Device and process for the production of hydrogen and solid carbon from C1- to C4-alkane containing gas

A process for the production of hydrogen and solid carbon from C1- to C4-alkane-containing gas by means of thermal plasma, wherein the process comprises the steps of:

• a) withdrawing a C1- to C4-alkane-containing plasma gas from a device for providing a C1- to C4-alkane-containing gas;
• b) introducing the C1- to C4-alkane-containing plasma gas withdrawn from the device for providing a C1- to C4-alkane-containing plasma gas into at least a first reactor;
• wherein said reactor is a reactor for generating a thermal plasma by means of an electric arc, said reactor comprising
• i) a plasma section comprising
• an anode and a cathode for generating an electric arc, the arc extending within the plasma section, and
• at least one first feed line for introducing a C1- to C4-alkane-containing plasma gas into the plasma section of the reactor,
• wherein the anode has a hollow channel along a flow direction of a main stream of the plasma gas which has an inner surface, an outlet in the flow direction of the main stream of the plasma gas which forms an open end of the anode in the flow direction of the main stream, and at least one inlet for receiving the C1- to C4-alkane-containing plasma gas introduced into the plasma section of the reactor via the at least one first feed line, wherein the at least one inlet forms an open end of the anode facing into the direction opposite to the flow direction to the main stream, and wherein the anode is configured such that the plasma gas flows through the hollow channel via the open end of the anode facing into the direction opposite to the flow direction of the main stream and the open end of the anode in the flow direction of the main stream, wherein the plasma gas contacts the inner surface of the hollow channel of the anode during passage through the anode, and
• wherein said anode and said cathode are arranged so that the arc generated by said anode and cathode is formed in said plasma section to form a plasmaeous plasma gas in said plasma section from the C1- to C4-alkane-containing plasma gas introduced into said plasma section through said at least one first feed line, and wherein foot points of the electric arc contacting the anode are located on the inner surface of the hollow channel of the anode, and
• ii) a second reactor section directly downstream of the plasma section of the reactor in the flow direction of the main stream, the second reactor section comprising
• a first subsection and a second subsection, wherein the second subsection is directly downstream of the first subsection in the flow direction of the main stream, and
• outlet means for withdrawing components from the reactor, wherein the outlet means are located at the end of the second reactor section in the flow direction of the main stream, and
• the first subsection comprises at least one second feed line for introducing a C1- to C4-alkane-containing gas into the second reactor section, wherein the position of the at least one second feed line along the flow direction of the main stream defines a beginning of the second reactor section and of its first subsection,
• and wherein the C1- to C4-alkane-containing plasma gas is introduced into the reactor via the at least one first feed line for introducing a C1- to C4-alkane-containing plasma gas into the plasma section of the reactor;
• c) generating an electric arc with the anode and cathode extending within the plasma section of the reactor;
• d) forming a plasmaeous plasma gas in the plasma section of the reactor by means of the electric arc from the C1- to C4-alkane-containing plasma gas introduced into the plasma section via the at least one first feed line for introducing a C1- to C4-alkane-containing plasma gas into the plasma section;
• e) introducing a C1- to C4-alkane-containing gas into the first subsection of the second reactor section via the at least one second feed line for introducing a C1- to C4-alkane-containing gas into the second reactor section, wherein
• the introduction is carried out in such a way that the C1- to C4-alkane-containing gas, which is introduced into the second reactor section via the at least one second feed line, is introduced into the plasmaeous plasma gas in the flow direction of the main stream downstream of the foot points of the electric arc produced by the anode and cathode, so that in the first subsection of the second reactor section downstream of the at least one second feed line a mixture is formed from the plasmaeous plasma gas leaving the plasma section and the C1- to C4-alkane-containing gas which is introduced into the first subsection of the second reactor section via the at least one second feed line, wherein
• the plasmaeous plasma gas at the position at which the C1- to C4-alkane-containing gas is introduced into the plasmaeous plasma gas via the at least one second feed line has a mean temperature in the range of 1200 to 3000° C. and comprises acetylene, thereby forming a mixture resulting from the introduction of the C1- to C4-alkane-containing gas via the at least one second feed line into the plasmaeous plasma gas which has in the range from the at least one second feed line down to the end of the first subsection of the second reactor section a mean temperature of at least 850° C., and less than 3000° C.;
• f) passing the mixture downstream through the second reactor section in the flow direction of the main stream, wherein
• said passing is such that in the first subsection of the second reactor section the mean residence time of the atoms of the mixture resulting from the plasmaeous plasma gas leaving the plasma section and the C1- to C4-alkane-containing gas of the at least one second feed line is in the range of 100 ms to 2000 ms, and
• the passing is such that in the total second reactor section the mean residence time of the atoms of the mixture resulting from the plasmaeous plasma gas leaving the plasma section and the C1- to C4-alkane-containing gas of the at least one second feed line is in the range of 200 ms to 20000 ms, and
• at least 5% of the atoms of the mixture resulting from the plasmaeous plasma gas leaving the plasma section and the C1- to C4-alkane-containing gas of the at least one second feed line have a residence time in the second reactor section which deviates in absolute numbers by at least 5% from the mean residence time of all atoms of the mixture resulting from the plasmaeous plasma gas leaving the plasma section and the C1- to C4-alkane-containing gas of the at least one second feed line in the second reactor section, and
• hydrogen and solid carbon are produced by the reactions taking place in the mixture in the second reactor section;
• g) adjusting the mean temperature of the mixture in the second subsection of the second reactor section to at least 650° C., wherein the mean temperature of the mixture of the plasmaeous plasma gas and the C1- to C4-alkane-containing gas introduced via the at least second feed line at the end of the second reactor section is adjusted to a mean temperature which is at least 200 K lower than the mean temperature of the plasmaeous plasma gas at the position at which the C1- to C4-alkane-containing gas is introduced into the plasmaeous plasma gas via the at least one second feed line;
• and
• h) withdrawing the mixture at the end of the reactor via outlet means for withdrawing the mixture from the reactor, wherein the outlet means are located at the end of the second reactor section in the flow direction of the main stream.