Fast quench reactor and method

Abstract

A fast quench reaction includes a reactor chamber having a high temperature heating means such as a plasma torch at its inlet and a restrictive convergent-divergent nozzle at its outlet end. reactants are injected into the reactor chamber. The resulting heated gaseous stream is then rapidly cooled by passage through the nozzle. This "freezes" the desired end product(s) in the heated equilibrium reaction stage.

Description

The United States Government has rights in this invention disclosed under contract number DE-AC07-76ID01570 between the U.S. Department of Energy and EG&G Idaho, Inc., now contract number DE-AC07-94ID13223 with Lockheed Idaho Technologies Company.

TECHNICAL FIELD

This disclosure pertains to equipment for thermal conversion of reactants to desired end products, which might be either a gas or ultrafine solid particles. It also relates specifically to methods for effectively producing such end products.

BACKGROUND OF THE INVENTION

The present rector and method are intended for high temperature reactions that require rapid cooling to freeze the reaction products to prevent back reactions or decompositions to undesirable products. They use adiabatic and isentropic expansion of gases in a converging-diverging nozzle for rapid quenching. This expansion can result in cooling rates exceeding 10¹⁰ K/s, thus preserving reaction products that are in equilibrium only at high temperatures.

The concepts of this reactor were originally developed in a study of hydrogen reduction of titanium tetrachloride. When the concept was found to provide the high quench rates required to produce titanium, the concept was then applied to other processes requiring rapid quenching, including conversion of methane to acetylene.

Titanium's properties of high corrosion resistance and strength, combined with its relatively low density, result in titanium alloys being ideally suited to many high technology applications, particularly in aerospace systems. Applications of titanium in chemical and power plants are also attractive.

Unfortunately, the widespread use of titanium has been severely limited by its high cost. The magnitude of this cost is a direct consequence of the batch nature of the conventional Kroll and Hunter processes for metal production, as well as the high energy consumption rates required by their usage.

The large scale production processes used in the titanium industry have been relatively unchanged for many years. They involve the following essential steps: (1) Chlorination of impure oxide ore, (2) purification of TiCl₄ (3) reduction by sodium or magnesium to produce titanium sponge, (4) removal of sponge, and (5) leaching, distillation and vacuum remelting to remove Cl, Na, and Mg impurities. The combined effects of the inherent costs of such processes, the difficulty associated with forging and machining titanium and, in recent years, a shortfall in sponge availability, have contributed to relatively low titanium utilization.

One of the most promising techniques currently undergoing development to circumvent the high cost of titanium alloy parts is powder metallurgy for near net shape fabrication. For instance, it has been estimated that for every kilogram of titanium presently utilized in an aircraft, 8 kilograms of scrap are created. Powder metallurgy can substantially improve this ratio. Although this technology essentially involves the simple steps of powder production followed by compaction into a solid article, considerable development is currently underway to optimize the process such that the final product possesses at least equal properties and lower cost than wrought or cast material.

One potential powder metallurgy route to titanium alloy parts involves direct blending of elemental metal powders before compaction. Presently, titanium sponge fines from the Kroll process are used, but a major drawback is their high residual impurity content (principally chlorides), which results in porosity in the final material. The other powder metallurgy alternative involves direct use of titanium alloy powder subjected to hot isostatic pressing.

Several programs are currently involved in the optimization of such titanium alloy powders. Results are highly promising, but all involve Kroll titanium as a starting material. Use of such existing powders involves a number of expensive purification and alloying steps.

The present disclosure is the result of research to develop a new plasma process for direct and continuous production of high purity titanium powder and/or ingot. The previously-described steps (1) and (2) of the Kroll or Hunter processes are retained in this process, but steps (3), (4), and (5) are replaced by a single, high temperature process. This new process can directly produce high purity titanium from TiCl₄ and eliminates the need for subsequent purification steps.

Depending upon collection conditions encountered in the present process, the resulting titanium product can be either a powder suitable for the elemental blend approach to powder metallurgy or in an ingot or sponge-substitute. Titanium alloy powders and other materials can also be produced in a single step process by such direct plasma production systems.

The formation of titanium under plasma conditions has received intermittent attention in the literature over the last 30 years. Reports have generally been concerned with the hydrogen reduction of titanium tetrachloride or dioxide with some isolated references to sodium or magnesium reduction.

The use of hydrogen for reducing titanium tetrachloride has been studied in an arc furnace. Only partial reduction took place at 2100 K. The same reaction system has been more extensively studied in a plasma flame and patented for the production of titanium subchloride (German Patent 1,142,159, Jan. 10, 1963) and titanium metal (Japanese Patents 6854, May 23, 1963; 7408, Oct. 15, 1955; U.S. Pat. No. 3,123,464, Mar. 3, 1964).

Although early thermodynamic calculations indicated that the reduction of titanium tetrachloride to metallic titanium of hydrogen could start at 2500 K, the system is not a simple one. Calculations show that the formation of titanium subchloride would be thermodynamically more favorable in that temperature region.

U.S. Pat. No. 3,123,464, Mar. 3, 1964, claims that reduction of titanium tetrachloride to liquid titanium can be successfully carried out by heating the reactants (TiCl₄ and H₂) at least to, and preferably in excess of, the boiling point of titanium (3535 K). At such a high temperature, it was claimed that while titanium tetrachloride vapor is effectively reduced by atomic hydrogen, the tendency of H₂ to dissolve in or react with Ti is insignificant, the HCl formed is only about 10% dissociated, and the formation of titanium subchlorides could be much less favorable. The titanium vapor product is then either condensed to liquid in a water-cooled steel condenser at about 3000 K, from which it overflows into a mold, or is flash-cooled by hydrogen to powder, which is collected in a bin. Since the liquid titanium was condensed from gas with only gaseous by-products or impurities, its purity, except for hydrogen, was expected to be high.

Japanese Patent 7408, Oct. 15, 1955, described reaction conditions as follows: a mixture of TiCl₄ gas and H₂ (50% in excess) is led through a 5 mm inside diameter nozzle of a tungsten electrode at a rate of 4×10^-3m³/min and an electric discharge (3720 V and 533 mA) made to another electrode at a distance of 15 mm. The resulting powdery crystals are heated in vacuo to produce 99.4% pure titanium.

In neither of the above patents is the energy consumption clearly mentioned. Attempts to develop the hydrogen reduction process on an industrial scale were made using a skull-melting furnace, but the effort was discontinued. More recently, a claim was made that a small quantity of titanium had been produced in a hydrogen plasma, but this was later retracted when the product was truly identified as titanium carbide.

