The method of determining the stability of water-hydrocarbon emulsions

 

(57) Abstract:

The method is based on continuous measurement of changes in weight gravimetric detector, part of which is immersed in this mixture. The method consists of a first stage of heating or cooling the emulsion to a predetermined temperature and a second stage during which the emulsion is maintained at this temperature, record the curve changes the specified weight specified detector in time, providing the definition of collected solid mass, and the speed of separation of the mixture into two phases by determining the slope of this curve, and the stability of the emulsion is determined by comparison with a reference emulsions, the stability of which is known. The technical result is the ability to quantitatively measure the separation of immiscible liquid and solid phases. 4 C.p. f-crystals, 7 ill., table 2.

The invention relates to a method of determining the stability of water-hydrocarbon emulsions.

This method can be used to determine the stability of the water-hydrocarbon emulsion, which is stable at ambient temperature and is typically used as fuel and which is affected by changes in the rate is slyvania or crystallization water, followed or preceded by the deposition of paraffins in the hydrocarbon matrix.

In the subsequent text, the term "emulsion" or "water-hydrocarbon emulsion" will mean, without preference, water emulsion dispersed phase hydrocarbons and possible additives in the emulsion comprising a continuous phase or alternative emulsion of hydrocarbons dispersed in the aqueous phase.

It is well known that the presence of a small amount of water dispersed in the hydrocarbon, improves the quality of combustion of the hydrocarbon and substantially reduces the amount of harmful unburned products and emissions of nitrogen oxides, and the evaporation of water leads to a decrease of the temperature in the combustion chamber. Unfortunately, the immiscibility of these two liquids is significantly restricts the use of this property for its implementation in the nozzles, in which the emulsion is prepared on-site. Attempts to obtain fuels and motor gasoline, comprising the emulsion, by delivery to a mixture of surface-active substances, were unsuccessful because they were not sufficiently stable for production use. In recent studies was obtained formulation of new fuels, the stability of the 17 March 1997).

For this industrial application is required to develop a reliable method of monitoring the stability of the thus obtained emulsions, and this method should be reliable over time, and depending on the temperature.

This problem is complicated due to the complex nature of the phenomena occurring in the environment, which by its nature is heterogeneous, in particular when its temperature is subject to change.

The reason for this is that the crude or refined hydrocarbons contain more or fewer paraffins, which are soluble in hot", but which under the influence of the reduction temperature may crystallize and then be deposited, and thus cause disruption during storage or during use of hydrocarbons. The stability of the emulsion sensitive to temperature, as hot as the temperature increases facilitates the phenomenon of delamination and cold, as in this case, the crystallization of free water speeds up the separation process.

Thus, the possibility of providing conditions in which liquid emulsion, which originally was and/or temperature effects, represents a significant contribution to the optimal use of this cleanser.

The emulsion can be obtained with any hydrocarbons, such as gasoline, gas oil, home heating fuel or heavy fuel oil fuel, and perhaps these fuels contain various additives or components, which are known to experts in this field of technology, such as oxygenated compounds (alcohols, ethers or methyl ester of vegetable oils). The same kind of problems arise for all of these products, especially for products containing paraffins, for which there are problems of filtering, pumping and clogging, in particular in internal combustion engines and in industrial and domestic heating systems. By analogy, we can refer to the recipe in summer and winter, emulsions, according to the common terminology for household fuel boiler, summer boiler fuel and winter fuel boiler, in accordance with existing specifications.

Additives are surfactants that facilitate the formation of emulsions and provide stability, add in a mixture of water and hydrocarbon, in order to avoid the phenomenon of Russ who I emulsion in cold conditions, additives that slow down the appearance of crystals, prevent their development, store them in a suspended state, or prevent their deposition, add in the emulsion, which already contain their own additives. Thus, it is important to assess the impact of these various additives on the phenomenon of phase separation of the emulsion.

There are different ways of measuring the characteristics of the emergence and separation of the solid phase in the liquid.

The first method is based on measuring the weight of solid substances, such as waxes in the oil, which crystallized at a given temperature. These waxes extracted from a hydrocarbon by centrifugation (patent EP-0355053 A2) or by aggregation in the gravitational precipitator (U.S. patent 4357244). These tests make it possible to determine only the total amount of paraffins, which secretaryshall and can be separated by sedimentation. They provide an assessment of excess precipitation.

In the second type of test is modeled deposition in real time, in small tanks (standard NF M 07-085), in which the hydrocarbon is maintained at a low temperature for 24 or 48 hours Then the operator visually evaluates the appearance and volume of each phase, the initial assessment of deposition.

There are also optical methods of measuring the characteristics of the appearance of two immiscible liquid phases or solid and liquid phases. It may be mentioned French patent 2577319, which is devoted to the determination of the cloud point of the gas oil, and French patent 2681428, which is dedicated to delamination of the two liquids (determination of aniline point hydrocarbons).

