Shigeharu Tanisho

Effect of CO2 removal on hydrogen production by fermentation

Abstract The improvement of the yield of hydrogen at fermentative production using molasses as a substrate was investigated from two points of view; i.e. firstly, through the control of production pathway and secondly, by the condition of nutrient source for growing. It was shown that succinate, one of the products of Enterobacter aerogenes strain E.82005, was produced inductively by accumulation of CO 2 which was produced simultaneously with acetate, ethanol and other products. The amount of residual NADH which is the base material of H 2 evolution increased when Ar or H 2 was blown into the culture liquid. From these results, it was concluded that the removal of CO 2 from culture liquid effected the promotion of the yield of hydrogen. It was also shown that the existence of sufficient nitrogen source for bacterial growth was a necessary condition to get entire yield of hydrogen. The combination of experiments to remove CO 2 and to give sufficient nitrogen source was found to yield 1.58 mol hydrogen from 1 mol sugar in terms of glucose.

Continuous hydrogen production from molasses by the bacterium Enterobacter aerogenes

Hydrogen was produced continuously for 42 days by fermentation using Enterobacter aerogenes strain E. 82005. Diluted molasses containing about 2% sugars were fed at a rate of approximately 80 ml h−1. The maximum and the available rate of hydrogen production at 38°C in a 300 ml fermenter with 250 ml molasses fluid were 36 mmol-H2/(l-culture h) and 20 mmol-H2/(l-culture h) respectively. Cell concentration in waste liquid was nearly constant at about 0.9 g-dry cell/l throughout the experiment, although the total cell concentration in the fermenter was about 6.2 g-dry cell/l at the final cultivation, since flocks of the cells adhered to the wall of the fermenter. The maximum yield of hydrogen was 2.5 mol-H2/mol sugar expressed in terms of sucrose, while the available yield of hydrogen was approximately 1.5 mol-H2/mol-sugar. The volumetric fraction of hydrogen was approximately 60% of the gaseous products. Catabolism in continuous cultivation was different from that in batchwise cultivation. Lactate was the richest catabolite at about 70% in the liquid catabolites. Butyrate and acetate amounted about 15% and 10% respectively.

Continuous hydrogen production from molasses by fermentation using urethane foam as a support of flocks

Continuous hydrogen production by fermentation was tried using molasses as a substrate. In the fermenter, pieces of urethane foam were suspended to make them suports for cells or cell flocks of a bacterium, Enterobacter aerogenes strain E.82005. The suspended cell density was ca 0.8 g dry cell 1−1 during cultivation, while the probability of adhesion of cells on or in the urethane foam was ensured from two different view points: the increment in the uptake rate of sugar, and the hydrogen evolution rate per unit cell mass. Lactate, butyrate and acetate were the main products of the fermentation, especially lactate which formed ca 70% of all products. The maximum and the available yields of hydrogen from sugar were ca 3.5 and ca 2.2 mol H2 mol sugar−1, estimated in terms of sucrose, respectively. The available yield was nearly equal to the yield predicted from the sugar composition of molasses. The pathway of hydrogen evolution of the bacterium was determined to be the NADH pathway, from balance accounts of NADH.

Fermentative hydrogen evolution by Enterobacter aerogenes strain E.82005

Fermentative hydrogen evolution by Enterobacter aerogenes strain E.82005 was studied with cultivations performed under both controlled and uncontrolled pH. Results show that the transient rate of hydrogen evolution on the glucose and peptone liquid culture exceeded 420 ml (g-dry cell h)−1 under uncontrolled cultivation and that about 1 mole of glucose was required to generate 1 mole of hydrogen by the bacterial fermentation. In addition, the pH of the culture was found to have important influences on the hydrogen evolving activities of the st. E.82005. The activity reached a maximum (520 ml (1-culture-h)−1) at pH 6.0 asnd 40.5°C. However, the most vigorous growth of cell was found to occur at pH 7.0.

Hydrogen evolution of Enterobacter aerogenes depending on culture pH: mechanism of hydrogen evolution from NADH by means of membrane-bound hydrogenase.

The pH dependency of cell mass productivity, the hydrogen evolution rate and the yield of hydrogen from glucose was measured by controlling the pH of the culture automatically. The cell mass productivity of Enterobacter aerogenes increased in a linear fashion up to a pH value of approx. 7.0. In contrast, both the evolution rate and the yield of hydrogen showed convex relationships up to a pH value of 7.0, both having maximum values at a pH of approx. 5.8. The maximum evolution rate was approx. 11.3 mmol H2 per g dry cell per h at 38 degrees C. A hypothetical mechanism for hydrogen evolution was proposed by taking our results and other research work into consideration. The proposed mechanism of hydrogen evolution was that NADH was oxidized on the inside surface of the cell membrane and protons were reduced on the outside surface by means of membrane-bound hydrogenase. This mechanism explains in a thermodynamic context the relation between the activity of the hydrogen evolution and the pH of the culture.

