Thermal synthesis apparatus and process

Details Thermal synthesis apparatus and process Thermal synthesis apparatus and process

2001-02-12

2004-11-23

Silverman, Stanley S. (Department: 1754)

Chemistry of inorganic compounds

Hydrogen or compound thereof

Elemental hydrogen

C075S010190, C075S010210, C075S010280, C075S346000, C075S620000, C420S590000, C422S207000

Reexamination Certificate

active

06821500

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a thermal synthesis process. In particular, the present invention relates to methods and apparatus for thermal conversion of reactants in a thermodynamically stable high temperature gaseous stream to desired end products, such as either a gas or ultrafine solid particles.
2. Relevant Technology
Natural gas (where methane is the main hydrocarbon) is a low value and underutilized energy resource in the United State. 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 acetylene as a starting raw material is well known and recognized. Current feed stocks for plastics are derived from petrochemical based raw materials. Supplies 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., C
2
H
4
) 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.) abstraction of hydrogen from methane, followed by coupling of hydrocarbon radicals. High temperature conversion of methane to acetylene by the reaction 2CH
4
→C
2
H
2
+3H
2
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 C
2
H
2
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.
A similar process with 9 MW reactors was built by DuPont and operated between 1963 and 1968 supplying acetylene produced from liquid hydrocarbon sources to a neoprene plant. The process was also reportedly demonstrated at the pilot-plant scale using methane feed. The plant-scale operation was limited to liquefied petroleum gas or liquid hydrocarbon distillates. The size of the DuPont pilot scale process is not reported. In the DuPont process the arc was magnetically rotated while in the original Huels process the arc is “swirl stabilized” by tangential injection of gases. In the DuPont process, all feedstock, diluted with hydrogen, passed through the arc column. In the Huels process, a fraction of the reactants are injected downstream of the arc.
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 H
2
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 Huels 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 H
2
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 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.
Accordingly, it is desirable to improve upon the modest methane conversion efficiencies, acetylene yields, selectivities, and specific energy requirements observed in the above processes.
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 TiCl
4
(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

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