Hydroisomerisation Hydrocracking Fischer-Tropsch Middle Distillates
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Solution Overview
Problem
The Fischer-Tropsch process produces linear hydrocarbons with poor cold resistance properties, making them unsuitable for middle distillate cuts, and unsaturated olefinic compounds in the feed reduce the lifespan of hydrocracking catalysts due to exothermic reactions and potential coking.
Innovation Solution
A process that includes a hydrogenation step before hydrocracking to eliminate unsaturated olefinic compounds under milder conditions, followed by hydroisomerization/hydrocracking, allowing for the direct routing of the hydrogenated effluent without separation, and using a catalyst with a hydrogen-rich environment to enhance catalyst protection and product quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If unsaturated olefinic compounds are present in the hydrocracking feed, then the feed composition reflects the Fischer-Tropsch effluent, but the hydrocracking catalyst lifespan is reduced due to exothermic reactions and coking
Solution Approach 1:
A hydrotreatment step is implemented before hydrocracking to pre-eliminate unsaturated olefinic compounds from the Fischer-Tropsch effluent. This preliminary action prevents these reactive compounds from reaching the hydrocracking catalyst, thereby extending catalyst lifespan by avoiding exothermic reactions and coking that would otherwise occur during hydrocracking
Solution Approach 2:
The conversion process is divided into two distinct stages: (1) a mild hydrotreatment stage operating at lower temperature and pressure to selectively remove olefinic compounds, and (2) a subsequent hydrocracking stage optimized for converting paraffins to middle distillates. This segmentation allows each stage to operate under optimal conditions without interference from reactive unsaturated compounds
2Productivity
If severe operating conditions are used for hydrocracking, then conversion of heavy fractions to middle distillates is achieved, but thermal runaway and coking occur due to hydrogenation of unsaturated compounds
Solution Approach 1:
The hydrotreatment step performed before hydrocracking preliminarily removes unsaturated olefinic compounds that would otherwise undergo highly exothermic hydrogenation during severe hydrocracking conditions. By eliminating these compounds in advance under milder conditions, the process avoids thermal runaway while maintaining high productivity in the subsequent hydrocracking stage
Solution Approach 2:
The presence of unsaturated olefinic compounds in the Fischer-Tropsch effluent, which would normally cause harmful exothermic reactions during hydrocracking, is converted into a benefit by using them as the target substrate for the preliminary hydrotreatment step. Their selective removal under controlled mild conditions eliminates the source of thermal runaway problems while enabling efficient hydrocracking thereafter
3Reliability
If a hydrotreatment stage is implemented upstream of hydrocracking to eliminate unsaturated compounds, then catalyst protection is improved, but process complexity increases
Solution Approach 1:
The hydrotreatment and hydrocracking operations are merged into a single integrated process flow where the effluent from the hydrotreatment step is directly fed to the hydrocracking reactor without intermediate separation or storage. This merging simplifies the overall process structure while maintaining the protective function of removing unsaturated compounds before they reach the hydrocracking catalyst
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 protects the hydrocracking catalyst, controls temperature, and improves the cold properties of paraffins, increasing the yield of middle distillates by effectively removing reactive unsaturated compounds and preventing thermal runaway, while reducing hydrogen consumption and eliminating the need for a recycle compressor.
Implementation Method 1
hydrogenation step before hydrocracking to eliminate unsaturated olefinic compounds
Implementation Method 2
hydrogenation step before hydrocracking to eliminate unsaturated olefinic compounds under milder conditions
Implementation Method 3
hydroisomerization/hydrocracking of the heavy fraction
Implementation Method 4
hydroisomerization/hydrocracking of the heavy fraction
Implementation Method 5
using a catalyst with a hydrogen-rich environment to enhance catalyst protection and product quality
Implementation Method 6
the transformation of the unsaturated compounds can have a negative impact on the hydroisomerization/hydrocracking stage and cause for example a thermal runaway of the reaction
Data Source
AI summary
The invention relates to a method in which the paraffin effluent from a Fischer-Tropsch synthesis unit is separated in order to obtain a C5+ heavy fraction, said heavy fraction being then hydrogenated in the presence of a hydrogenation catalyst at a temperature of between 100°C and 180°C, at a global pressure of between 0.5 and 6 MPa, at an hourly volumetric rate of between 1 and 10h-1, and at a hydrogen flow rate corresponding to a volumetric hydrogen/hydrocarbon ratio of between 5 and 80 Nl/l/h, the liquid hydrogenated effluent being then contacted with a hydroisomerisation / hydrocracking catalyst without any preliminary separation step, the hydroisomerised/hydrocracked effluent being then distilled for obtaining the middle distillates and optionally oil bases.