RU2444560C1 - Metal-containing fuel dope, method of its production and application - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: proposed dope comprises industrial powder of metal selected from the group: aluminium, magnesium, and solid oxidiser. The latter represents nanosized powder of molybdenum trioxide with mean particle size no exceeding 100 nm produced by mechanical activation on industrial powder of molybdenum trioxide. Ratio of components is as follows, in wt %: metal powder - 30-70, nanosized powder of molybdenum trioxide makes the rest. Components are subjected to joint mechanical activation by mixing and milling in power-intensive ball mil in inert atmosphere. Note here that mechanical activation is performed in two step. At first step, molybdenum trioxide powder is minced to mean particle size not exceeding 100 nm. At second step, obtained nanosized molybdenum oxide powder is mixed with industrial powder of metal and subjected to another mechanical activation.

EFFECT: notably reduced self-ignition delay and higher rate of fuel-air mix combustion.

3 cl, 6 dwg, 3 ex

Description

The invention relates to fuel additives, and in particular to metal-containing additives to fuels, and can be used for burning fuel in technological devices and power plants, in particular, in engines of land vehicles and aircraft.

The role of additives in the production and use of fuels is constantly growing. Additives differ in purpose and in the mechanism of action, while compounds of various classes, both organic and inorganic, are offered as additives to fuels (AM Danilov. The use of additives in fuels. - M .: Mir, 2005, 287 p. )

Many types of metal-containing fuel additives are known - from homogeneous solutions of metal compounds in aqueous or hydrocarbon media to suspensions (suspensions) of visible metal particles. Within the limits of this range are metal-containing additives based on nanoparticles of greatest interest.

Most metal fuel additives have catalytic properties (see, for example, RU 2304610, C10L 1/18, C10L 1/30, C10L 10/00, C10L 10/06, 08/20/2007; US 4892562, NKI 44/324, IPC C10L 1/30, C10L 1/10, C10L 1/14, C10L 1/18, C10L 10/00, 01/09/1990; RU 2296152, C10L 1/18, 03/27/2006; RU 2069774, F02B 51/02, F02B 77/02, F02M 27/02, 11/27/1996; US 5919276, NKI 44/370, IPC C10L 10/00, C10L 1/10, C10L 1/14, 07/06/1999).

Known metal-containing additives of catalytic action based on nanoparticles.

In the patent RU 2352618, C10L 1/12, C10L 10/02, C01F 17/00, publ. 04/20/2009, cerium oxide nanoparticles in combination with a detergent that covers particles of cerium oxide and other additives are proposed as a fuel additive. It is noted that the effectiveness of the additive depends on the size of the particles of cerium oxide - they should be less than 1 μm in size and preferably be 1-300 nm in size. To obtain this additive, cerium oxide is ground in a non-polar organic solvent in an ultrasonic or ball mill in the presence of a detergent, preferably imides of aliphatic dicarboxylic acids.

In the patent RU 2361903, C10L 1/00, C10L 1/10, C10L 1/12, publ. 07/20/2009, two or more metal alloys for fuel are proposed, which are obtained either by reducing a mixture of aqueous solutions of metal salts in the presence of a detergent, or by mixing and grinding metal powders at a temperature and pressure sufficient to form an alloy with subsequent addition of a detergent to form a coating on alloy particles. The duration of grinding in the presence of a detergent is 24-36 hours. The particle size of the nanosplit should not exceed 100 nm.

In patent RU 2259388, C10L 1/12, publ. 08/27/2005, as an additive to diesel fuel, it was proposed to use nanosized particles of a mixture of transition metal hydroxides, mainly iron hydroxide, obtained by alkali deposition of spent solutions for etching printed circuit boards and steel, drying the precipitate and dispersing it in a diesel fuel.

Known metal-containing additives to one degree or another provide an increase in the efficiency of fuel combustion and a decrease in emissions of harmful substances with exhaust gases due to the catalytic effect of metals, but do not allow to improve the flammability and combustion of the fuel-air mixture, which is currently one of the main problems in creating fuel additives.

The methods for producing the above known additives based on metal nanoparticles or their compounds are distinguished by the complexity of the technology and require the use of various substances, including inaccessible ones.

