Atsushi Kishita

Kinetics of oxidation of food wastes with H2O2 in supercritical water

Abstract In this study, supercritical water oxidation (SCWO) of carrots and beef suet was carried out in a batch reactor system with an H 2 O 2 oxidant, at a temperature between 400 and 450°C and reaction times from 10 s to 10 min. The results showed that the oxidative decomposition of carrots and beef suet proceeded rapidly and a high total organic carbon (TOC) decomposition of up to 97.5% was obtained within 3 min at 420°C for carrots and within 5 min at 450°C for beef suet when there was a sufficient supply of oxygen. It was also found that the oxidation reaction for both carrots and beef suet might be separated into a fast reaction at the early stage and a slow reaction at the later stage. In the later stage following the early stage reaction, acetic acid, which is a fairly stable product of the early stage reaction, is the reactant and the rate of overall oxidation reaction for complete decomposition is dominated by the later stage reaction. Global kinetic analysis based on the model described above showed that the early stage oxidative reaction of beef suet could be considered as a first-order reaction with respect to the concentration of organic carbon. The activation energy was 37.3 kJ mol −1 . Oxidation of acetic acid could also be expressed as a first-order reaction, and the activation energy was 106.5 kJ mol −1 . The early stage oxidation reaction of carrots was too fast to be analyzed. On the basis of intermediate products identified, reaction pathways were discussed. For carrots, polysaccharides may first be hydrolyzed to glucose and then oxidation of the glucose may take place. For beef suet, glyceride is first hydrolyzed to glycerin and carboxylic acids corresponding to the components of glyceride, followed by consecutive reactions for oxidative decomposition.

A new process for producing calcium acetate from vegetable wastes for use as an environmentally friendly deicer

A new process for producing calcium acetate, a non-corrosive deicer, is proposed. The process consists of a two-step continuous-flow hydrothermal conversion of vegetable wastes into acetic acid and the production of calcium acetate, followed by the separation and condensation of the product. The experiments for acetic acid production showed that there were almost no significant differences in acetic acid yields for the five different kinds of vegetables selected for the batch experiments or for their mixture in batch and continuous-flow experiments. Electrodialysis was chosen as a satisfactory method for separating and condensing the calcium acetate produced from the acetic acid solution obtained from the vegetable wastes. After purification by reverse-osmosis, the residual, depleted acid solution could be safely discharged. The calculation of the carbon balance for the proposed process showed that 21.3% of the TOC from vegetable wastes could be used as calcium/magnesium acetate (CMA) and over 22% as an environmentally friendly deicer.

Formic acid production from carbohydrates biomass by hydrothermal reaction

The formation of formic acid or formate salts by hydrothermal oxidation of model biomass materials (glucose, starch and cellulose) was investigated. All experiments were conducted in a batch reactor, made of SUS 316 tubing, providing an internal volume of 5.7 cm3. A 30 wt% hydrogen peroxide aqueous solution was used as an oxidant. The experiments were carried out with temperature of 250°C, reaction time varying from 0.5 min to 5 min, H2O2 supply of 240%, and alkaline concentration varying from 0 to 1.25 M. Similar to glucose, in the cases of the oxidation of hydrothermal starch and cellulose, the addition of alkaline can also improve the yield of formic acid. And the yield were glucose>starch> cellulose in cases of with or without of alkaline addition.

Oxidation of garbage in supercritical water

Abstract In the present study, 17 kinds of organic materials selected from groups of vegetable, meat, fat and fish as main components of garbage were oxidized with H2O2, using a batch reactor system under the condition of supercritical water, in order to treat organic wastes of high water content and low calorific value. It was found that they were easily oxidized, and remarkable influence of the kind of material in each group on the TOC decomposition was not recognized, but meats, fats and fishes, especially beef suet, were more difficult to be oxidized than vegetables. The residual intermediate product was acetic acid in reactions of one minute at 400°C for all materials. Based on this result, the rate expression for supercritical water oxidation of acetic acid was determined.