In summary, the history of attempts to treat TiCl₄ in hydrogen plasmas appears to indicate that only partial reduction, i.e., to a mixture of titanium and its subchlorides, is possible unless very high temperatures (>4000 K) are reached. Prior researcher have concluded that extremely rapid, preferential condensation of vapor phase titanium would be required in order to overcome the unfavorable thermodynamics of the system.

A second exemplary application of the present equipment and method pertains to production of acetylene from methane.

Natural gas (where methane is the main hydrocarbon) is a low value and underutilized energy resource in the U.S. Huge reserves of natural gas are known to exist in remote areas of the continental U.S., but this energy resource cannot be transported economically and safely from those regions. Conversion of natural gas to higher value hydrocarbons has been researched for decades with limited success in today's economy.

Recently, there have been efforts to evaluate technologies for the conversion of natural gas (which is being flared) to acetylene as a feed stock for commodity chemicals. The ready availability of large natural gas reserves associated with oil fields and cheap labor might make the natural gas to acetylene route for producing commodity chemicals particularly attractive in this part of the world.

Acetylene can be used as a feed stock for plastic manufacture or for conversion by demonstrated catalyzed reactions to liquid hydrocarbon fuels. The versatility of C₂H₂ as a starting raw material is well known and recognized. Current feed stocks for plastics are derived from petro-chemical based raw materials. Supplied from domestic and foreign oil reserves to produce these petrochemical based raw materials are declining, which puts pressure on the search for alternatives to the petrochemical based feed stock. Therefore, the interest in acetylene based feed stock has currently been rejuvenated.

Thermal conversion of methane to liquid hydrocarbons involves indirect or direct processes. The conventional methanol-to-gasoline (MTG) and the Fischer-Tropsch (FT) processes are two prime examples of such indirect conversion processes which involve reforming methane to synthesis gas before converting to the final products. These costly endothermic processes are operated at high temperatures and high pressures.

The search for direct catalytic conversion of methane to light olefins (e.g. C₂H₄) and then to liquid hydrocarbons has become a recent focal point of natural gas conversion technology. Oxidative coupling, oxyhydrochlorination, and partial oxidation are examples of direct conversion methods. These technologies require operation under elevated pressures, moderate temperatures, and the use of catalysts. Development of special catalysts for direct natural gas conversion process is the biggest challenge for the advancement of these technologies. The conversion yields of such processes are low, implementing them is costly in comparison to indirect processes, and the technologies have not been proven.

Light olefins can be formed by very high temperature (>1800°C C.) abstraction of hydrogen from methane, followed by coupling of hydrocarbon radicals. High temperature conversion of methane to acetylene by the reaction 2CH₄→C₂H₂+3H₂ is an example. Such processes have existed for a long time.

Methane to acetylene conversion processes currently use cold liquid hydrocarbon quenchants to prevent back reactions. Perhaps the best known of these is the Huels process which has been in commercial use in Germany for many years. The electric arc reactor of Huels transfers electrical energy by `direct` contact between the high-temperature arc (15000-20000 K) and the methane feed stock. The product gas is quenched with water and liquefied propane to prevent back reactions. Single pass yields of acetylene are less than 40% for the Huels process. Overall C₂H₂ yields are increased to 58% by recycling all of the hydrocarbons except acetylene and ethylene.

Although in commercial use, the Huels process is only marginally economical because of the relatively low single pass efficiencies and the need to separate product gases from quench gases. Subsidies by the German Government have helped to keep this process in production.

Westinghouse has employed a hydrogen plasma reactor for the cracking of natural gas to produce acetylene. In the plasma reactor, hydrogen is fed into the arc zone and heated to a plasma state. The exiting stream of hot H₂ plasma at temperatures above 5000 K is mixed rapidly with the natural gas below the arc zone, and the electrical energy is indirectly transferred to the feed stock. The hot product gas is quenched with liquefied propane and water, as in the Huel process, to prevent back reactions. However, as with the Huels process, separation of the product gas from quench gas is needed. Recycling all of the hydrocarbons except acetylene and ethylene has reportedly increased the overall yield to 67%. The H₂ plasma process for natural gas conversion has been extensively tested on a bench scale, but further development and demonstration on a pilot scale is required.

The Scientific and Industrial Research Foundation (SINTEF) of Norway has developed a reactor consisting of concentric, resistance-heated graphite tubes. Reaction cracking of the methane occurs in the narrow annular space between the tubes where the temperature is 1900 to 2100 K. In operation, carbon formation in the annulus led to significant operational problems. Again, liquefied quenchant is used to quench the reaction products and prevent back reactions. As with the previous two acetylene production processes described above, separation of the product gas from quench gas is needed. The overall multiple-pass acetylene yield from the resistance-heated reactor is about 80% and the process has been tested to pilot plant levels.

Like the Huels reactor, the present fast quench reactor can use an electric arc plasma process to crack the methane, but it requires no quenchant to prevent back reactions. In this manner it eliminates any need for extensive separation.

SUMMARY OF THE INVENTION

This invention relates to a reactor and method for producing desired end products by injecting reactants into the inlet end of a reactor chamber; rapidly heating the reactants to produce a hot reactant stream which flows toward the outlet end of the reactant chamber, the reactor chamber having a predetermined length sufficient to effect heating of the reactant stream to a selected equilibrium temperature at which the desired end product is available within the reactant stream as a thermodynamically stable reaction product at a location adjacent to the outlet end of the reaction chamber; passing the gaseous stream through a restrictive convergent-divergent nozzle arranged coaxially within the remaining end of the reactor chamber to rapidly cool the gaseous stream by converting thermal energy to kinetic energy as a result of adiabatic and isentropic expansion as it flows axially through the nozzle and minimizing back reactions, thereby retaining the desired end product within the flowing gaseous stream; and subsequently cooling and slowing the velocity of the desired end product and remaining gaseous stream exiting from the nozzle. Preferably the rapid heating step is accomplished by introducing a stream of plasma arc gas to a plasma torch at the inlet end of the reactor chamber to produce a plasma within the reactor chamber which extends toward its outlet end.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below with reference to the following drawings.

