Kyuya Nakagawa

Activated carbon from municipal waste

Abstract A refuse derived fuel (RDF) was carbonized by partial combustion at 623 K and the carbonized RDF (cRDF) was steam-activated at 1123 K. The cRDF was also treated by 3.3 or 5.2 N nitric acid at a boiling temperature for 3 h prior to the steam-activation. Porous properties of the activated carbons prepared were determined by the nitrogen adsorption method. The porous structure of the carbon prepared without the pretreatment of nitric acid was not so developed as a commercial carbon for dioxin adsorption. On the other hand, the carbons prepared via the nitric acid treatment had BET surface areas of 515 and 828 m2/g and more mesopore volumes than the commercial carbon. During the acid treatment, the ash dissolution from cRDFs to nitric acid was observed and resulted in the formation of activation sites for developing mesopores. Hence, the carbons prepared could be used to remove dioxins from the incinerators.

Gas adsorption on activated carbons from PET mixtures with a metal salt

Abstract Activated carbons were prepared from carbonized PET by steam activation via pretreatment by mixing PET with a metal salt [Ca(NO 3 ) 2 ·4H 2 O, Ca(OH) 2 , CaCO 3 , ZnO, and AlNH 4 (SO 4 ) 2 ·12H 2 O], and with acid treatment after carbonization. The porous properties of the activated carbons were determined by the nitrogen adsorption method. The adsorption isotherms of CO 2 , C 2 H 6 , nC 4 H 10 and iC 4 H 10 at 298 K on the prepared activated carbons were measured to determine practical applications and to obtain a better understanding of the porous structure of the prepared carbons. Steam-activated carbons via pretreatment have a larger mesoporosity than carbons with no pretreatment. The metal salt used in the pretreatment for steam activation has no influence on the microporous structure, but it does influence the mesoporous structure of the prepared carbons. Activated carbons prepared via pretreatment show a large adsorption capacity for nC 4 H 10 and iC 4 H 10 . These carbons are suitable as adsorbents for canisters, etc. Application of the potential theory to adsorption data for the prepared carbons suggests that the pretreatment contributes to the formation of pores larger than 0.50 nm at high burnoff.

Preparation and Characterization of Activated Carbons from Refuse Derived Fuel (RDF)

Activated carbons were prepared from a carbonized RDF (cRDF) by steam-activation. The cRDF was obtained by carbonizing the RDF at 773 K. Different conditions of heating rate at carbonization were selected. The cRDF was also treated by nitric acid (HNO3) or hydrogen chloride (HCl) prior to the steam activation. Porous properties of the carbons prepared were determined by the nitrogen adsorption method, and the effects of the carbonizing condition and the acid treatment on the properties were elucidated. The hydrophobic surface of the carbons prepared was also confirmed by water vapor adsorption. It was found that the carbons prepared from the RDF were effective for a practical use.

Characterization of casein-based nanoparticles formed upon freezing by in situ SAXS measurement.

The formation of casein-based nanoparticles from sodium caseinate and sodium caseinate-pectin solutions was investigated in a frozen system by protein self-aggregation and protein-polysaccharide complexation, respectively. Casein-based nanoparticles were prepared by controlling the pH levels of the solutions followed by freezing. The formation of precipitates was confirmed in the casein solutions at pH<5.5. However, an obvious effect of the freezing on the formation of aggregates could not be confirmed, although the freezing did have an effect on accelerating the formation of precipitates. The mean particle sizes analyzed from the produced nanoparticles suggested that freezing did not have any significant effects on altering the particle sizes. Similar trends were observed in the casein-pectin solution in terms of phase separation and particle sizes. A difference was confirmed in the solution at pH 4.6; that is, a clear phase separation was observed due to freezing. Nevertheless, it was found, both in the casein and casein-pectin systems, that the degradation rates of the freeze-thawed nanoparticles were considerably slower than that of the original nanoparticles. This suggested that the casein-based nanoparticles formed through freezing had structural features different from the ones in the unfrozen solution. It could be concluded from the SAXS analysis that the formation of the protein-based particulate systems certainly occurred in the cryoconcentrated phase associated with freezing. The present technique is advantageous for the encapsulation of heat-sensitive and/or acid-sensitive ingredients in protein nanoparticles.

