Today 90% of the chemical industry contains catalyst processes, which increase the reaction rate and selectivity in production. With the increase of industrial production time, the catalyst will be deactivated, which is a decrease in the rate of the catalytic reaction. The editor tells you how to regenerate the activity of the deactivated catalyst to produce better economic and environmental benefits.
Catalyst deactivation is a phenomenon in which the conversion rate of a catalytic reaction carried out under constant reaction conditions decreases with time. The catalyst deactivation process is divided into three types: chemical, thermal, and mechanical.
- Chemical inactivation
Coking (coking) surface area is reduced, clogging
Metal contamination Reduced surface area and reduced catalytic activity
Poison adsorption, active site reduction
- Heat inactivation
- Mechanical inactivation
Particle breakage Channeling and blockage of catalyst bed
Reduced surface area
- Catalyst regeneration
The general rule of industrial catalyst regeneration is that every time it is regenerated, its activity will be lower than the original activity. The operating temperature of the regenerated catalyst is significantly higher than that before regeneration. In addition, it is impossible for the deactivated catalyst to be frequently and endlessly repeated. Regeneration will eventually need to be replaced.
- Regeneration after coking (coking) deactivation:
During the use of the catalyst, the process of reducing the activity of the catalyst due to the gradual formation of carbon deposits on the surface.
Charcoal burning (air + water vapor) is commonly used in industrial catalysts after the deactivation of coke deposits
By oxidizing the carbon-containing deposits in the catalyst pores into carbon monoxide and carbon dioxide, the catalytic activity can be restored.
In the purge method, the organic by-products of carbon deposition, mechanical dust and impurities that are not very serious, block the pores of the catalyst or cover the active centers of the catalyst surface, and can be removed by the purge method in situ.
Matters needing attention during regeneration:
The regeneration temperature and time are well adjusted to prevent the catalyst from sintering; the regeneration cycle varies with the accumulation rate of coking.
- Metal pollution inactivation and regeneration
The sources of metal pollution are metal compounds in crude oil or coal directly liquefied liquid, metal porphyrin complexes or non-porphyrin compounds, mainly V, Ni, Fe, Cu, Ca, Mg, Na, K, etc.
Before catalyst regeneration
After catalyst regeneration
Prevention method: chemical method or adsorption method to remove porphyrin in raw materials, adding additives (antimony compounds), forming alloys with metal impurities to passivate them.
- Poisoning inactivation and regeneration
A small amount of impurities in the fluid contacted by the catalyst are adsorbed on the activity of the catalyst, and the activity of the catalyst is significantly reduced or even disappeared.
Poisoning is divided into: reversible poisoning, renewable, temporary poisoning;
Prevention measures: remove poisons before entering the reaction section.
- Regeneration after sintering deactivation
The sintering of the catalyst is a phenomenon in which the crystallite size gradually increases or the primary particles grow up during the use process.
Prevention measures: selection of operating conditions The working temperature is lower than the Tammann temperature, usually 0.5Tm. Carrier selection: Ni/Cr2O3 catalyst Ni/Cr2O3-Al2O3 structure, adding auxiliary agent (separator).
Regeneration method: After large-grained metal is oxidized by oxygen, it is reduced by H2.
Five, application examples
Regeneration of precious metal catalyst:
①Regeneration of platinum-oxidized fluoride catalysts, such catalysts usually used by petroleum companies, deactivation is mainly due to excessive carbon on the surface of the catalyst.
Solution: fluidized bed charcoal burning method, the catalyst is burned back and forth in natural air in a fluid bed for 3-4 times, the temperature gradually changes from low to high, and the maximum temperature does not exceed 450℃; nitrogen fixed bed charcoal burning method, fixed in the selection In the bed, nitrogen is added to the air, and slow charring and decoking activities are carried out at a temperature in the range of 255-455°C.
②Relevant research in the United States shows that for catalysts that are in contact with oxygen, the carbon deposits on the surface of the catalyst are removed by using the principle of oxygen oxidation, and gas reduction is used.