The closest in technical essence to the proposed method for producing the inventive metal-containing fuel additives is a method for producing mechanically activated pyrotechnic composition, previously developed at the Institute of Chemical Physics of RAS and described in patent RU 2235085, С06В 33/00, publ. 08/27/2004 (prototype). The prototype method consists in mechanically activating a mixture of industrial powders of energy-intensive materials - aluminum and molybdenum trioxide - by mixing and grinding in an energy-intensive ball mill in the presence of 30-50 wt.% Neutral liquid. A liquid volatile hydrocarbon is used as a neutral liquid. The mixture is treated in a mill for 3-4 minutes in cycles of 30 seconds at intervals of 1 minute. The mill drum is purged with argon. The particle size in the resulting homogeneous mixture of powders is 15-20 microns.

The prototype method is simple technology and the availability of the starting components, but does not allow to obtain a metal-containing powder in the nanoscale state.

The objective of the invention is the creation of such a metal-containing additive to fuels, which, thanks to a fundamentally different mechanism of its action compared to the known metal-containing additives, will improve the flammability and combustion of the fuel-air mixture - it will significantly reduce the delay of self-ignition and increase the burning rate of the fuel-air mixture.

The objective of the invention is the development of a method for producing the inventive additives to fuels, which, like the prototype method, will be distinguished by the simplicity of technology and the availability of the starting components and, at the same time, will make it possible to obtain a metal-containing additive in the form of a powder with nanoscale components.

The objective of the invention is the development of a method of applying the inventive additive to fuels, which will provide improved flammability of the fuel-air mixture and will increase its burning rate.

The solution to this problem is achieved by the proposed metal-containing fuel additive containing industrial metal powder selected from the group: aluminum, magnesium, and a solid oxidizing agent - nanoscale molybdenum trioxide powder with an average particle size of not more than 100 nm, obtained by mechanically activating an industrial molybdenum trioxide powder, in the following ratio components, wt.%:

industrial metal powder 30-70 nanosized molybdenum trioxide powder rest,

subjected to joint mechanical activation in an inert environment.

The solution of this problem is also achieved by the proposed method for producing the inventive metal-containing additives, including mechanically activating industrial metal powders and a solid oxidizing agent - molybdenum trioxide by mixing and grinding in an energy-intensive ball mill in an inert medium, in which industrial aluminum or magnesium powder is used as an industrial metal powder, and the process of mechanical activation is carried out in two stages: in the first stage, the industrial is subjected to mechanical activation molybdenum trioxide powder to an average particle size of not more than 100 nm in an inert gas medium; in the second stage, the obtained nanosized molybdenum trioxide powder is mixed with an industrial metal powder until the metal content in the mixture is from 30 to 70 wt.% and mechanical activation is repeated in an inert gas medium the presence of a neutral fluid.

The solution to this problem is also achieved by the proposed method of using the inventive metal-containing additive, which consists in the fact that the additive is added to the fuel in an amount of up to 5 wt.%.

The claimed invention was developed on the basis of detailed studies of the influence of the process of mechanical activation on the structure and reactivity of the proposed additive is a two-component energy-intensive metal / solid oxidizer system.

The fundamental difference between the claimed invention and the main number of existing patents lies in the mechanism of action of the proposed additive. In most cases, the metal-containing additive is used as a catalyst for the oxidation of fuel by a gaseous oxidizer. In the claimed invention, the additive contains both metal and a solid oxidizing agent, the interaction between which leads to a local increase in temperature and pressure and initiates self-ignition of the fuel. The choice of solid oxidizer is due to the sufficiently high thermal effects of the reaction:

Me + M _n O _m → MeO _x + M.

For these reasons, molybdenum oxide MoO ₃ was chosen as a solid oxidizing agent. In particular, the thermal effect of the conversion of 2Al + MoO ₃ → Al ₂ O ₃ + Mo is 1120 kcal / kg; 3Mg + MoO ₃ → 3MgO + Mo - 1170 kcal / kg.