FIG. 1 is a schematic cross-sectional view of a reactor system; FIG. 2 is an enlarged cross-sectional view of the reactor chamber and converging-diverging nozzle;

FIG. 3 is a plot of temperatures, pressures, specific volumes and nozzle throat areas as a function of gas velocity in the reactor apparatus;

FIG. 4 is a graph plotting equilibrium concentrations in a titanium tetrachloride and hydrogen system as a function of temperature;

FIG. 5 is a graph plotting equilibrium concentrations in a titanium tetrachloride and hydrogen system with added argon gas as a function of temperature;

FIG. 6 is a graph plotting equilibrium concentrations in a methane decomposition system with solid carbon precipitation; and

FIG. 7 is a graph plotting equilibrium concentrations in a methane decomposition system with solid carbon precipitation prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fast quench reactor and method of operation described in this disclosure take advantage of the high temperatures (5,000°C to 20,000°C C.) available in a high temperature heating means such as a thermal plasma to produce materials that are thermodynamically stable at these high temperatures. These materials include metals, alloys, intermetallics, composites, gases and ceramics.

A converging-diverging (De Laval) nozzle located downstream from the plasma and reactant addition inlet(s) produces a rapid drop in kinetic temperature in a flowing gas stream. This effectively "freezes" or stops all chemical reactions. It permits efficient collection of desired end products as the gases are rapidly cooled without achieving an equilibrium condition. Resulting end products which have been produced in the plasma at high temperature but are thermodynamically unstable or unavailable at lower temperatures can then be collected due to resulting phase changes (gas to solid) or stabilization by cooling to a lower equilibrium state (gas to gas).

The fast quench reactor and method of this invention shall be described and illustrated forthwith in terms of a rapid heating means comprising a plasma torch and a stream of plasma arc gas. However, it will be recognized that the rapid heating means can also include other rapid heating means such as lasers, and flames produced by oxidation of a suitable fuel, e.g. an oxygen/hydrogen flame.

A schematic diagram of an ultra fast quenching apparatus is shown in FIG. 12. An enclosed axial reactor chamber 20 includes an inlet at one end (shown to the left) and an outlet at its remaining end (shown to the right).

A plasma torch 21 is positioned adjacent to the reactor chamber. Torch 21 is used to thermally decompose an incoming gaseous stream within a resulting plasma 29 as the gaseous stream is delivered through the inlet of the reactor chamber 20.

A plasma is a high temperature luminous gas which is at least partially (1 to 100%) ionized. A plasma is made up of gas atoms, gas ions, and electrons. In the bulk phase a plasma is electrically neutral. A thermal plasma can be created by passing a gas through an electric arc. The electric arc will rapidly heat the gas by resistive and radiative heating to very high temperatures within microseconds of passing through the arc. The plasma is typically luminous at temperatures above 9000 K.

A plasma can be produced with any gas in this manner. This gives excellent control over chemical reactions in the plasma as the gas might be neutral (argon, helium, neon), reductive (hydrogen, methane, ammonia, carbon monoxide) or oxidative (oxygen, nitrogen, carbon dioxide). Oxygen or oxygen/argon gas mixtures are used to produce metal oxide ceramics and composites. Other nitride, boride, and carbide ceramic materials require gases such as nitrogen ammonia, hydrogen, methane, or carbon monoxide to achieve the correct chemical environment for synthesis of these materials.

The details of plasma generating touches are well known and need not be further detailed within this disclosure to make the present invention understandable to those skilled in this field.

An incoming stream of plasma gas is denoted by arrow 31. The plasma gas can also be a reactant or can be inert. A gaseous stream of one or more reactants (arrow 30) is normally injected separately into the plasma 29, which is directed toward the downstream outlet of the reactor chamber 20. The gaseous stream moving axially through the reactor chamber 20 includes the reactants injected into the plasma arc or within a carrier gas.

Reactant materials are usually injected downstream of the location where the arc attaches to the annular anode of the plasma generator or torch. Materials which can be injected into the arc region include natural gas, such as is used in the Huels process for the production of ethylene and acetylene from natural gas.

Gases and liquids are the preferred forms of injected reactants. Solids may be injected, but usually vaporize too slowly for chemical reactions to occur in the rapidly flowing plasma gas before the gas cools. If solids are used as reactants, they will usually be heated to a gaseous or liquid state before injection into the plasma.

A convergent-divergent nozzle 22 is coaxially positioned within the outlet of the reactor chamber 20. The converging or upstream section of the nozzle restricts gas passage and controls the residence time of the hot gaseous stream within the reactor chamber 20, allowing its contents to reach thermodynamic equilibrium. The contraction that occurs in the cross sectional size of the gaseous stream as it passes through the converging portions of nozzle 22 change the motion of the gas molecules from random directions, including rotational and vibrational motions, to straight line motion parallel to the reactor chamber axis. The dimensions of the reactor chamber 20 and the incoming gaseous flow rates are selected to achieve sonic velocity within the restricted nozzle throat.

As the confined stream of gas enters the diverging or downstream portions of the nozzle 22, it is subjected to an ultra fast decrease in pressure as a result of a gradual increase in volume along the conical walls of the nozzle exit. The resulting pressure change instantaneously lowers the temperature of the gaseous stream to a new equilibrium condition.

An additional reactant, such as hydrogen at ambient temperatures, can be tangentially injected into the diverging section of nozzle 22 (arrow 32) to complete the reactions or prevent back reactions as the gases are cooled. Supply inlets for the additional reactant gas are shown in FIG. 1 at 23.

Numerals 24 and 25 designate a coolant inlet and outlet for the double-walled structure of the reactor chamber 20. Coolant flow is indicated by arrows 33 and 34. The walls of nozzle 22 and a coaxial cool down chamber 26 downstream from it should also be physically cooled to minimize reactions along their inner wall surfaces.

Reaction particles are collectable within a cyclone separator shown generally at 27. A downstream liquid trap 28, such as a liquid nitrogen trap, can be used to condense and collect reactor products such as hydrogen chloride and ultra-fine powders within the gaseous stream prior to the gaseous stream entering a vacuum pump 29.

FIG. 2 further illustrates details of the converging-diverging nozzle structure. The same reference numerals are used in FIG. 2 as in FIG. 1. By proper selection of nozzle dimensions, the reactor chamber 20 can be operated at atmospheric pressure or in a pressurized condition, while the chamber 26 downstream from nozzle 22 is maintained at a vacuum pressure by operation of pump 29. The sudden pressure change that occurs as the gaseous stream traverses nozzle 22 brings the gaseous stream to a lower equilibrium condition instantly and prevents unwanted back reactions that would occur and more drawn out cooling conditions.

Typical residence times for materials within the free flowing plasma are on the order of milliseconds. To maximize mixing with the plasma gas the reactants (liquid or gas) are injected under pressure (10 to 100 atmospheres) through a small orifice to achieve sufficient velocity to penetrate and mix with the plasma. It is preferable to use gaseous or vaporized reactants whenever practical, since this eliminates need for a phase change within the plasma and improves the kinetics of the reactor. In addition, the injected stream of reactants is injected normal (90°C angle) to the flow of the plasma gases. In some cases positive or negative deviations from this 90°C angle by as much as 30°C may be optimum.