③The noble metal-containing zeolite catalyst has excessive carbonaceous sediment deposited on the surface. The common method to eliminate poisons on the catalyst surface is to redisperse the metal to ensure that the activity of the catalyst is restored.
④ Method for reactivating sulfur-poisoned zeolite-containing catalyst: contact the regenerated catalyst with an aqueous solution of Bronsted acid compound, and disperse the accumulated precious metals. If acid treatment is carried out, use oxidation method for treatment in order to improve The degree of dispersion of precious metals.
⑤ Regeneration of carbon carrier precious metal catalyst. It is usually used in the process of adding blue to acetic acid and oxygen to synthesize vinyl acetate. The general treatment method is to use lye washing and multiple washings. The multiple washing method is to wash the catalyst under hot water at 260-300℃. After washing with dilute lye, the catalyst and concentration must be 13%. Contact with -30% lye, keep the temperature in the range of 3-100℃, and the contact time is 1-10 hours. Not only makes the catalyst completely restored to its original level, but also prolongs the service life of the catalyst.
Non-precious metal catalyst regeneration:
① Ca poisoning, increase the amount of catalyst replacement, enhance the effect of electric desalination at normal pressure, inject decalcification agent, and use oil-soluble demulsifier;
V poisoning, increase the amount of catalyst replacement, replace with a better balance agent or magnetic separation agent, and use Ni and V bimetal passivators;
Ni series catalysts are regenerated. In the early stage of regeneration treatment, this kind of catalyst needs to clean the sulfided substances of the catalyst before the reactor is burnt, and it also needs to use the heating furnace tube for decoking treatment. The deoiling of the catalyst is mainly replaced by clear oil. Way to deal with it.
Secondly, water vapor-air regeneration technology. This kind of regeneration technology operation method is relatively simple, the exhaust gas produced has no effect on the downstream equipment, and the pollution degree is low.
② Regeneration of vanadium catalyst. The regeneration mechanism of vanadium-based catalysts is mainly to use deionized water soaking to directly dissolve poisoning substances that can be dissolved in water and then wash them away. Using sulfuric acid soaking treatment method can eliminate all alkali metal poisoning elements and at the same time produce sulfation on the catalyst.
The regeneration process of the vanadium-based catalyst is to first use the roasting method to clean the carbon deposits on the surface of the catalyst that has lost its activity, and select a more appropriate particle size for matching, and effectively organize the active tissue structure on the catalyst surface, and use impregnation to supplement Add the active components, and then use the drum for dehydration, drying, drying activation and other treatments.
③ Regeneration of Co-based catalysts. The price of Co is relatively high, and the regeneration technology is more complicated. During the operation of the Co-based catalyst, the catalyst loses its activity due to more carbon deposits on the surface of the catalyst. For this type of catalyst, the activity of the catalyst can be restored to a normal level through in-situ technology, but during the regeneration process, it is easier to cause the performance of the catalyst to change.
In addition, with the height of the temperature and height of the hydrotreating catalyst, the exposed Mo2+ ions will increase, and the Co2+ will decrease accordingly. Regeneration treatment is carried out at a high temperature above 400°C. The presence of water will affect the function of the catalyst to a certain extent, and the performance of hydrogenation conversion and hydrogenation activation will be reduced.
Six, several suggestions to prevent catalyst deactivation
- Strengthen the analysis and implementation of raw materials, and regularly analyze the content of impurities.
- Strengthen the management of raw materials, pay attention to the analysis of tank change, especially the secondary processing oil.
- Carefully choose desulfurization agent and dechlorination agent, choose chromium molybdenum, and try not to choose zinc and sodium.
- According to the characteristics of the device, select the catalyst reasonably.
- Strengthen operation management and personnel training, and improve the responsibility of operators.
- Develop corresponding plans and measures according to different causes of catalyst deactivation.
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