High Solid Loading Research Articles

Modeling pressure drop in curvature and reacceleration zones in bends during pneumatic conveying of fine powders

This paper presents the results of ongoing research aimed at modeling the pressure drop in bends during pneumatic conveying of fine powders. Based on the test results of conveying fly ash and two grades of cement through three different radii of curvature of the bends, two different bend diameters, and two different locations of the test bend, a semi-empirical relationship was developed for bend loss with various pressure drop components modeled separately. The newly developed model was used to predict the bend loss for a solid loading ratio in the range of 51–170 (very dense phase). The proposed model exhibited a satisfactory level of prediction accuracy, with relative error percentages of less than 12.2% and 19.6% for the high and low solids loading ratios, respectively.

High titer (>200 g/L) lactic acid production from undetoxified pretreated corn stover

Lignocellulosic biomass is a reliable feedstock for lactic acid fermentation, low product titers hamper the scale production of cellulosic lactic acid. In this study, a Densifying Lignocellulosic biomass with Chemicals (sulfuric acid) pretreatment based cellulosic lactic acid biorefinery system was developed and demonstrated from multi-dimensions of producing bacteria, fermentation modes, corn stover solid loadings, fermentation vessels, and product purification. Results suggested that several lactic acid bacteria exhibited high fermentation activity in high solid loading corn stover hydrolysates. Remarkably, simultaneous saccharification co-fermentation performed in 100-mL flasks enabled 210.1 g/L lactic acid from 40% solid loading corn stover hydrolysate. When simultaneous saccharification co-fermentation was performed in 3-L bioreactors, 157.4 g/L lactic acid was obtained from 35% solid loading corn stover hydrolysate. These obtained lactic acid titers are the highest reports until now when lignocellulosic biomasses are used as substrates, making it efficient for scale production of cellulosic lactic acid.

Integrating surfactants with low enzyme loading to increase the glucan conversion and ethanol concentration of reed after combined pretreatment

In this study, in order to obtain high concentration bioethanol, reed pretreated with liquid hot water and ammonia oxygen (LHW-NH3·H2O/O2) was used as the substrate for fermentation. Enzymatic hydrolysis becomes difficult by the ineffective lignin adsorption and the decline in cellulase activity. It is worth noting that even under low enzyme loading (9 FPU/g pretreated solid), this study was able to maintain a higher glucan conversion rate (97.60%). In addition, under high solid loading conditions, the combined effect of PEG 6000 and rhamnolipids increased ethanol yield (78.40%) and ethanol concentration (71.5 g/L). The combined LHW-NH3·H2O/O2 pretreatment with fed-batch semi-simultaneous saccharification and fermentation technique may be utilized to industrialize the production of bioethanol from reed since we concentrated on the maximum exploitation of biomass resources and reduction in energy consumption.

Coextrusion of Reaction‐Bonded Carbides by Robocasting

Coextrusion by robocasting is a suitable process for fabricating multimaterial ceramic structures. Herein, the robocasting process is used to fabricate core–shell structures, combined with subsequent liquid silicon infiltration (LSI). Thus, reaction‐bonded silicon carbide (RBSC), reaction‐bonded boron carbide (RBBC), and reaction‐bonded silicon–boron carbide composites are produced. The LSI process offers the possibility to circumvent high temperatures and pressures used in traditional fabrication. Pastes with high solid loading and necessary carbon content are used in order to combine the robocasting with the subsequent LSI process. The influence of the paste rheology on the sample fabrication of multimaterial core–shell structures of reaction‐bonded carbides is investigated. The key rheological data, such as the viscosities of the combined pastes, are correlated with the observations from the microstructural investigation using scanning electron microscopy. A correlation between the difference in viscosity and the core geometry can be established. Crack formation in the material combination of RBSC and RBBC is found and compared with layered multimaterial structures of reaction‐bonded carbides. Residual stresses, which can be used to explain the crack formation, are investigated using Raman spectroscopy.

