Intermittent liquid-phase mini-mass process for polypropylene
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Question: What are the prospects for the intermittent liquid-phase small-batch polypropylene production process? From what I’ve heard, it requires low investment and is simple to operate, but it occupies a large amount of space and involves many auxiliary systems. Therefore, those who are familiar with this process would be able to provide insights regarding its technical aspects, production capabilities, and investment requirements. In particular, I’ve heard that a separate circulating water system and a high-precision nitrogen supply station are needed for its operation
I should clarify upfront that I’m no hero; I’m a worker involved in intermittent bulk liquid-phase polymerization. I’ve just graduated and haven’t had much work experience, so what I say is for reference only. :The batch liquid-phase bulk polymerization process for P polypropylene is now well-established. This technology offers advantages such as a short process flow, low investment costs, flexible switching between different product grades, and no formation of intermediate products. However, it occupies a “relatively” large area. There are many operators. Here, both the purified air and the unpurified air supply for nitrogen are provided by the powered workshop; if it is a separate polypropylene workshop, these issues also need to be taken into consideration. If there is anything incorrect in what I said, please point it out; I am open to learning from your feedback:P
Description of the Polypropylene Plant
I. General Information on the Plant
Main product: Polypropylene
Design capacity: x ten thousand tons per year
Actual production capacity: x ten thousand tons per year
Authority responsible for project approval: **Development and Reform Commission
Design firm: xxxxx Engineering Design Co., Ltd.
Construction company: xxxxx Construction Engineering Company
Construction period: 1 year
Commencement of operation: October 10, 2003
Project investment: 50 million yuan
Investment in environmental protection:
Number of employees required: 50
Land area occupied: 2.05 hectares
II. Process Overview
1. Process description: Propylene obtained from gas separation is sent through a coalescing separator, dehydration tank, solid alkali tower, hydrolysis tower, desulfurization tower, molecular sieve tower, deoxidation tower, and arsenic removal tower to remove most of the impurities such as sulfur, water, oxygen, and arsenic, after which it enters the propylene raw material tank. First, hydrogen is introduced into the empty polymerization reactor that is ready for production, either by measurement using a pressure reduction method or via a hydrogen flow meter, in order to adjust the molecular weight of polypropylene. Open the vapor balance line valve between the polymerization reactor and the raw material storage tank again, allowing vapor to flow from the storage tank into the reactor; once the pressure in the reactor is equal to that in the storage tank, close the vapor balance valve of the reactor. The raw material propylene is metered and fed into the polymerization reactor by a feed pump. The activator is pumped from the transport tank into the activator storage tank using N2, and then further pumped into the activator metering tank using N2. After metering, it is added to the activator feed tank located on top of the reactor, after which it is introduced into the polymerization reactor along with the propylene. According to the polymerization ratio, a certain amount of the third component (DDS) is added to the catalyst feed hopper; a certain amount of propylene is introduced into the polymerization reactor, and then propylene is used to push the specified amount of catalyst from the catalyst feed hopper into the polymerization reactor. Start the hot water pump to feed the hot water from the hot water tank into the jacket of the polymerization reactor. Control the rate of temperature increase such that the reactor pressure rises from the initial value to 3.0 MPa within 30–60 minutes; depending on the progress of the reaction, switch from hot water to cold water at a pressure of 2.0–2.6 MPa, in order to keep the reaction temperature between 75–81°C and the reactor pressure between 3.4–3.8 MPa. Maintain this constant temperature for 2–6 hours, and determine the end point of the reaction based on its progress. Once the reaction reaches its endpoint, the unreacted propylene in the polymerization reactor is recovered. The recovery process ends when the pressure in the propylene recovery tank equals that in the polymerization reactor (1.0–1.6 MPa), after which the flash unit is contacted to feed the material into the already purified flash reactor. The feeding pressure should not exceed 1.2 MPa at any time; feeding stops when the pressure in the polymerization reactor drops to 0.3–0.4 MPa, after which preparation for polymerization resumes with further feeding. When the polymerization reactor feeds material into the flash drum, the flash drum must automatically or manually discharge gaseous propylene into the gas holder intermittently. After the spraying is complete, the flash tank uses an automatic or manual replacement procedure to alternately evacuate and fill it with nitrogen until the propylene content in the flash tank is less than 1.5%, at which point the replacement process is completed. Perform on-site packaging of the material, or transfer the material from the flash vessel to the silo for packaging, until all the powder has been packaged. 