Showing papers in "Journal of Applied Chemistry and Biotechnology in 1972"

Environmental effects on the growth of nitrogen‐fixing bacteria

Abstract: Studies with Azotobacter chroococcum in chemostats have clarified several aspects of the physiology of nitrogen fixation by this obligate aerobe. Sensitivity to excessive oxygenation was specific to nitrogen-fixing populations and was not shown by those assimilating ammonia; C- or P-limited populations were hypersensitive. Oxygen sensitivity was attributable to the known ease with which the enzyme nitrogenase is damaged chemically by oxygen and it represented a response by the organism to prevent such damage to the enzyme in vivo . In the presence of excess of all other nutrients, N 2 fixation was regulated intracellularly and chemostat populations showed the properties normally associated with N-limited populations (inverse relation of biomass to growth rate), complicated by a selection of fast-growing variants at dilution rates approaching wash-out. Populations could become adapted to high oxygen tensions and showed augmented respiration rates and increased contents of cytochrome oxidase. The acetylene reduction test indicated that the nitrogenase content was unchanged but that the optimal P 0 2 value for activity had increased. Thus respiration appeared to perform a protective function; when respiratory protection was inadequate, the organisms were able to inactivate their enzyme rapidly and reversibly. This process has been called “conformational protection” because evidence exists that the enzyme is then physically orientated, possibly by association with subcellular membranes, in a manner in which the oxygen-sensitive components are inaccessible to 0 2 . In this state it would be inactive towards N 2 .

Solubility of hydrogen sulphide, dimethyl ether, methyl chloride and sulphur dioxide in liquids. The prediction of solubility of all gases

Abstract: The solubilities of hydrogen sulphide, dimethyl ether, methyl chloride, and sulphur dioxide expressed as the mole ratio, Xgas, at different temperatures and 1 bara are given for a number of liquid compounds of types commonly used in operational chemistry Representative curves showing the variations of Xgas, and Ngas (mole fraction), with pressure, pgas, are discussed with reference to Henry's law and Raoult's law With the exception of hydrogen halides and ammonia, the Xgas (at a stated t° and pgas) for water is much less than for any other liquid reported as examined The primary factor determining the Xgas value at 1 bar is the boiling point of the gas (He to SO2) at 1 bar; the Raoult's law Xgas value emerges from this, and places the gases in the same order as the overlapping ranges of real Xgas values The actual Xgas value within a particular range for a chosen gas is, for a chosen liquid, seemingly determined by acid-base functions as defined herein The prediction of the Xgas value is discussed in these terms

Kinetics of benzene hydrogenation by supported nickel at low temperature

Abstract: A study of the kinetics of benzene hydrogenation at low temperatures is described which confirms and completes the present fragmentary information available in the literature. Such analysis may also be useful for the purposes of using the reaction as a model system in studies of reaction engineering problems. The results are consistent with a Rideal mechanism for the hydrogenation, proceeding via the molecular addition of hydrogen to adsorbed benzene. The very strong adsorption and the range of conditions over which zero order kinetics with respect to benzene are found support the π-bonding theory for benzene chemisorption.

Pyrolysis of methane in a single pulse shock tube

Abstract: The thermal decomposition of methane has been studied in a chemical shock tube at pressures up to 20 atm over a temperature range of between 1750 and 2700 K and for reaction times up to 2.5 ms. Attention is drawn to some of the experimental features of the shock tube and to the fact that reaction temperatures were measured. Optimum conditions for the production of acetylene from methane are suggested, and the relatively small effect of pressure on the acetylene yields is noted. Values for activation energy (93.6 kcal/mol) and frequency factor (3.8 × 1013 s−1 for methane decomposition are given. The experimental results obtained are discussed in connection with suggested mechanisms of decomposition. In the discussion attention is drawn to the difficulty of predicting acetylene yields arising from the incomplete understanding of the mechanism of acetylene decomposition and of “carbon” formation under the conditions employed.

