GB2156381A - Production of kerosene and distillate - Google Patents

Abstract

A process for production of kerosene and distillate useful as transport fuels, characterized by contacting a light olefin feedstock in the gaseous phase with a zeolite catalyst having pore sizes of at least eight-ring windows at moderate temperature and pressure, for example at temperature below 350 DEG and pressure less than 10 MPa, and under conditions that avoid development of hot spots within the catalyst bed, for example in a fluidized bed, whereby a product containing a substantial proportion of kerosene and distillate is obtained, and separating a kerosene and distillate fraction therefrom.

Description

SPECIFICATION Production of transport fuels This invention relates to the production of transport fuels from light olefins.

It is important that processes for the production of transport fuels be energy efficient and are available for a variety of feedstocks such as natural-gas or coal as well as crude oil.

In many parts of the world, e.g. Australia, the use of scarce petroleum resources can be offset by the utilisation of more abundant fossil fuels which are available in much greater quantities, e.g. coal or natural-gas. Although there are available many routes by which these fossil fuels can be converted into low grade petroleum substitutes, there is an increasing interest in their conversion into light olefins which can then be converted to higher grade petroleum substitutes. This might be first accomplished by first converting the fossil fuel, coal or natural-gas, into synthesis-gas (a mixture of carbon monoxide and hydrogen) then applying Fischer-Tropsch technology to convert the synthesis-gas into olefins. An example of a two step route is described by Murchison and Murdick in 'Hydrocarbon Processing' Jan. 1981 p. 159.A more direct single step route is described by Rao and Gormley in 'Hydrocarbon Processing' November, 1980 p. 139.

Olefins can be obtained from other sources, such as a refinery's FCC unit or from methanol or other alcohols, as described for example in U.S. Patent 4.025,576.

Andrews and Bonnifay, in Hydrocarbon Processing April, 1977 p. 161, have compared the IFP Dimersol process with alkylation routes for producing gasoline from olefins. Recently the use of zeolites (crystalline alumino-silicates) has been described for upgrading light olefins or olefinic naphthas to gasoline or gasoline components such as aromatic compounds. Thus U.S. Patent 3,760,024 describes the use of H-ZSM-5 zeolite to convert propylene to aromatics, whilst U.S. Patent 3,960,978 describes special treatments of zeolites to produce olefinic gasoline.

It is well known by those skilled in the art that the application of pressure to olefin oligomerisation reactions can be used to influence the molecular weight (length of the hydrocarbon chain) of the product, higher pressures favouring higher molecular weight materials. In the ultimate the reaction can be performed in the liquid phase, as for example using the zeolite ZSM-12 as described in U.S. Patent 2,254,295. At the ACS Division of Petroleum Chemistry Las Vegas meeting in March 1982, Garwood described the conversion of propylene over H-ZSM-5 zeolite and showed " that the boiling range of the heavy products from propylene increases steadily with increasing pressure. Propylene conversion is essentially complete at 400"F, 330 psig and higher.The range of the product at 1500 psig includes all carbon numbers from C5 to C35,,.

35 It is also well known that lower temperatures favour the formation of higher molecular weight oligomers.

However, the effect of temperature upon olefin oligomerisation over zeolite catalysts is complicated as higher temperatures favour the formation of aromatics. This has also been described by Garwood (ibid): "At 530"F, atmospheric pressure, 0.6 WHSV, propylene converts to a mixture of predominantly C3-C11 olefins.

The products are 95% olefins, with the remainder mostly paraffins and some naphthenes in the higher carbon numbers. At higher temperature conjunction polymerization occurs (involving olefin cyclization to naphthene, followed by hydrogen transfer of naphthene to olefin). The reaction proceeds essentially to completion at 730"F to give the (a) mixture of paraffins and aromatics....".