The high temperature of the plasma rapidly vaporizes the injected liquid materials and breaks apart gaseous molecular species to their atomic constituents. A variety of metals (titanium, vanadium, antimony, silicon, aluminum, uranium, tungsten), metal alloys (titanium/vanadium, titanium/aluminum, titanium/aluminum/vanadium), intermetallics (nickel aluminide, titanium aluminide), and ceramics (metal oxides, nitrides, borides, and carbides) can be synthesized by injecting metal halides (chlorides, bromides, iodides, and fluorides) in liquid or gaseous form into a plasma of the appropriate gas downstream from the anode arc attachment point and within the torch exit or along the length of the rector chamber. Titanium dioxide and antimony oxide are especially preferred ultrafine powders produced according to this invention. Solid metal halide materials are preferably vaporized and injected into the plasma as a liquid or gas to improve reaction kinetics.

The reaction chamber 20 is the location in which the preferred chemical reactions occur. It begins downstream from the plasma arc inlet and terminates at the nozzle throat. It includes the reactor areas in which reactant injection/mixing and product formation occurs, as well as the converging section of the quench nozzle.

Temperature requirements within the reactor chamber and its dimensional geometry are specific to the temperature required to achieve an equilibrium state with an enriched quantity of each desired end product.

There is a substantial difference in temperature gradients and gaseous flow patterns along the length of the reaction chamber 20. At the plasma arc inlet, flow is turbulent and there is a high temperature gradient; from temperatures of about 20,000 K at the axis of the chamber to about 375 K at the chamber walls, At the nozzle throat, the gaseous flow is laminar and there is a very low temperature gradient across its restricted open area.

Since the reactions chamber is an area of intense heat and chemical activity it is necessary to construct the reactor chamber of materials that are compatible with the temperature and chemical activity to minimize chemical corrosion from the reactants, and to minimize melting degradation and ablation from the resulting intense plasma radiation. The reactor chamber is usually constructed of water cooled stainless steel, nickel, titanium, or other suitable materials. The rector chamber can also be constructed of ceramic materials to withstand the vigorous chemical and thermal environment.

The reaction chamber walls are internally heated by a combination of radiation, convection and conduction. Cooling of the reaction chamber walls prevents unwanted melting and/or corrosion at their surfaces. The system used to control such cooling should maintain the walls at as high a temperature as can be permitted by the selected wall material, which must be inert to the reactants within the reactor chamber at the expected wall temperatures. This is true also with regard to the nozzle walls, which are subjected to heat only by convection and conduction.

The dimensions of the reactor chamber are chosen to minimize recirculation of the plasma and reactant gases and to maintain sufficient heat (enthalpy) going into the nozzle throat to prevent degradation (undesirable back or side reaction chemistry).

The length of the reactor chamber must be determined experimentally by first using an elongated tube within which the user can locate the target reaction threshold temperature. The reactor chamber can then be designed long enough so that reactants have sufficient residence time at the high reaction temperature to reach an equilibrium state and complete the formation of the desired end products. Such reaction temperatures can range from a minimum of about 1700°C C. to about 4000°C C.

The inside diameter of the reactor chamber 20 is determined by the fluid properties of the plasma and moving gaseous stream It must be sufficiently great to permit necessary gaseous flow, but not so large that desirable recirculating eddys or stagnant zones are formed along the walls of the chamber. Such detrimental flow patterns will cool the gases prematurely and precipitate unwanted products, such as subchlorides or carbon. As a general rule, the inside diameter of the reactor chamber 20 should be in the range of 100 to 150% of the plasma diameter at the inlet end of the reactor chamber.

The purpose of the converging section of the nozzle is to compress the hot gases rapidly into a restrictive nozzle throat with a minimum of heat loss to the walls while maintaining laminar flow and a minimum of turbulence. This requires a high aspect ratio change in diameter that maintains smooth transitions to a first steep angle (>45°C) and then to lesser angles (>45°C) leading into the nozzle throat.

The purpose of the nozzle throat is to compress the gases and achieve sonic velocities in the flowing hot gaseous stream. This converts the random energy content of the hot gases to translational energy (velocity) in the axial direction of gas flow. This effectively lowers the kinetic temperature of the gases and almost instantaneously limits further chemical reactions. The velocities achieved in the nozzle throat and in the downstream diverging section of the nozzle are controlled by the pressure differential between the reactor chamber and the section downstream of the diverging section of the nozzle. Negative pressure can be applied downstream or positive pressure applied upstream for this purpose.

The purpose of the diverging section of the nozzle is to smoothly accelerate and expand gases exiting the nozzle from sonic to supersonic velocities, which further lowers the kinetic temperature of the gases.

The term "smooth acceleration" in practice requires use of a small diverging angle of less than 35 degrees to expand the gases without suffering deleterious effects of separation from the converging wall and inducing turbulence. Separation of the expanding gases from the diverging wall causes recirculation of some portion of the gases between the wall and the gas jet exiting the nozzle throat. This recirculation in turn results in local reheating of the expanding gases and undesirable degradation reactions, producing lower yields of desired end products.

PHYSICS OF THE NOZZLE

The super fast quench produce produced, thereby maintaining the kinetic temperature of the resulting gaseous stream at a desired equilibrium level and preventing back reactions downstream from the nozzle.

In the case of experimental work to date this "cool down" has been accomplished by the use of length of water cooled tube having the same internal diameter as the internal exit diameter of the diverging section of the nozzle. With other applications of this device, it may be more desirable to supplement gas cooling by use of other types of heat exchangers.

Plasma quench processes for production of ultrafine materials require product collection capability downstream of the quench nozzle, preferably downstream of the cool down section. Bench scale experiments to date have used cyclonic collectors of standard dimensions described in the literature for gas and mass flows several time smaller than called for in the literature. This accommodates sonic or near sonic gas velocities through the cyclones, which allows efficient removal of ultrafine material (10 to 50 nm diameter powders).

In addition to mass flow and nozzle diameter, the third process parameter that determines the temperature drop across the nozzle is the ratio of the up stream pressure (P₀, in reaction zone) to the downstream pressure (P₁, cool down zone). In bench scale tests for the production of titanium metal powder and other materials, the ratio P₀/P₁ P₁/P₀ of 0.01 to 0.26 was maintained. The experimental systems were operated with the reaction zone pressure of approximately 700 to 800 Tar (ca. 1 atm.) and downstream pressure maintained between 10 and 200 Tar (0.26 to 0.01 atm.). In bench scale experiments, the low downstream pressure was accomplished using a mechanical vacuum pump.

