Active clay for treatment BTX

BTX modification unit

Benzene, toluene and xylene are among the most widely used industrial solvents. Apart from that, the para-isomer of xylene is the precursor of polymers such as PET (polyethylene terephthalate), which is widely used. The production of these compounds includes the refining of naphtha in the reformer to produce reformate. Reformate is then subjected to a series of operations such as solvent extraction, distillation and purification operations by Clay catalyst. For this, a highly active and selective catalyst is used. Clay used for these purposes is activated bentonite, the particle size of which varies depending on the purpose of use. An industrial setup representing BTX processing is shown in the figure.
Reframite contains BTX and some unsaturated compounds such as olefins. The reframite composition is important for the clay purifier, because at this point, the olefins are converted and then removed. Although the catalysts and adsorbents used in BTX processing are selective, they may be contaminated by the presence of compounds such as olefins (isomers of hexane, heptane and octane, cyclohexane, cyclic olefins and styrene), dienes and unsaturated compounds. Quantification of these pollutants is also done based on the bromine index (mg of bromine consumed per 100 grams). This index is between 5 and 20 in the standard of industrial solvents.

Benzene and toluene processing

The light reformate collected from the air separator is subjected to selective solvent liquid-liquid extraction. This step helps to concentrate benzene and toluene. Then, the extracted material is separated into benzene and toluene. The isolated toluene is passed through the fixed bed of the catalyst and is converted into benzene and xylene isomers due to disproportionation reactions in the presence of hydrogen. In order to reduce the bromine index, the product of these reactions is passed through a clay purifier. After that, the flow is recirculated to group separate the individual components. The obtained xylene is also pumped in the p-xylene processing unit.

Xylene processing

The heavy reformite collected from the separator is placed in a clay purifier to reduce the bromine index. In this purifier, selective clay is used to prevent side reactions such as transalkylation or dialkylation reactions, in which xylene is consumed. After reducing the bromine index, the stream passes through the p-xylene, benzene and C9 separation section. The C9 fraction is also transferred to the toluene disproportionation unit. In order to isolate p-xylene, the concentrated stream of p-xylene is subjected to liquid-solid absorption or batch crystallization. The residues of this process are called raffinite and are placed inside O, m-xylene and ethylbenzene. The raffinate passes through a fixed bed of selective catalyst that equilibrates the xylene isomers in the presence of hydrogen to produce p-xylene. After achieving the desired and optimal level of p-xylene, the stream is re-entered into the clay purifier to reduce the bromine index before flowing to the p-xylene separation unit.

During this process, a large amount of aromatic compounds are produced along with high quality hydrogen. Liquid reformite is separated into light or heavy fractions. The light fraction consists of benzene and toluene and the heavy fraction consists of xylene isomers plus heavy aromatics. The produced hydrogen is later used for processes such as naphtha hydrogenation, isomerization and toluene disproportionation.

Performance of Clay Catalyst

The activity of the clay catalyst depends on the processing of the clay and the nature of the feed. Clay becomes more inactive with a higher amount of bromine index and the presence of nitrogen and sulfur compounds in the feed. It is worth noting that moisture also deactivates clay. Selectivity of clay is a very important issue. This prevents side reactions that lead to the production of benzene and higher alkylation products and helps to increase the production capacity.

• The lifetime of this catalyst largely depends on the input feed and the amount of olefins.
• Feed with high bromine number and nitrogen and sulfur compounds will deactivate this catalyst.
• Other factors such as humidity and operating temperature can also shorten the life cycle of these catalysts.

Use of clay in the purifier

When using clay, full precautions should be taken so that no soil is lost during the operation and reaction. In order to achieve this, screening and ceramic balls of different sizes are used. The clay is distributed evenly with the help of sock loading method. This confirms the correct distribution flow. At this stage, the relevant moisture is removed. It should be mentioned that before draining the clay, it is steamed and cleaned with nitrogen, to remove the trapped hydrocarbons.

Factors affecting the activity and longevity of clay

• Raw Bentonite: In general, clay with higher ion exchange capacity shows lower passivation rate.
• Quality of raw materials: the presence of non-aromatic materials with high BP quickly deactivates the clay. Also, the presence of non-aromatic compounds, sulfur and nitrogen in the feed, deactivates the clay.
• Reaction temperature: Olefins undergo alkylation reactions with aromatic molecules and can also be polymerized. Alkylation is a pseudo-first-order reaction. The reaction at higher temperatures increases the rate of alkylation reaction. Also, at higher temperatures, usually less than 150 polymerization reactions are of interest. Polymerization side products are not soluble in the product stream, they remain in the pores of the clay and deactivate the acid sites.
• Pressure: The pressure must be within a certain range to keep the system in a liquid state.
• Moisture: The presence of moisture increases the polymerization of olefins. The previously mentioned polymerized olefin shortens the life of the clay.

SmartAC catalyst storage and use instructions

In order to maintain the high performance of this product, the following methods are suggested.

• SmartAC catalysts should be stored in closed rooms with as much dry air as possible.
• Air humidity in these rooms should be constant and as low as possible.
• Avoid exposing this catalyst to air for a long time because it absorbs moisture quickly.
• This catalyst should not be placed in the vicinity of volatile chemicals that may release absorbable volatiles. It is recommended to keep and store the catalyst separately in order to eliminate such possible risks.
• SmartAC catalyst should not be stored in silos and normally should not be moved by air without prior coordination with the SC.

Conclusion:

The goal of Smart Catalyst Group is to localize, develop and increase the quality of catalysts and absorbents used in various industries (oil, gas, petrochemical, steel and vegetable oil). So far, relying on the experiences of domestic experts, the knowledge of foreign engineers and university professors in its research and development staff, this company has managed to mass produce various types of catalysts. During its 15 years of operation, this company has become one of the main production hubs in the market, which, in addition to meeting domestic needs, also exports its products abroad. The vision and goal of Smart Catalyst to become the largest producer in the last few years; It is a proof of the growing path of this company.
Currently, various grades of vanadium pentoxide produced by Smart Catalyst are used in sulfuric acid and sulfonic acid plants, copper, zinc, steel and coke plants, petrochemicals and refineries, which include a high percentage of SmartV48 and A low percentage of SmartV38. SmartV69 and SmartDp are also protective catalysts. The experts and experienced engineers of Smart Catalyzer Company produce and sell catalysts in Iran and export them to neighboring countries. This company provides free services to sulfuric acid and sulfonic acid factories, chemical and petrochemical industries, including technical support and consulting during the project process.