The reactor is the heart of any sulphonation process.
By sulphonation, the industry identifies a set of processes based on reaction between a sulphur trioxide stream in air and an organic base. A large number of end products may be manufactured for use in detergent, toiletry and cosmetic industry.
The largest applications are for production of sulphonated alkylbenzene, for sulphonation of fatty alcohols, the latter in the alcohol form or extended with a 2-moles or 3-moles ethoxylated tail, or for sulphonation of alpha olefins.
Reaction takes place in a multi-tube reactor where the sulphur trioxide stream and the organic are conveyed in co-current. In each tube, a thin film of liquid falls down along the tube inner surface.
The gaseous stream runs along the tube in contact with the organic as necessary to react almost all the sulphur trioxide with the organic base.
To obtain a high quality product, vital features are the formation of the film by experienced calibration, the uniform and homogeneous falling rate in the tubes and the contact time SO3/organic to avoid early contact between the two reacting chemicals.
These features require high accuracy in the machining and in the construction, as well as a step-by-step approach to the manufacturing process, whereby each piece of the reactor is subject to accurate dimensional and constructional appraisal before green light be given for the progress of the construction.
The quality of the product is specified under a set of parameters, linked to the unreacted organic, to the formation of undesired side reaction products, such as sulphuric acid, and to colour.
These deviations from the performance are however caused more often by insufficient process control than by the reactor itself.
In general, a well constructed and calibrated reactor is the last factor causing a trouble in a troublesome sulphonation process.
The reaction develops heat that has to be removed to protect the integrity of the process and to limit the temperature of the product.
At this aim, the tube bundle is enclosed in a stainless steel envelope, behaving as a shell in a heat exchanger. The shell is full of cooling water held in circulation by a dedicated pump. The circulation is maintained at different rates in different segments of the shell in order to match the heat removal requirement along the reaction tubes. A well controlled temperature profile along the reaction path is obtained by a good reactor shell segmental control.