I. Process Introduction
1. Technology background
To meet the demand for high-octane gasoline as well as to improve the diesel quality, a new technology with integration of the hydrotreating process of LCO and the FCC process of hydrotreated LCO for converting inferior LCO to light aromatics and higher RON gasoline (LTAG) was developed by Sinopec. For LTAG, LCO hydrogenation has a low H2 consumption. It breaks through the thermodynamic limitations of ring opening cracking and hydrogen transfer reactions of hydrogenated monocyclic aromatic hydrocarbons during LCO hydrogenation. Efficient conversion of hydrogenated LCO (hydro-LCO) has been achieved.
2. Technology description
In hydrotreating process, di-aromatics enriched in LCO are hydrogenated moderately into mono-aromatics with tetralin structure by developed LCO PAHs directional hydrogenation control technology. In the subsequent FCC process, a hydro-LCO catalytic cracking conversion zone or a separate reactor is designed. At the same time, the process parameters and specific catalysts for catalytic cracking are optimized. In this case, mono-aromatics in hydro-LCO selectively cracks into alkylbenzene with higher RON.
LTAG with two operating modes has been successfully commercialized (see Figure). In Mode I, LCO is introduced into a hydrotreating unit, and the hydro-LCO produced returns to the original FCC riser reactor as sole feedstock. For gasoline produced by LTAG Mode I, the content of olefins is less than 10 vol% and the RON may reach to 94. Moreover, light aromatics can be produced, where the yield of C6-C10 alkylbenzene can be more than 35.5%. In Mode II, both heavy oil and hydro-LCO serve as the feedstock of FCC riser. To process hydro-LCO and heavy oil separately in the same FCC riser, an additional conversion zone at the lower section of the riser is introduced. For gasoline produced by LTAG Mode II, the content of olefins can decrease 4.0~ 5.0 units and the RON can increase 0.5~1.0 unit. Both in Mode I and in Mode II, ~70wt% of once-through conversion of hydro-LCO, ~90wt% of LPG and Gasoline selectivity and ~ 2.5wt% of H2 consumption can be achieved. Full conversion of LCO can be achieved by using cyclic operation.
3. Main technical performance
Typical process conditions are as follows:
| Items | Mode I | Mode II |
| Technical feature | Hydro-LCO produced returns to original FCC reactor as sole feedstock | Both hydro-LCO and heavy oil serve as the feedstock of FCC while being processed in different reaction zones |
| Once-through conversion of hydro-LCO | >70wt% | ~70wt% |
| LPG+Gasoline selectivity | ≮90wt% | ≮90wt% |
| Content of gasoline olefins | <10vol% | Base* – 4~5vol% |
| RON of gasoline | >94 | Base* + 0.5~1.0 |
| Yield of C6-C10 alkylbenzene | ≮35wt% | - |
* Taking conventional FCC before LTAG revamping as Base)
II. Technical characteristics
1. Higher once-through conversion of hydro-LCO (about 70wt%). Full conversion of LCO can be achieved by using cyclic operation.
2. Higher selectivity of LPG and Gasoline, which is about 90wt%. Moreover, the content of gasoline olefins is less than 10 vol% and the RON of gasoline is over 94. The yield of C6-C10 alkylbenzene can reach more than 35%.
3. Lower H2 consumption for LCO hydrogenation (about 2.5wt%)
4. Full use of the existing refinery units, simple equipment revamping, low investment, easy operation.
III. Proprietary catalysts
LTAG-supporting catalyst for LCO hydrogenation can achieve both high saturation rate of polycyclic aromatics and high selectivity of moderate hydrogenation to produce monocyclic aromatics, and the selectivity of both is above 80%.
LTAG-mode I-supporting FCC catalyst (SLA-1) for light aromatics production has strong cracking ability and low hydrogen transfer ability. It is used to process hydrogenated LCO to produce benzene-type monocyclic aromatic hydrocarbons, which can significantly improve the concentration of C6~C10 benzene-type monocyclic aromatics in gasoline (more than 55wt%).
LTAG mode II-supporting FCC catalyst (SLG-1) with high hydrothermal stability, small cell size and strong B acid center has strong ring-opening cracking ability, low hydrogen transfer ability and strong resistance to heavy metal contamination. The yield of LPG and gasoline can be increased by 2.12wt%.
The physicochemical properties of above LTAG proprietary catalysts are similar to those of conventional diesel hydrogenation catalysts and FCC catalysts.
IV. Commercial Installation
LTAG has been applied to more than 30 FCCUs in China so far, and more units are under revamping or construction. Based on a comprehensive evaluation of product slates, product quality, energy consumption and H2 consumption, the incremental profit margin of the LTAG technology is about 24USD per ton of recycled LCO.