Patent Application
20170240820
The present invention relates to a process for the production of a high quality hydrocarbon fraction boiling above 190° C., which may be used to provide high quality diesel fuel and lubricant base stocks from high boiling aromatic carbonaceous feedstock such as tar, typically originating from the processing of coal, but also from other heavy hydrocarbon sources. Particularly, the invention relates to a process for the production of quality diesel and lubricant base stocks from a carbonaceous material in which high levels of nitrogen, oxygen and aromatics are present. The carbonaceous material is subjected to hydrogenation and catalytic conversion typically by a highly active process involving active catalysts and process conditions in a hydrotreating process in optional combination with a hydrocracking process. The output of this process is multiple product streams, one of which is a lubricant base stock which falls within high quality industry standards such API Group II or API Group III base oil stock classification.
Tar is often considered an undesirable by-product from coal processing, and there is cost and effort associated with the disposal of surplus tar. This has sparked interest for an efficient conversion of the tar into products with an actual market demand. One such market demand is lubricant base stocks which are required for the blending of a wide range of finished lubricants for automotive, marine, industrial, and other applications. Most lubricant base stocks are traditionally manufactured from mineral crude oils. However, the present invention generates a high quality lubricant base stock by processing and upgrading an otherwise not very desirable industrial by-product.
GB 761,755 and GB 935,712 describe processes in which purified coal tar fractions are hydrogenated. GB 935,712 describes hydrogenation of a coal tar with the objective of forming cycloalkanes, which are not suited for use as diesel fuel or lubricant base stock. GB 761,755 describes a process for conversion of acid and base free coal tar fractions into decahydronaphthalene and other cycloalkanes. Both processes describe a procedure with an initial removal of heteroatoms by hydrogenation or other means, followed by a separate hydrogenation of aromatics. Such operation would in an industrial setting correspond to a two stage operation.
CN1243814C describes a two stage process for production of gasoline, diesel and lubricants, in which the H2:oil ratio is between 1100:1 and 1300:1 Nm3/m3. The feed to the process contained 1606 ppm sulfur and 8636 ppm nitrogen, and the hydrotreated product mixture contained 100 ppm nitrogen, and an undisclosed amount of sulfur. The hydrotreated product mixture is subsequently hydrocracked and fractionated into gasoline, diesel and lubricant base oil. The yield of the different fractions is not disclosed. The lubricant base oil fraction comprises 11.4% aromatics, which does not meet the requirements for API Group II or API Group III base oils. The diesel fraction comprises 53.2% aromatics and has a cetane number of 37, which indicate a diesel which was not fully hydrotreated.
CN103146424 relates to a two stage process for production of fuel and lubricants, in which light products from hydrotreatment in the first stage are separated from heavy products prior to dewaxing of heavy products in a second stage. The patent claims cover a wide range of process conditions, but only a single set of process conditions have been evaluated experimentally. The catalyst employed for hydrotreatment is only moderately active, and hydrotreatment is only conducted to a sulfur level around 300 wt ppm, which also indicates only moderate hydrodenitrogenation. The lubricant product has a moderate viscosity index (VI) of 102, which only is sufficient for API Group II base stock classification. The gasoline fraction comprises 2% oxygen and 0.03 wt % sulfur, which is indicative of a gasoline product which has only been moderately hydrotreated.
Operation of processes in two stages have the benefit of enabling removal of product or side-product, but they are also related to an increase in cost.
Now according to the present disclosure it has been identified that a single stage hydrotreatment process is able to provide a high quality fraction boiling above 190° C., for producing a high quality lubricating oil as well as high quality diesel, if deep hydrotreatment is carried out.
As used herein Group VIII shall be construed as elements from the periodic table according to the CAS definition, i.e. as the elements of the combined 1990 IUPAC Groups 8, 9 and 10. Similarly Group VIB shall be construed as the elements of the combined 1990 IUPAC Group 6.
As used herein a cold flow parameter or a cold flow property shall be understood as a temperature reflecting the viscosity of a hydrocarbon mixture at low temperatures, including the parameters cloud point, pour point, freezing point and cold filter plugging point (CFPP). Common for these parameters are that they define the requirement to low viscosity of diesel under cold conditions as it is also specified in the standard EN 590 specifying requirements to diesel, and the improvement of cold flow properties or of any one of these parameters shall unless stated otherwise be understood as equivalent.
