Assorted Co-staging in Hydrotreating for Deep Desulfurization
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Solution Overview
Problem
Current hydrodesulfurization processes face inefficiencies in removing 'difficult or refractory sulfur' species and aromatics from diesel range hydrocarbons, leading to suboptimal cetane number improvement and sulfur content reduction, with challenges in maintaining catalyst activity and minimizing unwanted thermal and catalytic cracking.
Innovation Solution
A two-stage hydrotreating process with co- and counter-stage configuration, segregating diesel feed streams based on sulfur species and aromatics content, optimizing contact time and hydrogen sulfide levels to concentrate 'easy' and 'difficult' sulfur streams for separate treatment, using conventional NiMo catalysts under specific temperature, pressure, and hydrogen-to-oil ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If higher temperatures and pressures are used to remove difficult sulfur species and aromatics, then desulfurization effectiveness and cetane number improvement are enhanced, but catalyst deactivation due to coking and unwanted thermal cracking increases
Solution Approach 1:
The hydrotreating process is divided into two distinct stages: first stage operates at moderate conditions (300-350°C, 40-60 barg) to remove easy sulfur species and perform initial aromatic saturation, while second stage operates at severe conditions (350-450°C, 60-100 barg) specifically targeting difficult sulfur species and multi-ring aromatics. This segmentation allows each stage to be optimized for its specific function, preventing catalyst deactivation by avoiding excessive temperatures in the first stage while ensuring deep desulfurization in the second stage.
Solution Approach 2:
The first stage performs preliminary hydrogenation of aromatic compounds and removal of easy sulfur species before the feed enters the second stage. This preliminary action reduces the burden on the second stage catalyst, allowing it to focus on the more challenging difficult sulfur species without being overwhelmed by easier reactions, thereby extending catalyst life and maintaining activity.
2Manufacturing precision
If higher catalyst volume and longer reaction time are used to treat difficult sulfur species, then desulfurization effectiveness improves, but productivity decreases
Solution Approach 1:
By segmenting the process into two stages with different operating conditions, the patent achieves deep desulfurization without requiring excessive catalyst volume in a single stage. The first stage handles the bulk of easy sulfur removal with smaller catalyst volume, while the second stage, operating at more severe conditions, efficiently treats the remaining difficult sulfur species, thereby improving overall productivity per unit catalyst volume.
Solution Approach 2:
The patent changes operating parameters between stages: temperature is increased from 300-350°C in the first stage to 350-450°C in the second stage, and pressure is increased from 40-60 barg to 60-100 barg. These parameter changes enable the second stage to achieve deep desulfurization of difficult sulfur species more rapidly, reducing the required catalyst volume and reaction time compared to using a single large-stage reactor.
3Manufacturing precision
If two-stage hydrodesulfurization is implemented to remove different sulfur compound molecules sequentially, then sulfur content reduction improves, but device complexity increases
Solution Approach 1:
The patent implements two separate hydrotreating stages, each with its own reactor and catalyst bed, allowing independent optimization of operating conditions for each stage. This segmentation enables the first stage to operate at moderate conditions for easy sulfur removal while the second stage operates at severe conditions for difficult sulfur species, achieving deep desulfurization below 10 ppm without requiring overly complex integrated systems.
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
Achieves deep desulfurization and hydro-treating, reducing sulfur content below 10 ppm and enhancing cetane number above 51, while maintaining catalyst activity and minimizing unwanted byproducts.
Implementation Method 1
The sulfur compound species found in the diesel pool can be broadly categorized into two types namely: 'easy sulfur' type species and 'difficult or refractory sulfur' type species. The 'easy sulfur' species undergoes desulfurization in hydrotreating by hydrogenolysis reaction mechanism.
Implementation Method 2
The 'easy sulfur' species undergoes desulfurization in hydrotreating by hydrogenolysis reaction mechanism. The reaction is much faster and hence diesel streams constituting the easy sulfur species require lesser amount of catalyst volume per unit volume of feed per hour
Implementation Method 3
segregating a full range diesel feed stream into a first feed stream and a second feed stream by a distillation technique, wherein the first feed stream has boiling point in the range of 200 to 320°C and the second feed stream has boiling point in the range of 320 to 390°C
Implementation Method 4
flashing the liquid part obtained in step (d) to obtain a top flashed liquid and a bottom flashed liquid
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The present invention relates to an assorted co-staging and counter stage hydro-treating process configuration scheme is disclosed for deep desulfurization and deep hydro-treating of diesel range hydrocarbons for obtaining diesel product having product sulfur less than 10 ppm and cetane number more than 51.