Patent Application
20180086988
This invention details an enhanced process that allows the selective removal of naphthenic acids from heavy and extra heavy crudes through catalytic hydrogenation, specifically crudes with a high TAN (Total Acid Number).
Currently, given the increased demand for crudes worldwide, it is necessary to use acid crudes as feeds to refineries. As it is well known, problems derived from the use of this type of crude involves fouling and corrosion given its high acidity, which is mainly connected to the naphthenic acids content in the same.
There are several reports on the status of the technique that mention the removal of naphthenic acids through catalytic hydrogenation processes. An example is patent EP0778873B1 that describes a removal process using NiMo/AL2O3 commercial catalysts at temperature conditions between 273 K-573 K, pressure conditions between 100 kPa-5000 kPa and at space velocity of 0.5-5 h−1, catalyst of 10 to 12 nanometers porosity, reaching an acidity reduction of 96% with 2.6 TAN crudes.
A similar approach is presented by U.S. Pat. No. 5,897,769 and U.S. Pat. No. 5,910,242, which describe a process through which reduction of TAN is achieved by using hydrogenation of acidic crudes and hydro treatment commercial catalysts such as NiMo or CoMo supported on alumina or on a mixture of alumina and silica. Hydro deoxygenation is performed at temperatures between 473 K and 643 K, pressures in the range from 0 to 13 MPa and LHSV (space velocity) between 0.1 and 1 h−1. In U.S. Pat. No. 5,897,769 the invention is given by the selectivity of the removal of naphthenic acids with small molecular weight, for which a catalyst with a pore diameter between 50 and 85 Å for removing acids with molecular weight below 450 (g/mol) is used. On the other hand, invention U.S. Pat. No. 5,910,242 sets forth a hydro treatment process by adding H2S to hydrogen to improve the reduction of naphthenic acids; such process requires gas purification plants to remove H2S.
Other patents, such as US20070000810/2007, describe an acidity reduction process by being exposed to one or two hydrogenation catalysts composed of one or more metals from columns 6 to 19 of the periodic table to obtain a 90% acidity removal at temperature conditions of at least 623.15 K, pressures of 3.5 MPa and LHSV of 0.1 h−1
Patent CN101230289 describes a hydro treatment process for removal of naphthenic acids by using NiMo commercial catalysts with the presence of textural promoters such as MgO at concentrations between 0.3-3.5%, thus allowing to improve the activity of the catalyst to obtain acid numbers of 1 mg KOH/g in crudes with an acidity of 3.5 mg KOH/g.
Although many efforts have been made to implement more efficient processes for the removal of acidity in heavy and extra heavy crudes, the status of the technical requires new economic processes to make the technology feasible and to implement it in production fields by having selective catalysts that will result in the elimination of some stages when processing sulfur, greater times of useful life of the catalyst and the reduction in consumption of hydrogen in the process.
This invention describes a catalytic hydrogenation process that allows the selective removal of naphthenic acids in heavy and extra heavy crudes with a low production of hydrogen sulfides, specifically in crude not previously distilled into fractions. The catalyst is composed of an alumina type support and/or magnesium aluminum spinel with Fe—Mo active phases. In addition, it has been surprisingly found that the hydrogenation process using Fe and Mo and/or their mixtures allows to obtain acid numbers of 1 mg KOH/g or lower in crudes with acidity greater than 4 mg KOH/g, allowing for the reduction of unwanted reactions in the process and extending the useful life of the catalyst as a result of the low deposition of metal sulphides.
Catalysts used in hydro treating heavy fractions are characterized by having a larger pore size than catalysts used in diesel and gasoline hydrodesulphurization, which, in general, are basically metal oxides partially or totally sulphurized for their activation. Hydrogenation, decarboxylation and decarboxylation process are carried out by active phases of the catalyst. The support of the catalyst provides a large superficial area, mechanical resistance and thermal stability, preventing sintering. This invention showed that there is a synergistic effect between metal sulfides of Mo (group VIB) and of Fe (group VIIIB) in reactions involved in the hydro treatment process. In such a way, the activity of catalysts containing sulfides of both groups is greater when compared to the activity of individual sulfides for the removal of naphthenic acids. Interaction of Fe—Mo active phase reduces deposition and disfavors unwanted reactions in the process. The catalyst used is FeMo supported on gamma alumina and/or Mg-alumina spinel. Different atomic relations of FeMo of the catalyst ranging between 0.05 and 1 were experimented. Optimal atomic relation of Fe to Mo found is 0.1 and molybdenum concentration in the catalyst ranges between 4-10% in molybdenum weight. Before processing crude, the catalyst was subject to an activation process with a 2% dimethyl disulfide mixture in diesel using hydrogen as gas to obtain molybdenum and Fe sulfide as active places in the catalyst.
