IV.4. Simulaciones: resultados numéricos y análisis
IV.4.5. Empresas
4.1 Thermal stability test
The results of thermal stability tests for the mixtures of LTCO and various petroleum fractions are summarized in Table 2 and the effects of LTCO addition for each fraction are compared. In case of naphtha, as shown in the pictures of the fl ask bottoms in Table 2, addition of LTCO clearly yielded signifi cant residual solid materials. In cases of kero-sene and gas oil, addition of LTCO signifi cantly promoted the residual solid formation.
Conversely, in case of VGO, addition of LTCO reduced the residual solid formation. The residual solid formation in the thermal stability tests is supposed to be corresponding to the fouling potential in the heating procedures of the hydrotreating processes. The results strongly suggest that hydrotreating in an existing process by using of combined feed of LTCO with naphtha, kerosene or gas oil fraction increase the fouling trouble risk compar-ing with the conventional operation for the individual petroleum fraction. On the other hand, addition of LTCO to an existing VGO hydrotreating process can be carried out at a lower risk of fouling problems. Consequently co-hydrotreating of VGO and LTCO has been selected as a favorable LTCO upgrading method.
The low residual solid formation in the mixture of LTCO and VGO is presumably due to the higher solubility of olefi n polymerized products into VGO comparing with the other light oil fractions.
[Typical condition]
Temperature: 300 oC Pressure: 2.5 Pa LHSV: 8 h-1
H2/Oil: 45L/L
Catalyst: NiMo cat.
Product Gas Hyd rogen
Feed
Catalyst Heater Separator
Pump
Figure 2: A simplifi ed fl ow scheme of hydrotreating pilot plant.
4.2 Nitrogen compounds in LTCO
Hydrodenitrogenation (HDN) is well-known as one of the most diffi cult reactions in pe-troleum refi ning, while LTCO contains much higher nitrogen than SR-N. Therefore HDN is the key factor for the successful upgrading in the aspects of hydrotreating reactions. At fi rst, nitrogen compounds in LTCO have been extensively characterized by GC-MS and GC-NPD. The results of analysis are shown in Table 3.
The main nitrogen compound in LTCO is benzonitrile. P-tolunitrile and isobutyronitrile are also detected. These three compounds occupied about 80% of all the nitrogen com-pounds in LTCO. The other nitrogen comcom-pounds are also mainly nitrile comcom-pounds. Such nitrile compounds presumably come from ABS (Acrylonitrile- Butadiene- styrene) and Nylon in waste plastics [4]. Major nitrogen compounds in petroleum are pyridines, qui-nolines and indoles. The nitrogen compounds in LTCO are greatly different from those in petroleum. Then, pilot plant tests of LTCO hydrotreating were carried out.
Petroleum fraction LTCO added
% Naphtha K erosene G as oil VGO
0
(0.5 mg) (0.6 mg) (8.5 mg)
10
(1.0 mg) (1.1 mg) (5.9 mg)
- + 0.5 mg* +0.5 mg* -2.6 mg*
The amounts of the residual solid materials are given in parentheses.
*: The increase of the residual solid materials by addition of 10% LTCO Table 2: Thermal stability test results.
Table 3: Nitrogen compounds in LTCO.
Nitrogen compound mg/ml N%
isobutyronitrile 0.04 3.0
benzonitrile 1.50 74.4
p-tolunitrile 0.07 2.8
hydrogen cyanide trace trace
acetonitrile trace trace
propionitrile trace trace
methacrylonitrile trace trace
crotononitrile trace trace
phenylacetonitrile trace trace
4.3 Pilot plant test of hydrotreating
LTCO hydrotreating experiments were performed under mild conditions similar to those for conventional naphtha hydrotreating. The results of hydrotreating of SR-N and the mix-ture of SR-N and LTCO (10%) are shown in Table 4.
Even under the mild reaction conditions (300 oC, 2.5MPa), HDN of the LTCO mixture feed was easily achieved to a substantially nitrogen-free level. The Achievement of HDN of the LTCO mixture feed under such mild conditions is presumably due to no necessity of heterocyclic ring saturation of nitrile compounds unlike that of pyridines, quinolines and indoles. Moreover, sulfur (300 ppm) and chlorine (8 ppm) were also easily reduced to substantially sulfur-free and chlorine-free levels, respectively. The hydrotreated products of the mixture of SR-N and LTCO can be upgraded to the same level in quality as those of SR-N.
Table 4: Properties of hydrotreated products.
Item Unit SR-N SR-N + LTCO (10%)
before after before after
Density g/cm3 0.7100 0.7045 0.7205 0.7184
Sulfur ppm 340 <1 306 <1
Nitrogen ppm <1 <1 80 <1
Chlorine ppm <1 <1 5 <1
Conditions: NiMo catalyst, 300°C, P(H2) 2.5 MPa, LHSV 8 h-1, H2/Oil 45 NL/L
4.4 Demonstration in oil refi nery
The demonstration operation in Mizushima Oil Refi nery was started in April 2004 in order to confi rm the effect on various units by accepting LTCO from SPR and Rekiseik-ouyu Co., Ltd.
Cumulative throughput of LTCO treated in the oil refi nery is shown in Figure 3. About 800 KL of LTCO was upgraded from April, 2004 to March, 2005 without any problem.
0 200 400 600 800 1000
4/1/04 6/30/04 9/28/04 12/27/04 3/27/05
Cumulative throughput (KL)
Figure 3: Cumulative throughput of LTCO treated in Mizushima Oil Refi nery.
5. Conclusion
We have developed a successful fl ow scheme to co-process LTCO with petroleum in an oil refi nery and demonstrated that utilizing an existing upgrading unit at Mizushima Oil Refi nery in 2004. Key issues in the application, fouling in oil refi ning equipment and the oil products’ qualities have been successfully solved.
The upgrading of LTCO has been continued and the throughput of LTCO will be increased in the near furture. Moreover, the upgrading technology of LTCO will be extended to that of the whole fractions of thermal cracking oil derived from waste plastics. The feedstock recycling by the co-processing of petroleum and thermal cracking oil derived from mu-nicipal waste plastics is promising as an useful way of recycling of plastics.
References
[1] E.Sugiyama, H. Muta, H.Ibe, 1st International Symposium on Feedstock Recycling of Plastics, 1999-11.
[2] E. Sugiyama, K. Wakai, N. Shiratori, T. Kawanishi, T. Abe, The Japan Society of Waste Management Experts., 15, 584- 586 (2004).
[3] C.Savu, C. Vasile, E. Voicu-Bosovei, Riv. Combust., 49, 145-153 (1995).
[4] Mihai Brebu, M.Azhar Uddin, Akinori Muto, and Yusaku Sakata, Energy & Fuels, 14, 920-928 (2000).