CO2 evolution measurements

CO2 evolution measurements, CO2 evolved during the reaction has been removed from the reactor by a stream of nitrogen carrier gas bubbled through the solution that provided also the stirring. The CO2, mixed with hydrogen, was converted to methane on a nickel catalyst and measured by a flame ionisation detector (FID) giving a CO2 evolution rate ws, time plot. The temperature of all the experiments was kept at 20.0 0.5°C. 

Figure 1 shows typical spectrophotometric and CO2 evolution measurements of an unperturbed and a polymer-perturbed BZ system. The experimental results obtained with the two different techniques are in fair agreement. 

PLA PLLA (poly(L-lactide)) -laboratory synthesized Controlled composting test (prEN14046) CO2 evolution measurement Biodegradation 92% ( 17%) for PLLA in 202 days (56% in 150 days) Whatman Chromatography paper as positive control [24]... 

PLA PLA (commercial extruded 1.5 mm thickness sheets) Composting yard waste compost CO2 evolution measurement and molecular weight changes by GPC Notable decrease in PLA molecular weight [10]... 

PLA Poly(lactic acid) commercial sample from Mitsui Chemicals Composting (ISO 14855-1, ISO 14855-2, enzymatic degradation) CO2 evolution measurement based on titration and gravimetric methods Biodegradation of PLA powder was 91% for 31 days (ISO 14855-1 method) and 80% for 50 days at 58°C (ISO 14855-2 method) Cellulose powder was used as reference material PLA in the form of powders of different size was used [17]... 

Pure starch degrades very rapidly in compost after 49 d [57]. Soil and compost tests showed that in PO/ starch blends, starch alone is the biodegradable fraction. The PE/starch blends degrade faster by light than by compost conditions (elevated temperature of 50-60°C, micro-organisms). In soil, molecular weight is reduced from 225,000 to 110,000 but CO2 evolution measurements indicated that only the starch component is degraded. 

Additionally, there is a growing use of off-gas analysis for measuring oxygen uptake, CO2 evolution and respiratory quotient measurement. 9, 641 However, this is not likely to find widespread use despite its usefulness unless the cost involved can be lowered. 

The ultimate biodegradability of a substrate, such as is depicted in Figure 4, may, in addition to oxygen uptake, be measured by disappearance of organic carbon, CO2 evolution and the formation of water. A radiotracer approach provides a more accurate determination and is the only feasible way of measuring the formation of water in the aqueous medium required for all metabolic processes. 

Soils amended with arsenic-contaminated plant tissues were not measurably affected in CO2 evolution and nitrification, suggesting that the effects of adding arsenic to soils does not influence the decomposition rate of plant tissues by soil microorganisms (Wang et al. 1984). The half-life of cacodylic acid is about 20 days in untreated soils and 31 days in arsenic-amended soils (Hood 1985). Estimates of the half-time of inorganic arsenicals in soils are much longer, ranging from 6.5 years for arsenic trioxide to 16 years for lead arsenate (NRCC 1978). 

COj/Oj in the Off-Gas CO2 evolution from a bioreactor is closely related to the physiological state and the activity of microorganisms in a bioreactor because CO, evolves as a result of catabolism and respiration by microorganisms or cells. Therefore, it is helpful to measure the content of CO2/O2 in the exhaust gas in order to understand the physiological climate of a bioreactor. The CO2 and O2 content in the exhaust gas are taken from the streamline and analyzed by infrared spectrophotometer (CO2) and galvanic cell probe (O,). The wet off-gas must be desiccated before being introduced into the gas analyzer. 

Figure 3. Carbon corrosion rate versus carbon weight loss for both conventional and graphitized KB-supported Pt catalysts. The carbon corrosion rate (in units of A/g( ) is based on the measured CO2 concentration at the exit of a 50 cnr cell using a GC, assuming 4e /( (T molecule. The carbon weight loss is obtained by integrating the measured CO2 evolution rate over time. The cell is operating on neat H2/N2 (95 °C, 80% RIIjn, and 120 kPaa, s) with potential held at 1.2 Volts versus RHE.

We will now develop an analytical framework to represent CO2 fixation in photosynthesis and its evolution in respiration and photorespiration (Fig. 8-16). The net flux of C02 into a leaf, Jcch> indicates the apparent (net) CO2 assimilation rate per unit leaf area by photosynthesis (see Fig. 8-1 for a measurement technique). The gross or true rate of photosynthesis, ygv minus the rate of CO2 evolution by respiration and photorespiration per unit leaf area, 7, equals Jcch-... 

Figure 7 shows CO2 evolution from the PET films with different thermomechanical histories and consequent differences in film thickness, ciystallinity and molecular orientation (9). In all three cases strong CO2 generation was observed and could be measured with good repeatability. Similar measurements have been made on poly(8-caprolactone) (PCL) and on PCL/PVC blends (10). These measurements on different polyesters demonstrate the applicability of the CO2 method to materials for which carbonyl absorption measurement is not very suitable. 

