Side Riser FCC for Light Paraffin Dehydrogenation
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Solution Overview
Problem
Current methods for converting light paraffins into gasoline boiling range hydrocarbons are limited, particularly in dehydrogenating propane and butane, which are key sources for olefins in refineries, leading to inefficiencies and unwanted coke formation.
Innovation Solution
A method involving a fluid catalytic cracking reactor with a side riser, where a paraffin-containing stream, predominantly isobutane, is dehydrogenated into olefins, and these olefins are then alkylated without intermediate separation, producing a product stream with hydrocarbons boiling between 100° F. and 400° F., utilizing traditional FCC catalysts and optimizing catalyst circulation and temperature conditions to enhance conversion and minimize coke formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If light paraffins are dehydrogenated to produce olefins using conventional methods, then olefin yield increases, but significant coke formation occurs
Solution Approach 1:
The process is divided into two separate risers: a main riser for cracking heavy feeds and a side riser for dehydrogenating light paraffins. This segmentation allows independent optimization of reaction conditions for each function, enabling high olefin yield from light paraffins while managing coke formation through separate catalyst circulation and regeneration pathways.
Solution Approach 2:
The side riser operates at elevated temperatures (700-900°C) and controlled pressure conditions to favor dehydrogenation reactions. By adjusting temperature, pressure, and catalyst-to-oil ratio parameters specifically in the side riser, the process maximizes olefin production from light paraffins while the separate regeneration system manages coke burn-off, resolving the contradiction between yield and coke formation.
2Quantity of substance
If ZSM-5 catalyst is added to convert naphtha olefins into butylenes and propylene, then propylene yield increases, but catalyst dilution reduces overall cracking efficiency
Solution Approach 1:
The process separates propylene production from the main cracking operation by using a dedicated side riser with ZSM-5 catalyst for light paraffin dehydrogenation. This segmentation allows the main riser to maintain optimal cracking efficiency for heavy feeds while the side riser specifically targets propylene production from light paraffins, avoiding the catalyst dilution problem that would occur if ZSM-5 were added to the main cracking catalyst.
3Quantity of substance
If main riser temperature is increased to boost olefin production, then olefin yield increases, but overcracking leads to hydrogen transfer and coke formation
Solution Approach 1:
The process divides the cracking function into two separate risers with different temperature profiles and catalyst types. The side riser operates at higher temperatures (700-900°C) optimized for dehydrogenation and olefin production from light paraffins, while the main riser operates at conventional cracking temperatures. This segmentation enables high olefin production in the side riser without the overcracking and coke formation problems that would occur if the main riser temperature were increased.
4Productivity
If intermediate separation of unreacted isobutane is performed before alkylation, then alkylation efficiency improves, but process complexity and energy consumption increase
Solution Approach 1:
The process continuously recycles unreacted isobutane from the alkylation unit back to the side riser for dehydrogenation. This creates a continuous loop where isobutane that doesn't react in the alkylation unit is converted back to olefins and then re-introduced to the alkylation process, maintaining high alkylation efficiency without requiring intermediate separation steps, thereby reducing process complexity and energy consumption.
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 increases the yield of gasoline boiling range hydrocarbons while reducing coke formation and energy-intensive separation processes, achieving high conversion rates and favorable product distributions favoring butylene over propylene, suitable for alkylation units.
Implementation Method 1
exposing a paraffin-containing stream to a catalyst in a side riser of a fluid catalytic cracking reactor under effective conditions for dehydrogenating at least a portion of paraffins in the stream into olefins
Implementation Method 2
exposing a residual fraction to a catalyst in a main riser of a fluid catalytic cracking reactor under first effective conditions to crack hydrocarbons of the residual fraction
Implementation Method 3
alkylating olefins in the olefin-containing stream, without intermediate separation of unreacted isobutane in the olefin-containing stream, to produce a product stream comprising an alkylate fraction comprising hydrocarbons boiling between 100° F. and 400° F.
Data Source
AI summary
Methods and systems producing gasoline boiling range hydrocarbons from light paraffins are disclosed. Such methods may include exposing a paraffin-containing stream to a catalyst in a side riser of a fluid catalytic cracking reactor under effective conditions for dehydrogenating at least a portion of paraffins in the stream into olefins and thereby producing an olefin-containing stream, wherein the paraffin-containing stream comprises greater than 50 wt % isobutane; and alkylating olefins in the olefin-containing stream to produce a product stream comprising an alkylate fraction comprising hydrocarbons boiling between 100° F. and 400° F.