Hydrothermal preparation of Nano crystalline Mo-V-Te-Nb-O oxides as multifunctional catalysts in propane selective oxidation to acrylic acid

A pilot reactor study to determine effectiveness factors of the commercial HDS

catalyst to produce ultra-low sulfur diesel (ULSD)

Nilesh Chandak,* Mikael Berthod, Adel Al Hamadi, Mohamed Yousef, Abdulhamid M, Kazuhiro Inamura

Takreer Research Centre, Abu Dhabi Oil Refining Company (TAKREER), P.O. Box: 3593, Abu Dhabi, U.A.E.

*Corresponding author. Email: nchandak@takreer.com, Tel # 971-2-6020903

Abstract:

A pilot plant test was carried out using the catalyst from refinery hydrotreater unit (HDS), part of the green diesel project. The objective of the pilot study was to assess whether the existing refinery HDS unit can produce 8 ppm Sulphur diesel with a difficult feed, blend made of 70 vol% Light Gas Oil – LGO (which is a regular feed to the refinery HDS unit) & 30 vol% hydrotreated Gas Oil - HDT GO. Pilot test results shown that the unit can process such blended feed to reach 8 ppm Sulphur product by an increase of the reactor bed temperature. However due to higher aromatic content in the blended feed, moderate increase in hydrogen consumption was also observed. Catalyst performance was evaluated at 55//42/32 bar PPH2 to determine catalyst deactivation rate and hydrogen consumption, targeting ULSD product. A decrease of hydrogen partial pressure (PPH2) from 52 bar (which is current operating condition) to 32 bar resulted in reduction of H2 consumption but also decrease of catalyst cycle length. In case of lowering H2 consumption, it is recommended to choose H2 partial pressure at 42 bar operation.
Keywords: Light Gas Oil, ULSD, HDS, H2 Consumption, Catalyst Deactivation, HDT pilot plant test.

1. Introduction

Pilot Plants are considered to be an important tool for tackling the commercial refinery unit problems. Even though the quantities of the feedstock/chemicals used are less compared to a commercial (scale up) plant, they are capable of creating significant data for scale up studies. This paper presents a series of experiments in order to determine effectiveness of commercial hydrodesulphurization (HDS) catalyst to produce Ultra Low Sulphur Diesel (ULSD). The effects of reaction temperature, pressure and different feedstock on the hydrodesulphurization process are discussed to determine the optimum operating conditions of the actual unit to produce ULSD and estimate hydrogen consumption & cycle life cycle of the catalyst.

2. Experimental

The tests were carried out with LGO and 70:30 blend of LGO/ HDT GO feed (Density: 0.8284 g/cc, Sulphur:
0.2390 wt%) using the fresh catalyst (CoMo/Al2O3) in a pilot reactor at fixed operating conditions (H2 partial pressure, reaction temperature and hydrogen to hydrocarbon ratio). The catalyst samples were loaded to a continuous high- pressure reactor and sulfided by typical activation conditions, followed by the introduction of the feed at predetermined process conditions on multiple key points as listed below Table # 01.

Test Point Nr	Day Nr.	Feed	Estimated temp. °C	Product S cont. ppm	LHSV h-1	H2 partial pressure barg	Reactor inlet H2/HC in Nl/l
Sulfiding	LGO + DMDS
1	48	LGO	Adjusted (est: 315)	8	1	52	190
2	55	Blend LGO + HDT GO	Adjusted (est: 322-326)	8	1	52	190
3	77	Blend LGO + HDT GO	Adjusted (est: 328-332)	8	1	32	190
4	106	Blend LGO + HDT GO	Adjusted (est: 324-328)	8	1	42	190

Table # 01

Laboratory analyses were performed on both gas & liquid products. Gas composition analyzed using online Refinery Gas Analyzer (RGA) and liquid products were tested using Trace Sulfur & Nitrogen Analyzer, Simulated distillation, X-Ray sulfur analyzer, TBP (True Boiling Point) distillation unit & other lab equipment.

3. Results and discussion

The test results have shown that the LGO / HDT GO blend is a difficult feed to process in refinery unit at full capacity with a Sulfur content target set at 8 ppm wt. It may be noted that as expected, it is easy to reach 8 ppm with the LGO (point 1 in Table # 01). This point has been used as the reference point. Further, with blended feed it was possible to reach 8 ppm keeping the same operating conditions except an increase of reactor temperature by 7°C (point 2 in Table # 01). From the catalyst pilot test parameters and laboratory analysis of the products at different operating conditions, kinetic parameters (reaction order, pre-exponential factors and activation energies), catalyst deactivation rate life cycle) and hydrogen consumption were studied. Some of the details of the study results are given below.

3.1 Deactivation Rate

After the initial testing period to reach the 8 ppm Sulphur product at the predetermined process conditions, pilot test was continued at return point at 52 / 42 / 32 bar PPH2 to estimate the catalyst deactivation rate, shown in below graph. The results of deactivation rate study indicated very good stability of the catalyst at 52 bar PPH2 with a rate of 0.1 °C / month. When the PPH2 is set at 32 bar, the catalyst starts to deactivate at a higher rate around 4

°C/month. This increase in the deactivation rate when operating with a lower PPH2 demands a higher reactor temperature. Nevertheless, 4 °C / month is a very high deactivation rate even though in pilot plant the deactivation rate is often higher compared to commercial unit. It is clear that with the blended feed, decreasing the pressure will reduce strongly the catalyst life cycle.
PPH2 = 52 bar, 0.1 °C / month PPH2 = 32 bar, 4.2 °C / month PPH2 = 42 bar, 0.7 °C / month

3.2 Hydrogen Consumption

Hydrogen consumption was estimated by performing a material balance for the selected test points accompanied by a series of analysis. Below Table # 02 summarize the H2 consumption & other relevant analyses data, at fixed LHSV=1.0 h-1 & H2/HC: 190 Nl/l during this pilot test study, at 52, 32 & 42 bar PPH2.

Sample # 8597/11963/9155	Density @ 15 °C	H (wt%)	N ppm_wt	Total Arom. (wt%)	RI @ 20 °C	Color ASTM	Sim Dist (°C) 5%-50%-90%-95%	H2 Cons. (Nl/l)
PPH2 = 52 bar T = 325 °C	0.8214	13.92	0.3	20.1	1.4558	<0.5	189-275-324-348	33 ± 2
PPH2 = 42 bar T = 330 °C	0.8219	13.90	0.3	21.1	1.4560	<0.5	193-274-325-371	28 ± 2
PPH2 = 32 bar T = 332 °C	0.8229	13.76	0.8	21.8	1.4572	<0.5	189-274-325-350	25 ± 2

4. Conclusion

Table # 02

The pilot plant testing of HDS catalyst using the blended feed, with in the design limits of operating conditions of refinery HDS unit, have shown that it is possible to reach 8 ppm ULSD. The temperature increase needed to reach this performance is 7 °C at 52 bar, 9 °C at 42 bar and 14 °C at 32 bar. At 52 bar pressure, hydrogen consumption is higher (compared to the results at 32 bar PPH2) @ 33 Nl/l and catalyst deactivation rate is just 0.1 °C / month. If pressure is reduced by 20 bar i.e. from 52 bar to 32 bar, chemical consumption of H2 decreases significantly to 25 Nl/l but catalyst deactivation rate increases to 4.2 °C/month. Considering the high deactivation rate at 4 °C / month, H2 pressure at 32 bar operation is not practical. In case of lowering H2 consumption, it is recommended to choose H2 partial pressure at 42 bar operation.