Increasing Solids Loading Research Articles

Spherical agglomeration kinetics: A mechanistic approach

Spherical agglomeration, a process of in-suspension particle size enlargement, can substantially improve critical quality attributes of powders. In this work, a paracetamol-heptane-water system is used to investigate the kinetics of spherical agglomeration, demonstrating for the first time the influence of true bridging liquid to solid ratio (TBSR) and suspension loading on the evolving size, shape and density of agglomerates. A critical range of TBSR is identified where robust agglomerates are formed that are round, moderately dense, and have a controlled size distribution. Immersion nucleation, drop breakage, and agglomerate densification by impact are the controlling rate processes. Increasing mixing intensity reduces agglomerate size, porosity and agglomeration time. Increasing solids loading increases agglomeration time while yielding smaller agglomerates with lower porosity. A first order consolidation model quantitatively predicts the agglomeration kinetics as well as agglomerate properties with increasing TBSR, and is a powerful tool for design and scale up.

Accumulation of Particles in an Annular Centrifugal Contactor Cascade and the Effect upon the Extraction of Nitric Acid

Centrifugal contactors (CCs) are a technology candidate for the development of advanced reprocessing flowsheets. While they offer many advantages, such as process intensification, there are still uncertainties regarding their industrial deployment. The presence of particles in the process streams in particular may present a challenge to both performance and operability. Preliminary studies have been undertaken to evaluate the accumulation of particles in the contactors and the effect upon the extraction behaviour of nitric acid. Aluminium oxide (Al2O3) particles were suspended in the aqueous feed solution during the operation of a three-stage, 40 mm diameter CC cascade. The presence of insoluble solid particles in the aqueous feed, up to 7 g/L, were not observed to affect phase separation and entrainment under the experimental conditions investigated. The particles were centrifuged out of solution and accumulated as a thin cake/bed in the rotors of each stage. This work also illustrates that particles do entrain through the cascade. The predominant effect on the rate of accumulation was particle concentration in the aqueous feed solution, and increasing solids loading was observed to have an impact upon the extraction of nitric acid across the cascade.

Fed-batch SSF with pre-saccharification as a strategy to reduce enzyme dosage in cellulosic ethanol production

The pulp and paper industry is a strategic sector to be converted into a forest-based biorefinery, taking advantage of know-how, existing infrastructures and well-established logistic operations to deal with a daily high volume of forest residues. Bioethanol production from Eucalyptus globulus bark previously pretreated by kraft pulping was assessed following two configurations at the bioreactor scale: separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). This last configuration was optimized by using a pre-saccharification and a fed-batch feeding (FB PS-SSF), allowing for a reduction in the enzyme dosage from 25 to 10 FPU gCH−1, which is very advantageous from an economic point of view. For 10 FPU gCH−1 enzyme dosage and 20 % (w/v) total solids loading, an ethanol concentration of around 70.6 g L−1 was accomplished, corresponding to overall conversion efficiency and productivity of about 78 % and 1.35 g L−1 h−1, respectively. Increasing solids loading from 20 to 26 % (w/v), using the same enzyme dosage, resulted in the highest ethanol concentration (84.6 g L−1) despite the too-long assay and the decline in productivity. Overall, FB PS-SSF improved bioethanol concentration and allowed decreased enzymatic usage over SHF, maintaining high ethanol concentration.

Enzymatic Hydrolysis Strategies for Cellulosic Sugars Production to Obtain Bioethanol from Eucalyptus globulus Bark

Cellulosic sugars production for the valorization of lignocellulosic biomass residues in an industrial site has economic benefits and is promising if integrated into a biorefinery. Enzymatic hydrolysis (EH) of pretreated Eucalyptus globulus bark, an industrial residue of low-economic value widely available in Portuguese pulp and paper mills, could be an excellent approach to attain resource circularity and pulp mill profitability. This work evaluated the potential for improving cellulosic sugars concentrations by operating with high solids loading and introducing the additives Triton X-100, PEG 4000 and Tween 80 using a commercial enzymatic consortium with a dosage of 25 FPU gcarbohydrates−1. Additives did not improve enzymatic hydrolysis performance, but the effect of increasing solids loading to 14% (w/v) in batch operation was accomplished. The fed-batch operation strategy was investigated and, when starting with 11% (w/v) solids loading, allowed the feeding of 3% (w/v) fresh feedstock sequentially at 2, 4 and 6 h, attaining 20% (w/v) total solids loading. After 24 h of operation, the concentration of cellulosic sugars reached 161 g L−1, corresponding to an EH conversion efficiency of 76%. Finally, the fermentability of the fed-batch hydrolysate using the Ethanol Red® strain was evaluated in a 5 L bioreactor scale. The present results demonstrate that Eucalyptus globulus bark, previously pretreated by kraft pulping, is a promising feedstock for cellulosic sugars production, allowing it to become the raw material for feeding a wide range of bioprocesses.

