Thermal measuring and testing – Thermal testing of a nonthermal quantity
Reexamination Certificate
1999-11-12
2002-02-19
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Thermal testing of a nonthermal quantity
C073S061440, C374S014000
Reexamination Certificate
active
06347884
ABSTRACT:
The present invention relates to a process for determining the stability of a water-hydrocarbon emulsion.
This process can be used to determine the stability of a water-hydrocarbon emulsion which is stable at ambient temperature, generally usable as a fuel, which, under the influence of a variation in temperature—cooling or heating—is capable of separating into two or more liquid and/or solid phases on account of demixing or crystallization of the water, followed or preceded by sedimentation of the paraffins in the hydrocarbon matrix.
In the text hereinbelow, the term “emulsion” or “water-hydrocarbon emulsion” will denote, without preference, an emulsion of an aqueous dispersed phase in hydrocarbons and the possible additives thereof constituting the continuous phase, or alternatively an emulsion of hydrocarbons dispersed in an aqueous phase.
It is well known that the presence of a small fraction of water dispersed in a hydrocarbon improves the quality of combustion of this hydrocarbon and substantially reduces the amount of harmful, unburnt and nitrogen oxides emissions, the vaporization of the water resulting in a lowering of the temperature in the combustion chamber. Unfortunately, the immiscibility of the two fluids substantially limits the use of this property to its implementation in burners preparing the emulsion in situ. Attempts to produce fuels and combustion spirits consisting of an emulsion by addition of surfactants to the mixture failed, since they were not sufficiently stable for industrial application. Recent investigations have allowed the formulation of novel fuels whose stability is such that their industrial exploitation appears possible (see patent application WO 97/34969 of Mar. 17, 1997).
This industrial application requires the development of a reliable process for controlling the stability of the emulsions thus manufactured, this process being reliable both over time and under the influence of temperature.
The problem is difficult on account of the complex phenomena which take place in a medium, which is heterogeneous by nature, in particular when it is subjected to variations in temperature.
The reason for this is that crude or refined hydrocarbons contain a larger or smaller proportion of paraffins, which are soluble “under hot conditions” but which, under the influence of a decrease in temperature, can crystallize and then sediment and thus give rise to dysfunctions on storage or during their use. The stability of the emulsion is temperature-sensitive both under hot conditions, since an increase in temperature promotes the demixing phenomenon, and under cold conditions, in which case the crystallization of the free water accelerates the separation process.
Thus, the possibility of providing conditions under which a liquid emulsion, which is initially stable at ambient temperature, can separate into at least two phases under the influence of time and/or temperature is a considerable asset for the optimum use of this emulsion.
The emulsion can be prepared with any hydrocarbon, such as spirits, gas oils, domestic fuel oils or heavy fuel oils, these fuels possibly containing various additives or components known to those skilled in the art, such as oxygenated compounds (alcohols, ethers or methyl esters of plant oil). The same types of problem arise for all the products, particularly products containing paraffins, for which filtration, pumping and blockage problems are observed, in particular in motors and in industrial and domestic heating systems. By analogy, reference will be made to summer or winter emulsion formulations, as common terminology, for domestic fuel oils, summer fuel oil and winter fuel oil according to the specifications in force.
Surfactant additives which facilitate the formation of the emulsion and ensure its stability are added to the water-hydrocarbon mixture to avoid the appearance of the demixing phenomenon. To avoid the crystallization and then sedimentation of the paraffins, during use under cold conditions, additives whose action delays the appearance of the crystals, prevents their development, keeps them in suspension or prevents their sedimentation are added to the emulsions already containing their own additives. It is thus important to measure the impact of these various additives on the phenomena of phase separation of an emulsion.
Various methods exist for measuring the characteristics of appearance and separation of a solid phase in liquid.
A first method is based on measuring the weight of the solids, such as the paraffins in the gas oils which have crystallized at a given temperature. These paraffins are extracted from the hydrocarbon by centrifugation (patent EP-0,355,053 A2) or by aggregation in a gravity sedimenter (U.S. Pat. No. 4,357,244). These tests make it possible only to determine the total amount of paraffins which have crystallized and which can sediment out. They gave a measure of the excess sedimentation.
A second type of test simulates the real-time sedimentation in small tanks (standard NF M 07-085) in which are stored hydrocarbons at low temperature for 24 or 48 hours. The appearance and volume of each phase are then assessed visually by the experimenter, in particular the position of the interface between the two phases. These tests give an approximate qualitative measure of the sedimentation.
Optical methods for measuring the characteristics of appearance of two immiscible-liquid or solid-liquid phases also exist. Mention may be made of patent FR 2,577,319 which is directed towards determining the cloud point of gas oils, and patent FR 2,681,428 which is directed towards the demixing of two liquids (measurement of the aniline point of hydrocarbons).
These methods all have drawbacks and inadequacies:
They are long, since they generally last 24 hours or 48 hours.
They are not reliable, since they depend only on subjectivity of the observer.
Most especially, however, they do not make it possible to measure the amounts of the separated phases, or to know the speed of separation of the phases, or even to explain and quantify the successive states through which the liquid passes when the temperature changes.
The process for determining the stability of a water-hydrocarbon emulsion by thermogravimetric analysis, which is the subject of the invention, solves the problem of the quantitative measurement of the separation of the liquid or solid immiscible phases using a liquid which has been made homogeneous.
A subject of the present invention is a process for determining the stability of a water-hydrocarbon emulsion liable to exhibit a phase separation, characterized in that
in a first step, by subjecting the said emulsion to a suitable heat treatment, it is brought to a predetermined test temperature and the variation in the apparent weight P of the gravimetric detector, a portion of which is immersed in the emulsion, is continuously measured by thermoaravimetry, then
in a second step, the emulsion is maintained at this temperature while continuously measuring the variation in the apparent weight of the said detector by thermogravimetry, and the curve of the variation of this weight is recorded simultaneously, and then
the mass of the separated phase collected, on the one hand, and the speed of separation of the phases corresponding to the slope of the said curve, mainly the speed measured at the breaking point corresponding to a substantial and continuous increase in the apparent weight P at the start of the second step, on the other hand, are determined from the said curve, and
the stability of the emulsion is deduced by comparison with known reference emulsions, whose stability over time has been corroborated by tests of long-lasting stability.
The expression “predetermined temperature” means here the steady temperature at which it is desired to measure the stability of the emulsion, but also, for the behaviour under cold conditions, the temperature at which the separation is visible, i.e. detectable to the naked eye or by infrared as described in patents FR 2,577,319 and FR 2,681,428.
The process of t
Faure Yan
Letoffe Jean-Marie
Schulz Philippe
Elf Antar France
Gutierrez Diego
Verbitsky Gail
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