Spray Drying of Casein Aggregates Loaded with β-Carotene: Influences of Acidic Conditions and Storage Time on Surface Structure and Encapsulation Efficiencies

Spray-dried casein-encapsulated β-carotene powders were prepared for encapsulation efficiency studies with respect to structural changes in casein aggregates prior to drying. The use of casein aggregates as shell matrix materials for encapsulation is of interest in encapsulation research; however, the relationship between process conditions and casein aggregation is not completely understood. Here, we report the investigation of the influence of solution pH and storage time on casein aggregate structural changes, in addition to encapsulation efficiency after spray drying. Total β-carotene loading quantities observed were higher when a solution with lower pH was employed in the dried powder preparation. Specimens obtained from a solution with pH 5.5 gave the highest total loading efficiency. Loading efficiencies were largely improved when the solutions were stored for 5 days prior to spray drying. Small-angle X-ray scattering analysis confirmed that surface structures and particle sizes were correlated to the solution pH used, as well as to storage time. At lower pH conditions (pH 5.5), particle sizes greatly increased over the entire storage duration, with a rough surface formed in the first 6 h, followed by a gradual surface smoothing. At higher pH conditions (pH 6.0–7.0), a rough surface formed accompanied by an increase in the particle size in the first 24 h, after which the size gradually decreased with the smoothed surface formation. The encapsulation efficiencies could be correlated with these structural changes during storage. The results obtained provide important insights into the encapsulation process and are expected to improve applications involving casein aggregation.

Impact of Ice Morphology on Design Space of Pharmaceutical Freeze-Drying

It has been known that the sublimation kinetics of a freeze-drying product is affected by its internal ice crystal microstructures. This article demonstrates the impact of the ice morphologies of a frozen formulation in a vial on the design space for the primary drying of a pharmaceutical freeze-drying process. Cross-sectional images of frozen sucrose-bovine serum albumin aqueous solutions were optically observed and digital pictures were acquired. Binary images were obtained from the optical data to extract the geometrical parameters (i.e., ice crystal size and tortuosity) that relate to the mass-transfer resistance of water vapor during the primary drying step. A mathematical model was used to simulate the primary drying kinetics and provided the design space for the process. The simulation results predicted that the geometrical parameters of frozen solutions significantly affect the design space, with large and less tortuous ice morphologies resulting in wide design spaces and vice versa. The optimal applicable drying conditions are influenced by the ice morphologies. Therefore, owing to the spatial distributions of the geometrical parameters of a product, the boundary curves of the design space are variable and could be tuned by controlling the ice morphologies.

Redistribution of Protein Biological Activity in a Freeze-Dried Cake

Lactate dehydrogenase (LDH) solutions were freeze dried in order to investigate the redistribution of the remaining LDH activity in the dried cake. D-Mannitol and a polysaccharide (κ-carrageenan, ι-carrageenan, or dextran) were mixed and used as stabilizers in freeze drying. It was found that the remaining LDH activity was significantly redistributed in the freeze-dried cake, and the enzyme concentration was not uniform along the axis of the dried cake due to variations in the freeze-drying conditions and stabilizer concentration. In some cases, active enzymes were highly localized in a specific portion of the dried cake. This was mainly due to the redistribution of the protein content. Further freeze-drying tests employing bovine serum albumin (BSA) and the above-mentioned polysaccharides showed that proteins (BSA) tended to accumulate in the lower portions of the dried cake, forming concentration gradients. Therefore, the concentration gradient in the freeze-dried cake was mainly due to the freezing process. This redistribution of protein content contributed considerably to the apparent redistribution of enzyme activity. The results suggest that a process that can control the redistribution of protein content in a freeze-dried cake would further improve the biological activity of freeze-dried proteins.

