Raw Coke Structure for Low Thermal Expansion and Alkali Removal
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Solution Overview
Problem
Existing methods for producing activated carbon for electric double layer capacitors struggle with efficiently removing alkali metals, leading to capacity deterioration over time, and needle coke for graphite electrodes face issues with high thermal expansion and puffing during graphitization.
Innovation Solution
A process involving hydrodesulfurization and fluidized catalytic cracking of heavy oils to produce raw coke, which is then graphitized at 2800°C, resulting in a structure that allows easy washing of alkali metals and reduces thermal expansion, inhibiting puffing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If activated carbon is produced by alkaline activation using alkali metal hydroxide, then initial capacitor capacity is improved, but alkali metals remain in the activated carbon causing capacity deterioration over time
Solution Approach 1:
The invention performs preliminary action by controlling the raw coke structure before activation to prevent alkali metal entrapment. Specifically, the raw coke is produced with controlled crystallite size (Lc002 ≤ 1.5 μm) and graphitization degree through specific coking conditions (400-600°C, 300-800 kPa), which creates a structure that facilitates subsequent alkali metal removal during washing while maintaining activation effectiveness
Solution Approach 2:
The invention applies parameter changes by optimizing the structural parameters of raw coke (crystallite size, graphitization degree) to achieve the desired balance between activation performance and alkali metal removal. The specific parameters controlled include Lc002 (crystallite size in c-direction) and La110 (crystallite size in a-direction), which directly influence the accessibility of alkali metals during washing
2Quantity of substance
If activated carbon is washed repeatedly with acid or water to remove alkali metals, then remaining alkali metal content is reduced, but washing complexity and cost increase
Solution Approach 1:
The invention performs preliminary action by pre-structuring the raw coke to facilitate easy alkali metal removal. The controlled crystallite size and low graphitization degree create a more open structure that allows alkali metals to be accessed and removed more easily during washing, reducing the number of washing cycles needed
Solution Approach 2:
The invention employs a simpler, more disposable-like washing approach by using basic water or mild acid washing that can be performed fewer times. The pre-structured raw coke allows effective alkali metal removal even with simpler washing agents, reducing the need for complex repeated washing procedures
3Reliability
If needle coke is produced using conventional methods, then graphite electrodes can be manufactured, but high thermal expansion causes puffing during graphitization
Solution Approach 1:
The invention applies parameter changes by controlling the raw coke structure parameters (crystallite size Lc002 ≤ 1.5 μm, graphitization degree) to achieve low thermal expansion in the final graphite electrode. The specific coking parameters (temperature 400-600°C, pressure 300-800 kPa) produce a needle coke structure that minimizes thermal expansion during subsequent graphitization at 2800°C
Solution Approach 2:
The invention performs preliminary action by pre-controlling the crystallite development and graphitization degree during coking to prevent excessive thermal expansion during the final graphitization process. The controlled structural parameters in raw coke create a more stable structure that resists puffing when heated to graphitization temperatures
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 process simplifies the washing of activated carbon, reduces remaining alkali metal content, and produces needle coke with low thermal expansion, enhancing the performance and durability of electric double layer capacitors and graphite electrodes.
Implementation Method 1
hydrodesulfurizing a heavy oil with a sulfur content of 2 percent by mass or more at a total pressure of 16 MPa or greater
Implementation Method 2
fluidized catalytic cracking a hydrocarbon oil to produce a second heavy oil
Implementation Method 3
coking the feedstock at a pressure of 300 to 800 kPa and a temperature of 400 to 600°C to produce the raw coke
Implementation Method 4
graphitizing the raw coke at a temperature of 2800°C under an inactive gas atmosphere
Data Source
AI summary
The present invention provides a raw coke having such a structure that the graphitized product resulting from graphitization of the raw coke at a temperature of 2800°C under an inactive gas atmosphere will have ratios of the crystallite size to the lattice constant of 360 or less in the (002) plane and 1500 or less in the (110) plane, as a raw coke providing active carbon produced by alkali-activating the raw coke, which is reduced in remaining alkali content and can simplify washing operation because washing liquid can easily pass through the activated carbon, or as a raw coke for the production of needle coke.