Production of lactic acid from C6-polyols by alkaline hydrothermal reactions

Production of lactic acid from C6-polyols (Mannitol) under alkaline hydrothermal conditions was investigated. Experiments were performed to examine the difference in the production of lactic acid between C6-polyols and C3-polyols (glycerine), as well as C6-aldoses (glucose). Results showed that the yield of lactic acid from C6-polyols was lower than that from both glycerine and glucose. It indicated that long chain polyols might follow a different reaction pathway from that of glycerine. Further investigation is needed to clarify the reaction mechanism and improve the relatively low lactic acid acid yield from C6-polyols.

Observation of the heavy crude oil dissolution behavior under supercritical condition of water

In development of on-site partial upgrading technology of the bitumen by using supercritical water as a reaction solvent, it is important to understand the role of water in the reaction field. Therefore experiments were carried out using a batch reactor system operating with varying reaction pressure at a temperature of 703 K, and reaction time of 15 min. From the results such as the viscosity and the boiling point distribution of oil product etc., it can be seen that higher density supercritical water inhibits the cracking of bitumen to lower molecular weight substance.

Production of acetic acid by hydrothermal two-step process of vegetable wastes for use as a road deicer

This study aimed to produce acetic acid from vegetable wastes by a new hydrothermal two-step process. A continuous flow reaction system with a maximum treatment capacity of 2 kg/h of dry biomass developed by us was used. Five kinds of vegetables of carrots, white radish, chinese cabbage, cabbage and potato were selected as the representation of vegetable wastes. First, batch experiments with the selected vegetables were performed under the condition of 300°C, 1 min for the first step, and 300°C, 1 min and 70% oxygen supply for the second step, which is the optimum condition for producing acetic acid in the case of using starch as test material. The highest yields of acetic acid from five vegetables were almost the same as those obtained from starch. Subsequently, similar the highest yield of acetic acid and experimental conditions from vegetables were also obtained successfully using the continuous flow reaction system. These results should be useful for developing an industrial scale process.

Formation of Lactic Acid from Cellulosic Biomass by Alkaline Hydrothermal Reaction

Glucose, as a model compound of cellulosic biomass, was used as a test material. Ca(OH)2 and NaOH were selected as alkali. Results showed that both NaOH and Ca(OH)2, can promote the formation of lactic acid in a hydrothermal reaction of glucose. In the case of the addition of NaOH, lactic acid was obtained with a good yield of 27% based on a carbon base at 300 °C for 60 s with a NaOH concentration of 2.5 M. In the case of the addition of Ca(OH)2, the highest yield of lactic acid is 20%, which occurred at 300 °C for 60 s with a Ca(OH)2 concentration of 0.32 M. The formation mechanisms of lactic acid from glucose were also discussed according to intermediate products identified. Lactic acid may be generated via formaldehyde, glycolaldehyde besides via the aldose having three carbon atoms in hydrothermal reaction which all formed by the reverse aldol condensation of hexoses.

Hydrogen Generation from Water with Hydrogen Sulfide as a Reducer at the Mild Conditions

The aim of this work is to investigate the hydrogen generation from water using H2S as a reducer in the hydrothermal reactions at the mild conditions. The effects of reaction temperature, reaction time and initial pH values of reaction solution on the yields of hydrogen from water were studied. The experiment results showed that hydrogen could be generated from water when the reaction temperature was beyond 200° C. Moreover, the hydrogen production strongly depended on the initial pH values of the solution. Under strong alkaline conditions the hydrogen production from water was much higher than that under acidity or weak alkaline conditions. The possible mechanism of hydrogen production was discussed.

Formation of Formic Acid by Hydrothermal Oxidation of Carbohydrate Biomass for Producing Hydrogen

The formation of formic acid by hydrothermal oxidation of glucose, a model compound of carbohydrate biomass, was investigated for applying formic acid as a source of hydrogen production. All experiments were conducted in a batch reactor made of SUS 316 tubing, providing an internal volume of 5.7 cm3. A 30 wt% hydrogen peroxide solution was used as an oxidant. The hydrothermal oxidation of glucose with and without the addition of alkali was carried out with temperature varying from 250 to 300 °C, reaction time varying from 30 s to 90 s, and H2O2 supply varying from 80% to 140%. Results showed that at a mild temperature of 250 °C, glucose was converted into formic acid in an excellent yield of 75% when adding alkali. This result should facilitate the study on the production of hydrogen from carbohydrate biomass via formic acid.