Declining carbohydrate solubilization with increasing solids loading during fermentation of cellulosic feedstocks by Clostridium thermocellum: documentation\xa0and diagnostic tests

BackgroundFor economically viable 2nd generation biofuels, processing of high solid lignocellulosic substrate concentrations is a necessity. The cellulolytic thermophilic anaerobe Clostridium thermocellum is one of the most effective biocatalysts for solubilization of carbohydrate harbored in lignocellulose. This study aims to document the solubilization performance of Clostridium thermocellum at increasing solids concentrations for two lignocellulosic feedstocks, corn stover and switchgrass, and explore potential effectors of solubilization performance.ResultsMonocultures of Clostridium thermocellum demonstrated high levels of carbohydrate solubilization for both unpretreated corn stover and switchgrass. However, fractional carbohydrate solubilization decreases with increasing solid loadings. Fermentation of model insoluble substrate (cellulose) in the presence of high solids lignocellulosic spent broth is temporarily affected but not model soluble substrate (cellobiose) fermentations. Mid-fermentation addition of cells (C. thermocellum) or model substrates did not significantly enhance overall corn stover solubilization loaded at 80 g/L, however cultures utilized the model substrates in the presence of high concentrations of corn stover. An increase in corn stover solubilization was observed when water was added, effectively diluting the solids concentration mid-fermentation. Introduction of a hemicellulose-utilizing coculture partner, Thermoanaerobacterium thermosaccharolyticum, increased the fractional carbohydrate solubilization at both high and low solid loadings. Residual solubilized carbohydrates diminished significantly in the presence of T. thermosaccharolyticum compared to monocultures of C. thermocellum, yet a small fraction of solubilized oligosaccharides of both C5 and C6 sugars remained unutilized.ConclusionDiminishing fractional carbohydrate solubilization with increasing substrate loading was observed for C. thermocellum-mediated solubilization and fermentation of unpretreated lignocellulose feedstocks. Results of experiments involving spent broth addition do not support a major role for inhibitors present in the liquid phase. Mid-fermentation addition experiments confirm that C. thermocellum and its enzymes remain capable of converting model substrates during the middle of high solids lignocellulose fermentation. An increase in fractional carbohydrate solubilization was made possible by (1) mid-fermentation solid loading dilutions and (2) coculturing C. thermocellum with T. thermosaccharolyticum, which ferments solubilized hemicellulose. Incomplete utilization of solubilized carbohydrates suggests that a small fraction of the carbohydrates is unaffected by the extracellular carbohydrate-active enzymes present in the culture.

Coculture with hemicellulose-fermenting microbes reverses inhibition of corn fiber solubilization by Clostridium thermocellum at elevated solids loadings