Zeolites are a class of open-pored crystalline alumino-silicates which can be identified by their characteristic powder X-ray diffraction spectra. The zeolites pertinent to this invention belong to a class comprising those zeolites with pore-sized of at least eight-ring windows (see D.W. Breck "Zeolite Molecular Seives" J. Wiley & Sons, 1974). Another characterising feature of the zeolite of this invention is the ability of the zeolite to be made in the hydrogen, (or acid or decationised) form. This may be brought about by ion exchange with acids, or ammonia ions or by ion exchange with multivalent cation (e.g. zinc or lanthanum) followed by a subsequent heat treatment to form Bronsted acid centres. Not all zeolites are stable to these treatments, but those skilled in the art will be able to chose a method appropriate to a particular zeolite in question.

For practical use, the zeolite requires fabrication into a solid particle, chip or pellet. This fabrication may or may not require the assistance of a binder or inert diluent material. The choice of binder and size of particle will be chosen by the engineering requirements of equipment in which the catalyst is to be used. In a fluid bed reactor small particle, of say 30-100 m, and of high attrition resistance, may be the choice, and this may necessitate supporting the zeolite within a silica matrix formed by a spray dried or sol-gel technique. For a fixed bed reactor, larger particles e.g. tablets of 5 mm or more in diameter may be the choice. These might be formed possibly with the aid of diluents such as alumina, or clays such as bentonite.In some instances the binder may not be totally inert but may provide a co-catalytic role by, for example, providing additional acid sites, or may provide a modification role by dilution of the catalyst, or provide moderating metal ions which, without being limited by theory, might, under the conditions of incorporating the zeolite and the binder, be transferred from the binder component to the zeolite component of the catalyst; or provide metal ions which, with the presence of hydrogen, fulfill a secondary role such as coke or heavy hydrocarbon reduction or will, in the presence of oxygen, facilitate catalyst regeneration.

What we have discovered is that utilizing a zeolite as defined above, light olefins can be oligomerised to hydrocarbon products which are in the gasoline, jet fuel and distillate boiling range, this oligomerisation being conducted at low pressure (atmospheric or near atmospheric) and low temperature (below 350"C and preferably below 300 ) which gives increased savings of processing costs. A critical parameter of the invention is the requirement to maintain the catalyst at a uniform temperature such that hot-spots do not develop within the catalyst bed which would result in the formation of aromatic molecules or coke.

The invention accordingly provides a process for production of kerosene and distillate useful as transport fuels characterized by contacting a light olefin feedstock in the gaseous phase with a zeolite catalyst having pore sizes of at least eight-ring windows at moderate temperature and pressure and under conditions that avoid development of hot spots within the catalyst bed, whereby a product containing a substantial proportion of kerosene and distillate is obtained, and separating a kerosene and distillate fraction therefrom.

The desired product fraction boils above 196"C.

In one embodiment of the invention, hot spots are avoided by carrying out the reaction with the catalyst in thermal contact with a heat sink.

In another embodiment, hot spots are avoided by carrying out the reaction in a fluidized bed.

The reaction is preferably carried out at pressure below 10 MPa, for example less than 1.5 MPa and may also be carried out at atmospheric or near atmospheric pressure.

The temperature is preferably beIow3500C, more preferably beIow3000C.

H-ZSM-5-is a preferred catalyst.

Mordenite is another preferred catalyst.

A preferred feedstock comprises propylene, which may be diluted with light paraffins.

The invention will be further illustrated by the following non-limiting examples.

EXAMPLE 1 Catalyst invention A zeolite was made from a gel consisting of aluminium (69), sodium hydroxide (1 5.2g), colloidal silica (Ludox HS40 (trade mark), 667g), tetrapropyl ammonium bromide (1489), sodium chloride (250g) and water (11009). The gel was crystallised by stirring in an autoclave heated to 175 C for 24 hours. The resulting crystalline aluminosilicate was filtered from the mother-liquor, washed with water then dried at 120"C. The product analysed at 2.21% A1203 and 1.5% Na2O, expressing all Al and Na as their oxides.The product was then acid washed (2M, hydrochloric acid), then filtered, then washed with water to remove excess acid, and then calcined at 5000C for 16 hours in a stream of air moistened with water at ambient temperature. The acid wash and calcination treatment was then repeated giving an acid form zeolite. Analysis by powder X-ray diffraction showed it to be a zeolite of the H-ZSM-Sfamily.

