Reduction of evaporation of natural water samples by monomolecular films

Abstract

A capacidade de filmes monomoleculares de álcoois graxos em reduzir a evaporação de amostras naturais de água, coletadas em dois reservatórios de São Paulo (Guarapiranga e Billings), foi estudada em laboratório. As reduções da evaporação foram determinadas diretamente, medindo-se o volume de água evaporado dos recipientes de teste após certo tempo. Filmes mistos de hexadecanol e octadecanol apresentaram alto potencial de redução da evaporação (até 57%) e persistência na superfície da água, por cerca de 48 horas. Uma breve discussão sobre a melhor eficiência desses filmes mistos na redução da evaporação de água é também apresentada.The ability of monomolecular films of fatty alcohols in reducing evaporation of natural water samples collected from two reservoirs in São Paulo (Guarapiranga and Billings) was studied in the laboratory. Evaporation reductions were determined directly by measuring the volume of water evaporated from the test recipients after a certain period of time. Mixed films of hexadecanol and octadecanol showed high potential of evaporation reduction (up to 57%) and persistence on the water surface of ca. 48 hours. A brief discussion on the better efficiency of these mixed films in reducing water evaporation is also presented. Keywords: water, evaporation, fatty alcohols, monomolecular films, surface tension IntroductionWater is the most precious natural resource available to mankind. Most of our usable fresh water is retained in lakes and reservoirs, but this type of storage allows for the greatest loss of water by evaporation. The increasing demand for municipal and industrial fresh water, and the current increase in the global temperature indicate that it is necessary to employ techniques for reducing evaporation aiming at the conservation of water supplies.It has been known for a long time that monomolecular films of certain surfactants can retard water evaporation. 1 This seems to be the only viable technology for reducing the evaporative losses of water from reservoirs. 2 For many years, important studies in laboratory scale were carried out in order to identify the optimal substances and conditions for reducing water evaporation. [3][4][5] Among the surfactants tested, biodegradable fatty alcohols of low toxicity presented the highest resistance to water evaporation, especially 1-hexadecanol and 1-octadecanol. 2 The first field experiment was conducted in Australia in the beginning of the 50's, and the obtained evaporation reductions of 30% called attention of many research groups and governments around the world. 6,7 In the following decades, several experimental and theoretical works were published, and the main conclusions were collected in a review published in 1986. 8 Although the spreading of a monomolecular film on the surface of a reservoir has been considered as an alternative technology for fresh water conservation by the United Nations Environment Programme, only a few investigations on this subject have been reported in the last years. 9 Among the most recent works on this subje...

Evaporation Retardation by Monomolecular Layers: An Experimental Study at the Aji Reservoir (India)

“…For large storage, the use of mono-molecular layers has the potential to be an attractive and cost-effective solution to reduce evaporation [18]- [20]. Mono-molecular layers are films that have the thickness of one molecule and form at the phase boundary of the air/water interface.…”

“…When these materials are applied to the water surface, they self-spread to create a monomolecular surface film that provides an evaporative resistance [30]- [33]. A mixture of Cetyl alcohol and Stearyl alcohol in 1:1 ratio is found to be more effective than a monolayer consisting of any single material [18] [34] [35].…”

Preparation of a type of water evaporation inhibiting monolayer based on epoxy resin

“…Meanwhile, the adsorption peaks at 2846 and 2921 cm À1 are the stretching vibration of C-H in the CH 3 and CH 2 groups, respectively, which can further prove that C 16 OH and C 4 OH have reacted with hydrogenated bisphenol A.…”

“…The relationship between spreading coefficient and film-forming work concluded from formulas [3] and [4] , which is as follows:…”

“…In the large storages, utilization of spreading monolayer at the air/water interface may be an attractive and effective method to reduce water evaporation. [1][2][3][4][5] However, there are still many problems in practical application, which are mainly associated with the effective use of monolayers in open air. Most of monolayers are easily damaged by blowing and rippling.…”