Multi-Stage Co-Hydrotreating for Low-Sulfur Diesel
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Solution Overview
Problem
Current processes for producing diesel fuels from biocomponent feedstocks, such as vegetable oils and animal fats, face challenges including poor cold flow properties, low oxidation stability, and high sulfur content, as well as equipment and cost inefficiencies, particularly in achieving low sulfur levels and managing exothermic reactions and hydrogen usage.
Innovation Solution
A multi-stage co-hydrotreating process involving two or more reactors with separate hydrotreatment stages, where the biocomponent feedstock is first deoxygenated and partially desulfurized in the first reactor, followed by further sulfur reduction in the second reactor, with hydrogen recycle loops to manage CO levels and optimize reaction conditions, allowing for up to 20% biocomponent feedstock and achieving sulfur levels of 10 ppm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrodeoxygenation reactions are used to convert biologically derived feeds to hydrocarbon liquids, then oxygen is removed and unsaturated bonds are saturated, but excessive heat is generated and high levels of hydrogen are required leading to undesirably high reaction temperatures or low hydrogen availability
Solution Approach 1:
The hydroprocessing is divided into multiple stages with different functions: first stage for hydrodeoxygenation of biocomponent feedstock, second stage for hydrodesulfurization of mineral feedstock, and optional third stage for final polishing. This segmentation allows each stage to operate under optimized conditions, preventing excessive temperature buildup in any single reactor while achieving complete deoxygenation and desulfurization.
Solution Approach 2:
A mineral hydrocarbon feedstock is introduced as an intermediary medium to absorb the excess heat generated during hydrodeoxygenation of the biocomponent feedstock. The mineral feedstock acts as a heat sink, allowing the biocomponent to be deoxygenated under controlled temperatures while the mineral portion undergoes concurrent hydrodesulfurization.
2Reliability
If hydrodeoxygenation reactions are used to convert biologically derived feeds to hydrocarbon liquids, then oxygen is removed and unsaturated bonds are saturated, but high levels of hydrogen are required leading to low hydrogen availability in the feed stream
Solution Approach 1:
Hydrogen consumption is segmented across multiple reaction stages. The first stage consumes hydrogen for hydrodeoxygenation of biocomponent feedstock, while the second stage consumes hydrogen for hydrodesulfurization of mineral feedstock. This segmentation allows for optimized hydrogen dosing and recycling at each stage, improving overall hydrogen utilization efficiency.
Solution Approach 2:
Hydrogen gas is recovered from the vapor stream produced during hydroprocessing and recycled back to the reaction zones. This hydrogen recovery and recycling system maintains high hydrogen availability in the feed stream while minimizing hydrogen loss and reducing the need for continuous fresh hydrogen supplementation.
3Reliability
If separate processing of mineral hydrocarbon feedstock and biologically derived feedstock is performed, then preferred conditions can be selected for each feedstock individually, but significant additional equipment footprint is required
Solution Approach 1:
The process merges the processing of biocomponent feedstock and mineral hydrocarbon feedstock into a single integrated hydroprocessing unit. Both feedstocks are co-fed into the multi-stage reactor system, allowing simultaneous hydrodeoxygenation of the biocomponent and hydrodesulfurization of the mineral feedstock under individually optimized conditions for each stage, eliminating the need for separate processing trains.
Solution Approach 2:
The multi-stage hydroprocessing unit performs multiple functions: hydrodeoxygenation of biocomponent feedstock, hydrodesulfurization of mineral feedstock, saturation of unsaturated bonds, and removal of unwanted side reaction products. This universal processing system handles both feedstock types with different chemical requirements using a single integrated facility.
4Area of stationary object
If single-stage co-processing is used, then equipment footprint is reduced, but undesirably high reaction temperatures and low hydrogen availability occur
Solution Approach 1:
The single integrated unit is divided into multiple reaction stages with distinct temperature and pressure conditions. The first stage operates at conditions optimized for hydrodeoxygenation, the second stage at conditions optimized for hydrodesulfurization, and the third stage for final polishing. This internal segmentation prevents excessive temperature buildup while maintaining compact equipment footprint.
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 process effectively reduces sulfur content to 10 ppm or less, improves cetane number, and maintains desired temperature conditions, overcoming catalyst inhibition and equipment footprint issues, while enabling the use of existing refinery infrastructure.
Implementation Method 1
hydrodeoxygenation reactions are highly exothermic relative to hydrodesulfurization and also require relatively large amounts of hydrogen
Implementation Method 2
The feedstock is hydrotreated in the first reaction zone under first effective hydrotreating conditions
Implementation Method 3
The portion of the first hydrotreated feedstock in the second reaction zone is hydrotreated under second effective hydrotreating conditions to produce a diesel boiling range product
Implementation Method 4
hydrotreated under second effective hydrotreating conditions to produce a diesel boiling range product
Implementation Method 5
hydrodeoxygenation reactions are highly exothermic relative to hydrodesulfurization and also require relatively large amounts of hydrogen. The excess heat generated by the hydrodeoxygenation reaction
Data Source
AI summary
Processes are provided for producing a diesel fuel product having a sulfur content of 10 ppm by weight or less from feed sources that include up to 10% by weight of a biocomponent feedstock. The mineral hydrocarbon portions of the feed sources can be distillate or heavier feed sources.