The thermal decomposition of ferrous sulphate heptahydrate. I. Dehydration and oxidation

Abstract: The intermediate products of thermal decomposition of ferrous sulphate heptahydrate, in a current of air, have been investigated by X-ray and chemical analysis. It was found that the monohydrate undergoes dehydration followed by oxidation, or combined hydrolysis and oxidation to Fe2O(SO4)2 and Fe(OH)SO4, respectively. The latter basic salt is converted to the former with loss of H2O. Fe2O(SO4)2 decomposes to Fe2(SO4)3 and α-Fe2O3 above 400 °C; the transformation is almost complete at 550 °C. Fe2(SO4)3 decomposes to Fe12O3(SO4)15 and SO3 at 475 °C. The last oxide sulphate decomposes to α-Fe2O3 and SO3 at higher temperatures.

The concentration of mammalian cells in a tangential flow filtration unit

Abstract: A tangential flow filtration unit is described through which cell suspension is continuously recycled. A pressure drop is incurred across the filter which forces liquid through the filter sheet, and cells in the remaining suspension are thus concentrated. The unit described has been used to concentrate 4 1 of cell suspension containing at least 2 × 106 cells/ml 12-to 23-fold in 2 to 4 h, with 94% viable cell recovery and little loss of viability. The filter is amenable to scale-up and a pilot scale version is under test in this laboratory.

Carbon‐supported platinum metal catalysts for hydrogenation reactions. Mass transport effects in liquid phase hydrogenation over Pd/C

Abstract: The efficient use of palladium charcoal catalysts in liquid phase hydrogenation processes is shown to depend on hydrogen transport limitations from the bulk liquid phase to catalyst particles, and on the diffusion of hydrogen through the porous structure of the support to the active metal crystallites. These processes impose a strict limitation on the maximum rate of hydrogenation, and can effect the selectivity of reaction processes. The factors which control the output of a reactor in terms of operating conditions, and catalyst design are examined.

Phase behaviour in the ammonia‐carbon dioxide system at and above urea synthesis conditions

Abstract: The bubble- and critical-points in the NH3—CO2 system, at complete chemical equilibrium, have been measured in the range of NH3/CO2 = 2 to 100% NH3, 160 ⩽ T ⩽ 260 °C, and 50 ⩽ P ⩽ 950 atm. With increasing temperature an increasingly large part of the NH3—CO2 system becomes critical. The possible relation between the occurrence of critical conditions and the reported decrease of conversion to urea in the liquid phase at temperatures above 200 °C is discussed. The effect of small quantities of inert gas (N2) on the bubble-point pressure is also discussed.

Kinetics of growth on aqueous — oil and aqueous — solid dispersed systems

Abstract: Dispersed phase continuous culture systems are very complicated. Indeed, they can differ considerably in their behaviour from the usual homogeneous continuous culture systems. Experimental studies on cell adsorption-desorption rates under various conditions of surfactant concentrations and droplet coalescence and break-up is needed in order to understand fully the mechanism of substrate utilisation in these continuous systems.

Some observations on the setting of calcium sulphate hemihydrate plaster in the presence of phosphoric acid and hydrated lime

Abstract: The effects of additions of phosphoric acid and hydrated lime on the setting of calcium sulphate hemihydrate plasters have been examined. At two levels of P2O5 concentration (0.75 and 1.5 wt-% P2O5) it has been found that extreme retardation of the plaster setting process occurs with lime additions in the range, Ca(OH)2/P2O5 (weight ratio) 0.5 to 1.5. The chemical nature of this effect has not been identified. Formation of either CaHPO4. 2H2O or hydroxyapatite in the paste is considered as deleterious to plaster hydration.

Concentration of the virus of foot-and-mouth disease in a tangential flow ultrafiltration unit

Abstract: Ultrafiltration by means of a thin channel tangential flow unit was used to concentrate suspensions of inactivated foot-and-mouth disease virus. When 5 to 7 1 batches were filtered, the liquid volume was reduced by approximately 98 % with little loss of antigen and good separation from nitrogenous compounds of low molecular weight.

