Copolyamide Gas Tank Liner for Low Permeability
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Solution Overview
Problem
Existing gas storage tanks, particularly for CNG, face challenges with permeability, durability, and manufacturing complexity, especially in terms of achieving low gas permeability and ease of production using techniques like extrusion blow-moulding.
Innovation Solution
A gas storage tank liner composed of a copolyamide with a random tree structure, made from a reaction between multifunctional and difunctional monomers, combined with an impact modifier and optional chain extenders, optimized for extrusion blow-moulding to achieve high impermeability and robust manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If polyethylene-based liners are used, then weight is reduced, but permeability and durability are insufficient
Solution Approach 1:
The patent uses a copolyamide composition combining linear polyamide chains with branched polyamide structures containing cyclic anhydride groups. This composite material structure achieves both low density (maintaining weight advantage) and enhanced gas barrier properties (improving permeability resistance), while the branched structure provides improved durability and resistance to environmental stress cracking.
2Reliability
If copolyamide liners are used, then gas permeability is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes specific parameters of the copolyamide composition: the branched polyamide content is controlled at 5-50 wt% of total polyamide, the cyclic anhydride content is limited to 0.1-5 mol% of total amide groups, and melt flow index is maintained at 2-20 g/10min. These parameter constraints ensure the material remains processable by conventional extrusion blow-moulding while achieving the desired low gas permeability.
3Reliability
If complex compositions with multiple additives are used, then liner properties are improved, but ease of manufacture decreases
Solution Approach 1:
The patent combines multiple functional requirements into a single copolyamide composition. The linear and branched polyamide segments are integrated at the molecular level through copolymerization, eliminating the need for separate blending of multiple additives. The cyclic anhydride-containing branches provide both structural reinforcement and gas barrier functionality simultaneously, simplifying the manufacturing process.
4Reliability
If high transformation temperature is required, then liner performance is achieved, but productivity decreases
Solution Approach 1:
The patent carefully controls the melting point of the copolyamide composition by adjusting the ratio of linear to branched segments and the cyclic anhydride content. The composition is designed to melt at 20-50°C above the melting point of the linear polyamide component, ensuring adequate flow during extrusion while minimizing the temperature window required for processing. This maintains liner performance while reducing energy consumption and cycle time.
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
The solution provides a liner with extremely low methane permeability, suitable for high-pressure gas storage, excellent impact strength, and ease of production, addressing the limitations of previous technologies while being cost-competitive and simple in composition.
Implementation Method 1
The liner especially acts as a barrier between the fluid or gas and the composite, thus preventing leaks and/or other degradations of the structure of the composite fibre
Data Source
AI summary
The present invention relates to a gas storage tank, for storing gas, especially CNG, methane and/or hydrogen, said tank comprising a liner comprising a high-viscosity polyamide composition comprising a branched polyamide and an impact modifier, and to a process for manufacturing said the tank. More particularly, the composition comprises a copolyamide of the random tree type resulting from the reaction between a multifunctional monomer comprising at least three reactive functions to form an amide function, these functions being of two different types, difunctional monomers conventionally used in the manufacture of linear polyamides, and optionally difunctional monomers.