HOT PASSIVATION

Rust as an oxygen carrier benefits peroxide and polymer formation during the storage or processing and finishing of butadiene.  The "Plastic Polymer" - a somewhat rubbery polymer - preferably forms in the liquid phase of 1.3-butadiene. The solid, white "Popcorn Polymer", on the other hand, forms in the gas phase. The growth of the popcorn polymer is self-initiating, in other words once a polymer has formed it continues to grow rapidly.

The popcorn polymer in particular causes choking, and lines or tanks can even burst under unfavourable conditions. If unalloyed steel is used as a construction material for systems that are to carry 1.3-butadiene, appropriate measures thus have to betaken to exclude the presence of oxygen (carriers) in the system.

Apart from an adequate stabilisation of the 1.3-butadiense, rust removal (pickling) and subsequent passivation are decisive steps to exclude an unwanted polymer formation, particularly in new plants. Pickling can be easily carried out with acetic or other acids. In accordance with the set goal of avoiding the introduction of oxygen carriers, the active surface produced by pickling is not passivated with hydrogen peroxide (oxygen radicals) but with sodium nitrite. Nitrite rinsing is carried out at temperatures of a least 90 degrees Celsius to accelerate the reaction. The reaction process is constantly monitored by laboratory analyses. Sampling and analysis is carried out on-the-spot by Lobbe personnel to ensure real-time controls.

Lobbe has helped hot passivation to a successful comeback over the past few years. A series of reference orders underlines both the competence of Lobbe and the efficiency of the method. Lobbe developed the special basic equipment that is needed itself. Standard technology is normally leased on site to reduce costs. Passivation work is in principle carried out by Lobbe around the clock in multi-shift work. References