Continuous Reactive Crystallization in a Mesoscale Oscillatory Baffled Reactor

AbstractContinuous reactive crystallization was carried out in a mesoscale oscillatory baffled reactor (meso‐OBR), using calcium carbonate as a case study to demonstrate the ability of high solid loadings and to examine the fouling potential in continuous processes. Plug flow behavior was easily achieved in reactive solid‐liquid phase reaction systems, as evidenced by the rapid establishment of a steady state. Effects of the operating conditions (reactant concentration, mixing conditions, and temperature) on the yield, particle size, and particle size distribution were studied. Increasing the reactant concentration and oscillation conditions reduced the particle size whereas increasing the operating temperature led to a large particle size. The meso‐OBR produced uniformly shaped spherical crystals, with a 35 % reduction in average particle size and high purity compared to conventional stirred tanks. The meso‐OBR could be used continuously for up to 6 h with less than 1 wt % of fouling (product loss).

An enhanced in situ fed-batch hydrolysis and kinetic study for producing biomass-based levulinic acid at high solid loadings

Levulinic acid (LA), regarded as one of the top twelve biomass-based platform chemicals, has been extensively studied by numerous researchers. In this study, a high LA concentration and yield were obtained through an enhanced in situ feeding strategy with a high loading of furfural residue (FR). The effects of batch process, one-time feeding and two-time feeding strategy on the hydrolysis performance (LA yield and concentrations, as well as intermediate glucose yield and concentrations) were investigated. The humin-based byproducts generated during different processes were also characterized by SEM, FT-IR and XRD analysis. The best results of one-time feeding strategy were obtained at 3 wt% H2SO4, 170 °C for 60 min with an initial FR concentration of 15% supplemented to 20% at 0th min. Under these conditions, the LA concentration and yield reached 30.00 g/L and 15% (51.1 mol%), respectively. Furthermore, a hybrid model integrated with the shrinking core model and a quasi-first-order kinetic model was adopted to elucidate the kinetic behavior of LA production from highly concentrated substrates through batch and feeding processes. The results indicated that a one-time feeding strategy can lower the activation energy required for FR degradation to glucose to 96.6 kJ/mol (R2 > 0.97). Similarly, the activation energy for the conversion of glucose to 5-hydroxymethylfurfural (5-HMF) and the subsequent formation of LA from 5-HMF were reduced to 80.9 kJ/mol (R2 > 0.97) and 23.3 kJ/mol (R2 > 0.97), respectively. Notably, the reaction rate of glucose to form humins was slightly reduced. This research helps to optimize the LA yield and concentration directly via an enhanced in situ feeding approach, providing valuable process operation and kinetic information for the industrial LA production from FR.

High-Efficient Production of Cellulosic Ethanol from Corn Fiber Based on the Suitable C5/C6 Co-Fermentation Saccharomyces cerevisiae Strain

As a potential alternative to fossil-based fuels, cellulosic ethanol has attracted much attention due to its great benefit to energy sustainability and environmental friendliness. However, at present, the industrial competitiveness of cellulosic ethanol production is still insufficient compared with fossil-based fuels because of the higher costs. Expanding the range of lignocellulosic biomass may be a promising measure to promote the economical production of cellulosic ethanol. Corn fiber, a byproduct from the corn deep-processing, is an attractive feedstock for cellulosic ethanol production because of its rich carbohydrate content (generally exceeding 65% of dry weight), almost no transportation cost, and low lignin content allow it to be easily handled. This study first optimized the hydrolysis conditions, including the pretreatment and enzymolysis process based on dilute sulfuric acid, to achieve a high sugar yield. Then, the corn fiber hydrolysates obtained under different hydrolysis conditions were suitably fermented by different C5/C6 co-fermentation Saccharomyces cerevisiae, indicating that the hydrolysate at high solid loading (20%) needs to detoxification to a certain extent but not low solid loading (10%) to achieve high ethanol yield. Finally, the fermentation of the 20% solid loading hydrolysates with resin detoxification was performed in a 50 L bioreactor, achieving the sugar (glucose and xylose) metabolic rate of 2.24 g L −1 h −1 and ethanol yield of 92% of the theoretical value, which are the highest reported levels to date. This study provided a potential process route for cellulosic ethanol production from corn fiber from the perspective of the suitability between the upstream hydrolysis process and the downstream fermentation strain.