All of these methods have inherent weaknesses and noncompliance:

they are long, as is usually the testing time is 24 or 48 hours,

- they are not reliable, as it depends only on the subjective assessment of the operator,

however, most characterized by the fact that they do not provide the possibility of determining the number of spin-off phase, or determine the rate of release of the phase, or even explanation and quantification of the successive States through which the liquid when the temperature changes.

In the method of determining the stability of water-hydrocarbon emulsions using thermogravimetric analysis, which is the subject of the invention solved the problem of quantitative measurement of the process of separating solid or liquid immiscible phases with the use of liquids is possible stability of water-hydrocarbon emulsions, obliged to identify the separation of the phases, characterized in that

- in the first stage is subjected to the specified emulsion appropriate heat treatment, it is brought to a predetermined test temperature and continuously measure thermogravimetric change in the observed weight R gravimetric detector, part of which is immersed in the emulsion, then

- in the second phase of the emulsion is maintained at this temperature and at the same time continuously measure thermogravimetric change in the observed weight of the said detector, and simultaneously recording the curve changes this weight and then

- collect mass segregated phase, on the one hand, and from this curve determines, on the other hand, the speed of separation of the phases corresponding to the inclination of the specified curve, mainly speed, measured at the temperature of the emulsion separation, corresponding to a significant and steady increase in the observed weight P at the beginning of the second stage, and

- determine the emulsion stability by comparison with known standard emulsions, the stability of which in time was confirmed by tests on the long-term stability.

The expression "pre-ass is lsii, and to obtain the characteristic temperature in cold conditions under which phase separation is visible, that is detected with the naked eye or in the infrared range, as described in patents France 2577319 and 2681428.

The method of this invention can be carried out in accordance with two main options, depending on whether it is for stability at a predetermined temperature higher than the crystallization temperature of water or exclusively above the crystallization temperature of some heavy paraffins (feature in hot conditions), or refers to stability at a predetermined temperature lower than the crystallization temperature of at least one of the components (characteristics in cold conditions). Significant differences in the profiles of the curves changes observed weight of the detector in a time-dependent and temperature - duration of the various stages, if the emulsion stability is investigated in cold or hot conditions.

The reason for this is that for stability in hot conditions, the duration of the first stage is related to the temperature difference between the temperature of the emulsion, the Oia is carried out at ambient temperature, the duration of this period may be equal to zero. If the test temperature above the initial temperature of the emulsion, it is necessary to heat. On the other hand, the second phase ends when the weight changes tend to zero (that is, when the phases are completely separated) can be quite long, especially if they test very stable emulsion. In this case, the speed of separation will not be the predominant factor that must be taken into account.

In order to assess thermal characteristics of the emulsion, pre-specified temperature is between 10 and 70oC, and the emulsion is brought to this temperature by heating or cooling from ambient temperature at a speed component usually from 0.05 to 10oC/min

The determination of the stability of the emulsion at low temperature is to study the crystallization and deposition of water on the one hand, and paraffins in the emulsion, on the other hand.

In the first variant embodiment, the first stage of gradually reducing the temperature, usually at rates between 0.05 and 10oC/min, to a temperature between the crystallization point of water and paraffin, at the same time continuously zapisyvaetal stage changes observed weight detector register, maintaining a constant temperature. This weight remains almost constant up to the crystallization temperature of one or the other of the two phases, depending on whether the crystallization temperature of the water is below or above the temperature of crystallization of paraffins.

In the second variant embodiment of the first stage of gradually reducing the temperature, usually at rates between 0.05 and 10oC/min, up to a preset temperature, which is lower than the crystallization temperature of the paraffin and water, but above the temperature fluidity of a mixture of a hydrocarbon-based.

The advantages of the method which is the subject of the invention is the precision, reliability and reproducibility of the obtained results, as when assessing the rate of phase separation and the measurement of weight changes segregated phases. Device for measuring the separation of the emulsion into several liquid and/or solid phases contains thermogravimetric scales, equipped with a gravimetric detector, part of which is immersed in a container (2) containing the specified emulsion in the crucible (5) with the specified capacity is connected to the cooling circuit; the crucible is a free, preferably located coaxial the meter capacity is between 0.1 and 0.9.

The crucible has a cylindrical shape and includes the base and edges, the height of which does not exceed the level of the liquid in the tank. The height of the edges is between 0.5 and 30 mm and is usually equal to 5 mm

The characteristics of the device of the present invention will become more apparent upon consideration of Fig.1A, 1B and 1C and their descriptions below.

Presented on Fig.1A, the device contains thermogravimetric scales (1) rocker (type Setar), tank (2) containing macroscopically homogeneous liquid mixture (3), subject to investigation, device temperature control (not shown) for cooling or heating capacity and a computer system (not shown) for recording and processing data.