BackgroundThe cellulolytic thermophile Clostridium thermocellum is an important biocatalyst due to its ability to solubilize lignocellulosic feedstocks without the need for pretreatment or exogenous enzyme addition. At low concentrations of substrate, C. thermocellum can solubilize corn fiber > 95% in 5 days, but solubilization declines markedly at substrate concentrations higher than 20 g/L. This differs for model cellulose like Avicel, on which the maximum solubilization rate increases in proportion to substrate concentration. The goal of this study was to examine fermentation at increasing corn fiber concentrations and investigate possible reasons for declining performance.ResultsThe rate of growth of C. thermocellum on corn fiber, inferred from CipA scaffoldin levels measured by LC–MS/MS, showed very little increase with increasing solids loading. To test for inhibition, we evaluated the effects of spent broth on growth and cellulase activity. The liquids remaining after corn fiber fermentation were found to be strongly inhibitory to growth on cellobiose, a substrate that does not require cellulose hydrolysis. Additionally, the hydrolytic activity of C. thermocellum cellulase was also reduced to less-than half by adding spent broth. Noting that > 15 g/L hemicellulose oligosaccharides accumulated in the spent broth of a 40 g/L corn fiber fermentation, we tested the effect of various model carbohydrates on growth on cellobiose and Avicel. Some compounds like xylooligosaccharides caused a decline in cellulolytic activity and a reduction in the maximum solubilization rate on Avicel. However, there were no relevant model compounds that could replicate the strong inhibition by spent broth on C. thermocellum growth on cellobiose. Cocultures of C. thermocellum with hemicellulose-consuming partners—Herbinix spp. strain LL1355 and Thermoanaerobacterium thermosaccharolyticum—exhibited lower levels of unfermented hemicellulose hydrolysis products, a doubling of the maximum solubilization rate, and final solubilization increased from 67 to 93%.ConclusionsThis study documents inhibition of C. thermocellum with increasing corn fiber concentration and demonstrates inhibition of cellulase activity by xylooligosaccharides, but further work is needed to understand why growth on cellobiose was inhibited by corn fiber fermentation broth. Our results support the importance of hemicellulose-utilizing coculture partners to augment C. thermocellum in the fermentation of lignocellulosic feedstocks at high solids loading.

Phase distribution in Fischer-Tropsch mimicked slurry bubble column via computed tomography

This study aims to investigate the phases distribution and hydrodynamics in an air-Therminol LT-glass beads slurry bubble column reactor in bubbly and churn-turbulent flow regimes by implementing a gamma-ray computed tomography. It is found that gas holdup increases with increasing superficial gas velocity and operating pressure while increasing solids loading has an opposite effect on gas holdup measurements. It is noticed that the pressure effect is more significant at high solids loading and the solids loading is relatively more substantial at lower pressure. Solids loading has the most significant a stronger effect on the solids holdup profile than on the gas holdup profile. Current results were compared with the Sedimentation-Dispersion Model (SDM) predictions. The findings of this study advance the knowledge of the true behavior of phases distribution in FT mimicked slurry bubble columns which are pertinent in designing such reactors.

Gas Phase Back-Mixing in a Mimicked Fischer-Tropsch Slurry Bubble Column Using an Advanced Gaseous Tracer Technique

Abstract An advanced gaseous tracer technique and procedures were developed and executed to study for the first time the axial dispersion of the gas phase in a slurry bubble column reactor (SBCR) using air-C9C11-FT catalyst. Residence time distribution (RTD) curves were obtained by measuring the pulse-input’s response of the gaseous tracer. The gas phase axial dispersion coefficient (Dg) was obtained from minimum square error fit of the one-dimensional axial dispersion model to the measured tracer response data. The effects of solids loading on the axial dispersion of gas phase and the overall gas holdup have been studied. It was demonstrated that increasing solids loading improves the gas axial dispersion while decreasing the overall gas holdup. This work suggests that gas phase axial dispersion is significant in reactor performance evaluation of bubble columns or slurry bubble columns.

Toward high solids loading process for lignocellulosic biofuel production at a low cost.

High solids loadings (>18 wt%) in enzymatic hydrolysis and fermentation are desired for lignocellulosic biofuel production at a high titer and low cost. However, sugar conversion and ethanol yield decrease with increasing solids loading. The factor(s) limiting sugar conversion at high solids loading is not clearly understood. In the present study, we investigated the effect of solids loading on simultaneous saccharification and co-fermentation (SSCF) of AFEX™ (ammonia fiber expansion) pretreated corn stover for ethanol production using a xylose fermenting strain Saccharomyces cerevisiae 424A(LNH-ST). Decreased sugar conversion and ethanol yield with increasing solids loading were also observed. End-product (ethanol) was proven to be the major cause of this issue and increased degradation products with increasing solids loading was also a cause. For the first time, we show that with in situ removal of end-product by performing SSCF aerobically, sugar conversion stopped decreasing with increasing solids loading and monomeric sugar conversion reached as high as 93% at a high solids loading of 24.9 wt%. Techno-economic analysis was employed to explore the economic possibilities of cellulosic ethanol production at high solids loadings. The results suggest that low-cost in situ removal of ethanol during SSCF would significantly improve the economics of high solids loading processes. Biotechnol. Bioeng. 2017;114: 980-989. © 2016 Wiley Periodicals, Inc.