Improved crude was physic-chemically characterized by the following methods: ASTM D1552 standard method for total sulfur; digital density at 288 K ASTM D4052; 353 K ASTM D445 standard test for kinematic viscosity; ASTM-664 standard test for acid number of petroleum products; 309 K-1013K-ASTMD7169 tests for simulated distillation at high temperatures for crudes; ICP-OES hydrocarbon quantitative analysis (Al, Ba, Ca, Cu, Fe, Mg, Mo, Ni, K, Na, V); UST-LAS-I-193-2012 determination and distribution of molecular weight. Gas resulting from the reaction was analyzed using the Gas Refinery Method (% weight)—UOP 539.
Results obtained through tests conducted with hydro treatment commercial catalysts such as CoMo, NiMo1, NiMo2, NiMo3 and Fe—Mo catalyst supported on alumina with a molybdenum concentration of 10% and a variation of the atomic ratio of Fe with respect to Mo between 0.1 and 0.5 are shown below. The Fe—Mo catalyst has a total area of 256 m2/g, pore volume of 0.63 cm3/g and pore diameter of 97.84 Å.
All of the catalysts were evaluated with heavy crude (Table 1) in a shaker tank reactor in presence of hydrogen and catalyst feed of 90 cm3; operating conditions for the hydro treatment were 573.15 K and 623.15 K at pressure of 4.13 MPa psi and LHSV of 1.1 h−1.
Experimental results show that commercial catalysts such as CoMo when compared to NiMO and FeMo catalysts have a lower selectivity to hydro deoxygenation reactions and a greater affinity to unwanted reactions such as hydrodesulphurization.
The FeMo catalyst in an atomic ratio lower that 0.3 shows a 75% reduction in Sulphur generation when compared to CoMo and NiMO commercial catalyst and a removal of acidity near 90%.
According to the above, the technology, using FeMo catalysts, allows technical and economic advantages given the longer useful life of the catalyst by the reduction in deposition of metal sulphides, lower consumption of hydrogen and without the likelihood of needing to consider a Sulphur treatment plant.
A similar behavior is observed in
Finally, it is worth noting that although Fe belongs to group VIIIB of the periodic table when processing heavy crudes with acidity greater than 4 mg KOH/g it shows a different behavior than that of Ni and Co in terms of desulphurization reactions.
FeMo and Mo catalysts supported in alumina and Mg-aluminum spinel were evaluated at pilot scale, aimed at analyzing the contribution of the Fe and that of the support in the hydro deoxygenation process. A CSTR reactor with a 90 cm3 loading catalyst was used for such tests, which was previously activated with dimethyl disulfide at 2% (v/v) under 593 K, LHSV: 1.1 h−1 conditions and a hydrogen/dimethyl disulfide relation of 120 Nm3/m3.
Subsequently, each catalyst was fed with 7 mg KOH/g acidity crude, at two different temperature conditions: 573 K and 623 K at a pressure of 4.13 MPa, LHSV: 1.1 h−1 and at a volume flow of hydrogen of 0.014 Nm3/h. At the same time the stability of each catalyst was evaluated returning to the initial temperature condition of 573 K.
The textural characterization reported in Table 2 showed that the pore diameter varies from 90 Å to 115 Å, total area between 180 and 280 m2/g and the pore volume goes from 0.4 to 0.7 cm3/g. Based on gases adsorption measurements, the superficial area and the distribution of the pore sizes of the solid materials were determined, and the pore diameter was determined by the BJH method.
To prepare the catalysts, the starter was alumina, followed by an impregnation with Mg to obtain the spinel support and subsequently the Mo metal is impregnated. This catalyst is compared to the Mo/γ-alumina and the FeMo/γ-alumina.