Effects of Formate on Fermentative Hydrogen Production by Enterobacter aerogenes

This paper describes the effects of formate on fermentative hydrogen production by Enterobacter aerogenes by way of batch culture. When 20 mM formate was added to pH 6.3 and pH 5.8 E. aerogenes glucose cultures (formate culture) at the beginning of cultivation, hydrogen evolution through both glucose consumption and decomposition of the extrinsic formate occurred together, while hydrogen evolution occurred only through glucose consumption in the control cultures. The hydrogen evolution rates in the formate cultures were faster than in the control cultures, although cell growth and glucose consumption rates in the formate cultures were slower than the control cultures’. The decomposition rate of the extrinsic formate in the pH 5.8 formate culture was faster than in the pH 6.3 fomiate culture. The hydrogen yield from glucose in the pH 6.3 formate culture increased due to the increasing amount of the nicotinamide adenine dinucleotide for hydrogen production.

Methanation of carbon dioxide by using membrane reactor integrated with water vapor permselective membrane and its analysis

Using membrane reactor integrated with water vapor permselective membrane, the Sabatier reaction for the methanation of carbon dioxide with hydrogen, CO2+4H2 ⇔ CH4+2H2O, was investigated. The reaction experiments were carried out under the conditions of superficial space velocity 0.030−0.123 s−1, molar ratio of H2 to CO2 in the feed gas, 1–5, operating pressure 0.2 MPa absolute, and temperature 480–719 K. The conversion was increased about 18% in maximum with the membrane. Theoretical equations for Sabatier reaction with and without membrane were derived and applied to analyze the experimental data of CO2 conversion.

Study on molecular weight cut-off performance of asymmetric aromatic polyimide membrane

Abstract Asymmetric aromatic polyimide membranes for a petroleum refinery were made by casting solution of 18 wt.% polyamic acid blending of the trade name Pyle-ML5057 (Du Pont Co.) and PMDA-DABP in the ratio of 1:1 and 20 wt.% phenanthrene in dimethylacetamide at 303–363 K, with 1 and 3-min evaporation times, followed by a cycle process of thermal treatment in a bath of dioctyl sebacate under N2 in three steps: 1 h at 373 K, 1 h at 473 K and 1 h at 573 K. The asymmetric aromatic polyimide membranes fabricated with combinations of preparation conditions had a molecular weight (MW) cut-off ranging from 170 to 400 Da. The membrane which has a MW cut-off of 170 Da succeeded in separating the gasoline-kerosine mixtures. A separation factor (for gasoline/kerosene) of 19.5 was obtained.

HYDROGEN PRODUCTION BY FACULTATIVE ANAEROBE Enterobacter aerogenes

Enterobacter aerogenes is a facultative anaerobic bacterium. It grows under both aerobic and anaerobic conditions. In our experiments, it assimilated glucose at a rate as high as 17 mmol glucose/(g-dry cell h) and consequently evolved hydrogen at near-equal speed. The yields of hydrogen, though, were small, at 1.0 mol from 1 mol glucose and 2.5 mol from 1 mol sucrose. The optimum temperature for bacterium growth was about 40 °C and the optimum pH for hydrogen evolution was roughly 5.7, though 7.0 was the optimum pH for growth. This bacterium immediately restored the respiratory function to its aerobic condition when cultivation was changed from anaerobic to aerobic conditions. Based on the mechanism of hydrogen evolution through a NADH (Nicotinamide Adenine Dinucleotide, reduced form) pathway, two methods were proposed to improve the yield of hydrogen from glucose. One was to inhibit the electron transport chain at the sites of the NADH dehydrogenase complex or cytochrome b-c1 complex and the other was to cultivate in the range of pH 5 to 4 under anaerobic conditions.

Hydrogen purification using zirconia-silica composite membranes for thermochemical process

Abstract For the purpose of purifying H 2 from a gaseous mixture of thermochemical water decomposition processes, the characteristics of zirconia-silica composite membranes coated on porous ceramic tubing were investigated up to 773 K. The maximum content of the Zr(OC 3 H 7 ) 4 in the metal-alkoxides solution used successfully in the coating process was 60 mol %. Separation experiments of gaseous mixtures of H 4 -H 2 O-HBr (UT-3 process) and of HI-H 2 O (IS process) were carried out at 423–773 K, and it was found that hydrogen can be purified as a reject stream and that HBr and HI can be recovered on the permeation side through the membranes.