Demethanizer Absorption Process for Pyrolysis Gas Separation
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Solution Overview
Problem
The separation and purification of lower carbon olefins such as ethylene and propylene from pyrolysis gas is energy-intensive and inefficient, particularly in cryogenic separation processes, which results in high energy consumption and loss of targeted products.
Innovation Solution
A process using composite absorbents in a demethanizer to separate methane and hydrogen from C2+ fractions at moderate temperatures and pressures, with a mixed hydrocarbon fraction as the primary absorbent and a pure or mixed hydrocarbon fraction as the secondary absorbent, to minimize energy consumption and product loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cryogenic separation process is used to separate methane and hydrogen from C2+ fractions, then separation effectiveness is improved, but energy consumption and investment cost increase significantly
Solution Approach 1:
The patent changes the operating parameters from cryogenic temperatures to moderate temperatures (above -40°C), and from high pressure to relatively low pressure (0.3-2.0 MPa). This parameter change allows the use of absorption process instead of cryogenic separation, significantly reducing energy consumption while maintaining separation effectiveness between methane/hydrogen and C2+ fractions
Solution Approach 2:
The patent replaces the mechanical cryogenic separation system with an absorption-based chemical process. Instead of using complex cryogenic equipment operating at extremely low temperatures, the invention uses absorbents (mixed hydrocarbon fractions like C3-C6) to selectively absorb C2+ fractions at moderate conditions, substituting a simpler chemical absorption mechanism for a complex mechanical separation system
2Quantity of substance
If circulation of large amount of absorbent or decreasing absorbent temperature is used to increase absorption capacity, then absorption capacity is improved, but energy consumption increases
Solution Approach 1:
The patent changes the temperature parameter from low temperatures to moderate temperatures (above -40°C), which improves the vapor pressure and reduces the energy required for heating and circulation of absorbent. This parameter change allows achieving adequate absorption capacity without the high energy consumption associated with cooling and circulating large amounts of cold absorbent
Solution Approach 2:
The patent uses a relatively small amount of absorbent (L/G ratio of 0.5-5.0) compared to conventional processes, achieving sufficient absorption capacity through optimized absorbent selection and moderate operating conditions, rather than circulating excessive amounts of absorbent which would require high energy input
3Use of energy by moving object
If absorption process at moderate temperature and pressure is used, then energy consumption is reduced, but separation effectiveness may deteriorate
Solution Approach 1:
The patent uses composite absorbent systems consisting of mixed hydrocarbon fractions (C3-C6) rather than single pure components. This composite approach leverages the complementary absorption characteristics of different hydrocarbon fractions to achieve effective separation at moderate conditions, where no single component would be sufficient alone
Solution Approach 2:
The patent introduces mixed hydrocarbon fractions as intermediary absorbents that mediate between the gas phase (methane/hydrogen/C2+ fractions) and liquid phase. These intermediary absorbents provide the necessary interaction mechanism to achieve separation at moderate temperatures and pressures, bridging the gap between the separated components under milder operating conditions
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 cooling capacity and minimizes the loss of ethylene and propylene, achieving efficient separation and purification with reduced energy consumption.
Implementation Method 1
separating methane and hydrogen by absorbing C2+ fractions with an absorbent at moderate temperature and pressure
Data Source
AI summary
The provided is a process for separating by absorption the pyrolysis gas from preparation of lower carbon olefins, wherein a primary absorbent and a secondary absorbent are introduced into the demethanizer to separate by absorption the feedstock of the demethanizer through countercurrent contact therewith at a moderate temperature and pressure, thereby to obtain a top fraction primarily comprising hydrogen and methane and a bottom fraction primarily comprising the absorbents and C2+ fraction, wherein the primary absorbent essentially is a mixed Cn or Cn+ fraction, the secondary absorbent essentially is a Cn′ alkane fraction or mixed Cn′ or Cn′+ fraction, and wherein n and n′ are independently 3, 4 or 5 with the proviso when the secondary absorbent is a mixed fraction, n′ is not 3.