Developing Cost-Effective Dense Continuous SDC Barrier Layers for SOFCs

Significantly improved performance during electrochemical testing of a cell with a dense continuous pulsed laser deposited (PLD) samarium doped ceria (SDC) layer spurred investigations into the fabrication of dense continuous SDC barrier layers by means of cost-effective deposition using screen printing which is amenable to industrial production of SOFCs. Many approaches to improve the SDC density have been explored including the use of powder with reduced particle sizes, inks with increased solids loading, and doping with sintering aids (1). In terms of sintering aids, dopants like Mo or binary systems of Mo+Cu or Fe+Co greatly enhance SDC sinterability. In fact, adding dopants to a screen printed, pre-fired, porous SDC layer made it possible to achieve a dense continuous barrier layer atop the YSZ electrolyte without sintering above 1200°C. Although the objective of fabricating a dense continuous layer was achieved, additional studies have been initiated to improve the cell performance. Underlying issues with constrained sintering and dopant-enhanced ceria-zirconia solid solubility are also addressed in this paper.

CFD simulation of gas-liquid floating particles mixing in an agitated vessel

Gas dispersion and floating particles suspension in an agitated vessel were studied numerically by using computational fluid dynamics (CFD). The Eulerian multi-fluid model along with standard k-? turbulence model was used in the simulation. A multiple reference frame (MRF) approach was used to solve the impeller rotation. The velocity field, gas and floating particles holdup distributions in the vessel were first obtained, and then, the effects of operating conditions on gas dispersion and solid suspension were investigated. The simulation results show that velocity field of solid phase and gas phase are quite different in the agitated vessel. Floating particles are easy to accumulate in the center of the surface region and the increasing of superficial gas velocity is in favor of floating particles off-surface suspension. With increasing solids loading, the gas dispersion becomes worse, while relative solid holdup distribution changes little. The limitations of the present modeling are discussed and further research in the future is proposed.

Developing Cost-Effective Dense Continuous SDC Barrier Layers for SOFCs

Solid oxide fuel cells (SOFCs) with lanthanum strontium cobalt ferrite (LSCF) cathodes often employ a samaria-doped or gadolinia-doped ceria (SDC or GDC, respectively) barrier layer between the cathode and the yttria-stabilized zirconia (YSZ) electrolyte to inhibit Sr from migrating to the YSZ surface where it reacts to form electrically-resistive strontium zirconate during cathode sintering. Because the SDC must be sintered at limited temperatures (generally ≤1200°C) to avoid forming a CeO2-ZrO2 solid solution that has significantly lower ionic conductivity, screen printed barrier layers are often porous after firing. Electrochemical tests of cells with dense, continuous pulsed laser deposited (PLD) SDC found that these cells exhibited significantly higher performance than those with the conventional screen-printed porous SDC layers. Thus, PNNL began investigating the fabrication of dense, continuous SDC barrier layers using cost-effective deposition by screen printing which is amenable to industrial production of SOFCs. Many approaches to improve the SDC density have been explored including the use of powder with reduced particle sizes, inks with increased solids loading, and doping with sintering aids. While some of these tests were successful in enhancing the density of the SDC, the stresses induced by constrained sintering on the surface of previously-fired YSZ caused cracks and discontinuities in the SDC barrier layer. These results together with steps that have been taken to address the constrained sintering issue will be presented.

