Catalyst change outs are a necessary evil in the oil refining industry. Next to the fact that they are expensive and time consuming, they also require an extensive amount of

high-tech expertise and specialist safety measures onsite.

Traditionally catalysts come in an inactive/inert form, based mostly one a metal-oxide composition. To activate them, a defined quantity of sulphur is required on the catalyst surface.

To keep the time and costs of the shutdown and change-out of catalysts as low as possible, this process needs to be carried out in the minimum time, with the highest degree of safety.

There are several ways to add sulphur to the catalyst surface. One of them is by starting the unit up with a sulphur-rich feed stream. The highest risk will be that on start-up of a new catalyst with sulphur-rich feed, the possible poisoning contaminants reach the catalyst surface more rapidly than the sulphur, and the efficiency is already reduced before the catalyst is taken in use.

An alternative for many years has been the use of di-methyl di-sulphide (DMDS). There are several dangers associated with DMDS, which make it difficult to produce, transport, store and apply.

Due to its extremely low flash point of 16°C, this product requires many precautions in the potentially high-risk environment of a refinery, especially at re-start time after a shutdown. Special containers and transport are required to transfer this material from the DMDS production location to the customer.

Transportation needs to be at times of the day when there is low traffic pressure on the roads. Temporary storage of this product on the customer’s site requires special attention. People applying the product as well as people in the immediate surroundings of the application site require space suit like fire-protective clothing. Last but not least, this product has an extremely unpleasant odour, which can be a nuisance for the surrounding community as well as workers. DMDS producers are now incorporating additives to the product to mask the unpleasant odour, thus creating a so-called next generation DMDS. However, these additives are often serious hazards too, so the problems associated with DMDS remain.

The Lubrizol Corporation, a major producer of process additives, has carefully looked at the catalyst sulphiding hazards and obstacles that occur when applying DMDS.

As a result, it has developed a sulphur-rich product that contains practically none of the above-mentioned hazardous properties, or the negative aspects associated with DMDS. The product, branded SulfrZol54, is a polysulphide chemical, trapped in a bridge of t-butyl groups, designed specifically for in-situ catalyst pre-sulphiding.

Thanks to its significantly higher flash point of 100?C, SulfrZol 54 is much safer to work with than DMDS. Consequently, no special measures are required for production, packaging, transportation and storage and no special clothing is necessary.

SulfrZol 54 also has no unpleasant odour. The normal diesel-like smell originates from the chemistry itself. No environmentally unfriendly odour masking agents are applied. A minor inconvenience, says the company, is the lower sulphur content when compared to DMDS (~54percentv~65percent), which results in a small extra dosage being required to obtain the same amount of sulphur available for the catalyst.

Lubrizol and catalyst manufacturers worldwide have cooperated in the development and testing of the new product as a catalyst sulphiding agent, and as a possible alternative to DMDS.

Based on those tests, says Lubrizol, all catalyst producers have concluded that it is an acceptable and efficient alternative. Although for some exceptional applications the product has not yet been tested and approved by all catalyst manufacturers, theoretically there is no limitation to its use for much safer and user-friendly catalyst sulphiding processes.

The product has already been successfully applied for catalyst sulphiding by many major European refineries such as Exxon, Tamoil, Shell (in several countries), Czech Refinery, Nynas, Repsol and several more. Lubrizol says that catalyst producers/developers as well as operators/managers of a (sulphur activated) catalyst bed who have used SulfrZol54 have reported positive feedback on its ease of use.

Brenntag Oil & Gas is the official, virtual worldwide distributor on behalf of the Lubrizol Corporation for SulfrZol54 (Fig.1). The company also now offers catalyst sulphiding injection services onsite on a turnkey basis, if requested by the client. In fact, says Brenntag, since the level of risks accompanied with the use of SulfrZol54 is so low, the refinery staff or catalyst manufacturers staff can inject it with a regular high-pressure pump themselves.

SulfrZol54 can also be applied as an anti-coking agent in (ethylene) crackers, by continuous injection to avoid deposit formation.

Unlike DMDS, which needs to be placed under nitrogen pressure in closed IBC containers to reduce its smell and to reduce the low flashpoint dangers, SulfrZol54 can be stored onsite in regular containers and does not need to be in a closed system, which is again a safety advantage.

Overall, therefore, the company believes that its new sulphiding solution should provide a welcome alternative to traditional chemicals, while at the same time doing away with the need for DMDS and the safety implications associated with it.