Destabilization of mayonnaise induced by lipid crystallization upon freezing

The thermal and rheological history of mayonnaise during freezing and its dispersion stability after the freeze-thaw process were investigated. Mayonnaise was cooled to freeze and stored at −20 to −40 °C while monitoring the temperature; penetration tests were conducted on the mayonnaise, which was sampled at selected times during isothermal storage at −20 °C. Significant increases in the temperature and stress values due to water-phase crystallization and subsequent oil-phase crystallization were observed. The water phase crystallized during the cooling step in all the tested mayonnaise samples. The oil phases of the prepared mayonnaise (with rapeseed oil) and commercial mayonnaise crystallized during isothermal storage after 6 and 4 h, respectively, at −20 °C. The dispersion stability was evaluated from the separation ratio, which was defined as the weight ratio of separated oil after centrifuging to the total amount of oil in the commercial mayonnaise. The separation ratio rapidly increased after 4 h of freezing. This result suggests that crystallization of the oil phase is strongly related to the dispersion stability of mayonnaise. Graphical abstract Temperature changes during storage at −20 °C and separation ratio, X, after the freeze-thaw process of commercially available mayonnaise.

Digestibility and structural parameters of spray-dried casein clusters under simulated gastric conditions

The digestibility of casein clusters prepared from sodium caseinate solution (plain or pH-adjusted (pH=6.0)) was studied. The prepared solutions were spray-dried at different inlet air temperatures (150°C and 180°C), and the properties (i.e. encapsulation efficiency, surface hydrophobicity, and digestibility) of the resultant powders were investigated. The specimens obtained from the pH-adjusted solution had higher encapsulation efficiencies than the specimens obtained from the plain solution. A higher spray-drying temperature resulted in lower encapsulation efficiencies and higher surface hydrophobicities. Simulated gastric digestion tests were carried out to study the digestibility of the obtained casein clusters, which was analyzed in terms of reaction kinetics and structural changes during digestion. The effects of drying temperature and pH on the amount of casein digested were not significant; that is, approximately 30% of casein was digested in 120min for all specimens. Small-angle and ultra-small-angle X-ray scattering measurements were used to analyze the structure of the obtained clusters and their changes during digestion. The results suggested that all the obtained casein clusters, with an average size of approximately 428nm, had a rough, fractal-structured surface with many dense primary clusters. These structures changed during digestion; specifically, the cluster size increased both in the overall diameter and on the primary structure scale. The fractal characteristics changed from surface to mass fractals, and simultaneously, the cluster density decreased. The drying temperature affected the cluster size during digestion, and the trends were different in the specimens obtained from the plain and pH-adjusted solutions. These results could be useful in the design of protein-based encapsulation systems with desirable digestibility and bioavailability.

Protein-Based Microencapsulation with Freeze Pretreatment: Spray-Dried Oil in Water Emulsion Stabilized by the Soy Protein Isolate–Gum Acacia Complex

Spray-dried microparticles with lipid cores that dissolve β-carotene were prepared using a technique based on the complexation of soy protein and gum acacia. A freeze-pretreatment was applied to modify the resultant properties of the dried particles. An oil in water emulsion stabilized by soy protein isolate was mixed with gum acacia. The pH of the solution was adjusted to a selected value; this solution was frozen and thawed under controlled thermal protocols, then spray-dried to obtain the final products. Complexation was induced on the surface of the oil droplets owing to electrostatic interactions that occur below the isoelectric point (ca. pH 4.0) of the employed soy protein isolate. The freeze-pretreatment prior to spray-drying was expected to induce this interaction by freeze concentration and to control the kinetics of complex formation. When solutions with a pH of 4.0 and 3.0 were spray-dried, the encapsulation of β-carotene had similar efficiencies. The freeze-pretreatment was observed to have a significant effect on the specimens prepared from the solution with a pH of 4.0. Slow freezing conditions successfully improved the encapsulation efficiency and simultaneously reduced the amount of surface oil. Moreover, this pretreatment augmented the mass transfer resistance of the shell matrix, so that the release rate of dissolved β-carotene in the lipid core could be retarded.