Preparation of granulated powders via freeze drying at different levels of slurry solid loading and comparison of their powder bed quality in roller-compaction-assisted binder jetting

Granulation can improve the flowability of nanopowder and the density of resultant parts printed by binder jetting. Forward-rotating roller compaction has the potential for further improving the density. In this study, for the first time, powder recoating tests of different granulated alumina powders were conducted on a commercially available binder jetting printer equipped with a forward-rotating roller compaction system. Freeze drying was used to prepare the granulated powder. Four different granulated powders were prepared from slurries with different levels of solid loading: 2, 5, 10, and 15 vol%, respectively. Powder bed quality, including defects on powder bed surface and maximum powder bed density without defects, was compared among the granulated powders. When the compaction ratio was too high, granulated powders with low solid loading levels of 2 and 5 vol% showed much fewer compaction-induced defects (including surface ridges and edge ridges) on powder bed surface than those with high solid loading levels of 10 and 15 vol%. As the solid loading level increased from 2 to 15 vol%, the maximum powder bed density without defects decreased from 19.5% to 16.0%. This study showed that a granulated powder prepared from a low level of slurry solid loading could reduce the compaction-induced defects on powder bed surface and enhance the powder bed density in roller-compaction-assisted binder jetting.

Quantitative understanding of the impact of stress factors on xylose fermentation at different high solid biomass loads

During lignocellulosic fermentation, cells are challenged by multiple stresses, leading to decreased performances, especially xylose conversion. Quantitatively understanding stress factors in alcoholic fermentation on xylose fermentation is prerequisite for designing and/or modifying lignocellulosic ethanol fermentation. Nonetheless, most studies only focus on just one type of stress, even only one target chemical compound, making it difficult to comprehensively understand the whole stress factors on xylose fermentation. In this study, stress factors in alcoholic fermentation of lignocellulosic hydrolysate were divided into five categories: inhibitors, fermentation metabolites, solid biomass residues, metal ions, and ethanol. Especially, extracted inhibitors, instead of target known inhibitors, were used for studying their effects on fermentation. The effects of each stress on xylose utilization were detailed investigated and compared. Principal component analysis was then performed for comprehensively analyzing effects of the above-mentioned five stresses on xylose fermentation. Results showed that high dose of ethanol is the most significant inhibition factor for xylose fermentation, followed by inhibitors and fermentation metabolites. Metal ions and solid biomass residues in hydrolysate have small effects on xylose fermentation. This study will provide fundamental theoretical support for designing efficient xylose conversion processes and constructing robust xylose-utilizing S. cerevisiae.

Comparison of marine and rushton impeller in high solid loading of two-step pretreated oil palm trunk using simultaneous saccharification and fermentation for ethanol production

Substrate loading enhancement in fermenter generates difficulty in mixing that results in low ethanol yield owing to insufficient mass transfer. Thus, this study evaluated the efficiency of a six-blade Rushton turbine and a three-blade marine type propeller in a 3 L stirred tank bioreactor (STBR) by using steam exploded and alkaline pretreated oil palm trunk (OPT) fibers in a unique batch and fed-batch strategy. The fed-batch began with 5% (w/v) solid loading and after 12 h of simultaneous saccharification and fermentation (SSF) reaction, 2.5% (w/v) solid was added in the bioreactor with 6 h interval. The marine and Rushton impellers were compared at 5% (w/v) batch and 20% (w/v) fed-batch SSF, using agitation rate of 100 rpm. At 5% (w/v) solid loading, the highest ethanol concentration and theoretical yield were 15.66 ± 1.71 g/L and 61.69 ± 2.34%, and 12.10 ± 0.98 g/L and 54.01 ± 3.52%, respectively for marine and Rushton impeller. At high solid loading (20% w/v), the marine impeller achieved maximum ethanol concentration of 41.33 ± 2.02 g/L at 72 h of fermentation, with a low power consumption of 54.73 kW. The Rushton impeller resulted in ethanol concentration of 39.08 ± 1.47 g/L at 96 h of fermentation with relatively higher power consumption of 83.62 kW. The marine impeller is therefore efficient with the fed-batch strategy.

Additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic composites

AbstractA material extrusion (MEX) technology has been developed for the additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic (Cf/SiC) composites. By comparing and analyzing the rheological properties of the slurries with different compositions, a slurry with a high solid loading of 48.1 vol% and high viscosity was proposed. Furthermore, several complex structures of Cf/SiC ceramic composites were printed by this MEX additive manufacturing technique. Phenolic resin impregnation–carbonization process reduces the apparent porosity of the green body and protects the Cf. Finally, the reactive melting infiltration (RMI) process was used to prepare samples with different Cf contents from 0 to 2 K (a bundle of carbon fibers consisting of 1000 fibers). Samples with Cf content of 1 K show the highest bending strength (161.6 ± 10.5 MPa) and fracture toughness (3.72 ± 0.11 MPa·m1/2) while the thermal conductivity of the samples with the Cf content of 1 K reached 11.0 W/(m·K). This study provides a strategy to prepare Cf/SiC composites via MEX additive manufacturing and RMI.

An optimum biomass fractionation strategy into maximum carbohydrates conversion and lignin valorization from poplar

Appropriate fractionation of lignocellulosic biomass into useable forms is a key challenge to achieving an economic bioethanol production. In the present study, four different fractionation strategies of hydrothermal-, NaOH-, ethanol-, and NaOH catalyzed ethanol pretreatment were investigated to compare their abilities of cellulose conversion. Results showed that NaOH catalyzed ethanol pretreatment showed a rather high extent of delignification of 85.92%, which also enhanced the retention of cellulose (92.56%) and hemicellulose (76.57%); while other pretreatments tended to produce cellulose fraction which was insufficient to achieve the whole component utilization. After simultaneous saccharification and fermentation at high solids loading, synergistic maximization of xylose (42.47 g/L) and ethanol (85.74 g/L) output was achieved via alkaline ethanol pretreatment. Lignin characterization information showed that alkaline ethanol pretreatment facilitates the cleavage of β-O-4 linkage and further converts into arylglycerol. Moreover, less condensed substructure units with high processing activity were also generated in S- and G- lignin.

Enzymatic One-Pot Hydrolysis of Extracted Sugar Beet Press Pulp after Solid-State Fermentation with an Engineered Aspergillus niger Strain

Extracted sugar beet press pulp (SBPP) is a promising agricultural residue for saccharification and further bioconversion. Combining solid-state fermentation of SBPP with engineered Aspergillus niger for enzyme production followed by hydrolysis of additionally added SBPP in the same bioreactor was studied to produce a sugar solution (hydrolysate) in a one-pot process. The initial aerobic solid-state fermentations were carried out in duplicate on non-milled, wet SBPP (moisture content of 72% (w/v)) with an A. niger strain engineered for constitutive pectinase production for 96 h, and this resulted in polygalacturonase activities of up to 256 U mL−1 in the wet media. Afterwards, water was added to the bioreactor, and the remaining solids were suspended by stirring to dissolve the hydrolytic enzymes. Metabolic activities of A. niger were inactivated by a N2-atmosphere and by increasing the temperature to 50 °C. High solid loads of milled SBPP were added to the stirred-tank reactor with a delay of 24 h to enable sugar yield calculations based on the compositional analysis of the SBPP used. The resulting final sugar concentrations of the hydrolysate after 166 h were 17 g L−1 d-glucose, 18.8 g L−1 l-arabinose, and 12.5 g L−1 d-galacturonic acid, corresponding to sugar yields of 98% d-glucose, 86% l-arabinose, and 50% d-galacturonic acid, respectively. Including the other sugars released during enzymatic hydrolysis in the one-pot process (d-xylose, d-mannose, d-galactose), a total sugar concentration of 54.8 g L−1 was achieved in the hydrolysate. The one-pot process combining hydrolytic enzyme production in solid-state fermentation with high solid loads during enzymatic hydrolysis of the milled SBPP reduces hydrolytic process costs by replacing chemical pre-treatments, enabling the in situ production of SBPP-adapted hydrolytic enzymes, as well as avoiding intermediate enzyme extraction and preparation steps.