For large scale production of ultrafine powders, it is expected that the quench system would be designed to operate with elevated pressures in the plasma torch and reaction chamber of 5 to 10 atmospheres pressure. This would accomplish the desired pressure drop across the nozzle while reducing a possibly eliminating the need for a vacuum device to lower the pressure on the downstream side of the nozzle.

Using design considerations given in the section above and equations outlined in published texts relating to nozzles, a bench sale reactor was constructed for synthesis of titanium, vanadium, aluminum, and TiN Alloys. This equipment was designed for operation at 12 KW input power to the plasma torch, using a plasma gas flow of 50 scfh and a plasma gas made up of 95% argon and 5% hydrogen gas. The equipment used to produce these materials consisted of a small bench scale plasma torch operated at 12 kW electrical input power attached to a reactor section, quench nozzle, cyclone powder collector, liquid nitrogen cold trap to collect by-product HCL and mechanical vacuum pump.

To produce titanium metal particles, titanium tetrachloride was heated above its boiling point and injected into the reaction chamber at the junction between the plasma torch and the reaction section. The reaction section, quench nozzle, and expansion chamber were constructed of water cooled nickel. The reaction section was 11.0 mm inside diameter and 150.0 mm in length. The quench nozzle section consisted of a high aspect ratio converging section followed by a 6.2 mm nozzle, and 12°C included angle expansion section followed a 20.0 mm I.D., 50.0 cm cool down section. The cooled mixture of titanium powder and gas was passed through two sonic cyclone particle separators to collect the ultrafine powder. Hydrogen chloride vapor was condensed out in a liquid nitrogen cooled cold trap to prevent damage to the mechanical vacuum pump down stream from the particle collection. Titanium was produced according to equation (1) below:

TiCl₄(g)+2H₂(g)+T>3000°C C.→Ti(s)+2HCl(g)

Ultrafine vanadium metal powder was produced using the bench scale apparatus described above. Vanadium tetrachloride liquid (B.P 145°C C.) was heated to vapor and injected in the same manner as titanium tetrachloride described above with hydrogen carrier gas. Ultrafine vanadium metal powder was produced at the rate of a 0.5 gram per hour according to one of the following equations:

2VCl₃(g)+3H₂(g)+T>3000°C C.→2V(s)+6HCl(g)

VCl₄(g)+2H₂(g)+T>3000°C C.→V(s)+2HCl(g)

An ultrafine powder consisting of an alloy of titanium and vanadium was produced by two methods. Method 1 used a mixture of solid vanadium trichloride dissolved in liquid titanium tetrachloride. This mixture was then heated to vapor and injected into the plasma quench reactor in the same manner as with titanium above. In Method 2, vaporized liquid vanadium tetrachloride and vaporized liquid titanium tetrachloride were injected into the plasma quench reactor using separate injectors locate1 in the same axial position but 180°C apart on the circumference of the reactor. The chemical equations used are:

10TiCl₄(g)+2VCl₃(g)+23H₂(g)+T>3000°C C.→10Ti(s)+2V(s)+46HCl(g)

STiCl₄(g)+VCl₄(g)+12H₂(g)+T>3000°C C.→5Ti(s)+V(s)+24HCl(g)

Ultrafine aluminum metal powder was produced by vaporizing (subliming) solid aluminum trichloride in a specially designed oven and carried into the plasma quench reactor in a stream of hydrogen gas in the manner described for titanium above. Special care was needed to insure all sections of the injection system were maintained above 200°C C., to prevent formation of solid aluminum trichloride. The process utilized the following equation:

2AJCl₃(g)+3H₂(g)+T>3000°C C.→2AJ(s)+6HCl(g)

In compliance with the statute, the invention has been described in language more or less specific as to the experimental mental equipment and methodical features. It is to be understood, however, that the invention is not limited to the specific features described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.

Claims

1. A fast quench reactor for thermal conversion of one or more reactants in a thermodynamically stable high temperature gaseous stream to a desired end product in the form of a gas or ultrafine solid particles, comprising:

a reactor chamber having axially spaced inlet and outlet ends along a reactor axis;

a high temperature heating means positioned at the inlet end of the reactor chamber;

a reactant stream inlet for introducing a stream comprising at least one reactant within the reactor chamber where said stream is heated by said high temperature heating means to produce a hot gaseous stream flowing axially toward the outlet end of the reactor chamber;

the reactor chamber having a predetermined length sufficient to effect heating of the reactant stream by the high temperature heating means to a selected equilibrium temperature at which a desired end product is available within the reactant stream as a thermodynamically stable reaction product at a location adjacent the outlet end of the reaction chamber;

a convergent-divergent nozzle located coaxially within the outlet end of the reactor chamber for rapidly cooling the gaseous stream by converting thermal energy to kinetic energy as a result of adiabatic and isentropic expansion as the gaseous stream flows axially through the nozzle, the convergent-divergent nozzle having a converging section and a diverging section respectively leading to and from a restrictive open throat, the diverging section having a conical configuration centered along the reactor axis and having an included angle in the range of 6°C to 14°C; and

a cool down chamber leading from the nozzle for retaining the desired end product within the flowing gaseous stream, and wherein the nozzle and cool down chamber are designed to minimize back reactions .

2. The fast quench reactor of claim 1, wherein the high temperature heating means comprises a plasma torch, a plasma torch exit disposed between the plasma torch and the reaction chamber, and a plasma arc inlet for introducing a stream of plasma arc gas to the plasma torch to produce a plasma within the reaction chamber and extending toward the outlet end of the reaction chamber, the plasma containing at least one reactant, whereby the inlet reactant stream is mixed into the plasma to progressively effect heat transfer between the plasma and a resulting gaseous stream.

3. The fast quench reactor of claim 2 1, further comprising:

a reactant inlet connected to a source of gas which dissociates at or below the equilibrium temperature to produce the desired end product.

4. The fast quench reactor of claim 2 1, further comprising:

separate reactant inlets respectively connected to sources of two different gaseous reactants which react with one another at or below the equilibrium temperature to produce the desired end product.

5. The fast quench reactor of claim 2 1, wherein the minimum temperature within the reactor chamber is between about 1700°C C. and about 4000°C C.

6. The fast quench reactor of claim 2 1, wherein the maximum temperature of the gaseous stream exiting the nozzle is less than about 500°C C.

7. The fast quench reactor of claim 2 1, further comprising:

a reactant inlet operably connected to a source of reactant under positive pressure, whereby the reactant is positively injected into the reactor chamber to penetrate and mix with the plasma.