As used herein, boiling in a given range, shall be understood as a hydrocarbon mixture of which at least 80 wt % boils in the stated range.
As used herein naphtha shall be understood as a hydrocarbon product boiling in the range 20-150° C.
As used herein diesel shall be understood as a hydrocarbon product boiling in the range 150-390° C., even though it may not fulfill all formal requirements for commercial diesel.
As used herein lubricants shall be understood as a hydrocarbon product boiling above 350° C. and having attractive viscosity properties.
As used herein, deep hydrotreatment shall be understood as the hydrotreatment to a very low level of sulfur and nitrogen, typically below 30 wt ppm, below 20 wt ppm or even below 10 wt ppm.
As used herein, base oil shall be understood as a raw material for production of lubricants, which may not fulfill all requirements to lubricant products, such as cold flow properties.
As used herein a fraction shall be understood as a part of a stream. The part of the stream in a fraction may be defined simply by splitting the stream or by the boiling point of the fraction, either as the boiling range from a fractionator or as a vapour or liquid stream from a separator operating at a given pressure and temperature.
As used herein excess hydrogen shall be understood as the provision of hydrogen beyond what is stoichiometrically required for all hydrotreatment reactions to occur.
As used herein Viscosity Index (VI) shall be understood as a measure of the temperature influence of lubricant oil viscosity, in accordance with ASTM standard D2270. Increasing VI indicates decreasing temperature influence on viscosity, which is preferred.
As used herein single stage shall be understood as a section of the process in which no stream is withdrawn. Typically a single stage does not include equipment such as compressors, by which the pressure is increased.
API (American Petroleum Institute) base oil classifications is a series of quality definitions for base oils, and are a.o. used for trading the oil. API base oil Group III requirements include less than 300 wt ppm sulfur, at least 90% saturates and a VI above 120. API base oil Group II requirements include less than 300 wt ppm sulfur, at least 90% saturates and a VI between 80 and 120. In addition to the API classifications, standards by other organisations such as SAE exist, and base oils may also be traded based on individual product specifications, often with a minimum VI of 110.
As used herein coal gasification shall be understood as a process comprising coking processes, which destructively distill the coal feedstock, to produce coke with a high carbon content, a gas phase and a liquid phase, coal tar. The coal tar produced is differentiated by its mode of production—either a high temperature or low temperature process. High temperature coal tars are the condensation products obtained by the cooling of the gas evolved at processing temperatures of greater than about 700° C. and up to about 1350° C. Typically, temperatures for the low temperature process ranged from about 200° C. to about 700° C.
Tar is a heavy hydrocarbonaceous liquid. Terms such as coal tar and coke oven tar may be used to indicate the source of the tar. For the purpose of the present application tar is typically a product of coal gasification. Such coal tar is characterized by a high presence of heteroatoms (especially nitrogen, sulfur and oxygen) as well as a high content of aromatics.
As used herein aromatics shall be defined by well-established chemical definitions. However, when quantified, aromatics amounts are determined and defined according to the established ASTM D-6591 method.
A broad embodiment of the present disclosure relates to a process for removal of at least 20%, 40% or 80% of the aromatics content of the fraction boiling above 190° C. from a heavy hydrocarbonaceous feedstock comprising at least 30 wt % aromatics, at least 3000 wt ppm nitrogen and at least 0.5 wt % oxygen said method being carried out in a single stage in which no intermediate stream is withdrawn and comprising the steps of
In a further embodiment the material catalytically active in hydrotreatment comprises a group VIII metal compound, a group VIB metal compound and an oxidic support, taken from the group consisting of alumina, silica, titania and combinations thereof with the associated benefit of such a catalyst being highly active in hydrodenitrogenation, while being substantially inactive in hydrocracking, such that the yield loss is minimized.
In a further embodiment the hydro-treatment conditions involve a hydrogen pressure from 120, 140 or 160 to 200 bar with the associated benefit of such a high hydrogen pressure supporting deep hydrotreatment, and thus providing the low amount of nitrogen required for high saturation of aromatics.