2. Process steps for raw material purification: The raw materials come from spherical tanks or gas separation units — to the feed cooler E6301 — then to the propylene dehydration tank V6201 — followed by the solid alkali tower T6204/AB — another solid alkali tower T6201/AB — the hydrolysis tower T6202/AB — the desulfurization tower T6203/AB — the molecular sieve tower T6205/AB — the arsenic removal tower T6208/AB — the deoxidation tower T6206/AB — yet another molecular sieve tower T6207/AB — and finally to the metering tank V6101/AC — as well as the propylene raw material tank P6101/AB — and the polymerization reactors/1-12. 3. Some processes in the polymerization unit: Activator transport tank — Activator intermediate tank V6102 — Activator metering tank V6103 — Activator feed hopper ； DDS, catalyst—catalyst feeder—polymerization reactor R6101/1-12—high-pressure recovery centrifuge V6111/1-8—propylene condenser E6101/A-D—metering tank/BD. 4. Some processes in the flash evaporation unit: Polymerization reactor R6101/1-12 — Flash evaporation reactor R6102/1-12 — Gas holder centrifuge V6112/ABCD — Gas holder R6301 ； Flash drum R6102/1-12—Vacuum pump buffer tank V6108/AB—Vacuum pump P6103/ABCD—Venting ； Nitrogen buffer tank V6106/AB—Flash drum/1-12—Vent ； Flash drum powder – polypropylene silo – automatic discharging. 5. Low-pressure recovery process: Gas holder R6301 — Propylene compressors 01/02 — Outlet sediment tank V6302 — Condensers E6201/EF — Condensate tank V6302 — Gas station sphere tank area ； Condensate tank—membrane recovery—gas holder R6301 ； Condensate tank—membrane recovery—flare. III. Process Characteristics (simultaneously describe the new technologies adopted in terms of energy conservation, clean production, and environmental protection) 1. A relatively advanced process flow is employed: ① Raw materials are fed using a pump, with measurement carried out by instruments. The feed rate can be automatically controlled for smooth operation. ②Hot water operates as its own system and is reused. Control valves are installed for the hot water entering the polymerization reactor as well as for the jacket, enabling automatic control of the reaction heating process. ③A control valve is added before the circulating cold water enters the reactor to achieve automatic control of the constant-temperature reaction process. ④The propylene recovery system is equipped with control valves to determine the end point of the reaction and automatically ensure smooth recovery. 2. Advanced control system: It utilizes the patented technology from Tianjin Tianhua Technology Center, namely \"Achieving automatic control of the entire polymerization process using a DCS control system.\" 3. An advanced control system is employed, which increases the output per reactor and reduces the production cycle per reactor, thereby **increasing the output ； It improves product quality and reduces the defect rate; this leads to better economic benefits as well as an enhancement of the company’s reputation ； It reduces the workload on workers, decreases the need for staff, and helps to cut costs. 4. Advanced and reliable domestic process technologies and control solutions are adopted, ensuring that the designed equipment operates in a safe, stable, efficient, optimal manner. The quality of the products is highly competitive, while the energy and material consumption of the equipment is kept as low as possible. 5. Vigorously promote the use of new processes, technologies, equipment, and materials; increase the proportion of advanced technologies, save energy and reduce consumption, lower production costs, improve the quality of products, produce goods that meet environmental standards, and enhance the competitiveness of these products. The device’s material and energy consumption levels are among the best in the country, and its production costs are competitive compared to similar devices in China. 6. To reduce project costs, in line with the principles of seeking truth from facts and ensuring stability and reliability, efforts are made to increase the degree of localization by sourcing the required equipment domestically; only those key instruments and equipment whose technical and quality standards cannot be met domestically are imported. 7. Centralized control using DCS is employed to optimize operations, thereby enhancing the reliability of the plant’s operation, improving product yield and quality, and ensuring safe, stable, long-term, full-capacity, and high-quality operation of the plant. 8. Strictly comply with the environmental protection and occupational safety and health design regulations, procedures, and standards established by **, local authorities, and relevant regulatory bodies; reduce the emission of waste materials, protect the surrounding ecological environment, carry out simultaneous treatment measures, and meet the requirements of clean production.
I. General Information on the Plant
Main product: Polypropylene
Design capacity: x ten thousand tons per year
Actual production capacity: x ten thousand tons per year
Authority responsible for project approval: **Development and Reform Commission
Design firm: xxxxx Engineering Design Co., Ltd.
