Andrussow process

Abstract: The effect of hydrogen addition on HCN production by the ammoxidation of methane over Pt–Rh gauze catalyst has been examined. Upon adding small amounts of H2, the HCN selectivity increased from ∼74 to 82% on NH3 basis at 35% N2 dilution and (CH4+NH3)/O2=2, while selectivities on CH4 basis were nearly unchanged. Using air instead of oxygen, the HCN selectivity increased from 76 to 86%. However, the increase in HCN selectivity with H2 addition was accompanied by a decrease in the NH3 conversion. H2 addition with different (CH4+NH3)/O2 and CH4/NH3 ratios and with preheating of feed gases has also been investigated. The H2 produced was observed to be greater than that fed for all conditions, so that with recycle the process would require no additional source of H2. Experimental results obtained here can be qualitatively explained on the basis of a surface reaction model for Andrussow reactor described previously.

Abstract: Primary O 2 –NH 3 –CH 4 interactions in the Andrussow process were investigated in the temporal analysis of products (TAP) reactor over three commercial Pt-Rh gauzes having been applied for different times on-stream in this reaction (fresh, activated and spent catalysts). The gauzes were characterized by scanning electron microscopy combined with energy dispersive X-ray analysis. It was established that they underwent severe morphological changes including deposition of various impurities with increasing time on-stream. Content and type of these impurities possess local variations. However, the near-to-surface Pt/Rh ratio of the deposit-free areas does not change with time on-stream. These areas are strongly faceted on the spent Pt-Rh gauze. Despite the gauzes differ in their morphology and in the content of impurities, the overall scheme of HCN production via oxidative coupling of CH 4 and NH 3 is valid for all the gauzes studied. Nitric oxide primarily formed via ammonia oxidation reacts further with methane and ammonia yielding hydrogen cyanide and nitrogen, respectively. The formed HCN is consecutively converted to N 2 . The surface restructuring, coverage by oxygen species and/or the presence of iron oxide influence the interplay between the reaction pathways leading to HCN and its further transformations.

Abstract: Reaction pathways governing HCN selectivity in the oxidative coupling of methane and ammonia were investigated over three commercial Pt–Rh gauzes (fresh, activated, and spent) in the temporal analysis of products reactor with submillisecond-time resolution using isotopic traces. These gauzes differed in the extent of reaction-induced restructuring as well as impurity content. The ability of the gauzes to form HCN in the dual interactions of CH4 with NH3 or NO was compared considering the morphological differences of the gauzes. It was found that the progressive structural changes increased the gauze activity for methane conversion and facilitate the stabilization of methane fragments on the catalyst surface, but did not influence significantly the surface residence time of N-containing species. The well-known increase in HCN selectivity within first hours on-stream in the Andrussow process was suggested to be likely due to restructuring-induced stabilization of surface methane fragments. The decrease in the HCN selectivity after a stable phase of operation is mainly related to consecutive oxidation of HCN over iron oxide accumulated on the catalyst surface under industrial conditions of the Andrussow process.

Abstract: A reactor for preparing hydrogen cyanide by the Andrussow process is provided. The reactor comprises at least one gas inlet which opens into a gas inlet region, an outlet for the reaction products and a catalyst, wherein at least one mixing element and at least one gas-permeable intermediate layer are within the reactor between the gas inlet region and the catalyst. The mixing element is arranged between the gas inlet region and the gas-permeable intermediate layer. A process for preparing HCN, in the reactor is also provided.