In a further embodiment the hydro-treatment conditions involve a temperature from 340° C. or 360° C. to 400 or 420° C. with the associated benefit of ensuring a high activity, but still avoiding thermal cracking.
In a further embodiment the hydro-treatment conditions involve a liquid hourly space velocity of 0.1 hr−1 or 0.2 hr−1 to 0.5 hr−1, 0.6 hr−1 or 1.0 hr−1 with the associated benefit of such conditions providing a very high conversion with respect to hydrodenitrogenation and dearomatization, while avoiding a very large reactor size.
In a further embodiment the process comprises the further steps of
In a further embodiment the material catalytically active in hydroprocessing is a material catalytically active in hydrocracking such as a material comprising a metal component selected from Group VIII and/or VIB of the Periodic System and being supported on a carrier containing one or more oxides taken from the group consisting of alumina, silica, titania, silica-alumina, molecular sieves, zeolites, ZSM-11, ZSM-22, ZSM-23, ZSM-48, SAPO-5, SAPO-11, SAPO-31, SAPO-34, SAPO-41, MCM-41, zeolite Y, ZSM-5 and zeolite beta with the associated benefit of such a hydrocracking processs of converting high boiling products to lower boiling products, e.g. for providing increased diesel yield of the hydroprocessed product over the hydrotreated product.
In a further embodiment the reaction step in the presence of a material catalytically active in hydrocracking is carried out a temperature between 200° C. and 400° C.,
In a further embodiment at least 80 wt % of either said hydrotreated product or said hydroprocessed product is a fraction boiling above 360° C. with the associated benefit that such a high boiling product having a low aromatic content will be a valuable lubricant base oil.
In a further embodiment the hydroprocessed product fraction boiling above 360° C. is a lubricant or a lubricant base stock having a viscosity index of at least 110 or 120 with the associated benefit that such a lubricant has a high value. Typically the final boiling point of this fraction will be below 600° C.
In a further embodiment at least 80 wt % of either said hydrotreated product or said hydroprocessed product is a fraction boiling between 150 and 350° C., with the associated benefit that such a product having a low aromatic content will be a valuable diesel product or diesel blend component.
In a further embodiment said fraction boiling between 150 and 350° C. is a diesel or a diesel blend stock having a cetane index of at least 35, 38 or 40, with the associated benefit that such a product will be of immediate use as a valuable diesel product. Typically the cetane index will be below 70, 90 or 100.
A feedstock according to the present disclosure comprises high amounts of aromatics (>30 wt %) as well as high amounts of heteroatoms, especially oxygen (>0.5 wt %) and nitrogen (>3000 wt ppm). Such feedstocks, may originate as side streams from production of coke, or from gasification or so-called destructive distillation of coal, as well as from pyrolysis processes. According to the prior art such feedstocks have been hydrotreated with the objective of providing naphtha for gasoline production and middle distillate for diesel production. The naphtha and diesel have however not been of high quality, and a yield of low quality heavy hydrocarbons has also reduced the economics of the process.
Now, according to the present method it is possible to provide an amount of quality diesel and quality lubricant base oil by hydrogenation and saturation of the aromatics. This is based on the identification of the criticality of the ability of the hydrotreatment process to remove a high amount of organic nitrogen. Without being bound by theory, it is assumed that only when the organic nitrogen is reduced to a low level, the catalytic hydrogenation of aromatics is sufficiently active for the successful conversion of aromatics required in production of high quality diesel and high quality lubricant base oil. It is further assumed—again without being bound by theory—that the high amount of oxygen in the hydrocarbon structures may contribute to the formation of high boiling hydrocarbons with a high viscosity index by rupturing the molecular structure during hydrodeoxygenation, and providing a product with a high amount of paraffins.
