Coal Depolymerization Naphthalene Recovery Process
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Solution Overview
Problem
Naphthalene, a valuable chemical feedstock, is difficult to recover during coal depolymerization due to decomposition, resulting in significant loss and pressure issues in reactors, necessitating a method to avoid its decomposition and recover it effectively.
Innovation Solution
A process involving partial distillation of the input feedstock blend at temperatures between 220° C. to 260° C. at atmospheric pressure, using a high temperature depolymerizing medium with a hydrogen-to-carbon ratio higher than 7.0, which includes coal tar distillate or soybean oil, to recover naphthalene and maintain fluidity and depolymerization capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If coal depolymerization is performed in a high temperature reactor, then liquid hydrocarbon products are produced, but naphthalene decomposes and is lost
Solution Approach 1:
The patent applies preliminary action by conducting partial distillation before the main depolymerization reaction to remove naphthalene from the feedstock blend. This prevents naphthalene from being present during high-temperature processing where it would decompose, thereby recovering naphthalene before it can be lost while still enabling subsequent liquid hydrocarbon production from the remaining feedstock.
Solution Approach 2:
The patent segments the processing into distinct stages: first performing partial distillation at controlled temperatures (220-260°C) to separate and recover naphthalene, then conducting the main depolymerization reaction at higher temperatures. This segmentation allows each process to operate under optimal conditions without interfering with the other, preventing naphthalene decomposition while maintaining productivity.
2Loss of substance
If distillation temperature is increased to recover naphthalene, then naphthalene recovery is improved, but other valuable components may decompose
Solution Approach 1:
The patent applies parameter changes by carefully controlling the distillation temperature range at 220-260°C, which is specifically selected to be above naphthalene's boiling point (218°C) but below the decomposition temperatures of other valuable components. This precise parameter control enables selective naphthalene vaporization and recovery while protecting other components from thermal degradation.
Solution Approach 2:
The patent applies local quality by creating different thermal environments in different parts of the process: the distillation section operates at moderate temperatures (220-260°C) specifically for naphthalene recovery, while the main depolymerization reactor operates at higher temperatures. This localized temperature control allows naphthalene recovery without exposing other components to excessive heat that would cause decomposition.
3Stability of the object's composition
If hydrogen-rich medium is added to maintain fluidity, then depolymerization capability is maintained, but process complexity increases
Solution Approach 1:
The patent uses a hydrogen-rich medium as an intermediary substance that facilitates the depolymerization reaction by maintaining fluidity and preventing repolymerization. This intermediary enables the reaction to proceed effectively under controlled conditions, and the medium can be selected from common materials like coal tar distillate or vegetable oils, avoiding the need for complex specialized equipment or procedures.
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 method effectively recovers most of the naphthalene, preventing its decomposition and ensuring the production of valuable liquid hydrocarbon products while maintaining reactor stability by adjusting the distillation conditions and using a hydrogen-rich medium.
Implementation Method 1
heating the mixture to a temperature between 350° C. and 450° C. for a period of at least one minute to create a digested coal slurry
Implementation Method 2
Naphthalene does not absorb hydrogen to become tetrahydronaphthalene because there is no discernable tetrahydronaphthalene in the post-reaction assay. Hence most of naphthalene must have decomposed.
Implementation Method 3
performing a first distillation at a temperature below 250° C. to recover naphthalene
Implementation Method 4
the cut point, or temperature at which distillation is to be terminated, should be about 220° C. to 260° C. at atmospheric pressure
Implementation Method 5
naphthalene (C10H8) has a hydrogen content of 6.25%, it should be replaced by the addition of additional liquid with equivalent or higher hydrogen content in order to maintain fluidity and depolymerization capability
Data Source
AI summary
A method of depolymerizing coal includes preparing a high temperature depolymerizing medium consisting of heavy hydrocarbon oils and mixing it with coal to form a mixture, performing an optional first distillation at a temperature below 250° C. to recover naphthalene, heating the mixture to a temperature between 350° C. and 450° C. to create a digested coal, centrifuging the digested coal to remove ash and obtain a centrate, and distillation of the centrate into separate fractions. The high temperature depolymerizing medium may be a heavy hydrocarbon with a hydrogen to carbon (H/C) ratio higher than 7.0% and may include liquids chosen from the group consisting of: coal tar distillate, decant oil, anthracene oil, and heavy aromatic oils. The high temperature depolymerizing medium may be blended with an oil, preferably with H/C ratio higher than 10.0%, such as soybean oil, other biomass derived oil, lignin, petroleum oil, pyrolysis oil such that the overall hydrogen-to-carbon mass ratio in a digestion reactor is over 7.0% for the mixture of depolymerizing medium and coal. The depolymerized coal is an aromatic liquid that can itself be, either wholly or in part, a depolymerizing medium so that the process can be repeated.