One of the main tasks of the mechanical activation of mixtures of energy-intensive materials containing metallic fuels and solid oxidizing agents is to maximize the reactivity of such systems. The increase in reactivity can be achieved by increasing the contact area of the components of the reaction mixture and the accumulation of defects in each of the components. It is natural to expect that upon transition to nanoscale components, the contact area of the components in the reaction mixture will increase.

The method of preparing a two-component mixture of nanosized particles by mechanical activation, in principle, allows for various options: joint mechanical activation of a mixture of the initial industrial metal and oxidizer samples with sizes of tens of microns, or preliminary preparation of each of the components in the nanoscale state, and then joint additional homogenization and activation of nanosized particles.

The first activation option was tested at the IHP RAS earlier (RU 2235085, СВВ 33/00, published on August 27, 2004 — prototype method). It turned out, however, that a mixture of nanoscale components in this way cannot be obtained. During mechanical activation of the individual components, only brittle MoO _{3 was} able to be transferred to the nanoscale state (average particle size less than 100 nm, for more details see below in example 1). For plastic industrial metal powders (magnesium, aluminum), it is not possible to obtain particles smaller than a few microns in size by the method of mechanical activation, even in the presence of surfactants.

As a result of the studies carried out during the creation of the claimed invention, the method of mechanical activation was developed in two stages: at the first stage, nanosized MoO _{3 is} obtained, and then a mixture of the initial metal powder and nanosized MoO _{3 is} activated. This approach turned out to be very effective - the presence of nanosized MoO ₃ in the mixture contributes to a sharp increase in the destruction efficiency of metal particles (see examples 2 and 3 below).

As the starting components in the proposed additive, industrially produced powders of aluminum or magnesium and molybdenum trioxide of technical purity with an active component content of more than 95% are used. The average particle size of the starting industrial MoO ₃ powder was 30 μm. Aluminum powders of different grades have different fineness. In the proposed additive, various industrial aluminum powders can be used: for example, spherical Al with an average particle size of 3-7 μm (type ASD-4 or ASD-6) or lamellar Al with scaly particles of a thickness of 1-2 microns and transverse sizes up to several tens μm (type PP-2 or PAP-2). The particle size of the starting industrial Mg powder can reach 35-40 microns.

Mixing and mechanical activation of the components of the proposed additive is carried out in an energy-intensive ball mill, for example, in a vibration mill Aronova (Aronov MI Instruments and experimental equipment, 1959, No. 1, p.153). The degree of mechanochemical effect is characterized by the specific dose of supplied mechanical energy D kJ / g, calculated by the ratio: D = It, where I is the specific energy intensity of the mill, t is the processing time. The energy intensity of the mill is determined by the test object method. The preparation of nanosized particles of MoO ₃ (first stage) is carried out in an inert gas (argon). The processing time (specific dose of energy input) is determined by the achievement of the minimum particle size (for details, see example 1). The second stage - mechanical activation of the mixture of the initial industrial metal powder and nanoscale MoO ₃ (prepared in stage 1) is carried out in an inert gas in the presence of a neutral liquid. A neutral liquid is a liquid hydrocarbon: aliphatic, cyclic or aromatic, for example, hexane, toluene, cyclohexane, gasoline, diesel fuel, etc. The processing conditions in the second stage were selected so that the largest sizes of large metal particles were reduced and maximum homogenization was achieved (mixing ) mixture, but there was no chemical interaction between the components. Processing at both stages of mechanical activation is carried out in fractional mode: 30 seconds of grinding - 5 minutes of rest.

The structure of mechanically activated powders was analyzed by x-ray structural analysis, optical and scanning electron microscopy with elemental microanalysis. The particle size distribution was measured by nanometer granulometry. The specific surface of the powders was determined by the BET method using low temperature (80 K) adsorption of argon.

To illustrate the invention, examples and figures are given.

A brief description of the drawings.

Fig. 1:

(a) SEM image of the original industrial powder MoO ₃ ;

(b) a change in the specific surface area S as the activation dose D increases;

(c) SEM image of an activated MoO ₃ sample, D = 0.72 kJ / g;

(d) particle size distribution of MoO ₃ powders: activation for 4 minutes and 36 minutes.

Fig. 2. SEM image of an activated Mg / MoO ₃ mixture.

Fig. 3. SEM image of an activated Al / MoO ₃ mixture.