In the process design for feedstocks with high amounts of heteroatoms, the typical design will be driven by cost optimization, such that the process engineer will select a process with sufficient hydrotreatment for meeting official sulfur standards, in order to reduce reactor size, catalyst cost, hydrogen consumption and to yield losses. To this process a hydrocracking process step as in CN1243814C may be added, as this would provide the highest possible diesel yield by conversion of high boiling hydrocarbons to lower boiling hydrocarbons. In addition some hydrodenitrogenation takes place during hydrocracking. However when replacing the “sufficient hydrotreatment” with “deep hydrotreatment” consuming a higher amount of hydrogen, it was discovered that the extra cost is rewarded by a yield of high quality lubricant and diesel, which surprisingly outweighed the extra cost of deep hydrotreatment.
A requirement to the hydrogenation process used according to the present disclosure therefore is a combination of high hydrodenitrogenation activity with a high dearomatization activity. This combined high activity may be obtained by employing a high H2 partial pressure, which shifts the hydrotreatment equilibria towards hydrogenated products. As the feedstock includes high amounts of heteroatoms, the requirement for high H2 excess in combination with low space velocity becomes especially important.
The conditions required for sufficient hydrodenitrogenation depend on the specific feedstock and the specific catalyst used, but in general a high pressure, a high hydrogen purity and a catalyst highly active in hydrodenitrogenation and dearomatization, a.o. due to a high surface area and a high dispersion of active metals are beneficial for the process according to the present disclosure.
In theory, even a moderately active catalyst could be operated under conditions such as a low space velocity, which would enable the full hydrodenitrogenation. This would however require a large reactor and high amounts of catalyst. The moderate activity of the catalyst may be compensated by increasing the temperature, and an increase in pressure would also favor hydrodenitrogenation. In the practical design of such processes, the individual values of such parameters is dependent on each other, as well as the catalyst used, the specific feed and the desired products. Still, the extent of hydrodenitrogenation can be considered a variable which may be controlled by the overall process conditions, in a manner known to the skilled person.
A process for dearomatization would be favored by the same conditions as those favoring hydrodenitrogenation. However, in addition organic nitrogen is known to inhibit the dearomatization by adsorption to the active sites, and therefore it is important that organic nitrogen is removed extensively if a high dearomatization is to be observed. If the process activity is moderate, hydro-denitrogenation of organic nitrogen molecules may not be completed until a position proximate to the exit of the reactor, and in this case, the initial part of the reactor will contain catalyst which is highly inhibited with respect to hydro-dearomatization by the presence of organic nitrogen on the active sites of the catalyst surface. In such a case the product mixture from hydrogenation will have a low nitrogen level, but an intermediate or even high aromatics level.
The dearomatization will only be active in the section of the reactor which contains catalytically active material not inhibited by the nitrogen. Dearomatization will proceed as a saturation reaction providing saturated hydrocarbon rings or as a ring opening reaction, providing normal or branched paraffins.
One example of a catalyst active in hydro-denitrogenation and hydro-dearomatization is the Haldor Topsøe A/S TK-609T HyBRIM™ catalyst. This catalyst is based on HyBRIM technology, according to which the active metals (Ni and Mo) are highly dispersed, to provide a high amount of active sites at the edge of the dispersed metal particles.
This objective of deep hydrotreatment can be achieved by a conventional but severe hydrotreating step that normally involves operation at temperatures between 340° C. and 420° C., hydrogen pressures from 120 bars up to 200 bars, while the space velocity (LHSV) is quite low at 0.1 hr−1 to 0.6 hr−1 or 1.0 hr−1. The inlet temperature may often be lower by 20° C. or more, as significant hydrodeoxygenation occurs, which is highly exothermic. If the temperature is increased further there is risk that thermal cracking occurs, which gives a yield loss. The high hydrogen pressure is required to shift the thermodynamical equilibrium to promote the saturation of aromatics, and may require a purity of hydrogen above 90% or even 95%. In addition the H2/oil ratio is preferably in the range 2000-3000 Nm3/m3, as the high amount of heteroatoms in the process consumes a high amount of hydrogen, and the catalyst is preferably highly active.
The hydrotreating catalyst comprises a sulfided metal component selected from the non-noble metals of Group VIII and VIB of the Periodic System and being supported on a carrier containing alumina, silica, titania or combinations thereof, and optionally in combination with further promoting constituents. These catalysts are preferably those employed conventionally, such as mixed cobalt and/or nickel and molybdenum sulfides (Co—Mo, Ni—Mo, Ni—W) supported on alumina, silica, silica-alumina or combinations of these. Most preferably the hydrotreating catalyst is Ni—Mo/alumina, Co—Mo/alumina or Ni—W/alumina.
