Dehydration of 2-Propanol to Propene

A microchannel reactor designed for periodic operation and a process to deposit alumina as a catalyst inside the reactor channels can also be used for the dehydration of 2-propanol to propene [23]. 

Propose a mechanism for the acid-catalyzed dehydration of 2-propanol to propene. 

The coupled set of non-linear, ordinary differential equations governing the dehydration of 1-propanol to propene by the E2 mechanism (omitting for the moment the formation of 2-propanol) is given by... 

Figures 2a and 2b display the acid catalyzed E2 and El mechanisms for the dehydration of 1-propanol and 2-propanol. Note that the El mechanism involves four more rate constants (kinetic parameters) than the related E2 dehydration mechanism. Chemists employ the terminology (1) Adg3 to describe the hydration mechanism which forms 2-propanol from propene in Figure 2a, and Ad 2 to refer to the mechanism which forms 2-propanol from propene in Figure 2b. In this paper we do not distinguish between bare carbocations, Il-complexes, encumbered carbocations and symmetrically solvated carbocations, since these intermediates all manifest themselves similarly in the El kinetic model.

A first approach to the problem has been the development, by Mitsui Petrochemical, of a recycle scheme for converting the acetone back into propene (via hydrogenation to 2-propanol and subsequent dehydration of the latter) to be added to the feed of the alkylation step (Scheme 13.1). 

Removal of the elements of water (i.e. hydrogen and oxygen in a 2 1 ratio) to form a new compound. An example is the dehydration of propanol to propene over hot pumice ... 

Note that a total of 36 independent concentration measurements are available to estimate the values of eight to twelve kinetic parameters (i.e. the number of degrees of freedom ranges from 24 to 28). The trial mechanisms tested in this work include (i) the E2 mechanism for 1-propanol dehydration combined with the Adj 3 mechanism for 2-propanol formation from propene (E2AdE3)/ (ii) the El mechanism for 1-propanol dehydration and the Adg2 mechanism for 2-propanol formation (ElAdE2)/ (iii) the E2 mechanism for... 

Neither the AdE3 nor the AdE2 mechanism is consistent with available data concerning the acid catalyzed hydration of propene to 2-propanol in supercritical water at 375 C and 34.5 MPa. More data are being accumulated to sustain a rigorous kinetic examination of the hydration/dehydration mechanism. 

The dehydrogenation reaction produces acetone and hydrogen, and is dominant over basic oxides ( ) The dehydration reaction produces propene and water, and is dominant over acidic oxides. It would be interesting to see if the competition between these two pathways depend on the exposed crystal planes of ZnO. We report here the results of such an investigation. 2-Propanol was decomposed on ZnO single crystal surfaces by the temperature programmed decomposition technique. To assist the interpretation of data, the temperature programmed desorption of propene and acetone were also studied. 

The product profiles for 2-propanol dehydration on VOAIPO4 show only one product (propene) but for methanol reaction (Fig.6) on the same catalyst shows two types of products (DME and C2+ hydrocarbons). But within 40-45 mol% conversion the decomposition product is negligible. As it is marked both DME and C2+ are present from the onset of the reaction which indicate that both reaction products are formed by direct dehydration. The downward deviation marked, in case of DME plot indicates the instability of the product. It means DME further dehydrates to C2+ hydrocarbons in a secondary reaction. All other catalysts also show nearly similar behaviour. Thus the path way for the formation of C2+ hydrocarbons on M0.05AI095PO4 catalysts is a combination of parallel and consecutive (primary and secondary) reactions. 

The production of different labeling patterns in the products from the addition of 1-propanol and 2-propanol permits some definition of the structure of the species derived from propanol that functions as initiator. First the C3 carbon skeleton remains intact on the catalyst surface. The difference in products precludes dehydration to produce propene which then initiates chain growth if this were to happen, the same products and " C-labeling would be produced from the two alcohols. The loss of the OH group to produce a... 

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