Technical White Paper on Process for Deeply Desulfurizing Catalytic Cracking Gasoline

Technical White Paper: Process for Deeply Desulfurizing Catalytic Cracking Gasoline (EHDS)

Authors: Tianzhen Hao, Jinsen Gao, Dezhong Li, Liang Zhao, Zhiyuan Lu, Xingying Lan
Patent Number: US 9,856,423 B2
Date of Issue: January 2, 2018
Assignees: Tianzhen Hao (Hebei, CN), China University of Petroleum-Beijing (Beijing, CN)

Abstract

This white paper details an innovative process for deeply desulfurizing catalytic cracking gasoline, as outlined in U.S. Patent No. 9,856,423 B2. The method employs solvent extraction to remove sulfur compounds from gasoline fractions, enhanced by a saturated C5 hydrocarbon reflux mechanism, and integrates with selective hydrodesulfurization for heavier fractions. The process achieves sulfur content below 10 ppm—often as low as 5 ppm—while limiting octane number loss to less than 0.2 units, offering significant improvements over existing technologies. This paper explores the technical foundation, process flow, operational parameters, and industrial relevance of this patented invention.

1. Introduction

Background

Catalytic cracking gasoline constitutes approximately 70-80% of gasoline products in many regions, making its desulfurization a critical focus for meeting stringent environmental regulations. Standards such as China’s State IV (sulfur < 50 ppm, implemented 2014) and State V (sulfur < 10 ppm, implemented in Beijing, Shanghai, and Guangzhou in 2013) underscore the urgency of reducing sulfur emissions to combat hazy weather and air pollution. Existing technologies like Sinopec’s S-zorb, RSDS, and Axens’ Prime-G+ achieve deep desulfurization but incur significant drawbacks:

• S-zorb: Sulfur < 10 ppm, octane loss of 1.0-2.0 units, full-range hydrogenation.
• RSDS: Sulfur < 10 ppm, octane loss of 3.0-4.0 units, 80% hydrogenation of fractions.
• Prime-G+: Sulfur < 10 ppm, octane loss of 3.0-4.0 units, moderate hydrogenation.

These methods rely heavily on hydrodesulfurization, leading to high octane loss and operational complexity, highlighting the need for a low-octane-loss, non-hydrogenation alternative.

Objective

The patented process aims to:

• Reduce sulfur content in catalytic cracking gasoline to < 10 ppm.
• Limit octane number loss to < 0.2 units, outperforming existing benchmarks.
• Minimize the proportion of hydrodesulfurization, enhancing efficiency and preserving gasoline quality.

Significance

By integrating solvent extraction with a novel C5 reflux mechanism and selective hydrodesulfurization, this process addresses environmental compliance and economic efficiency. Its adaptability to existing refinery systems positions it as a transformative solution for global gasoline production.

2. Technical Foundation

Sulfur Distribution in Catalytic Cracking Gasoline

The invention leverages the distinct distribution of sulfur compounds across gasoline fractions:

• C5 Fraction (<40°C): Dominated by mercaptan sulfur, removable via extraction or conversion to high-boiling-point sulfides.
• C6 Fraction (40-80°C): Primarily thiophene sulfur, extractable due to its similarity to benzene.
• C7 Fraction (70-110°C): Mostly methylthiophene sulfur, extractable like toluene.
• C8+ Fraction (>110°C): Contains alkylthiophenes and thioethers, less extractable but suitable for selective hydrodesulfurization due to lower olefin content (16% by weight).

This distribution enables a hybrid approach: solvent extraction for lighter fractions (C5-C7) and hydrodesulfurization for heavier fractions (C8+).

Core Innovation: Solvent Extraction with C5 Reflux

The process uses solvent extraction to target sulfur compounds in lighter fractions, enhanced by a saturated C5 hydrocarbon reflux. In the extraction tower:

• The C5 reflux displaces olefins from the solvent, preserving octane-critical components.
• Sulfur compounds, aromatics, and cycloolefins remain in the solvent, separated and treated further.
• This minimizes olefin saturation, reducing octane loss while achieving deep sulfur removal.

3. Process Description

3.1 Solvent Extraction Process

Overview

The solvent extraction process targets light gasoline fractions (boiling range 40-100°C or <130°C):

• Feed Introduction: Gasoline enters the extraction tower at the lower-middle section; solvent enters from the top.
• C5 Reflux: Saturated C5 hydrocarbon is injected into a reflux device at the tower bottom.
• Operating Conditions:
  • Top temperature: 55-100°C (preferred 65-80°C).
  • Bottom temperature: 40-80°C (preferred 50-60°C).
  • Top pressure: 0.2-0.7 MPa (preferred 0.5-0.6 MPa).
  • Solvent-to-feed ratio: 1.0-5.0 (preferred 2.0-3.0).
  • C5-to-feed ratio: 0.1-0.5 (preferred 0.2-0.3).
• Outputs:
  • Desulfurized gasoline (Material A) exits the top.
  • Sulfur-rich solvent with C5 hydrocarbons (Material B) exits the bottom.

Solvent Selection

Solvents include tetraethylene glycol, sulfolane, dimethyl sulfoxide, N-methyl pyrrolidone, and others, with water content optimized at 0.6-0.8% by weight for extraction efficiency.

