Crosslinked PDMS Defoamer Reduces Silicon Contamination in Coker Feedstocks
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Solution Overview
Problem
The delayed coking process in petroleum refineries faces issues with foaming, which leads to undesirable silicon contamination in products, poisoning catalysts and requiring premature replacement, as existing silicone-based defoamers are not viable alternatives due to high silicon content and thermal instability.
Innovation Solution
The use of crosslinked polydimethylsiloxane (PDMS) with a siloxane or alkyl polysilicate crosslinker, which reduces the amount of silicon in coker products while effectively controlling foam, allowing for less crosslinked material to achieve the same foam reduction as traditional linear PDMS, thereby minimizing catalyst poisoning and contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If silicone-based defoamers (polydimethylsiloxanes) are added to control foaming in delayed coking, then foam control is improved, but silicon contamination of products increases causing catalyst poisoning
Solution Approach 1:
The patent changes the molecular weight parameter of the polydimethylsiloxane from conventional high molecular weight to a specific range (500-50,000 cst viscosity) that provides effective foam control while reducing thermal degradation and silicon carryover in products. This parameter optimization resolves the contradiction by finding a viscosity range that balances defoaming effectiveness with reduced catalyst poisoning.
Solution Approach 2:
The patent uses composite defoamer formulations combining polydimethylsiloxane with specific hydrocarbon carriers and optional additives to achieve effective foam control with reduced silicon contamination. The composite nature allows the active silicone component to be delivered efficiently while minimizing the amount that reaches downstream catalysts.
2Stability of the object's composition
If high molecular weight silicone oil is used as defoamer, then thermal stability is improved, but silicon distills over with liquid products at coker temperatures
Solution Approach 1:
The patent optimizes the molecular weight and viscosity parameters of the polydimethylsiloxane to a specific range that provides sufficient thermal stability for coking conditions while preventing excessive distillation. The viscosity range of 500-50,000 cst represents an optimal balance where the silicone is stable enough to withstand coker temperatures but not so high molecular weight that it breaks down into distillable fragments.
3Ease of operation
If conventional linear PDMS is used for foam control, then defoaming effectiveness is achieved, but large quantities are required leading to increased silicon carryover
Solution Approach 1:
The patent changes the viscosity parameter of the polydimethylsiloxane to an optimized range that enhances defoaming effectiveness per unit quantity. By selecting specific viscosity grades within the 500-50,000 cst range, the patent achieves better foam control with smaller dosages, thereby reducing total silicon carryover to downstream units.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces silicon carryover and foam levels, enabling more efficient coking operations, longer catalyst life, and increased product output by minimizing the need for frequent catalyst replacement and reducing downtime due to foaming.
Implementation Method 1
Due to silicone oil's unique surface properties and thermal stability
Implementation Method 2
crosslinked polydimethylsiloxane (PDMS) with a siloxane or alkyl polysilicate crosslinker
Implementation Method 3
Breakdown products are primarily cyclic trimers and tetramers of polydimethylsiloxane, and have boiling points of 134° C. (273° F.) and 175° C. (347° F.)
Implementation Method 4
the original silicone molecule can break down into small enough pieces to distill over with the liquid products
Data Source
AI summary
It has been discovered that crosslinked polydimethylsiloxane (PDMS) resins are useful defoamers and antifoamers for hydrocarbon-containing liquids, such as delayed coker feedstocks and feedstocks to preflash and atmospheric towers. These PDMS resins are crosslinked with either alkyl polysilicate or siloxane. The crosslinked PDMS resins may be used alone or together with linear PDMS, and are typically blended with a carrier such as kerosene for easier handling. Importantly, the use of crosslinked branched PDMS resins permit less total amount of polysiloxanes to be used, which reduces the silicon carryover in coker products and reduces poisoning of downstream catalysts.