In a further disclosure of the process, a hydroisomerization catalyst or a hydrocracking catalysts may be included to improve the cold flow properties of the liquid product. As the hydrogenation of aromatics results in paraffins with moderate branching which have poor cold flow properties, it may be necessary to decrease the cloud or pour point in order to meet industry specifications. Such an adjustment by hydroisomerization may however also be carried out in a different plant, if a lubricant base oil is sold to a company with capability to perform hydroisomerization of their raw material if required. As both diesel and lubricant fractions may require dewaxing by hydroisomerisation, it is possible that the hydroisomerisation is carried out on the full product mixture, but separate treatment of the diesel and the lubricant fraction may also be preferred in order to reduce the yield loss.
The hydroisomerization catalyst comprises a metal component selected from Group VIII and/or VIB of the Periodic System and being supported on a carrier containing alumina, silica, titania, silica-alumina, molecular sieves, zeolites, ZSM-11, ZSM-22, ZSM-23, ZSM-48, SAPO-5, SAPO-11, SAPO-31, SAPO-34, SAPO-41, MCM-41, zeolite Y, ZSM-5, and zeolite beta. Preferably the hydroisomerization catalyst is Ni—W supported on a carrier containing alumina, zeolite beta and silica-alumina.
The hydroisomerisation step may be carried out in the same reactor and/or same catalyst bed as the previous step(s) or it may be carried out in a separate reactor. The catalyst bed may therefore be a combination of catalysts active in hydrodeoxygenation (HDO), hydrotreatment (HDS, HDN, HDA), hydroisomerisation (HI) and hydrocracking (HC).
The hydroisomerization step involves operation between 200 and 500° C., at pressures up to 200 bars. In a particular embodiment, the hydrotreating step and hydroisomerization step are carried out at a hydrogen pressure of 1-200 bar and at a temperature of 250-450° C., preferably at a pressure of 10-150 bar and a temperature of 250-410° C. and at a liquid hourly space velocity of 0.1-10 h−1. The H2/oil ratio is preferably in the range 100-3000 Nm3/m3.
The hydroisomerization catalyst converts the normal paraffins into iso-paraffins with better cold-flow properties. The bifunctional hydroisomerization catalyst contains both acidic sites typically associated with the oxide carrier and hydrogenation sites typically associated with the metal component. If the active metal component is one or more Group VIII noble metals, the hydroisomerization should preferably be carried out in a separate process stage after separation of hydrogen sulfide, ammonia and water, or at least in a separate reactor or catalyst bed and the feed to the hydroisomerization catalyst should be virtually free of nitrogen and sulfur species, i.e. contain less than 100 wtppm sulfur and less than 100 wtppm nitrogen, preferably less than 10 wtppm sulfur and less than 10 wtppm nitrogen. If the active phase of the metal components is a metal sulfide (e.g. Ni—Mo—S, Co—Mo—S, Ni—W—S) then the step may be carried out in a sour environment and the costly installment of equipment to remove H2S and NH3 formed in the previous step(s) is thus not necessary.
In
In
If the further hydroprocessing reactor 56 is operating as a hydroisomerisation reactor, the product 58 will have only moderate change in boiling point, but instead a conversion of linear paraffins to branched paraffins will occur, which is beneficial as the cold flow properties of the isomerized product will be improved; i.e. the pour point will be lower. However, a reduction of viscosity index may also be observed as a result of paraffin isomerization. The yield loss will be moderate, but very often hydroisomerisation will be carried out only on a specific fraction after fractionation not shown in the figures, in a separate reactor to reduce yield loss even further. Typically the hydroisomerisation catalyst is similar to a hydrocracking catalyst, but selectivity is increased by operating at less severe conditions.
The hydroprocessed hydrocarbon 58 may be cooled in cooler 60 and separated in a high pressure separator 66, to a vapor stream 72 and a product stream 68. The vapor stream 72 is pressurized in compressor 74 and combined with make-up hydrogen 76. The product stream is depressurized in a low pressure separator (or optionally more), and an amount 78 may be directed for liquid recycle. Another amount of a hydroprocessed product 80 is directed to a fractionator 82.