This zeolite was fabricated into a catalyst by mixing with bentonite (2:1, catalyst: bentonite) and water, forming it into 3mm diameter extrusions and hardening by firing to 500"C.

EXAMPLE 2 Prior art This illustrates the prior art conversion of propylene over a zeolite catalyst prepared as described in Example 1.

709 of the fabricated catalyst was charged into a downflow tubular reactor. The bed length was approximately 15cm and the diameter 3.5cm. The bed was fitted with thermocouples down the centre of the bed so that any hot spots could be observed. After purging the bed with nitrogen the reactor was heated to 300"C, the heater set to maintain that temperature at the reactor wall, and propylene feed passed over the catalyst. Upon contact with the feed there was immediately observed an increase in bed temperture. The maximum temperature observed was 445"C i.e. an exotherm in the bed equivalent to 1450C. Pertinent details of the conversion of propylene over the catalyst are given in Table 1. The experiment was conducted at atmospheric pressure.

TABLE 1 on-stream-time (hr) 4 6 12 18 WHSV (hr-1) 1.1 1.2 1.1 1.9 propylene conversion (a) (%) 100 > 95 > 95 > 95 Liquid yield (a.b) 0.40 0.5 0.55 0.37 % aliphatics in liquid, (a,c) (%) 33 46 49 67 I (AlO) (ad) 17.6 6.1 1.8 0.8 Accululated liquid product: RON (clear) = 98.6 : density = 0.7655gcm-3 The superscripts designate as follows: (a) results from product accumulated since previous periods.

(b) grams of liquid product at ambient per grams of propylene converted.

(c) by g.l.c. analysis.

(d) ratio of intensity of aromatic protons to intensity of olefinic protons determined by 1H.n.m.r.

The accumulated liquid product was further analysed by gic and the approximate boiling range determined as: < 196 (gasoline) 92.0% 196-235 (kerosene) 3.8% 235-317 (middledistillatel) 3.6% > 317 (middle distillate 2) 0.6% EXAMPLE 3 A process of the invention The same catalyst as in Example 2 was used to convert propylene except in this case the catalyst was used in a bed of 4mm diameter, which is very narrow when compared with the extrusion diameter of 3mm. The reactor was embedded in a metal block to provide good heat transfer from the catalyst, and in this way hot spots were eliminated. Propylene was passed over the catalyst at 2900C. and three such reactors were simultaneously run using different propylene contact times.Pertinent details of the three are given in Table 2.

TABLE 2 Approx. WHSV of propylene 1 1 2 Ratio N2 diluentto propylene (VN) 0 1/1 1/1 Contact time of propylene (sec) 6 3 1.5 Propylene conversion based on 80 56 35 accumulated product after 2 hrs (%) The liquid effluent from the reactors was combined and further analysed by glc and the approximate boiling ranges determined as: < 196 (gasoline fraction) 47.3% 196-235 (kerosene) 28.9% 235-315 (middle distillate 1) 21.4% > 315 (middle distillate 2) 2.4% EXAMPLE 4 Another process of the invention, using different catalyst A mordenite catalyst (Norton Co, Zeolon-900-Na (trade mark)) was used to convert propylene diluted (1::1, VN) with nitrogen using the process generally otherwise as described in Example 2. The temperature of conversion was 270"C, the WHSV of propylene 1 hr-1. There was approximately 20% propylene conversion to higher boiling products. A sample of liquid product was collected and the following boiling range determined by glc.

