Gas/solid phase reaction

Abstract

The invention relates to a process and reactor for the quasi-continuous performance of a chemical reaction on the surface of a fixed reactant in a gas/solid phase reaction. In particular, the invention relates to a thermal process and a reactor for the continuous preparation of hydrogen from water vapor on the surface of a metal oxide in a gas/solid phase reaction.

1 . A process for the quasi-continuous performance of a chemical reaction consisting of at least two sequential reversible steps, characterized in that:
 at least two reaction chambers in each of which at least one reactant is locally fixed are operated in parallel, wherein   cyclically alternating reaction conditions are provided in the reaction chambers.   
   
   
       2 . The process according to  claim 1 , characterized in that radiation-heated reactors are employed as reaction chambers. 
   
   
       3 . The process according to  claim 1 , characterized in that said cyclically alternating reaction conditions are provided by cycling the temperature of the reaction chambers, especially by varying the heating power. 
   
   
       4 . The process according to  claim 3 , characterized in that the reaction chambers are shifted relative to the radiation source. 
   
   
       5 . The process according to  claim 1 , characterized in that a temperature within a range of from 500° C. to 1000° C., especially up to 900° C., is set in a first reaction chamber, and a temperature within a range of from 1000° C. to 1400° C. is set in a second reaction chamber. 
   
   
       6 . The process according to  claim 1 , characterized in that fossil energy, electric energy, light energy and/or nuclear energy is employed. 
   
   
       7 . The process according to  claim 1 , characterized in that a chemical compound having redox properties is employed as said fixed reactant. 
   
   
       8 . The process according to  claim 7 , characterized in that said chemical compound having redox properties is employed as a coating of a heat-resistant ceramic support structure. 
   
   
       9 . The process according to  claim 7 , characterized in that a support structure having a conical, hemispherical, cylindrical or paraboloid shape is employed. 
   
   
       10 . The process according to  claim 1  for producing hydrogen from water vapor on a surface of at least one chemical compound having redox properties, wherein:
 in the first step, water vapor is thermally split by associating oxygen to the chemical compound having redox properties to release hydrogen; and   in the second step, the chemical compound having redox properties is regenerated at a temperature which is higher than that of the first step to release bound oxygen.   
   
   
       11 . The process according to  claim 1  for the quasi-continuous production of hydrogen from water vapor on a surface of a metal oxide followed by regeneration of the surface. 
   
   
       12 . A thermal process for the preparation of hydrogen from water vapor on a surface of at least one metal oxide in a gas/solid phase reaction, wherein in a reaction chamber:
 in a first step, water vapor is split thermally by associating oxygen to the excited metal oxide to release hydrogen, and   in a second step, the metal oxide is regenerated at a temperature which is higher than that of the first step to release bound oxygen, so that the metal oxide is available for further reactions.   
   
   
       13 . The process according to  claim 12 , wherein water vapor is split at a temperature within a range of from 500 to 1000° C., especially from 550 to 850° C., and the metal oxide is regenerated at a temperature within a range of from 1000 to 1400° C., especially from 1050 to 1350° C. 
   
   
       14 . The process according to  claim 12 , wherein a cyclic alternation of the temperature of the metal oxide is set by varying the heating power in accordance with the different energy demands of the involved reactions to be performed sequentially. 
   
   
       15 . The process according to  claim 12 , wherein the required temperature is generated by burning fossil energy carriers and/or utilizing electric energy. 
   
   
       16 . The process according to  claim 12 , wherein the required temperature is generated by light energy. 
   
   
       17 . The process according to  claim 12 , wherein sunlight is irradiated into the reaction chamber by means of optical set-ups to generate the required temperature. 
   
   
       18 . The process according to  claim 16 , wherein the reaction chamber is shifted relative to the radiation source in order to vary the heating power. 
   
   
       19 . The process according to  claim 16 , wherein the position of the reaction chamber is changed relative to the optical set-up to vary the heating power. 
   
   
       20 . The process according to  claim 12 , wherein optical components which reduce the irradiation are used to vary the solar-thermal heating power. 
   
   
       21 . The process according to  claim 20 , wherein the absorbed energy of the optical component is utilized for heating fluids. 
   
   
       22 . A thermal process for the quasi-continuous production of hydrogen from water vapor on a surface of a metal oxide followed by regeneration of the surface according to the preceding claims, wherein the production of hydrogen is performed in at least two reaction chambers. 
   
   
       23 . The process according to  claim 22 , wherein the required temperature in the reaction chambers is varied by periodically changing the heating power to enable a quasi-continuous product stream. 
   
   
       24 . A photoreactor for performing the process according to  claim 1 , characterized by having two reaction chambers. 
   
   
       25 . A reactor for the thermal preparation of hydrogen from water vapor on a surface in a gas/solid phase reaction comprising at least one connected tube that enables a gas stream of educt gases to flow into a reaction chamber and of product gases to flow out, and a heat source, said reaction chamber comprising at least one metal oxide as a reactant. 
   
   
       26 . The reactor according to  claim 25 , wherein the metal oxide is coated on a heat-resistant ceramic support structure. 
   
   
       27 . The reactor according to  claim 26 , wherein said support structure includes a porous honeycomb structure. 
   
   
       28 . The reactor according to  claim 25 , wherein said metal oxides include iron mixed oxides. 
   
   
       29 . The reactor according to  claim 25 , wherein said metal oxides include ferrites, zinc oxides, lanthanum oxides, cerium oxides, lanthanoide oxides and/or manganese oxides. 
   
   
       30 . The reactor according to  claim 25 , wherein said metal oxides correspond to general formula Me x   2+ Zn 1-   x   2+ Fe 2 O 4 , wherein Me x   2+  is a divalent metal ion selected from the group of Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Sr, Sn, Ba, Cd, Pb or lanthanoides. 
   
   
       31 . The reactor according to  claim 25 , wherein said metal oxides include mixtures of said metal oxides. 
   
   
       32 . The reactor according to  claim 25 , wherein said reaction chamber contains a transparent window. 
   
   
       33 . The reactor according to  claim 25 , wherein tubes that attenuate the energy flow run between the reaction chamber and energy source. 
   
   
       34 . The reactor according to  claim 33 , wherein said tubes contain a fluid. 
   
   
       35 . The reactor according to  claim 25 , comprising a multiport valve for supplying the gaseous educts. 
   
   
       36 . The reactor according to  claim 25 , comprising a multiport valve for separating the gaseous products. 
   
   
       37 . The reactor according to  claim 25 , wherein said reactor has a modular structure consisting of at least two reaction chambers. 
   
   
       38 . The reactor according to  claim 25 , comprising a multiport valve by which the reaction chambers are alternately supplied with water vapor or nitrogen, and a switching mode that enables a hydrogen production constant in time. 
   
   
       39 . The reactor according to  claim 25 , comprising concentrating solar-thermal systems, especially solar tower systems, paraboloid concentrators, sun ovens, elliptical or spherical mirrors or line-focusing concentrators, as the energy source. 
   
   
       40 . The reactor according to  claim 39 , comprising a first group of heliostats for achieving the radiated power and a second group of heliostats for achieving the radiated power required for regeneration, the focus of the second group of heliostats being rearrangeable onto individual reaction fields.