The results of Figure 7 demonstrate that CO2 evolution from polyester films can also be measured and offers a convenient way of monitoring the photodegradation of polymers such as polylactones which are of increasing interest because of their biodegradability. However, unlike polyalkenes. 

The reaction between 65/35-TDI (65% 2,4-isomer, 35% 2,6-isomer) and a poly(oxypropylene)glycol, in the presence of small amounts of water, was studied by Aleksandrova and Lakosina [196]. The reaction rates were followed by disappearance of NCO, representing the combination of the two reactions, and by the rate of CO2 evolution as a measure of the NCO/water reaction. Tertiary amines were found to catalyse the reaction with water about the same as that with the glycol. Dibutyltin dilaurate catalysed the TDI/glycol reaction about 1.5 times as strongly as the TDI/water reaction. 

In (Section 8) we have considered kinetic phenomena encountered during the copolymerization of L- and D-enantiomorphs of a single type of NCA. Copolymerization of mixtures of NCAs of different a-amino acids to give random copolymers is readily realizable [2], one of the earliest examples reported being the synthesis of a DL-phenylalanine L-leucine copolymer by Woodward and Schramm [78]. However, there are few reports on the kinetics of random copolymerization. Shalitin and Katchalski [79] studied the copolymerization of the NCAs of 7-benzyl L-glutamate (A) and e,N-carbobenzoxy L-lysine (B) initiated by diethyl-amine in N,iV-dimethylformamide at 25°C and obtained the interesting result that the over-all rate of reaction (measured by the CO2 evolution) is equal to the sum of the rates of reaction of the individual monomers under similar conditions. The copolymerization is represented schematically in (60)... 

Uronic Acid. Uronic acid is determined by measuring carbon dioxide (CO2) generation when wood is boiled with 12% HCl (45). Results from this method may be somewhat high because of CO2 evolution from material containing carboxyl groups other than uronic acid. A method developed by Scott (46) is rapid and selective. The sample is treated with 96% H2SO4 at 70 °C, and a product, 5-formyl-2-furancarboxylic acid, is derived from uronic acids. This compound reacts selectively with 3,5-dimethylphenol to yield a chromophore absorbing at 450 nm. 

Raven, J.A., 1972. Endogenous inorganic carbon sources in plant photosynthesis. II. Comparison of total CO production with measured CO2 evolution in the light. New Phytol., 71 995—1014. 

Fig. 1.95. CO2 formation measured for Pdso (a) and Pds (b) at several temperatures. These CO2 transients were measured at an isotropic CO pressure of 5 X 10 mbar CO and an NO pulse with a width of 100 ms, resulting in an effective pressure of 1 X 10 mbar. Prom the calibrated integral of the CO2 peak and by dividing by the number of deposited atoms and the pulse width, the turn-over frequencies (TOFs) at various temperatures are obtained. The evolution of the absolute TOFs as a function of temperature are shown in (c). Pdg is more reactive, the temperature of maximal reactivity, however, is 30 K higher [468]...

Volatilization and adsorption of lube oil by the catalysts is followed by catalytic oxidation to CO2 at higher temperatures as is shown in Figure 8. In the Pyran -GCMS experiments, CO2 is the only non-condensable oxidation product measured from the combustion of lube oil in the "lean" gas stream by either Catalyst "C" or the gamma-alumina. The onset of CO2 evolution with Catalyst "C" occurs at approximately 180°C, which is just above the temperature range for the lube oil volatilization curve which is also shown. Lube conversion to CO2 is virtually complete with Catalyst "C" as determined by CO2 mass balance (95-100%) and the absence of detectable condensable species. 

Growing bacteria can be detected and quantified by the reaction products they produce or the growth media they consume. There are several approaches that can be taken to measure the change in products or reagents. One method is to utilize specific ion or gas electrodes to measure O2 consumption, H2 evolution, CO2 evolution, sulfide ion production, ammonium ion production, etc. Another technique is to measure changes in bulk electrolyte conductivity due to microbial biochemistry. A third method involves the detection of bacterial enzymes using specific substrates and ion-specific electrodes. A brief description of the three approaches follows. 

The present work is the next step where we have undertaken a systematic study of the perturbed BZ system with an alcoholic and a nonalcoholic polymer, namely polyethylene glycol with different molecular weights and polyethyleneglycol dimethyletiier (MPEG), respectively. The dynamical behaviour of the BZ system has been monitored by means of CO2 evolution rate and spectrophotometric measurements. Moreover, for the sake of comparison we have also performed spectrophotometric measurements in the presence of etiiylene glycol. 

The current study utilizes two complementaiy techniques to monitor the behaviour of the BZ system in the absence and presence of additives CO2 evolution rate measurements (6), which reflects the rate of the overall reaction, and UV-vis spectrophotometric measurements. 

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