8. The fast quench reactor of claim 2 1, further comprising:

a product collector positioned downstream from the cool down chamber.

9. The fast quench reactor of claim 2 1, further comprising:

an external cooling system operably connected to the cool down section chamber.

10. The fast quench reactor of claim 2, wherein both the plasma torch exit opening and the reactor chamber are coaxially centered along the reactor axis.

11. The fast quench reactor of claim 2, wherein both the plasma torch exit opening and the reactor chamber are coaxially centered along the reactor axis, the width of the reactor chamber being no larger than approximately 200% of the plasma torch exit opening width.

12. The fast quench reactor of claim 2, wherein both the plasma torch exit and the reactor chamber are circular in cross section and are coaxially centered along the reactor axis, the diameter of the reactor chamber being in the range of approximately 110% to 150% of the plasma torch exit opening diameter width.

13. The fast quench reactor of claim 2 1, wherein the nozzle has a converging section and a diverging section respectively leading to and from a restrictive open throat; the converging section of the nozzle having has a high aspect ratio.

14. The fast quench reactor of claim 2 1, wherein the nozzle has a converging section and a diverging section respectively leading to and from a restrictive open throat; the converging section of the nozzle having has a high aspect ratio presented by successive convex and concave surfaces leading into a the nozzle throat having a circular cross section, the radius of the convex and concave surfaces being approximately equal to the diameter of the nozzle throat.

15. The fast quench reactor of claim 2, wherein the nozzle has a converging section and a diverging section respectively leading to and from a restrictive open throat; the diverging section of the nozzle having a conical configuration centered along the reactor axis.

16. The fast quench reactor of claim 2, wherein the nozzle has a converging section and a diverging section respectively leading to and from a restrictive open throat; the diverging section of the nozzle having a conical configuration centered along the reactor axis with an included angle of less than about 35°C.

17. The fast quench reactor of claim 2, wherein the diverging section of the nozzle has a conical configuration centered along the reactor axis and having an included angle in the range of 6°C to 14°C.

18. The fast quench reactor of claim 2, wherein the nozzle has a converging section and a diverging section respectively leading to and from a restrictive open throat; the fast quench reactor 1, further comprising:

an additional inlet leading to the throat of the nozzle for directing an quenching gas into the hot gaseous stream at a rate that condenses a desired reaction product and inhibits formation of other equilibrium products as the resulting hot gaseous stream exits the nozzle.

19. The fast quench plasma reactor for thermal conversion of one or more reactants in a thermodynamically stable high temperature gaseous stream to a desired end product in the form of a gas or ultrafine solid particles, comprising:

an enclosed reactor chamber arranged along a reactor axis, the reactor chamber having axially spaced inlet and outlet ends;

a plasma torch including at least one pair of electrodes positioned at the inlet end of the reactor chamber;

a plasma arc gas inlet upstream from the electrodes for introducing a stream of plasma arc gas between the electrodes at a selected plasma gas flow while the electrodes are subjected to a selected plasma input power level to produce a plasma within the reactor chamber and extending toward the outlet end of the reactor chamber, the plasma containing at least one reactant, whereby an incoming reactant stream is mixed into the plasma to progressively effect heat transfer between the plasma and a resulting gaseous stream as the gaseous stream flows axially toward the outlet end of the reactor chamber ;

at least one reactant inlet leading into the reactor chamber at or adjacent to its inlet end at a selected injection angle, whereby an incoming reactant stream is mixed into the plasma to progressively effect heat transfer between the plasma and a resulting gaseous stream as the gaseous stream flows axially toward the outlet end of the reactor chamber;

the reactor chamber having a predetermined length sufficient to effect heating of the gaseous stream by the plasma to a selected equilibrium temperature at which a desired end product is available as a thermodynamically unstable stable reaction product at a location adjacent the outlet end of the reactor chamber;

a coaxial convergent-divergent nozzle positioned in the outlet end of the reactor chamber for rapidly cooling the gaseous stream by converting thermal energy to kinetic energy as a result of adiabatic and isentropic expansion as it flows axially through the nozzle, the nozzle having a converging section and a diverging section respectively leading to and from a restrictive open throat;

the converging section of the nozzle having a high aspect ratio for accelerating the gaseous stream rapidly into the nozzle throat while maintaining laminar flow;

the size of the restrictive open throat within the nozzle being selected to control the residence time and reaction pressure of the resulting gaseous stream in the reactor chamber;

the gaseous stream being accelerated to sonic velocities during passage through the throat of the nozzle to transform thermal energy of the moving gaseous stream into kinetic energy in the axial direction of gas flow, thereby retaining the desired end product within the flowing gaseous stream;

the diverging section of the nozzle then subjecting the gaseous stream to an ultra fast decrease in pressure by smoothly accelerating and expanding the moving gaseous stream;

a coaxial cool down chamber leading from the diverging section of the nozzle for reducing the velocity of the moving gaseous stream while removing heat energy at a rate sufficient to prevent increases in its kinetic temperature to retain the desired end product within the gaseous stream; and wherein the diverging section of the nozzle and cool down chamber are designed to minimize undesired side or back reactions; and

a product collector downstream of the cool down chamber to separate a desired reaction product from the gases exiting the cool down chamber.

20. The fast quench plasma reactor of claim 19, further comprising:

an external cooling system operably connected to the cool down section chamber to remove heat energy from the moving gaseous stream at a rate sufficient to prevent the gas from increasing in kinetic temperature as it traverses the cool down chamber.

21. The fast quench plasma reactor of claim 19, wherein both the torch includes a plasma inlet coaxially centered along the reactor chamber axis and both the plasma inlet torch exit disposed between the plasma torch and the reactor chamber and coaxially centered along the reactor chamber axis, and both the plasma torch exit and the interior of the reactor chamber are circular in cross section.

22. The fast quench plasma reactor of claim 19 21, wherein both the torch includes a plasma inlet coaxially centered along the reactor chamber axis and both the plasma inlet and the interior of the reactor chamber are circular in cross section, the diameter of the reactor chamber being is no larger than approximately 200% of the torch exit diameter to prevent recirculation of reaction gases in the reaction chamber of the plasma torch exit.

23. The fast quench plasma reactor of claim 19 21, wherein both the torch includes a plasma inlet coaxially centered along the reactor chamber axis and both the plasma inlet and the interior of the reactor chamber are circular in cross section, the diameter of the reactor chamber being is in the range of approximately 110% to 150% of the torch exit diameter to prevent recirculation of reaction gases in the reaction chamber of the plasma torch exit.