Combination of surfactants and enzyme cocktails for enhancing woody biomass saccharification and bioethanol production from lab-scale to pilot-scale

Converting woody biomass to bioethanol might be more affordable, environmentally friendly, and efficient for making biofuel commercially feasible, but it would still need a significant optimization process and expand pilot-scale research. A combination of commercial low enzymes loading at 10 FPU/g glucan and compound additives utilizing Tween 80, PEG8000 and sophorolipid applied from lab-scale to pilot-scale have been studied in this work at economically viable dosages for enhancing bioethanol production. In lab-scale saccharification and fermentation, pretreated poplar at a high solid loading of 20% yielded the highest ethanol titers of 30.96 g/L and theoretical ethanol yield of 92.79%. Additionally, pilot-scale operation was used to investigate the bioethanol amplification, a final volume of 33 m3 which yielded the greatest ethanol amount of 599.6 kg from poplar wood while gaining on-site value-added production of hemicellulosic and cellobiose liquor 1122 kg and lignin residues 2292 kg.

Preparation of large-size alumina ceramic parts by DLP 3D printing using high-solid-loading paste and optimizing the debinding process

Digital light processing (DLP) is a promising additive manufacturing method for creating complex structural alumina ceramic with high precision, high efficiency, and low cost. However, printing large-size parts with high feature resolution by DLP, obtaining high-performance pastes, and optimizing the debinding process are challenges that still need to be overcome. In this study, an advanced top-down Matrix-DLP technology that seamlessly connects two high-definition-resolution DLP projectors, with high resolution and a large projection area, was used to achieve fine-structured large-size alumina green bodies. The homogeneous and stable non-self-levelling alumina pastes suitable for the DLP technology were developed, with a high solid loading up to 55 vol%, viscosity of 35.0 Pa s at 30 s−1, and good rheological properties by innovatively using 2.5 wt% P5318 as surface modifiers of alumina powders and with only a 0.244% volume of bubble residue by using 0.5 wt% BYK-066N defoamer in combination with a vacuum planetary stirring defoaming process. The debinding processes were designed based on TG-DSC analysis and then optimized, and it was proved that the segmented-atmosphere debinding process was the best approach and can obtain defect- and carbon residue-free bodies with uniform grain distribution, and can also achieve non-destructive debinding for the thick-walled parts with thickness greater than 10 mm. The effects of the debinding residual carbon and the solid loading on the microstructure and properties after sintering were also investigated. Consequently, the high-precision large-size alumina ceramic with good interlayer bonding, dense microstructure, and high microhardness of 17.92 GPa was obtained.

Improving lactic acid yield of hemicellulose from garden garbage through pretreatment of a high solid loading coupled with semi-hydrolysis using low enzyme loading

Byproduct (acetate and ethanol) generation and carbon catabolite repression are two critical impediments to lactic acid production from the hemicellulose of lignocellulosic biomass. To reduce byproduct generations, acid pretreatment with high solid loading (solid–liquid ratio 1:7) of garden garbage was conducted. The byproduct yield was only 0.30 g/g during in the subsequent lactic acid fermentation from acid pretreatment liquid and 40.8% lower than that of low solid loading (0.48 g/g). Furthermore, semi-hydrolysis with low enzyme loading (10 FPU/g garden garbage cellulase) was conducted to regulate and reduce glucose concentration in the hydrolysate, thereby relieving carbon catabolite repression. During the lactic acid fermentation process, the xylose conversion rate was restored from 48.2% (glucose-oriented hydrolysis) to 85.7%, eventually achieving a 0.49 g/g lactic acid yield of hemicellulose. Additionally, RNA-seq revealed that semi-hydrolysis with low enzyme loading down-regulated the expression of ptsH and ccpA, thereby relieving carbon catabolite repression.