Construction company: xxxxx Construction Engineering Company
Construction period: 1 year
Commencement of operation: October 10, 2003
Project investment: 50 million yuan
Investment in environmental protection:
Number of employees required: 50
Land area occupied: 2.05 hectares
II. Process Overview
1. Process description: Propylene obtained from gas separation is sent through a coalescing separator, dehydration tank, solid alkali tower, hydrolysis tower, desulfurization tower, molecular sieve tower, deoxidation tower, and arsenic removal tower to remove most of the impurities such as sulfur, water, oxygen, and arsenic, after which it enters the propylene raw material tank. First, hydrogen is introduced into the empty polymerization reactor that is ready for production, either by measurement using a pressure reduction method or via a hydrogen flow meter, in order to adjust the molecular weight of polypropylene. Open the vapor balance line valve between the polymerization reactor and the raw material storage tank again, allowing vapor to flow from the storage tank into the reactor; once the pressure in the reactor is equal to that in the storage tank, close the vapor balance valve of the reactor. The raw material propylene is metered and fed into the polymerization reactor by a feed pump. The activator is pumped from the transport tank into the activator storage tank using N2, and then further pumped into the activator metering tank using N2. After metering, it is added to the activator feed tank located on top of the reactor, after which it is introduced into the polymerization reactor along with the propylene. According to the polymerization ratio, a certain amount of the third component (DDS) is added to the catalyst feed hopper; a certain amount of propylene is introduced into the polymerization reactor, and then propylene is used to push the specified amount of catalyst from the catalyst feed hopper into the polymerization reactor. Start the hot water pump to feed the hot water from the hot water tank into the jacket of the polymerization reactor. Control the rate of temperature increase such that the reactor pressure rises from the initial value to 3.0 MPa within 30–60 minutes; depending on the progress of the reaction, switch from hot water to cold water at a pressure of 2.0–2.6 MPa, in order to keep the reaction temperature between 75–81°C and the reactor pressure between 3.4–3.8 MPa. Maintain this constant temperature for 2–6 hours, and determine the end point of the reaction based on its progress. Once the reaction reaches its endpoint, the unreacted propylene in the polymerization reactor is recovered. The recovery process ends when the pressure in the propylene recovery tank equals that in the polymerization reactor (1.0–1.6 MPa), after which the flash unit is contacted to feed the material into the already purified flash reactor. The feeding pressure should not exceed 1.2 MPa at any time; feeding stops when the pressure in the polymerization reactor drops to 0.3–0.4 MPa, after which preparation for polymerization resumes with further feeding. When the polymerization reactor feeds material into the flash drum, the flash drum must automatically or manually discharge gaseous propylene into the gas holder intermittently. After the spraying is complete, the flash tank uses an automatic or manual replacement procedure to alternately evacuate and fill it with nitrogen until the propylene content in the flash tank is less than 1.5%, at which point the replacement process is completed. Perform on-site packaging of the material, or transfer the material from the flash vessel to the silo for packaging, until all the powder has been packaged. 2. Process steps for raw material purification: The raw materials come from spherical tanks or gas separation units — to the feed cooler E6301 — then to the propylene dehydration tank V6201 — followed by the solid alkali tower T6204/AB — another solid alkali tower T6201/AB — the hydrolysis tower T6202/AB — the desulfurization tower T6203/AB — the molecular sieve tower T6205/AB — the arsenic removal tower T6208/AB — the deoxidation tower T6206/AB — yet another molecular sieve tower T6207/AB — and finally to the metering tank V6101/AC — as well as the propylene raw material tank P6101/AB — and the polymerization reactors/1-12. 3. Some processes in the polymerization unit: Activator transport tank — Activator intermediate tank V6102 — Activator metering tank V6103 — Activator feed hopper ； DDS, catalyst—catalyst feeder—polymerization reactor R6101/1-12—high-pressure recovery centrifuge V6111/1-8—propylene condenser E6101/A-D—metering tank/BD. 4. Some processes in the flash evaporation unit: Polymerization reactor R6101/1-12 — Flash evaporation reactor R6102/1-12 — Gas holder centrifuge V6112/ABCD — Gas holder R6301 ； Flash drum R6102/1-12—Vacuum pump buffer tank V6108/AB—Vacuum pump P6103/ABCD—Venting ； Nitrogen buffer tank V6106/AB—Flash drum/1-12—Vent ； Flash drum powder – polypropylene silo – automatic discharging. 