A comparison of microstructure and uniaxial compressive response of ice-templated alumina scaffolds fabricated from two different particle sizes

This study investigates the effects of two different particle sizes (0.3μm vs. 0.9μm) on the microstructure and uniaxial compressive response of ice-templated sintered alumina scaffolds as a function of the solids loading of the ceramic suspensions and freezing front velocity (FFV). For a comparable solids loading and FFV, variation of the particle size is observed to have a significant effect on the microstructure of the fabricated scaffolds. Moreover, transition of the pore morphology with the increasing solids loading and FFV is observed to be more drastic for the scaffolds processed from the 0.9μm size powder particles compared to the scaffolds processed from the 0.3μm size powder particles. Similarly, particle size variation also influenced significantly the relative density and porosity of the scaffolds. Interestingly, in spite of the observed significant differences of the microstructure and relative density, uniaxial compressive stress-strain measurements revealed marginal effects of the particle size variation on the compressive strength. The measured comparable uniaxial compressive response of the sintered alumina scaffolds fabricated from two different particle sizes are rationalized based on the relative density, pore aspect ratio, and interlamellae bridge density.

Enhanced CO2 Absorption and Desorption by Monoethanolamine (MEA)-Based Nanoparticle Suspensions

In this study, three different nanoparticles—SiO2, TiO2, and Al2O3—were employed to enhance the CO2 gas absorption by monoethanolamine (MEA) solvent. It is observed that, with increased solids loading, the total mass-transfer enhancement has a tendency to be dominated by the bubble breaking effect. It is concluded that nanoparticles result in an increased CO2 absorption rate of >10%. On the other hand, nanoparticles exhibit much more attractive impact on CO2 desorption. Under the same desorption extent, solvent with 0.1 wt % TiO2 nanoparticles saved 42% desorption time, compared to that without nanoparticles. Under higher heat flux density, more input heat would be supplied to the heat of desorption, rather than the heat of water evaporation, which is due to the enhancement of desorption rate by nanoparticles. The issue of particle aggregation was also investigated by analyzing the size distribution of nanoparticle clusters and zeta potential of MEA solvents.

Preparation of tubular hierarchically porous silicate cement compacts via a tert-butyl alcohol (TBA)-based freeze casting method

Tubular porous silicate cement compacts with hierarchical porosity were successfully fabricated via a tert-butyl alcohol (TBA)-based freeze-casting technique in one single step. These samples were characterized by unidirectional aligned pore channels and completely open porosity. Various experimental parameters affecting the macropore size, mesopore size, porosity, and compression strength were investigated, including the initial solids loading, freezing temperature and curing period. Both the research findings of microstructure observations and property tests show that the pore size decreased significantly with decreasing freezing temperature and increasing solids loading. The porosity increased significantly with decreasing solids loading, while the compressive strength decreased remarkably. In addition to their tunable physical characteristics, these brand-new inorganic porous materials with oriented aligned pore channels and dense layer surface showed high permeation performance and desirable separation ability. These results endow the silicate cement, a kind of low-cost and high-performance architecture material, with great potential as a novel ordered porous inorganic material for numerous applications, especially in separation process.

Impact of fiber source and feed particle size on swine manure properties related to spontaneous foam formation during anaerobic decomposition

Foam accumulation in deep-pit manure storage facilities is of concern for swine producers because of the logistical and safety-related problems it creates. A feeding trial was performed to evaluate the impact of feed grind size, fiber source, and manure inoculation on foaming characteristics. Animals were fed: (1) C–SBM (corn–soybean meal): (2) C–DDGS (corn–dried distiller grains with solubles); and (3) C–Soybean Hull (corn–soybean meal with soybean hulls) with each diet ground to either fine (374μm) or coarse (631μm) particle size. Two sets of 24 pigs were fed and their manure collected. Factors that decreased feed digestibility (larger grind size and increased fiber content) resulted in increased solids loading to the manure, greater foaming characteristics, more particles in the critical particle size range (2–25μm), and a greater biological activity/potential.

Investigation into the use of cement kiln dust in high density sludge (HDS) treatment of acid mine water