Fig. 4-6 shows the results of measurements of the dependence of the ignition delay when adding the proposed additive to the fuel.

Example 1

10 g of industrial purity MoO ₃ powder _of technical purity with an average particle size of 30 μm (Fig. 1a) is placed in a vibration mill. The mill drum is purged with argon. The powder in the mill is processed for various times (from 30 seconds to 36 minutes) in 30 sec cycles with 5 min intervals. After grinding, the X-ray diffraction spectra and the specific surface are measured. X-ray diffraction data confirm that phase transformations do not occur during mechanical activation. The dependence of the specific surface area S of the activated MoO ₃ powder _on the specific dose D of the supplied energy (grinding time) is shown in Fig. 1b. It can be seen that at the initial stage of activation, the specific surface area (S) sharply increases and at a dose of D = 0.72 kJ / g (4 min of grinding) S reaches 23 m ² / g. The average particle size <d> calculated from the specific surface according to the relation S = 6 / (ρ <d>), where ρ is the density, is <d> = 55 nm. This value is consistent with the results of scanning electron microscopy (SEM) (Fig. 1c) and measurements of particle size distribution (Fig. 1d, Ar-4 ′ curve, <d> = 60 nm). Further mechanical activation is impractical. With an increase in the activation dose, the specific surface ceases to grow and even decreases (Fig. 1b), and the nanoparticles aggregate, and their average diameter increases (Fig. 1d, curve Ar-36 ′, <d> = 100 nm).

Thus, the optimal dose for the preparation of nanosized MoO ₃ powder is 0.72 kJ / g.

Example 2

5.52 g of a polydispersed industrial magnesium powder (<d> = 33-40 μm) and 5.37 g of a nanosized MoO ₃ powder obtained according to Example 1 (average particle size 60 nm) are placed in a drum of a vibration mill. An additional 35 ml of heptane is poured into the drum and it is purged with argon. The mixture is processed in a mill for 12 minutes in 30 second cycles at intervals of 5 minutes. The specific dose of supplied mechanical energy is D = 3.5 kJ / g. The obtained two-component homogeneous mixture consists of MoO ₃ nanoparticles with a size of 30-100 nm, combined into spherical aggregates with sizes from 200 to 1000 nm, and submicron magnesium particles with sizes from 100 nm to 500 nm (see Fig. 2) with deposited on them MoO ₃ nanoparticles.

Example 3

3.08 g of industrial aluminum powder grade PAP-2 and 7.84 g of nanopowder powder MoO ₃ obtained according to example 1 (average particle size 60 nm), are placed in a drum of a vibration mill. An additional 30 ml of heptane is poured into the drum and it is purged with argon. The mixture is processed in a mill for 12 minutes in 30 second cycles at intervals of 5 minutes. The specific dose of supplied mechanical energy is D = 3.5 kJ / g. In the obtained two-component homogeneous mixture, aluminum is represented by thin plates up to several microns in size, the surface of which is coated with either individual MoO ₃ nanoparticles of 30-100 nm in size or spherical aggregates of MoO ₃ nanoparticles with sizes from 200 to 800 nm (see Fig. 3).

When developing the proposed method for the use of the inventive additive, studies were carried out on the conditions and mechanism for self-ignition of hydrocarbon fuels containing the proposed additive in various concentrations - from 1% to 5%. The increase in the amount of additives in the fuel above 5 wt.% Does not increase its effectiveness. The addition of other known target fuel additives does not impair the effectiveness of the inventive additives.

The experiments were carried out in a static installation of a bypass type with an inner diameter of the reactor of 120 mm in the temperature range from 500 to 700 K at a pressure of 1.4-1.5 at. A portion of the test fuel supplied through a U-shaped tube to the reactor corresponded to the mass required to create a stoichiometric (average) air-fuel mixture in the reactor. After opening the valve, fuel dispersed in a stream of cold air is introduced into a reactor heated to a predetermined temperature and mixed with hot air. The valve opening time was 0.2 s. The self-ignition delay time was determined as the time interval from the moment the fuel bypass into the reactor was completed until the mixture exploded.

