REACTIVE DISTILLATION

Reactive distillation combines reactions and distillation in a single column. The reaction can be thermal, homogeneously or heterogeneously catalysed. In the latter case the catalyst is fixed in the distillation column in various ways. Many process applications are described by Harmsen, notably hydrogenations of crude oil fractions and etherifications in refineries and bulk chemical plants [1]. 
Reactive distillation has been known in the base chemicals industry for over 60 years.

The first commercial scale application at Shell was back in 1953 [2]. Eastman Chemical installed a large reactive extractive distillation for the production of methyl acetate in 1983 and also explained the complete scale-up method and history [3]. These reactive distillations however did not receive any significant follow-up in the petrochemicals and oil refinery industry. This changed when the technology provider CDTECH brought their catalytic distillation technology to the market. Their first commercial scale implementation was a hydrogenation at the Shell Motiva oil refinery in 1987 [1]. It was a revamp of an existing distillation column, using the Texas tea bags catalyst technology of CDTECH. Heterogeneous catalyst particles inside porous bags where placed on the distillation trays.
CDTECH had a total of 123 implementations in 2007, of which 60 were etherifications [1]. On their present website they report more than 100 implemented etherifications [4], an increase of 40. For the other applications the website provides no new data. This means then that CDTECH has installed more than 160 reactive distillations.
Sulzer does not give numbers of implementations on their website or otherwise. They only gave implemented RD per process type to me in 2007 and for each application the region of implementation [1]. If each process type and per region is installed once only then they have installed at least 10 commercial scale RDs. It is interesting to note that BASF has installed more than 50 RD [5]. Whether this is all by in-house development or whether some have been obtained from Sulzer is not reported.
It can then be concluded that the total number of RD's installed by the CDTECH and Sulzer Chemtech is well over 170.

Concept design methods are provided in text books. The most recent one is by Luyben [6]. Detailed design knowledge is available from CDTECH and Sulzer Chemtech. Scale-up methods applied for novel applications are brute force pilot plant design and model based pilot plant design [1]. Brute force involves a scaled-down pilot plant with all conditions and parameters the same as the commercial scale design, except for the column diameter. This method is mostly applied for oil refinery applications where detailed kinetic information of all reactions is not available. The model based scale-up method involves a scaled-down pilot plant where the structured catalytic packing is also reduced in size so that the height of the pilot plant can also be reduced. Mass transfer and residence time distribution characteristics of the packing are known so the design process model can be disproven or validated with pilot plant test results.

By Jan Harmsen (Harmsen Consultancy BV)