The effects of the acid nature and its concentration on the physico chemical properties of the membranes were studied. How these parameters impact the performance of Nafion 117 as a polymer Electrolyte membrane is shown.In particular the effect of this membrane treatment on its properties was studied with the following five strong acids: -Nitric, Sulphuric, Perchloric, Phosphoric or Hydrochloric acid- in six different concentrations: -0.025 M, 0.05 M, 0.25 M, 0.5 M, 0.75 M and 1 M.It was found that the membrane shows a similar behaviour when it is treated with different strong acids, incorporating between 16 to 21 molecules of water depending on the concentration of the acid. The results show that the effect of the different concentrations on the membrane behaviour is remarkable. This leads to the conclusion that the best treatment is to use solutions 0.025 M and 0.05 M (twenty times more diluted than the most concentrated solution tested in the experience) of the strong acid.It was also shown that after the membrane hydration its size increases by 10 percent (average).
Dark fermentation is a hydrogen generating process carried out by anaerobic spore-forming bacteria that metabolize carbon sources producing gas and short-chain acids. The process can be controlled, and the hydrogen harvested if bacteria are grown in a reactor with favorable conditions. In this work, bacteria selected from natural sources were grown with a defined culture media, while pH was monitored, with the aim of relating the amount of generated hydrogen to the increase in hydron ion concentration. Therefore, a model based on the acid-base species mass balance is proposed and solved to estimate the lag phase time and measure the hydrogen production efficiency and kinetics. Hydrogen production in a stirred batch reactor was performed for 150–200 h, at given operating conditions using a previously defined growth media, to validate the model. Using the proposed model, the cumulated moles of produced hydrogen correlate well with those predicted from the pH curve. Hence, the modified Gompertz model parameters, largely used for describing the hydrogen generation kinetics by dark fermentation, were estimated from the pH curve and from the experimentally measured generated hydrogen. Satisfactory agreement was found, thus, validating the method.
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