24. The fast quench plasma reactor of claim 19, wherein the converging section of the nozzle has a high aspect ratio presented by successive convex and concave surfaces leading into a the nozzle throat, the nozzle throat having has a circular cross section, and the radius of the convex and concave surfaces being is approximately equal to the diameter of the nozzle throat.

25. The fast quench plasma reactor of claim 19, wherein the diverging section of the nozzle has a conical configuration centered along the reactor axis with an included angle of less than 35°C for optimum expansion and acceleration of the hot gaseous stream passing through it to minimize undesired size and back reactions.

26. The fast quench plasma reactor of claim 19, wherein the diverging section of the nozzle has a conical configuration centered along the reactor axis with an included angle in the range of 6°C to 14°C for optimum expansion and acceleration of the hot gaseous stream passing through it.

27. The fast quench plasma reactor of claim 19, further comprising:

an additional inlet leading to the throat of the nozzle for directing a quenching gas into the hot gaseous stream at a rate that condenses desired reaction products and inhibits formation of other equilibrium products as the resulting hot gaseous stream exits the nozzle.

28. The fast quench plasma reactor of claim 19, further comprising:

vacuum means operatively connected downstream of the convergent-divergent nozzle for applying vacuum pressure to the gaseous stream exiting from the nozzle.

29. An apparatus as set out in The fast quench plasma reactor of claim 19, further comprising:

first cooling means for cooling the walls of the reactor chamber to prevent reactions with its materials of construction.

30. An apparatus as set out in The fast quench plasma reactor of claim 19, further comprising:

first cooling means for cooling the walls of the reactor chamber to prevent reactions with its materials of construction; and

second cooling means for cooling the convergent-divergent nozzle to prevent reactions with its materials of construction.

31. A method for thermally converting one or more reactants in a thermodynamically stable high temperature gaseous stream to a desired end product in the form of a gas or ultrafine solid particles, comprising the following steps:

introducing a reactant stream at one axial end of a reaction reactor chamber having an inlet end and an outlet end, the reactant stream before reaction or thermal decomposition thereof comprising at least one reactant selected from the group consisting of titanium tetrachloride, vanadium tetrachloride, aluminum trichloride and natural gas;

rapidly heating the incoming reactant stream as the reactant stream flows axially toward the remaining outlet end of the reactor chamber;

the reactor chamber having a predetermined length sufficient to effect heating of the gaseous stream to a selected reaction temperature at which a the desired end product is available as a thermodynamically unstable stable reaction product at a location adjacent the outlet end of the reactor chamber;

passing the gaseous stream through a restrictive convergent-divergent nozzle arranged coaxially within the remaining outlet end of the reactor chamber to rapidly cool the gaseous stream by converting thermal energy to kinetic energy as a result of adiabatic and isentropic expansion as it flows axially through the nozzle and minimizing back reactions, thereby retaining the desired end product within the flowing gaseous stream; and

subsequently cooling and slowing the velocity of the desired end product and remaining gaseous stream exiting from the nozzle.

32. The method of claim 31, wherein the rapid heating step is accomplished by introducing a stream of plasma arc gas to a plasma torch at the one axial inlet end of said reactor chamber to produce a plasma within the reaction reactor chamber which extends toward its remaining axial outlet end.

33. The method of claim 31, wherein the step of rapidly cooling the desired end product is accomplished by use of a converging section of the nozzle having a high aspect ratio and further comprising the following additional step: separating the desired end product from the remaining gases in the cooled gaseous stream.

34. The method of claim 31, wherein the step of rapidly cooling the desired end product is accomplished by use of converging-diverging nozzle has a converging section of the nozzle having a high aspect ratio and presented by successive convex and concave surfaces leading into a nozzle throat having a circular cross section, the radius of the convex and concave surfaces being approximately equal to the diameter of the nozzle throat.

35. The method of claim 31, wherein the step of rapidly cooling the desired end product is accomplished by use of a converging-diverging nozzle having has a converging section and a diverging section respectively leading to and from a restrictive open throat, the diverging section of the nozzle having a conical configuration.

36. The method of claim 31, wherein the step of rapidly cooling the desired end product is accomplished by use of a converging-diverging nozzle having has a converging section and a diverging section respectively leading to and from a restrictive open throat, the diverging section of the nozzle having a conical configuration with an included of less than about 35°C.

37. The method of claim 31, wherein the step of subsequently cooling and slowing the velocity of the resulting desired end product and remaining gaseous stream as it exits from the nozzle is accomplished by directing a quenching gas into the gaseous stream at a rate than condenses a the desired end product and inhibits formation of other equilibrium products as the resulting gaseous stream exits the nozzle.

38. The method of claim 31, wherein the desired end product is titanium metal and the reactants are at least one reactant comprises titanium tetrachloride and hydrogen.

39. The method of claim 31, wherein the desired end product is vanadium metal and the reactants are at least one reactant comprises vanadium tetrachloride and hydrogen.

40. The method of claim 31, wherein the desired end product is aluminum metal and the reactants at least one reactant comprises are aluminum chloride and hydrogen.

41. The method of claim 31, wherein the desired end product is a titanium-vanadium alloy and the reactants are at least one reactant comprises a mixture of titanium tetrachloride, and vanadium tetrachloride, plus and hydrogen, or a mixture of titanium tetrachloride, vanadium trichloride and hydrogen.

42. The method of claim 31, wherein the desired end product is a titanium-boron composite ceramic powder and the reactants are at least one reactant comprises titanium tetrachloride and boron trichloride.

43. The method of claim 31, wherein the desired end product is titanium dioxide and the reactants are at least one reactant comprises titanium tetrachloride and oxygen.

44. The method of claim 31, wherein the desired end product is acetylene and the reactants are at least one reactant comprises methane and hydrogen.

45. A method for thermal conversion of one or more reactants in a thermodynamically stable high temperature gaseous stream to a desired end product in the form of a gas or ultrafine solid particles, comprising the following steps:

introducing a stream of plasma arc gas between the electrodes of a plasma torch including at least one pair of electrodes positioned at the inlet end of an axial reactor chamber, chamber having an inlet end and an outlet end, the stream of plasma arc gas being introduced at a selected plasma gas flow while the electrodes are subjected to a selected plasma input power level to produce a plasma within the reactor chamber and extending toward its outlet end;

thoroughly mixing an incoming reactant stream into the plasma by injecting at least one reactant into the reactor chamber at or adjacent to its inlet end at a selected injection angle and at a selected reactant input rate to progressively effect heat transfer between the plasma and the resulting gaseous stream as it flows axially toward the outlet end of the reactor chamber, the at least one reactant selected from the group consisting of titanium tetrachloride, vanadium tetrachloride, aluminum trichloride and natural gas;

the length of the reactor chamber being sufficient to effect heating of the gaseous stream to a selected equilibrium temperature at which a desired end product is available as a thermodynamically unstable stable reaction product within the gaseous stream at a location adjacent to the outlet end of the reactor chamber;

directing the gaseous stream through a coaxial convergent-divergent nozzle positioned in the outlet end of the reactor chamber to rapidly cool the gaseous stream by converting thermal energy to kinetic energy as a result of adiabatic and isentropic expansion as it flows axially through the nozzle, the nozzle having a converging section and a diverging section respectively leading to and from a restrictive open throat;

cooling the gaseous stream exiting the nozzle by reducing its velocity while removing heat energy at a rate sufficient to prevent increases in its kinetic temperature; and

separating the desired end products product from the gases remaining in the cooled gaseous stream.