The transformation: Brushite → calcium monofluorophosphate under aqueous conditions

Abstract: The reaction between CaHPO4. 2H2O and 10−1 M solution of Na2PO3F have been studied in the pH range 7 to 5 at 25 °C. The formation of CaPO3F · 2H2O, rather than CaF2 or Ca5F (PO4)3 by initial hydrolysis and subsequent reaction with the F− formed, appeared to occur. The value of ΔG for CaPO3F · 2H2O has been calculated as – 530.9 kcal mol−1. A comparison is drawn to the exchange reactions reported here, and to the similar reactions reported to occur in calcium deficient apatite.

The sorption of sulphur dioxide by indoor surfaces. IV. Flooring materials

Abstract: The sorption of sulphur dioxide by a number of carpet and solid flooring material samples has been investigated at a concentration of 50 to 60 μg/m3 using 35S-labelled sulphur dioxide. The amount of sulphur dioxide sorbed by the samples varied little with their chemical composition and was of such a magnitude as to suggest a low affinity of the surfaces for sulphur dioxide. The sorption of sulphur dioxide by artificial fibre carpet pile was shown to be significantly reduced by the application of dyes.

The application of an infrared absorption technique to the measurement of moisture content of building materials

Abstract: The principles underlying the use of differential infrared absorption for measuring moisture contents are explained and it is shown how a commercial moisture recorder of this type, intended for measuring the moisture content of paper, may be adapted for the measurement of the moisture content of the surface and interior of some building materials. Encouraging results are obtained with mortars and aerated concrete, but the results with bricks are inexplicably erratic. The results are substantially independent of changes in the soluble salt concentration in the moisture. The method seems to merit further investigation though the present high cost of the apparatus will restrict its use.

Improvements in the design and operation of the chemostat

Abstract: All chemostats are continuous fermentors, but some are more continuous than others. ( with apologies ).

The decomposition of N-benzoylleucomethylene blue during the pressure-sensitive copying process. I. Identification of reaction products

Abstract: N-Benzoylleucomethylene blue in benzene, toluene, xylene or petroleum ether when applied to either attapulgus clay or silica gel slowly decomposes to give a blue dye which has always been assumed to be methylene blue. Factors affecting the reaction have been examined and it is suggested that a photon-induced free radical reaction is operating. Initial products of the reaction are colourless mono-, di- and trimethyl derivatives of N-benzoylleucothionine and a mixture of methylene blue and mono-, di and trimethylthiazines. Irradiation of the colourless products gives further quantities of both methylene blue and demethylated products. The irradiation of methylene blue on silica gel gives a mixture of demethylated products but the decomposition is more extensive and the fully demethylated thiazine, thionine is also present in the reaction mixture.

The effect of various alkali metal fluoride solutions on the brushite—fluoroapatite transformation

Abstract: The brushite—fluoroapatite transformation reaction has been examined in 10−1 M solutions of NaF, KF, RbF, CsF and NH4F at room temperature The nature of the alkali metal ion has no effect on the fluoride-diffusion-controlled reaction, although the incorporation of the cation into the apatite structure is dependent the nature of the alkali metal cation

Reactions of benzene in a microwave discharge reactor

Abstract: A study has been made of the reactions of benzene in a continuous-flow microwave-discharge reactor. The distribution of reaction products was found to depend on the reactor pressure and flow-rate. By accounting for all reaction products (solid, liquid and gas) an overall mass balance was obtained. The reactions are not the result of simple pyrolysis. The insertion of nickel wire into the reactor enhanced the reactions which proceed via a radical—radical mechanism. The addition of carbon dioxide to the benzene feed appeared to retard reactions which involve highly energetic ionisation processes. Thus, the presence of carbon dioxide changed the reaction selectivity. The carbon dioxide did not react chemically. Comparison with other work with benzene shows that the behaviour of this reactor system is significantly different from the behaviour of reactors which operate at a lower frequency. It is suggested that the distribution of electron energies in the microwave discharge is narrower than the energy distributions which are encountered in lower-frequency and d.c. discharges.