Analyse expérimentale des propriétés mécaniques des tanins

Abstract

Substantial amount of money is spent each year to replace parts damaged by corrosion. Several types of products are available to protect the heating and cooling closed-loops against corrosion, including green chemistry such as purified tannins. The objectives of this thesis are to study the effects of varying the flow rate and concentration of tannins on the protective layer created by the tannins. Moreover, the goal is to identify the parameters that can be detrimental to tannins such as oxygen. Earlier laboratory studies and industrial empirical observations have shown that a concentration of tannins in the order of 275 ppm should be sufficient to fully protect the system. A benchtop closed-loop, was used to study fifteen different combinations from the two following conditions: the concentration of tannins and the flow velocity. Concentrations of 37,5, 75, 275, 550 and 1100 ppm and the flow rates 0,05, 0,91 and 2,13 m/s were studied. The recommended concentration of 275 ppm proved insufficient to protect the surface and react with oxygen for the benchtop closed-loop system. The use of higher tannin concentrations (550 ppm and 1100 ppm) would meet the corrosion limits (criteria) set by the water treatment industry. Indeed, the surfaces are clean and the image analysis of coupons showed a damaged area (presence of iron oxide and black and brown spots) of less than 6%, regardless of the velocity, compared to 40% for 275 ppm. Laboratory tests were carried out in three environments: open in the presence of oxygen, closed in the presence of oxygen and closed in the absence of oxygen. Coupons subjected to an open environment are covered by iron oxide and black and/or brown spots while in the absence of oxygen, coupons are in good condition and a characteristic tannins colour appeared on surfaces. Oxygen is a critical factor that affects the tannins and the full protection of the surface. To determine the origin of these spots, the X-Ray analysis performed on some samples show that these spots consist mainly of iron and oxygen. The spectrophotometers absorbance (concentrations of tannins) shows that at a wavelength of 280 nm there is a characteristic shoulder, while at 420 nm wavelength used by handheld spectrophotometers the absorbance intensity is much lower. The velocity has no effect on the quality of the protective layer if the amount of tannin molecules in water is sufficient. A higher dosage of tannins is recommended. In this case, it is recommended to use 550 ppm, but further research could determine the critical concentration which is likely between 275 ppm and 550 ppm.

Date	18 Nov 2016
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Stéphane Hallé (Supervisor) & Roger Gaudreault (Co-supervisor)