46. The method of claim 45, further comprising the following step:

accelerating wherein the converging section of the nozzle has a high aspect ratio and is configured so that the gaseous stream accelerates rapidly into the nozzle throat while maintaining laminar flow by passage of the gaseous stream through a converging section of the nozzle having a high aspect ratio .

47. The method of claim 45, further comprising the following step:

controlling the residence time and reaction pressure of the gaseous stream in the reactor chamber by selection of selecting the size of the restrictive open throat within the nozzle.

48. The method of claim 45, further comprising the following step:

accelerating wherein the converging-diverging nozzle is adapted to accelerate the gaseous stream to sonic velocities during passage through the throat of the nozzle to transform thermal energy of the moving gaseous stream into kinetic energy in the axial direction of gas flow, thereby retaining the desired end product within it.

49. The method of claim 45, further comprising the following step:

subjecting the gaseous stream to an ultra fast decrease in pressure by smoothly accelerating and expanding the moving gaseous stream along the diverging section of the nozzle to further decrease its kinetic temperature and prevent undesired side or back reactions.

50. A method for producing titanium, titanium or titanium oxide, comprising the following steps:

decomposing a titanium compound by introducing it as a stream of vapor into a hot plasma together with one or more reactants;

directing the resultant hot gaseous stream through a convergent-divergent nozzle to allow its contents to reach thermodynamic equilibrium prior to being subjected to an ultrafast decrease in pressure; and

quenching the titanium or titanium oxide within the hot gaseous stream by introducing cold gas into it the hot gaseous stream as it passes through the nozzle to cool its contents as a rate that condenses titanium and titanium oxide and inhibits formation of equilibrium products as the resulting gaseous stream exits the convergent-divergent nozzle.

51. The method of claim 50, further comprising the step of introducing sufficient carbon to the hot plasma to prevent formation of titanium oxides.

52. The method of claim 50, further comprising the step of introducing methane to the hot plasma in quantities sufficient to supply adequate carbon to prevent formation of titanium oxides.

53. The method of claim 50, further comprising the step of introducing sufficient wherein the one or more reactants comprises oxygen to the hot plasma in an amount sufficient to produce titanium dioxide as the desired end product.

54. The method of claim 50, wherein the temperature of the hot plasma is in excess of 4000 K.

55. The method of claim 50, wherein the one or more reactants include comprises hydrogen.

56. The method of claim 50, wherein the stream of titanium compound vapor is contained within argon as an inert carrier gas comprising argon.

57. The method of claim 50, wherein the hot plasma is maintained at atmospheric pressure and the resulting gaseous stream exiting the convergent-divergent nozzle is at a vacuum pressure.

58. A method of forming a metal, metal oxide, metal alloy, or ceramic from a metal-containing compound, the method comprising the steps of:

(a) providing a plasma formed from a gas comprising an inert gas, hydrogen, or a mixture thereof;

(b) providing a reagent or a reagent mixture, the reagent or reagent mixture comprising a gaseous or volatilized compound of a selected metal;

(c) contacting the reagent or reagent mixture with the plasma for a time and at a reaction temperature sufficient to form an equilibrium mixture comprising the selected metal, metal oxide, metal alloy, or ceramic thereof, the selected metal, metal oxide, metal alloy, or ceramic being thermodynamically stable at the reaction temperature; and

(d) adiabatically and isentropically expanding the equilibrium mixture to rapidly cool the mixture, thereby retaining the selected metal, metal oxide, metal alloy, or ceramic in a cooled product mixture.

59. The method of claim 58, wherein the gaseous or volatilized compound of the selected metal is a gaseous or volatilizable halide.

60. The method of claim 58, wherein the selected metal is titanium, vanadium or aluminum.

61. The method of claim 58, wherein the compound of the selected metal is titanium tetrachloride, vanadium tetrachloride or aluminum trichloride.

62. The method of claim 58, wherein the reagent or reagent mixture further comprises at least one additional reagent capable of reacting at the reaction temperature to form an equilibrium mixture comprising an oxide or alloy of the selected metal.

63. The method of claim 58, wherein the method forms titanium metal, and the reagent or reagent mixture comprises titanium tetrachloride.

64. The method of claim 58, wherein the method forms vanadium metal, and the reagent or reagent mixture comprises vanadium tetrachloride.

65. The method of claim 58, wherein the method forms aluminum metal, and the reagent or reagent mixture comprises aluminum trichloride.

66. The method of claim 58, wherein the method forms an alloy of titanium and a second metal, and the reagent or reagent mixture comprises titanium chloride and a gaseous or volatilizable compound of the second metal.

67. The method of claim 66, wherein the second metal is vanadium.

68. The method of claim 58, wherein the method forms a metal oxide of the selected metal, and the reagent or reagent mixture further comprises oxygen.

69. The method of claim 58, wherein the method forms titanium oxide, and the reagent or reagent mixture comprises titanium tetrachloride and oxygen.

70. A method of forming a desired product from a hydrocarbon, the method comprising the steps of:

(a) providing a plasma formed from a gas comprising an inert gas, hydrogen, or a mixture thereof;

(b) providing a reagent or a reagent mixture, the reagent or reagent mixture comprising a gaseous or volatilized hydrocarbon;

(c) contacting the reagent or reagent mixture with the plasma for a time and at a reaction temperature sufficient to form an equilibrium mixture comprising the desired product, the desired product being thermodynamically stable at the reaction temperature; and

(d) adiabatically and isentropically expanding the equilibrium mixture to rapidly cool the mixture, thereby retaining the desired product in a cooled product mixture.

71. The method of claim 70, wherein the reactant or reactant mixture comprises natural gas.

72. The method of claim 70, wherein the reactant or reactant mixture comprises methane.

73. The method of claim 70, wherein the desired product comprises acetylene.