Process and apparatus for operation of a slurry bubble column with application to the fischer-tropsch synthesis

#The present invention concerns a process for optimal operation of a slurry bubble column containing three phases, namely a liquid phase, a solid phase and a gas phase. In this type of column, particles are held in suspension in the liquid by introducing gas bubbles close to the lower portion of the column. The present invention also concerns an apparatus for operating the bubble column under the optimal conditions of the present process. It also concerns the application of this process and apparatus to the synthesis of essentially linear and saturated hydrocarbons, preferably containing at least 5 carbon atoms per molecule, by reduction of synthesis gas CO--(CO.sub.2)--H.sub.2, i.e., a mixture of carbon monoxide and hydrogen, and optionally carbon dioxide, using the Fischer-Tropsch process. More particularly, the present invention is applicable to exothermic reactions which occur at high temperature, for example above 100.degree. C., normally above 150.degree. C., and generally at an absolute pressure of more than 0.1 megapascals (MPa), normally above 0.5 MPa. Among these reactions are hydrogenations, aromatizations, hydrodesulphurization, hydrodenitrogenation, hydrotreatments, in particular the hydrotreatment of residues, and hydroformylation. Such reactions are described, for example, in the book by J. F. LePage published by Technip in 1987, entitled "Applied Heterogeneous Catalysis". The present invention is particularly applicable to hydrogenation reactions. The invention was developed for application to hydrogenation of carbon monoxide and is particularly suitable thereto; it constitutes the preferred field of application of the present invention.

#Bubble columns comprise a liquid medium containing solid particles in suspension, the majority in general being catalytic particles, and comprise at least one means for introducing at least one gas phase of reactants by means of at least one distribution means which produces bubbles of gas generally of small diameter, namely (by way of indication) 0.5 to 20 mm in diameter. These gas bubbles rise in the column and the reactants are absorbed by the liquid and diffuse towards the catalyst, in contact with which the reactants are converted into gaseous and/or liquid products formed depending on the conditions of the reaction and the type of catalyst. The gaseous products comprising the unconverted gaseous reactants and the gaseous products formed during the reaction are collected close to the top of the column and the suspension containing the liquid which forms the suspension of catalyst and the liquid products formed during the reaction is recovered via a line located near the upper level of the suspension in the column. The solid particles are then separated from the liquid using any method which is known to the skilled person, for example filtering, to recover the liquid products formed during the reaction.

#In the case of highly exothermic reactions such as the Fischer-Tropsch process, bubble columns used as a slurry reactor are generally preferred to reactors operating as a fixed bed reactor. In particular, this technique can produce better heat transfer coefficients, better temperature homogeneity and small pressure drops. However, this reactor technology has a major disadvantage which is known to the skilled person: the productivity of the catalyst is limited, in particular when the diameter of the reactor is increased or the linear velocity of the gases is increased.

#FIGS. 1 to 3 illustrate the invention. The same elements are given the same reference numerals.

#FIG. 4 is a graph of linear gas velocity versus conversion for a slurry reactor (A) and a conventional bubble column (B).

#In FIG. 1, a reactor R1 comprises a conduit 1 for introduction of gaseous reactant(s) into a gas bubble distributor D1, an outlet conduit 2 for gas formed during the reaction and residual gases which are not transformed during the reaction, and a conduit 3 for recovering a portion of the suspension. Reactor R1 comprises a heat exchanger E1 supplied by an exchange fluid via a line 4 which is recovered via a line 5. It comprises a draft tube 7 for circulating the suspension.

#FIG. 2 shows a reactor with natural external circulation comprising a line 10 for recirculating the suspension. Line 10 opens into a chamber containing a heat exchanger Ec supplied with heat transfer fluid via a line 8. The heat transfer fluid is recovered after exchanging heat via a line 9. The cooled suspension leaves the heat exchange zone external to reactor R1 via a line 11 and is reintroduced into reactor R1.

#FIG. 3 schematically illustrates the case of mechanically assisted circulation using a pump P1.