Post-Extraction Processing

• Material A: Washed with 2-4% water by weight to remove residual solvent, yielding desulfurized gasoline.
• Material B: Processed via:
  1. Extraction Distillation Tower: Separates C5 hydrocarbons (Material C) at 150-180°C and 0.15-0.3 MPa, recycled to the reflux device.
  2. Recycling Tower: Separates sulfur-rich oil (Material E) and solvent (Material F) at 130-180°C and 0.015-0.05 MPa. Solvent is recycled; water from oil separation is reused for washing.

Process Flow (Figure 1)

• Equipment: Extraction tower, washing tower, extraction distillation tower, recycling tower, sulfur-rich oil tank, water fractionation tower, reflux accumulator, solvent regeneration tower.
• Recycling: C5 hydrocarbons, solvent, and water are recirculated, enhancing sustainability.

3.2 Deep Desulfurization Variants

The patent offers flexible embodiments combining solvent extraction with existing technologies:

Embodiment 3 (Figure 2)

• Steps:
  1. Separate gasoline into light (<40°C), medium (40-100°C), and heavy (>100°C) fractions.
  2. Remove mercaptans from light fraction via alkali extraction.
  3. Apply solvent extraction to medium fraction.
  4. Hydrodesulfurize heavy fraction with sulfur-rich components.
• Outcome: Sulfur < 5-10 ppm, yield > 95%.

Embodiment 4 (Figure 3)

• Pre-treat with alkali-free sweetening or Prime-G+ to convert mercaptans, followed by solvent extraction and hydrodesulfurization.

Embodiment 5 (Figure 4)

• Two-fraction split (50-130°C), with solvent extraction for light fraction and S-zorb for heavy fraction.

Embodiment 6 (Figure 5)

• Combines mercaptan removal, fine separation, solvent extraction, and S-zorb, optimized for RSDS systems.

Embodiment 7 (Figure 6)

• Similar to Embodiment 6, with dual sulfur-rich streams for hydrodesulfurization.

Embodiment 8 (Figure 7)

• Full-range solvent extraction followed by hydrodesulfurization of sulfur-rich oil.

4. Technical Advantages

Sulfur Removal Efficiency

• Achieves sulfur content < 10 ppm (often < 5 ppm), exceeding State V standards.
• Maintains yield > 95% by mass.

Octane Preservation

• Limits total octane loss to < 0.2 units, compared to 1.0-4.0 units in existing methods.
• C5 reflux preserves olefin content, critical for octane value.

Reduced Hydrodesulfurization

• Confines hydrogenation to heavy fractions (40% of full-range gasoline), lowering costs and complexity.

Flexibility

• Integrates seamlessly with S-zorb, RSDS, Prime-G+, and other systems.

5. Experimental Validation

Embodiment 1

• Feed: Gasoline (40-100°C, 200-400 ppm sulfur).
• Conditions: Top temp 65-70°C, solvent ratio 2.0-2.5, C5 ratio 0.2-0.25.
• Results: Sulfur < 5 ppm, yield > 95%.

Embodiment 2

• Feed: Gasoline (40-100°C, 600-800 ppm sulfur).
• Conditions: Top temp 80-100°C, solvent ratio 1.0-2.0, C5 ratio 0.3-0.5.
• Results: Sulfur < 10 ppm, yield > 95%.

These outcomes validate the process’s efficacy across a range of sulfur concentrations.

6. Industrial Applications

Refinery Integration

• Utilizes existing aromatics extraction equipment, minimizing capital investment.
• Compatible with refineries employing S-zorb, RSDS, or Prime-G+ technologies.

Environmental Impact

• Enables compliance with ultra-low sulfur regulations, reducing emissions.

Economic Benefits

• Preserves octane value, enhancing product quality.
• Reduces hydrogen consumption, lowering operational costs.

7. Comparison with Other Solutions

Technology	Sulfur Content (ppm)	Octane Loss (Units)	Hydrodesulfurization Proportion
S-zorb	< 10	1.0-2.0	High (full-range)
RSDS	< 10	3.0-4.0	High (80% of fractions)
Prime-G+	< 10	3.0-4.0	Moderate (heavy fractions)
EHDS	< 5-10	< 0.2	Low (40% of fractions)

This process excels in octane preservation and hydrogenation efficiency.

8. Conclusion

The process for deeply desulfurizing catalytic cracking gasoline (US 9,856,423 B2) sets a new benchmark in refining technology. By combining solvent extraction with a C5 reflux mechanism and selective hydrodesulfurization, it delivers ultra-low sulfur levels with minimal octane loss. Its adaptability and economic advantages make it a compelling solution for refineries worldwide, aligning environmental compliance with operational excellence.

9. References

• U.S. Patent No. 9,856,423 B2, "Process for Deeply Desulfurizing Catalytic Cracking Gasoline," issued January 2, 2018.
• Chinese Patent Application No. 201310581366.8, filed November 18, 2013.
• International Application No. PCT/CN2014/070817, filed January 17, 2014.

This white paper provides a detailed, standalone overview of the patented process, suitable for technical audiences seeking to understand its mechanics and implications.