5. Low-pressure recovery process: Gas holder R6301 — Propylene compressors 01/02 — Outlet sediment tank V6302 — Condensers E6201/EF — Condensate tank V6302 — Gas station sphere tank area ； Condensate tank—membrane recovery—gas holder R6301 ； Condensate tank—membrane recovery—flare. III. Process Characteristics (simultaneously describe the new technologies adopted in terms of energy conservation, clean production, and environmental protection) 1. A relatively advanced process flow is employed: ① Raw materials are fed using a pump, with measurement carried out by instruments. The feed rate can be automatically controlled for smooth operation. ②Hot water operates as its own system and is reused. Control valves are installed for the hot water entering the polymerization reactor as well as for the jacket, enabling automatic control of the reaction heating process. ③A control valve is added before the circulating cold water enters the reactor to achieve automatic control of the constant-temperature reaction process. ④The propylene recovery system is equipped with control valves to determine the end point of the reaction and automatically ensure smooth recovery. 2. Advanced control system: It utilizes the patented technology from Tianjin Tianhua Technology Center, namely \"Achieving automatic control of the entire polymerization process using a DCS control system.\" 3. An advanced control system is employed, which increases the output per reactor and reduces the production cycle per reactor, thereby **increasing the output ； It improves product quality and reduces the defect rate; this leads to better economic benefits as well as an enhancement of the company’s reputation ； It reduces the workload on workers, decreases the need for staff, and helps to cut costs. 4. Advanced and reliable domestic process technologies and control solutions are adopted, ensuring that the designed equipment operates in a safe, stable, efficient, optimal manner. The quality of the products is highly competitive, while the energy and material consumption of the equipment is kept as low as possible. 5. Vigorously promote the use of new processes, technologies, equipment, and materials; increase the proportion of advanced technologies, save energy and reduce consumption, lower production costs, improve the quality of products, produce goods that meet environmental standards, and enhance the competitiveness of these products. The device’s material and energy consumption levels are among the best in the country, and its production costs are competitive compared to similar devices in China. 6. To reduce project costs, in line with the principles of seeking truth from facts and ensuring stability and reliability, efforts are made to increase the degree of localization by sourcing the required equipment domestically; only those key instruments and equipment whose technical and quality standards cannot be met domestically are imported. 7. Centralized control using DCS is employed to optimize operations, thereby enhancing the reliability of the plant’s operation, improving product yield and quality, and ensuring safe, stable, long-term, full-capacity, and high-quality operation of the plant. 8. Strictly comply with the environmental protection and occupational safety and health design regulations, procedures, and standards established by **, local authorities, and relevant regulatory bodies; reduce the emission of waste materials, protect the surrounding ecological environment, carry out simultaneous treatment measures, and meet the requirements of clean production.
The information provided is for reference only; small-scale units are being phased out gradually due to their high consumption of propylene, high energy consumption in production, and unstable product quality. It is recommended that if you have the means, opt for continuous polypropylene production
Given the large fluctuations in the quality of the raw material propylene, I believe that smaller reactors still have their advantages :)
How is the SPG process? It’s currently being implemented, and it’s time for our senior colleague to see results from his efforts
I believe that small-volume polypropylene has expanded too rapidly in recent years, and its applications are relatively limited. To have a promising future, technological innovation is necessary; however, since manufacturers of small-volume polypropylene lack sufficient technical expertise and capital, new products emerge slowly, making it difficult to achieve significant breakthroughs. It’s still very promising for large companies to develop smaller entities! !
I’m aware of one with an annual output of 7. In the 50,000-ton liquid-phase process, why are the power consumption, coal consumption, and propylene consumption all so low? (Power consumption: 109 kWh/ton; coal consumption: 0. 03 tons per ton, with an acrylic monomer consumption of 1. 024 tons/ton), while looking at the information provided by other companies, these figures are much higher than this value. Is it the data provided by this company that is incorrect, or are the figures of other companies on the high side? Who has accurate statistical data on energy consumption, water consumption, and specific consumption for the small-scale bulk liquid phase method? Let’s exchange ideas and improve together.
Also, there is the issue of water consumption in the small-body method, as well as the amount of water that needs to be added to the cooling circulation water system – how much water does the system require per day? What is the daily fresh water consumption of the entire plant? Has anyone compiled statistics on this data?
Dear experts, in large and medium-scale continuous liquid-phase bulk polymerization of polypropylene, do they have stripping towers in the propylene purification unit? Thank you!