Investigating the effect of solid loading on microstructure, mechanical properties, and translucency of highly translucent zirconia ceramics prepared via stereolithography-based additive manufacturing

A study was conducted to explore the potential of 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) ceramics for dental restorations, using stereolithography (SLA) printing technique. Four different solid loadings were established in the ceramic paste systems to study their effects on microstructure, mechanical properties, and translucency. The study examined the rheological behavior and photopolymerization performance of the ceramic pastes with varying solid loadings. Results showed that, an increase in powder concentration resulted in a decrease in cure depth (Cd) and penetration depth (Dp). A narrower pore size distribution was observed in the green bodies with a high solid loading, facilitating the achievement of final densification. The green and sintered densities were highest at 52 vol%, with values of 3.46 ± 0.01 g/cm3 and 6.01 ± 0.02 g/cm3, respectively. Additionally, all of the green strengths exceeded 30 MPa, with a maximum of 35.09 ± 2.02 MPa obtained at 44 vol%. The maximum flexural strength and minimum contrast ratio (CR) value of 746 ± 75 MPa and 0.40 ± 0.01 were achieved at 52 vol% after sintering. No significant differences were observed in the phase composition and hardness of the as-sintered ceramics. Though significant differences were observed in photopolymerization performance, four materials showed similar structural reliability considering Weibull modulus and characteristic strength.

Binary additives for in-situ mitigating the inhibitory effect of lignin-derived phenolics on enzymatic hydrolysis of lignocellulose: Enhanced performance and synergistic mechanism

Separation-free sugar-platform biorefinery from lignocellulose has drawn increasing attention due to its feasibility. However, the presence of lignin-derived phenolics within the whole slurry after pretreatment, is highly inhibitory toward enzymatic hydrolysis of lignocellulose especially at high solid loadings. Developing effective methods to mitigate the phenolics-caused enzyme inhibition in-situ can further improve the cellulose hydrolysis, while the relevant studies are limited. In this study, the effects of different kinds of additives on mitigating the phenolic-caused inhibition was determined and the synergy among the additives were systematically evaluated. Based on the analysis, we developed novel binary additives to alleviate the phenolic-caused inhibition of cellulose hydrolysis in-situ. In addition to surfactants, a reducing agent (l-cysteine) was introduced to enhance the enzymatic hydrolysis of cellulose and the strong synergism between the reducing agent and the surfactant was firstly demonstrated. Further, the mechanism study indicated that these additives could prevent the strong interactions between phenolics and cellulase and improve the major cellulase activities. Finally, with the addition of the binary additives, the cellulose hydrolysis for acid/alkaline pretreated corn stover were significantly improved with low enzyme loading without detoxification. This study provides directions for designing novel additives to improve the enzymatic hydrolysis of pretreated lignocellulosic biomass.

Synergistic Ball Milling–Enzymatic Pretreatment of Brewer’s Spent Grains to Improve Volatile Fatty Acid Production through Thermophilic Anaerobic Fermentation

Brewer’s spent grain (BSG) as the major byproduct in the brewing industry is a promising feedstock to produce value-added products such as volatile fatty acids (VFAs). Synergistic ball mill–enzymatic hydrolysis (BM-EH) process is an environmentally friendly pretreatment method for lignocellulosic materials before bioprocessing. This study investigated the potential of raw and BM-EH pretreated BSG feedstocks to produce VFAs through a direct thermophilic anaerobic fermentation process without introducing a methanogen inhibitor. The highest VFA concentration of over 30 g/L was achieved under the high-solid loading fermentation (HS) of raw BSG. The synergistic BM-EH pretreatment helps to increase the cellulose conversion to 70%. Under conventional low TS fermentation conditions, compared to the controlled sample, prolonged pretreatment of the BSG substrate resulted in increased VFA yields from 0.25 to 0.33 g/gVS, and butyric acid became dominant instead of acetic acid.

Commentary: polymer binding modules accelerate enzymatic degradation of poly(ethylene terephthalate)

The large scale production and indiscriminate use of plastics led to serious environmental pollution. To reduce the negative effects of plastics waste on the environment, an approach of enzymatic degradation was put forward to catalyze plastics degradation. Protein engineering strategies have been applied to improve the plastics degrading enzyme properties such as activity and thermal stability. In addition, polymer binding modules were found to accelerate the enzymatic degradation of plastics. In this article, we introduced a recent work published in Chem Catalysis, which studied the role of binding modules in enzymatic hydrolysis of poly(ethylene terephthalate) (PET) at high-solids loadings. Graham et al. found that binding modules accelerated PET enzymatic degradation at low PET loading (< 10 wt%) and the enhanced degradation cannot be observed at high PET loading (10 wt%-20 wt%). This work is beneficial for the industrial application of polymer binding modules in plastics degradation.