Results are reported in Table 2 and such results demonstrate a reduction of the average diameter in the catalyst when the texture of the catalyst is modified with Mg and when there is an impregnation of Mo and Fe metals.
In terms of the sulfur reduction in the load, as shown in
According to the results it may be inferred that the Fe metal provides greater hydrogenating properties to the catalyst to favor hydro deoxygenation reactions in naphthenic acids with a lower removal of Sulphur components when compared to the Mo/alumina catalyst. On the other hand, it is observed that the spinel Mg-alumina support diminishes the removal of sulfurs in the load, most likely due to the occupation of the vacancies thus avoiding the deposition of sulfurs in the surface of the catalyst.
Finally, when comparing the three catalysts over time and temperature, it may be inferred that the catalysts are stable since they keep an acidity removal and a low production of Sulphur components.
In terms of hydrogen consumption,
On the other hand, the logarithm distribution for the molecular weight was performed for both the acid and the enhanced crude with a FeMo/γ-alumina catalyst, as shown in
Properties such as viscosity, water and density were measured for the load crude and the product obtained from the tests performed with the FeMo/γ-alumina catalyst. The results on Table 3 show a reduction of 23% in viscosity and an increase of one point in °API. These quality progresses are reflected in economic benefits due to the improvement in crude fluidity and to a smaller quantity of thinner used for transportation.
One of the most attractive methods to perform the removal of acidity is the decarboxylation of the naphthenic acids on basic catalysts. The adequate catalytic materials to carry out the reaction are composed by inorganic metals, specifically carbonates, basic carbonates and oxide of alkaline-earth metals (Be, Mg, Ca, Sr and Ba). Under such conditions, a set of experiments that included the comparison of the commercial MgO/γ-alumina and the CaO catalysts (supported in γ-alumina and bohemite) were conducted using different percentages of Ca to verify the selectivity in the process of removal of naphthenic acids.
All the catalysts were evaluated with heavy crude according to the characterization reported in Table 4, in a reactor of a shaken tank in presence of hydrogen with a 9 e-5 m3 of catalyst load. The operation conditions of hydro treatment were of 573 K and 623 K at a pressure of 4.13 MPa and LHSV of 1.1 h−1.
Experimental results showed that the decarboxylation and hydro deoxygenation reactions are favored when more severities are used in the process with 7 mg KOH/g acidity crudes. However, the activity of basic catalysts is not enough to obtain crude with acidity lower than 2 mg KOH/g as it is the case of the FeMo/γ-alumina catalyst where the acidity removals mount to 80% and the stability is higher as time goes by.
Table 4 shows that secondary reactions as the hydro desulfurization are not favored in the basic catalysts where sulfur removal in the 623 K load fluctuates between 1% and 3%, thus, that of the 10% CaO/bohemite catalyst being greater. On the other hand, it is evident that the CaO catalysts present lower stability as time goes by when compared to the MgO and FeMo catalysts, as a result, the useful life of the catalysts is expected to be less than the one reported in previous examples herein.
It is evident that the naphthenic acids present in the crude, are carboxylic acids, characterized for being an aliphatic ring (or several rings) or naphthenic with a corresponding alkyl group, which ends in a carboxylic acid group. Naphthenic acids produce atypical corrosion phenomena, since they are capable of producing a localized attack without any presence of water at temperatures between 473 K and 693 K thus hindering the processing of these types of crudes at refineries.
This invention describes a catalytic hydrogenation process that allows the selective removal of naphthenic acids in heavy and extra heavy crudes with a low production of hydrogen sulfides, specifically in crude not previously distilled into fractions. The catalyst is composed by an alumina and/or aluminum-magnesium type support with active Fe—Mo phases.
Additionally, the applicant has surprisingly found that the hydrogenation process using Fe and Mo catalysts and/or mixtures between them allows to reach acid numbers of 1 mg KOH/g in crudes with TAN greater than 4 mg KOH/g, thus achieving the reduction of unwanted reactions in the process thus extending the useful life of the catalyst as a result of the low deposition of metal sulphides.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15073602 | Mar 2015 | CO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2016/051811 | 3/31/2016 | WO | 00 |