The rocker (4) weights (1) is the crucible (5), suspended from the left arm in the schema and loaded into the container (2) containing the mixture. Capacity (2) has a jacket (6), which provides a change in the temperature of the mixture using a loop heating or cooling, not shown in the diagram.

The crucible (5) has a cylindrical shape, similar capacity, and includes the base and edges (7).

Standard optical and magnetic system (10) in combination with weights allows you to measure and semisimplicity measurements obtained in the various examples of phase separation.

Characteristics and advantages of the method of the present invention will become more clear when reading the examples of the method, which are presented below in non-limiting, with reference to Fig.2-5.

EXAMPLE 1

In the present example describes the application of the method of the invention for determining stability in cold conditions, the emulsion of water and oil winter recipes. The emulsion is brought to a temperature below the crystallization temperature of the water and paraffin, but of course higher temperature fluidity, and investigate the crystallization and deposition of water on the one hand, and paraffins, on the other hand.

This method is as follows.

Using thermogravimetric scales, model B60 or TGA92, with electromagnetic compensation, which sells the firm to the Setar. The crucible is a plate with a diameter of 20 mm and with edges a height of 5 mm, It is placed in a cylinder with a diameter of 30 mm and a height of 100 mm, which contains the test gas.

The crucible is dipped into the vessel 33 mm below the level of the oil. Then the temperature of the emulsion is reduced to -7,5oWith speeds of 0.7oC/min, and at this temperature>Register a change in the relative weight of the crucible during lower temperature and at a constant temperature. Thus, there is a decline in the relative weight of the crucible is mainly due to changes in density of the emulsion, which increases as the temperature drops, then the relative weight increase due to water and paraffin in the crucible.

The increase of Gpweight in the crucible due to precipitated paraffins and/or water is determined by subtracting (for each point) relative weight Psthe device, measured at the beginning of the second stage (at constant temperature), the weight P of the detector, the measured time t: Gp=P-Ps. Thus the total weight gain is the difference of the observed weight of the device between the end and beginning of the second stage. The recorded curve is shown in Fig.2:

The first segment of the curve is explained by the obvious loss of relative weight due to the growth of the density of the gas at reduced temperature (OA).

- Then there is a waiting period during which the relative weight of only slightly increased (AB) due to the deposition of one of the wax, and water, the phenomenon of supercooling.

Fourth section (CD) is observed fracture curve (D), and after this point the increase in the relative weight is only caused by the deposition of paraffins. Because the water has completely precipitated, at this point, according to visual observations are separated phases.

- Continuation of the trial would have shown on this curve after point D, the fracture, and from this point the increase in the relative weight of zero. Thus, in the crucible no further deposition, and measured the relative weight remains almost constant. In practice, it is inefficient, since the deposition of free water causes instability of the emulsion.

From the curve of precipitation in Fig.2 you can define three characteristics:

1. The increase in relative weight (Gp) in milligrams, which represents the total amount of water and paraffin deposited during the experiment.

2. The deposition velocity (V) of the emulsion, in mg/hour, which is determined from the slope of the curve at the site of the aircraft at the point of inflection. Thus, the magnitude of the deposition rate provides an opportunity to compare different chemusa the curve AB, during which the emulsion is stable at the temperature of test.

In the case of obtaining the curve of Fig.2 when tested emulsions can see that the waiting period is 8 hours.

EXAMPLE 2

In this example, analyze the other emulsion winter recipes containing paraffins, which crystallize at lower temperatures, by adding additives with specific characteristics in cold conditions, the first stage is interrupted when the temperature -8,5oWith, to the crystallization of paraffins, i.e. above the cloud point. Crystallizes only water.

When the change of the weight gain curve shown in Fig.3.

After reducing the relative weight of the crucible (OA), one can observe a waiting period (AB) corresponding to the subcooling of the water, and finally, very quick weight gain (SU) as a result of crystallization water. After the point With the weight gain becomes zero, because all the water secretaryshall. The temperature profile of the environment is characteristic of a phenomenon with the peak due to the exothermic crystallization of water.

Thus, this device makes it possible to accurately distinguish each cat is edstam measuring the deposition rate and growth observed weight.

EXAMPLE 3

This example illustrates the definition, using the method of this invention, stability at ambient temperature (20o(C) two emulsions EMU01 and EMU02 obtained by mixing 13 weight. % water with oil type EN590 containing specific additives to preserve the emulsion and in which the distribution of the oil droplets of water on the particle size varies considerably:

Emulsion EMU01 has a monodisperse distribution of particles by size, and is dominated by drops with a diameter of about 1 μm (see Fig.6).

Emulsion EMU02 is worse dispergirovannoyj the aqueous phase, which is called polydisperse phase, the diameter of the droplets is changed from 0.1 to 50 μm (see Fig.7).

