How to control the circulation air volume for Innovene polypropylene grades?

Let’s first give a brief introduction to the Innovene process: The Innovene process is also known as the BP-Amoco process. The main feature of the process is the use of a unique horizontal stirred-tank reactor with a flow pattern close to that of piston flow. With this unique reactor, copolymer products with excellent rigidity and impact resistance can be produced, as the particle residence time distribution is very narrow. This type of reactor with **push-flow can prevent catalyst short-circuiting. In the presence of ethylene, large polymer particles can be formed, rather than fine particles within homopolymer particles; these fine particles would reduce the low-temperature impact strength of the copolymer and cause unnecessary gelation. Therefore, the narrow reaction residence time distribution of this process enables it to meet the requirements for high-impact copolymers that can only be produced using multiple fully mixed reactor polymerization units. Furthermore, thanks to this unique reactor design, the product transition time for this process is very short; theoretically, it is 2/3 shorter than that in continuous stirred-tank reactors or fluidized-bed reactors. As a result, product switching is easy, and there is little transitional product. 　　The Innovene process uses propylene flashing to remove heat. Liquid propylene is injected into the reactor from various feed points in a manner that keeps the reactor bed dry. After vaporizing, the partial pressure of the monomer is lower than its dew point pressure, which is sufficient to remove the heat of reaction. During operation, it is essential to strictly control the feed rate of liquid propylene and its vaporization in the reactor, in order to maintain a balance among the degree of dryness of the bed, the degree of fluidization, and the reaction temperature range. The air lock system is another feature of this process. When the material is transferred from the first reactor to the second reactor, the air lock system prevents cross-flow between the two reactors. Especially when producing copolymers, the gas compositions in the two reactors differ: the first reactor contains a large amount of hydrogen, while the second reactor contains ethylene along with a small amount of hydrogen. If hydrogen from the first reactor enters the second reactor, or if ethylene from the second reactor enters the first reactor, it will severely affect the quality of the product. Therefore, it is crucial to isolate the two reactors from each other. The CD catalyst used in this process exhibits excellent morphological control, high activity and selectivity; it enables the suppression of the formation of random polypropylene. The resulting product has a high isotactic index, a narrow particle size distribution, good flowability of the powder, low ash content, and an excellent color. The use of this catalyst can simplify the process flow. All grades of products can be produced using only one type of catalyst, without the need to switch catalysts. The activity of the CD catalyst ranges from 25,000 to 55,000 kg PP/kg cat, depending on the purity of the raw materials and the number of reactors. The isotactic index of the powder products produced can reach up to 99%. Another advantage of CD catalysts is that they require no pretreatment or pre-polymerization; they can be added directly to the reactor, and this catalyst can be used to produce all polypropylene products. The MFR of the homopolymer products obtained using this process can range from 0.5 g/10 min to 100 g/10 min, and the toughness of these products is higher than that of products produced by other gas-phase polymerization processes ； The MFR of the random copolymer products is 2–35 g/10 min, and their ethylene content can reach 7%–8% (by mass) ； The MFR of the impact-resistant copolymer products ranges from 1 to 35 g/10 min, with an ethylene content of 5% to 17% (by mass). 　　Due to the plug-flow reactor design, the catalyst residence time distribution is narrow, resulting in a more uniform distribution of the rubber phase in the impact-resistant copolymer and superior performance, particularly in terms of the balance between impact resistance and stiffness. This process can also use a single reactor to produce homopolymers and random copolymers, but it has its drawbacks: the ethylene content in the product (or the proportion of the rubber component) is not high, making it impossible to obtain PP products with high or ultra-high impact resistance. Another important feature of this process is that the polymerization reaction can be stopped quickly and smoothly by ceasing catalyst injection (in about 15–20 minutes), and it can be restarted after a few hours without affecting the conditions inside the reactor or the quality of the polymer. In the event of an outage or similar incident, the reactor can be brought to a stop within 3 minutes by releasing its pressure, either through an emergency shutdown or a gradual shutdown; it can then be restarted after the pressure is restored and catalyst is added. Due to the short process flow of the Innovene process, its unique reactor design, relatively low polymerization pressure, and the absence of large rotating equipment, its electricity consumption is among the lowest among various PP processes. Since it is a gas-phase polymerization system, there is no need to heat the liquid propylene discharged along with the polymer using steam as in the liquid-phase method; as a result, steam consumption is very low, and the energy consumption for producing homopolymer products is the lowest among all processes. Like other gas-phase processes, the Innovene gas-phase process does not involve large amounts of liquid hydrocarbons in the polymerization system, making it inherently safer than the bulk method. The operating pressure of the Innovene gas-phase process reactor is the lowest among various process technologies.

The key point wasn’t mentioned; I still don’t understand

I’ve never done this process before, so I’m taking this opportunity to share some basic information so that everyone can understand it. Currently, this process must belong to Ineos! !

The circulating gas volume is proportional to the amount of quench liquid; each reaction zone has a gas-liquid ratio. The circulating gas volume is controlled by adjusting the amount of quench liquid, which in turn is controlled by the reactor temperature.

This process seems to have a pneumatic lock system as well. Could you explain its function and the key points for operation?

The air lock system is essentially designed to prevent backflow of gas from the first and second reactors. It seems similar to UNIPOL’s PDS system and the intermediate transfer system, but many people say that the air locking capability of this system is an advantage of this process over UNIPOL’s system.

What was said upstairs is correct; a gas lock is used to transfer the powder from one reactor to the other, while preventing mixing of materials between the two reactors. Generally, an intermittent sequential control system is employed to manage this process.

The air lock system uses a sequence control program for system isolation. What is the significance of adjusting the components in each reactor?

Because the production conditions of the two reactors are different, isolation is required