Creosote hydrotreating is a process that utilizes hydrogen and catalysts to upgrade creosote oil, a complex mixture of organic compounds derived from coal tar. Here’s a breakdown of the key aspects:
Purpose:
Reduce sulfur content: Creosote naturally contains high levels of sulfur compounds, which can be harmful to the environment and pose health risks. Hydrotreating aims to convert these sulfur compounds into hydrogen sulfide gas, significantly lowering the overall sulfur content.
Improve product quality: The process also aims to:
Reduce the concentration of polycyclic aromatic hydrocarbons (PAHs): These are potentially carcinogenic compounds present in creosote.
Enhance stability and reduce the risk of spontaneous combustion.
Tailor the product properties: Depending on the desired end product, the process can be optimized to produce specific fractions like naphthalene or lighter aromatic hydrocarbons.
Feedstock:
Crude creosote oil, a dark brown to black viscous liquid obtained from coal tar distillation.
Key Steps:
Feedstock Preparation:
The creosote oil may undergo preliminary fractionation to remove heavy pitch components that can deactivate the catalyst.
The feed is then preheated and mixed with hydrogen gas.
Reactor:
The mixture enters a fixed-bed reactor containing a catalyst, typically a molybdenum-based catalyst.
Under high temperatures (around 230-350°C) and moderate to high pressures (around 30-100 bar), the catalyst promotes various reactions:
Hydrogenation of sulfur compounds to hydrogen sulfide gas.
Partial hydrogenation of aromatic rings, reducing the concentration of PAHs.
Cracking of heavier molecules into lighter hydrocarbons, including naphthalene and lower-boiling aromatics.
Separation:
The product stream leaving the reactor is cooled and sent to separators:
Hydrogen gas is separated and recycled back to the process.
The treated creosote oil, with reduced sulfur content and potentially tailored product composition, is separated from water and gas byproducts.
Further Processing:
Depending on the desired end product, the treated creosote oil may undergo further fractionation to isolate specific components like naphthalene.
Benefits:
Produces cleaner creosote oil with significantly lower sulfur content, meeting environmental regulations and reducing health risks.
Reduces the concentration of harmful PAHs.
Enhances product stability and reduces the risk of spontaneous combustion.
Enables production of specific valuable products like naphthalene.
Additional Points:
The specific catalyst type, operating conditions, and fractionation steps can be adjusted depending on the desired product properties and level of sulfur removal required.
Creosote hydrotreating is a complex process requiring specialized equipment and safety measures due to the hazardous nature of creosote and hydrogen gas.
This process plays a crucial role in upgrading creosote oil for various applications, including wood preservation, pharmaceutical production, and specialty chemicals.
Here are some resources for further exploration:
US Patent: Method of making naphthalene and lower-boiling compounds from creosote oil: https://patents.google.com/patent/US2920116A/en
Creosote: https://en.wikipedia.org/wiki/Creosote