Registration of the increase observed weight gives the curves shown in Fig. 4, which will be analyzed. In this case, the steady-state temperature (20oC) higher than the crystallization temperature of the water and paraffin. There is a linear relationship of increasing the relative weight in time. Two main parameters (V and Gpsignificantly higher for emulsions EMU02, which is thus less stable than the emulsion EMU01. Because the sample EMU01 has a more uniform dispersion of water in the, the use of the method according to the invention it is possible to justify a quantitative scale stability of the produced emulsions by comparison with a tested at a given temperature standard. In addition, analysis of particle size by processing the image gives only a local analysis, which, although it may be statistically processed, is long and complex, while the method according to the invention provides a global analysis of the whole sample volume, regardless of the temperature, without the need for sample dilution.

EXAMPLE 4

The purpose of this example is to demonstrate that the method according to the invention gives the possibility to characterize and optimize the production process of the emulsion. Specifically, on an industrial scale were prepared with different emulsion on the installation of a closed loop containing emulsion mill and the output line of the sample, providing sampling after a certain number of recycling operations or runs. The stability of these samples at ambient temperature was measured by the method according to the invention under the conditions described in example 3 and compared it with the stability of a reference emulsion EMU, containing 13% of water, which is Alon was prepared in the laboratory for in order to obtain monodisperse distribution of water droplets on the particle size with the predominant size of about 1 μm, and this distribution was analyzed by electron microscopy with image processing.

Mix a certain amount of gasoil EN590 and 13% water by weight from the amount of oil and emulsified mixture (EMU03) is injected into the closed loop industrial installation.

Samples taken after 4 and 7 recirculating mixture runs. Emulsion analyzed using the method according to the invention. Measure the increase in the observed weight and the deposition rate after 1 hour (V1) and 6 hours (V2); these values are mapped in a table.1.

You can clearly see that it is possible to regulate the stability of the emulsion by modifying the production process, in order to reach the level of the Standard.

EXAMPLE 5

In this example investigated the stability of the two emulsions EMU04 (summer recipe) and EMU05 (winter formula) depending on the pre-set temperature between 40oC and -8oC. Methodology described in examples 1 and 3 to increase or decrease the temperature during the first step of the method according to the invention. The obtained results are compared * to the point, when the emulsion is destroyed due to the crystallization of water and paraffin.

EXAMPLE 6

In this example investigated the stability of the emulsion at a temperature of 70oC. during the first stage of the method the temperature of the emulsion is slowly increased at a rate of 1oC/min, until not reached steady-state value 70oC. Carried out continuous measurements of the observed weight of the crucible permit to construct a curve shown in Fig.5.

First, during the first stage, there is a significant increase in weight caused mainly by the decrease of the density of the hydrocarbon part of the emulsion. Then there is a nonlinear change (AV, uniformly accelerated) relative weight due to the separation of water present in the emulsion, up to the point of complete separation of the phases.

1. The method of determining the stability of water-hydrocarbon emulsions, for determining the phase separation, which is subjected to emulsion appropriate heat treatment, characterized in that in the first phase of the emulsion is adjusted to a predetermined test temperature and continuously measure thermogravimetric change in the observed weight P gravimetry temperature and at the same time continuously measure thermogravimetric change in the observed weight of the said detector, and simultaneously recording the curve changes this weight and then collect the mass of the spin-off phase, on the one hand, and from this curve determines, on the other hand, the speed of separation of the phases, corresponding to the slope of the curve, mainly speed, measured at the temperature of the emulsion separation, corresponding to a significant and steady increase in the observed weight P at the beginning of the second stage, and determine the stability of the emulsion by comparison with known standard emulsions, the stability of which in time was confirmed by tests on the long-term stability.

2. The method according to p. 1, wherein the predefined temperature is between 10 and 70oC, and the emulsion is brought to this temperature by heating or cooling from ambient temperature at a speed component usually from 0.05 to 10oC/min

3. The method according to p. 1, wherein the predefined temperature is between the temperature of crystallization of water and the temperature of crystallization of paraffins, and the first temperature is higher than the second, or Vice versa, and the emulsion is brought to this temperature accelerated cooling, usually with a speed of between 0.05 and 10oC/min

4. The method according to p. 1, wherein the predefined temperature is Nove hydrocarbons and the emulsion is brought to this temperature by cooling, usually with a speed of between 0.05 and 10oC/min

5. The method according to one of paragraphs. 1-4, characterized in that it is carried out using gravimetric scales, equipped with a gravimetric detector containing crucible, immersed in a vessel containing the above emulsion, and this capacity is connected to the cooling circuit, and the crucible is suspended freely, and the cross-section of the listed capacity is such that the ratio of maximum diameter of the crucible to the tank diameter is in the range from 0.1 to 0.9.

 

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