Selective Hydrogenation for FCC Gasoline Purification
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Solution Overview
Problem
Catalytic cracking units face challenges in producing middle distillate products due to the inhibitory effects of nitrogen and sulfur compounds on catalyst cycle duration, despite existing processes optimizing for light products like gasoline and propylene.
Innovation Solution
A selective hydrogenation step is added to the gasoline output from the catalytic cracking unit to convert diolefins and sulfur compounds, reducing their content and thereby extending the catalyst cycle duration without altering the product distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If catalytic cracking unit operates to produce middle distillate with added oligomerization unit, then production flexibility and middle distillate yield improve, but dienes and sulfur compounds in feedstock inhibit catalyst cycle time
Solution Approach 1:
The patent applies preliminary action by implementing a selective hydrogenation step before the oligomerization unit to pre-treat the gasoline feedstock. This hydrogenation step converts dienes to olefins and removes sulfur compounds in advance, preventing catalyst inhibition before the oligomerization process begins, thereby extending catalyst cycle time while maintaining production flexibility
2Reliability
If purification step is added to reduce nitrogen compounds, then reaction poison content decreases, but dienes and sulfur compounds remain as reaction inhibitors
Solution Approach 1:
The patent converts the harmful effect of dienes and sulfur compounds into a benefit by using selective hydrogenation to transform dienes into olefins (useful products) and remove sulfur compounds. This approach not only eliminates the harmful inhibitors but also improves the quality of the oligomerization feedstock, extending catalyst life without adding complex purification equipment
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
The selective hydrogenation process significantly increases the operating cycle duration of the oligomerization catalyst, improving the efficiency and flexibility of middle distillate production while maintaining desired product yields.
Implementation Method 1
A selective hydrogenation step is added to the gasoline output from the catalytic cracking unit to convert diolefins and sulfur compounds
Data Source
Figure 1
AI summary
The method comprises (a) catalytic cracking (FCC) of a heavy cut producing a cut petrol C5-220[deg] C when the FCC is directed towards the production of petrol and C5-150[deg] C when the FCC is directed towards the production of average distillate, (b) performing selective hydrogenation of the cut petrol output from a catalytic cracking unit (2), (c) separating the petrol output from of the step (b) by distillation to separate two cuts including a cut light petrol C5-pF and a cut heavy petrol pF-220[deg] C, and (d) purifying light petrol C5-pF output to reduce nitrogen to less than 0.2 ppm. The method comprises (a) catalytic cracking (FCC) of a heavy cut producing a cut petrol C5-220[deg] C when the FCC is directed towards the production of petrol and C5-150[deg] C when the FCC is directed towards the production of average distillate, (b) performing selective hydrogenation of the cut petrol output from a catalytic cracking unit (2) functioning at a pressure of 0.5-5 MPa, a temperature of 80-220[deg] C and liquid hourly space velocity (LHSV) of 1-10 hours -> 1>, where the LHSV is expressed in liters of load per liter of catalyst per hour, (c) separating the petrol output from of the step (b) by distillation to separate two cuts including a cut light petrol C5-pF and a cut heavy petrol pF-220[deg] C, where the temperature pF is a boundary between light petrol and heavy petrol and in a range of 50-80[deg] C, (d) purifying light petrol C5-pF output from of the step (c) to reduce nitrogen to less than 0.2 ppm, (e) performing oligomerization of light petrol C5-pF output from the step (d), and (f) separating oligomers obtained at the step (e) to release two cuts including a cut petrol C5-150[deg] C and a cut distillate 150[deg] C+. The operating conditions of the step (e) are: temperature of 120-250[deg] C; pressure of 3-6 MPa; and catalysts based on sulfonic resin type when the method functions in maximum mode propylene. The cut petrol C5-150[deg] C and the cut distillate 150[deg] C+ output from of the step (f) are recycled with the FCC when the method functions in the maximum mode propylene. The cut distillate 150[deg] C-360[deg] C output from the step (f) after the step (e) is recycled in the FCC to improve aggregate output of petrol such as selectivity of petrol compared to the average distillate when the method functions in a maximum mode petrol. The operating conditions of the step (e) are: temperature of 150-350[deg] C; pressure of 3-6 MPa; and catalyst based on silica-alumina or amorphous aluminosilicate or crystalline zeolite when the method functions in a maximum mode distillate. The cut light petrol PI-150[deg] C is recycled with the FCC when the method functions in the maximum mode distillate. The step (d) located upstream of the step (e) is removed when the nitrogen content of the light petrol output from of the step (c) is lower than 1 ppm. A purification unit (15) located upstream unit of an oligomerization unit (17) uses a prior wash with water followed by adsorption onto adsorbents.