Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
2000-08-04
2001-12-04
Richter, Johann (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C518S715000, C204S164000, C585S700000, C585S514000, C585S943000
Reexamination Certificate
active
06326407
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of transforming a normally gaseous composition consisting essentially of methane into a material comprising a major portion, at least, of hydrocarbons containing at least two carbon atoms. Furthermore the present invention relates to an apparatus for transforming a normally gaseous composition consisting essentially of methane into a material comprising a major portion, at least, of hydrocarbons containing at least two carbon atoms. Moreover, the present invention relates to a method of transforming a normally gaseous mixture consisting essentially of normally gaseous hydrocarbons into a product stream, at least a portion of which containing normally liquid hydrocarbons, and to an apparatus for transforming a normally gaseous mixture consisting essentially of normally gaseous hydrocarbons into a product stream, at least a portion of which containing normally liquid hydrocarbons.
Within the past years there has been an increased interest from both the academic and industrial community to develop processes for transforming gaseous hydrocarbons, in particular for transforming natural gas and methane as its principal constituent into more valuable higher hydrocarbons. The driving force of new research in this field derives from the considerable reservoir of natural gas and the desire to utilize recent gas finds.
PRIOR ART
Since methane is the principal constituent of natural gas, as indicated above, the major research activity has focused on the transformation of methane. There are two general pathways to upgrade methane into higher hydrocarbons, first, by way of indirect conversion mainly requiring syngas production in a first step, and second, by way of direct conversion. A major difficulty, in particular for direct methane conversion, is the high strength of the C—H bonds in the methane molecule causing methane to be a very stable molecule and its reactions to have a high activation energy. There are many ways to activate methane such as photochemical and electrochemical activation, laser-induced activation, and radiolysis, as well as catalytic or even thermal activation. However as reported by J. M. Fox in Catal. Rev.-Sci. Eng., 35 (1993) 169-212 (report being incorporated herein for all purposes by way of reference) the right combination to directly convert methane into higher hydrocarbons has yet to be discovered. So far the direct methane transformations show poor economics, low conversions and low yields making them not suitable for practical applications.
Plasmas have been found to be a versatile tool for the development of new industrial processes and products. The properties of plasmas can be modified and a distinction is made between thermal plasma and nonthermal plasma differing markedly in both discharge characteristics and applications.
The energy distribution of the gas molecules, ions and electrons in thermal plasma indicates that the system is in thermal equilibrium and thus close to thermodynamic equilibrium. The temperature in the discharge region is uniformly very high for all particles. Moreover, there is a high energy flux in the plasma volume as well as at the electrodes if present. Thermal plasmas are therefore often called “hot plasmas”. Hot plasmas include, in particular, arc discharges.
An essential condition for the formation of a thermal plasma is a sufficiently high working pressure usually being over 10 kPa. The resulting large number of collisions between particles, in particular between electrons and heavy positive ions or neutral particles, leads to rapid redistribution of energy so that equilibrium is reached.
Nonthermal plasmas, in contrast, are far from thermodynamic equilibrium. Nonthermal plasmas have comparatively low gas temperatures and energy-conversion rates. Thus, the electrons in these plasmas have typically a very much higher temperature than the heavy ions and neutral particles. Nonthermal plasmas are therefore also named “cold plasmas”. This group typically includes glow and silent discharges.
Cold plasma, particularly, silent gas discharges have demonstrated its suitability for large-scale industrial applications. The ozone generation, as its most important industrial application so far, is described by Eliasson et al. in IEEE Transactions on Plasma science, Vol. 19 (1991), page 309-323 and 1063-1077 (these reports being incorporated herein for all purposes by way of reference). It is to be noted that a characteristic of the silent discharge is the presence of a dielectric. Therefore silent gas discharges are also referred to as dielectric barrier discharges.
Plasma pyrolysis of methane has been operated for a long time to produce acetylene and carbon black with hydrogen as a by-product. Such plasma cracking usually requires a thermal plasma. As indicated, transformations via thermal plasma are typically high temperature processes and often requires an extra immmediate quenching step to get a sufficient selectivity of the desired products. This induces a complex system. A lot of energy is thereby consumed and wasted respectively due to the heating and cooling of the reaction gases that reduces the energy-efficiency and leads though to an significant increase of the production costs.
Recently, non-thermal plasmas have been found to be effective in the activation of methane at low temperature and atmospheric pressure. Thus, in a report by L. M. Zhou, B. Xue, U. Kogelschatz and B. Eliasson in Plasma Chemistry and Plasma Processing, Vol. 18 (1998), No. 3, 375-393 (this report being incorporated herein for all purposes by way of reference) and in DE 196 05 547 a method of producing methanol by subjecting a gaseous mixture containing methane and oxygen and/or nitrogen to a dielectric barrier discharge is disclosed. In the attempt to shift the selectivity towards the formation of higher hydrocarbons the inventors of the above-mentioned DE 196 05 547 conducted a series of experiments, in which pure methane was submitted to a dielectric barrier discharge (B. Eliasson, U. Kogelschatz, E. Killer and A. Bill in Proceedings of the 11th World Hydrogen Energy Conference, Stuttgart, Germany, Jun. 23-28, 1996, Vol. 3, 2449-2459; this report being incorporated herein for all purposes by way of reference). The major products were hydrogen and ethane with small amount of higher hydrocarbons. However, carbon black in fine particles was formed, in particular, on the surface of the dielectric material. The formation of carbon black is highly undesired since it changes the performance of the dielectric barrier discharge plasma and induces some uncertain phenomena for long term operation.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide for a method of transforming a normally gaseous composition consisting essentially of methane into higher hydrocarbon products, particularly, into a material comprising a major portion, at least, of hydrocarbons containing at least two carbon atoms, which method can be carried out economically, at low pressures and low temperatures and preferably at ambient conditions.
It is another object of the present invention to provide for a method, which transforms a normally gaseous composition consisting essentially of methane in reasonable yields, and particularly, in a direct manner into higher hydrocarbon products.
It is a further object of the present invention to provide for a method of transforming a normally gaseous mixture consisting essentially of normally gaseous hydrocarbons into products at least a portion of which contain normally liquid hydrocarbons, which method can be carried out economically, at low pressures and low temperatures.
It is another object of the present invention to provide for a method that produces normally liquid hydrocarbons in reasonable yields from normally gaseous hydrocarbons. A further object of the present invention is a method for transforming normally gaseous hydrocarbons into normally liquid hydrocarbons, which liquid hydrocarbons are free of sulfur and heavy metal elements.
It
Eliasson Baldur
Killer Eric
Liu Chang-jun
ABB Research Ltd.
Blank Rome Comisky & McCauley LLP
Parsa J.
Richter Johann
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