According to
In further embodiments, not illustrated in figures, the stream 48 may be separated into a heavy and a lighter stream. Often the lighter stream may be directly available as a diesel product or possibly require isomerization to improve the cold flow properties, whereas the heavy stream may require hydrocracking to yield a product in a desirable boiling range. By separating the hydrotreated product into a light fraction and a heavy fraction, it becomes possible to treat each fraction of the hydrotreated product optimally—which may or may not involve hydroprocessing of that fraction. This can reduce one or more of the total reactor size, the yield loss and the consumption of hydrogen, and it may even lead to a more attractive product mix. By providing a fractionator prior to the further hydroprocessing it may also be possible to avoid the fractionator 82 downstream further hydroprocessing.
In further embodiments, one or both of the optional separations may be carried out in simple gas liquid separators, operating at suitable pressure and temperature, or in a more complex distillation based fractionator operating at low pressure, providing a better separation. It may be beneficial to maintain an elevated pressure during separation as this will be more energy efficient, since the pressure in downstream reactors may not have to be re-established.
Three experiments were conducted to demonstrate the effect of highly effective hydrodenitrogenation and dearomatization processes.
A hydrotreatment catalyst was made as follows. Alumina powder, alumina gel and diluted nitric acid are mixed for 12 minutes and extruded, in 1/20″ trilobe shape. The extrudates are dried for 2 hours at 200° C. and then calcined at 550° C. The extrudates are then impregnated with an acidic NiMo solution prepared with phosphoric acid, molybdenum trioxide and nickel carbonate, adjusting the amounts to produce a catalyst with 16 wt % Ni, 3 wt % Mo and 3 wt % P. The catalyst is calcined at 370° C. for 2 hours.
The experiments were carried out in a unit with two isothermal reactors in series. The first reactor was loaded with 63 ml of commercial demetallization catalyst TK-743, followed by commercial dearsenation catalyst TK-47, whilst the second reactor was loaded with commercial hydrotreatment catalyst TK-609T HyBRIM™ from Haldor Topsøe A/S. The catalyst beds in both reactors were diluted by 40 vol % inert carborundum (SiC) prior to loading in order to improve the liquid distribution of the reactors. Pure hydrogen was used in once-through mode.
A straight-run fossil diesel spiked with TBDS was used for sulfiding the catalysts. Conditions at three different pressures were tested (168 barg, 120 barg and 100 barg) were tested. Results from the experiments are shown in Table 2.
The feed for the experiments was a tar from gasification of coal, having the properties of Table 1. The determination of aromatic content was carried out according to method ASTM D6591.
Experiments 1, 2 and 3 were carried out in two isothermal reactors in series, with the conditions of the hydrotreatment reactor being stated in Table 2.
The results of Table 2 demonstrate that a significant yield of a high viscosity index lubricant is possible.
When compared to the prior art it is seen that the product according to Experiment 1 is having a 5 wt % yield of a fraction with excellent lubricant base stock properties, as well as about 70 wt % diesel of good quality. Also the product of experiments 2 and 3 were deeply hydrotreated, and included middle distillate and lube base oil of good quality, but the lower severity of hydrotreatment was reflected in a higher aromatic content. This was reflected in a lower product quality; for the middle distillate a lower cetane index and for the lube base oil a lower VI. In comparison, the lubricant products according to the prior art were documented to have inferior VI of only 105. This is assumed to be due to insufficient dearomatization, which again is believed to be related to insufficient hydrodenitrogenation.
All three examples fall under the present disclosure; examples 1 and 2 show a high extent of saturation of all aromatics, while example 3 shows a high extent of saturation of di-aromatics and tri-aromatics.
The high viscosity index lubricant fraction of the present disclosure indicates that this fraction has a high content of paraffins. Similarly the middle distillate of experiment 1 has a higher cetane index that the middle distillates of experiments 2 and 3, which is also believed to indicate a high paraffin content.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14184953.9 | Sep 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/070952 | 9/14/2015 | WO | 00 |
