Activity protection during operation of reforming catalysts

In normal operation, in order to keep the plant running for a long time, in addition to reasonable adjustment of process parameters, it is necessary to understand the working performance of the catalyst in order to protect its activity well. The most important of the activity index is to prevent the rapid carbon accumulation of the catalyst, to maintain the bifunctional components of the catalyst and to maintain the balance of water and chlorine.

1) Water-chlorine balance
There are strict requirements for chlorine and water content in catalytic reforming. The purpose of controlling the chlorine content is to control the ratio of the acidic component to the metal component in the bifunctional catalyst. There is a balance between chlorine in the gas phase (feedstock and circulating hydrogen) in the reactor and the chlorine on the catalyst. When the feedstock contains too much chlorine, the chlorine content on the platinum catalyst increases, making the catalyst more acidic. Therefore, there is a limit to the amount of chlorine contained in the feedstock.
A small amount of water in the feedstock or circulating hydrogen ensures good chlorine dispersion, but a large amount of water can lead to chlorine loss on the catalyst. Therefore, the water content in the feedstock should be limited.
The chlorine balance can be maintained by regularly sampling and analyzing the chlorine to water molar ratio from the reactor feed, generated oil and incoming and outgoing gas, or by judging the operation, e.g., whether to inject water or chlorine based on changes in the octane value of the product, the total temperature drop of the reactor, and the purity of the circulating hydrogen. When there is little chlorine on the catalyst, organic chlorides such as dichloroethane and propane chloride can be injected into the feedstock. When there is more chlorine on the catalyst, water can be injected into the raw material (water injection is usually done with alcohols, which can avoid corrosion). When there is much water in the original section, the chlorine should be properly replenished.

2) Reasonable control of carbon accumulation
The effective way to prevent this carbon accumulation is to increase the hydrogen-oil ratio. In any case, the hydrogen-oil ratio should not be lower than the index of the operating procedures, otherwise it will aggravate the carbon accumulation and shorten the operation cycle. It should be noted that it is important to control the initial activity of the fresh reforming catalyst at start-up, as if the strong cracking of the fresh catalyst is not controlled, carbon will be generated rapidly and the operating cycle will be affected.

3) Control of catalyst poisons
①Inhibit hydrocracking and isomerization poisons
Toxic substances of hydrocracking and isomerization are mainly water and chlorine. When excessive water (or chlorine) contamination occurs during operation, the methane content in the reaction products will drop abruptly.
An effective way to control water contamination is to enhance system drying and feedstock dehydration. When the water content of the system is found to be too high, the reaction temperature should be lowered appropriately and the operation of the pre-hydrogenation steam tower should be adjusted until the water content is acceptable, and then the temperature should be gradually raised to the required reaction temperature. To counteract the effect of water when necessary, the method of chlorine injection is often used to add organic chlorides to the raw material.
②The most common inhibitor of enhanced cracking activity is chlorine, and excess chlorine can upset the bifunctional balance of the reforming catalyst. In order to wash away chlorine from the catalyst or to suppress excess chlorine in the feedstock, water injection can be used.