As a result of the studies, it was found that, starting with some “threshold” values of the reactor temperature, the addition of the proposed additive to the fuel significantly — by more than an order of magnitude — reduces the self-ignition delays of fuel-air mixtures as compared to an air mixture of pure liquid fuel.

Figure 4 shows the results of measurements of the dependence of the ignition delay on the wall temperature of the reactor for the Mg / MoO ₃ additive obtained in Example 2: squares - n-heptane; triangles - n-heptane with the addition of Mg / MoO ₃ in an amount of 2.0 wt.%. It can be seen from the above data that when the threshold value of the reactor wall temperature is ~ 567 K, the self-ignition delay of the n-heptane mixture with the addition of Mg / MoO ₃ - air sharply decreases.

To determine the speed of flame propagation in an n-heptane mixture with the addition of Mg / MoO ₃ - air, after self-ignition of the mixture, high-speed video was recorded using a movie camera with a frequency of 600 frames / s. The speed of flame propagation, determined by video recording, is 30-50 m / s, which is 1.5-2 orders of magnitude higher than the speed of normal flame propagation in air mixtures of pure hydrocarbon fuel.

Figure 5 shows the results of measurements of the dependence of the ignition delay on the wall temperature of the reactor for the Al / MoO ₃ additive obtained in Example 3: squares - n-heptane; triangles - n-heptane with an additive of Al / MoO ₃ in the amount of 3.0 wt.%. It can be seen from the data that, when the threshold temperature of the reactor wall is 651 K, the self-ignition delay of the n-heptane mixture with Al / MoO ₃ additive - air decreases sharply.

Figure 6 shows the results of measurements of the dependence of the ignition delay on the temperature of the reactor wall for the Mg / MoO ₃ additive obtained by the method similar to Example 2: squares — diesel fuel; triangles - diesel fuel with the addition of Mg / MoO ₃ in an amount of 4.5 wt.%. From the above data it is seen that when the threshold value of the wall temperature of the reactor reaches 575 K, the self-ignition delay of the mixture of diesel fuel with the addition of Mg / MoO ₃ - air sharply decreases.

One of the possible explanations for the observed effects is the “microexplosion” of fuel droplets containing the proposed additive due to the rapid exothermic reaction between its activated components during heating of the droplet. The interaction of nanoscale and submicron metal particles with oxygen from the fuel-air mixture on the hot wall of the reactor is not excluded.

Thus, a metal-containing fuel additive is proposed, which, due to the presence of a metal fuel and solid oxidizer in it, can significantly reduce the self-ignition delays of the fuel-air mixture and increase its combustion rate.

A method has been developed to obtain the proposed fuel additive, which is distinguished by the simplicity of the technology and the availability of the starting components and allows to obtain a metal-containing additive in the form of a powder with nanoscale components.

A method for the use of a metal-containing additive is proposed, which improves the flammability of the fuel-air mixture and increases its burning rate.

Claims (3)

1. A metal-containing fuel additive containing an industrial metal powder selected from the group: aluminum, magnesium, and a solid oxidizing agent is a nanosized molybdenum trioxide powder with an average particle size of not more than 100 nm, obtained by mechanical activation of an industrial molybdenum trioxide powder, in the following ratio of components, wt .%:
industrial metal powder 30-70 nanosized molybdenum trioxide powder rest,
subjected to joint mechanical activation. 2. The method of producing a metal-containing additive according to claim 1, comprising mechanically activating industrial metal powders and a solid oxidizing agent, molybdenum trioxide, by mixing and grinding in an energy-intensive ball mill in an inert medium, characterized in that industrial aluminum or magnesium powder is used as an industrial metal powder, and the process of mechanical activation is carried out in two stages: in the first stage, an industrial powder of molybdenum trioxide is subjected to mechanical activation to an average particle size not more than 100 nm in an inert gas medium; in the second stage, the obtained nanosized molybdenum trioxide powder is mixed with an industrial metal powder until the metal content in the mixture is from 30 to 70 wt.% and mechanical activation is repeated in an inert gas medium in the presence of a neutral liquid. 3. The method of using a metal-containing additive according to claim 1, which consists in the fact that the additive is added to the fuel in an amount of up to 5 wt.%.

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