The purpose of this study was to investigate the potential to replace lime with cement kiln dust (CKD) in high density sludge (HDS) treatment of acid mine drainage (AMD). The bench-scale study used two water samples: AMD sampled from a lead-zinc mine with high concentrations of iron (Fe), zinc (Zn), and arsenic (As) (Fe/Zn-AMD) and a synthetic AMD solution (Syn-AMD) spiked with ferric sulfate (Fe2(SO4)3). Arsenic was found to be significantly reduced with CKD-HDS treatment of Fe/Zn-AMD compared to lime-HDS treatment, to concentrations below the stringent mine effluent discharge regulation of 0.10 mg As/L (i.e., 0.04 ± 0.02 mg/L). Both CKD- and lime-HDS treatment of the two AMD samples resulted in settled water Fe concentrations above the stringent discharge guideline of 0.3 mg Fe/L. CKD addition in the HDS process also resulted in high settled water turbidity, above typical discharge guidelines of 15 mg TSS/L. CKD-HDS treatment was found to result in significantly improved settled solids (i.e., sludge) quality compared to that generated in the lime-HDS process. HDS treatment with CKD resulted in 25–88% lower sludge volume indices, 2 to 9 times higher % wet solids, and 10 to 20 times higher % dry solids compared to lime addition. XRD and XPS testing indicated that CKD-HDS sludge consisted of mainly CaCO3 and SiO2 with Fe3+ precipitates attached at particle surfaces. XRD and XPS testing of the lime-HDS generated sludge showed that it consisted of non-crystalline Fe oxides typical of sludge formed from precipitates with a high water concentration. Increased sedimentation rates were also found for CKD (1.3 cm/s) compared to lime (0.3 cm/s). The increased solids loading with CKD addition compared to lime addition in the HDS process was suggested to both promote surface complexation of metal precipitates with insoluble CKD particles and increase compression effects during Type IV sedimentation. These mechanisms collectively contributed to the reduced water content of CKD-HDS sludge. The results of this study suggest that solids loading is a significant factor in increased sludge density found with the HDS process compared to conventional lime precipitation-sedimentation.

Sequential bioethanol and biogas production from sugarcane bagasse based on high solids fed-batch SSF

Sugars released from alkali-pretreated SCB (sugarcane bagasse) were used for biofuel (bioethanol and biogas) production based on a high-solids fed-batch SSF (simultaneous saccharification and fermentation) process with delayed inoculation (DSSF). A DSSF process with 24 h delayed inoculation increased the ethanol production rate by eliminating glucose inhibition in the early stages of fermentation, and shortened the duration of the process. Increasing solids loading from 18 to 36% (w/v) enhanced glucose concentration, while ethanol conversion efficiency was decreased. Gradual feeding of the hydrolyzed medium could improve the DSSF process. DSSF, with batch feeding mode, achieved as high as 68.047 g/L (74.13% of theoretical yield) ethanol concentration with 30% (w/v) solids loading at 96 h. After evaporation, the residual stillage obtained 306.974 mL/g volatile solids (VS) methane through anaerobic digestion. Sequential bioethanol and biogas production improved the yield of utilized biomass.

Correlation between microstructure evolution and drying behavior of gelcast alumina green bodies

Wet alumina green bodies with a dimension of 400mm ×50mm ×10mm, respectively gelcast by PIBM (a copolymer of isobutylene and maleic anhydride) and EA (epoxy-amine) gel system, were dried at controlled temperature and humidity. Microstructure evolution and drying behavior of the green bodies with different solids loading and organic network were investigated. Pores among alumina particles became smaller and the constant rate period (CRP) became shorter with the increased solids loading or organic network. Further, the shrinkage of the body using PIBM ceased earlier and was smaller than that of the body using EA gel system. The typical microstructure of the body using PIBM gel system was thin organic networks on the particles and gradually a cocooned structure evolved during drying. While, the body using EA gel system had dense organic networks which evolved into a dense layer and strand-like structure around the particles. Such microstructures played different roles in water transportation and stress relaxation. As a result, the PIBM body was successfully dried without malformation but the EA body was bowing.

Thermal conductivity enhancement of alumina/polyamide composites via interfacial modification

Ceramic/polymer composite materials with higher thermal conductivity are required in industries, as they will improve product reliability, functionality and manufacturing cost. An important question concerning the thermally conductive composites is how to alleviate the negative effects of interfacial thermal resistance. A novel preparation method of thermally conductive composites is described in this paper. The process can be characterized by creating an organic substance layer with ordered structure between crystalline fillers and polymer matrices. The unique framework should result in decreased scattering for phonon transfer, and the thermal conductivity of the prepared composites exhibits a significant improvement without increasing solids loading. The methodology reported herein is promising for practical thermal management using composites with lower solids loading.