< 196 (gasoline) 24.6% 196-235 C (kerosene) 36.8% 235-315 (middle distillate 1) 34.7% > 315 (middle distillate 2) 4.9% EXAMPLE 5 Preparation of fluid bed catalyst A spray dried gel containing a zeolite catalyst prepared similarly to Example 1 was made for the purpose of using in a fluid bed reactor. The spray dried gel was made in two parts and then added together in equal proportions ion by weight. The final mixture contained 10% zeolite.

In the first part of the preparation a gel containing colloidal silica (Ludox HS40 (trade mark), 40Og), acid washed kaolin (700g), 70% nitric acid (80g), aluminium hydroxide (BDH (trade mark), 1340g),water (243809) and ZSM-5 zeolite (3009). The zeolite had an alumina content of 1.6% Awl203. The resulting mixture was spray dried at 250"C.

In the second part of the preparation another gel was made containing sodium silicate (Ajax (trade mark), 21609), acid washed kaolin (5009), water (20297g), sulphuric acid (2009), aluminium sulphate (409) and zirconium nitrate (29). This mixture was also sprayed dried.

EXAMPLE 6 Conversion in a fluidized bed The conversion of propylene over a zeolite catalyst prepared as described in Example 5 and employing a fluid bed reactor.

800 g of the fabricated catalyst with particle size between 38 and 75 microns was charged into a fluid bed reactor. The bed height was approximately 80cm and diameter 4.5cm. The bed was fitted with thermocouples set at different heights in the bed so that catalyst fluidization patterns and temperature gradients could be observed. Nitrogen fed to the bottom of the reactor was used to purge the catalyst mixture and to establish fluidization as the reactor set temperature was increased to 300or.

Pressure in the reactor was increased from atmospheric pressure to 1100 kPa and fluidization was maintained by increasing the nitrogen flow rate accordingly. Afterfluidization at the desired pressure and temperature had been achieved propylene was added to the nitrogen feed at a feedrate to obtain a WHSV of 1.0. The fluid bed reactor is essentially an isothermal reactor and the variation of temperature experienced within the bed was less than 20"C with a maximum temperature of 298 C. Pertinent details of the conversion of propylene over the catalyst are given in Table 3.

TABLE 3 on-stream-time (hr) 3 9 15 21 WHSV (hr-') 1.0 1.0 1.1 1.0 propylene conversion(a) (%) d d 21.6 18.6 Liquid yield (alb) d d 0.34 0.37 Liquid analysis (C) 196" (gasoline) 71.5 71.1 72.9 75.4 196-235(kerosine) 17.2 17.6 15.9 15.0 235-317 9.7 10.1 9.7 8.3 317 1.6 1.2 1.5 1.3 The superscripts designate as follows: (a) calculated from gas and liquid analysis.

(b) grams of liquid product at ambient per grams of propylene converted.

(c) by g.c. analysis.

(d) not available It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove.

Claims (11)

1. A process for production of kerosene and distillate useful as transport fuels, characterized by contacting a light olefin feedstock in the gaseous phase with a zeolite catalyst having pore sizes of at least eight-ring windows at moderate temperature and pressure and under conditions that avoid development of hot spots within the catalyst bed, whereby a product containing a substantial proportions of kerosene and distillate is obtained, and separating a kerosene and distillate fraction therefrom.

2. Process according to Claim 1, in which hot spots are avoided by carrying out the reaction with the catalyst in thermal contact with a heat sink.

3. Process according to Claim 1, carried out in a fluidized bed.

4. Process according to any one of the preceding claims, carried out at a pressure of less than 10 MPa and a temperature below 350"C.

5. Process according to claim 4, carried out at a pressure of less than 1.5 MPa.

6. Process according to claim 5, carried out at atmospheric or near atmospheric pressure.

7. Process according to anyh one of claims 4 to 6, carried out a temperature below 300"C.

8. Process according to any one of the preceding claims, in which the catalyst is of the H-ZSM-5 family.

9. Process according to claim 8, in which the catalyst in mordenite.

10. Process according to any one of the preceding claims, in which the feedstock comprises propylene.

11. Process according to claim 10 in which the feedstock is propylene diluted with light paraffins.