.     

Effects of MgO catalyst on depolymerization of poly-l-lactic acid to l,l-lactide

To control the depolymerization of poly-l-lactic acid (PLLA) into l,l-lactide, effects of altering the physical and chemical properties of magnesium oxide (MgO) on its ability as a catalyst were investigated. Four kinds of MgO particles: MgO-heavy, 0.2, 0.05, and 0.01 μm, having primary particles of different dimensions, surface areas, and chemical structures/species were used. Thermo-gravimetric profiles of PLLA/MgO composites shifted into a lower temperature range due to an increase in the catalytic surface area resulting from a decrease in the dimensions of the MgO particles. However, decreasing the dimensions caused frequent side reactions with unfavorable products: cyclic oligomers and meso-lactide, due to the presence of different chemical structures/species. Heat treatment of the MgO particles not only effectively suppressed the oligomer production and enhanced the l,l-lactide production, but also accelerated the meso-lactide production at lower temperatures. These results indicate that the surface properties of MgO considerably influence the depolymerization of PLLA, with the catalytic behavior of MgO controllable by heat treatment and selection of the depolymerization conditions.     

Overview of Special Session B—Compositional and Structural Analysis of Biomass

Special Session B at the 29th Symposium on Biotechnology for Fuels and Chemicals was the first invited session at this symposium devoted to analytical methods. The special topic was added in response to numerous requests for information on new and innovative methods that could be applied in the growing renewable fuels industry. Presentation topics include analytical methods for the characterization and analysis of maize traits, tools for investigating cell wall limitations to enzymatic degradation, methods for customizing enzyme cocktails for biomass, new techniques for the analysis of carbohydrates, analytical methods that enhance our understanding of pretreatment, improved methods for monitoring process intermediates, and published standard analytical methods for biomass conversion processes.     

Techno-economic feasibility of biochar as biosorbent for basic dye sequestration

Biochar has a global scientific attention for its ability to remove toxic elements from wastewaters. However, due to the disparity between practical short-term agronomic benefits and aspirations of biochar as an everlasting sustainable bio sorbent for the adsorption process, economic assessments of biochar have yet to be established. In this context, the current study, an economic approach of the biochars derived from agricultural wastes (Coconut shell, Groundnut Shell and Rice husk) for the removal of Basic Red 09 from wastewaters were demonstrated. Batch adsorption experimental set up was used to carry out the adsorption process. At equilibrium batch adsorption conditions, the maximum adsorption capacity of the biochars were 10, 46.3, and 44 ​mg/g for coconut shell, groundnut shell, and rice husk based biochars, respectively. A complete cost assessment was carried out for the agro-waste biochars for their adsorption performance. The biochars derived from groundnut shell and rice husk were shown to be the most cost effective for the Basic Red 09 sequestration from wastewater. The eco-friendly characteristics of these low-cost adsorbents for industrial applications were also discussed.