EP0663434B1 - Fluid catalytic cracking process for hydrocarbon feed, particularly a high basic nitrogen content feed - Google Patents

Abstract

A fluid catalytic cracking (FCC) process for the cracking of a hydrocarbon charge, partic. one contg. a high basic N content in a tubular reaction zone comprises: - a supply of catalyst particles (at least in part regenerated) to the upper part of the reaction zone; - introduction and dispersion of the charge to be treated in the upper part of the reactor (beneath the entry pt. of the catalyst); - co-current circulation in mutual contact in the reaction zone of the catalyst and charge to be treated; - sepn. at the lower part of the reaction zone, of the deactivated catalyst from the reaction prods.; - stripping of the deactivated catalyst; - regeneration of at least part of the stripped catalyst in a regeneration zone; - recycling of the regenerated catalyst to the upper reaction zone, and - transfer of the cracked prods. to a sepn. zone. The process has the following characteristics: the catalyst circulates from top to bottom co-currently with the charge in the tubular zone; a catalyst is used which in equilibrium state (150 degrees C and 5 mbars) adsorbs less than 250 mu moles (pref. < 50 mu moles)/g of pyridine and retains after heating at 350 degrees C in a vacuum, no more than 20% (pref. 10%) of the amt. absorbed.

Description

The present invention relates to a method of catalytic cracking in a fluidized bed of a charge hydrocarbons, especially a filler with a high content of basic nitrogen compounds.

We know that in the petroleum industry, cracking catalytic of hydrocarbon feedstocks has gradually replaced, for more than fifty years, cracking thermal. Fixed catalyst beds initially used were quickly replaced by movable beds and, in particular, by fluidized beds, to lead to processes now known as cracking fluidized bed catalytic (Fluid Catalytic Cracking, or FCC process).

In these processes, cracking of the charge is carried out at a temperature of the order of 500 ° C., at a pressure close to atmospheric pressure, in the absence of hydrogen. During cracking, the catalyst is coated with coke and heavy hydrocarbons, and continuously regenerates it outside the cracking reactor. The heat resulting from the combustion of coke and traces of hydrocarbons remaining in the presence of air or oxygen serves to bring the desired temperature the catalyst particles, which are recycled to the reactor.

The catalysts can be of various types and we can refer on this point, for example, to EP-A-0 206 871.

These FCC processes lead to gasolines for quality cars far superior to those obtained by thermal cracking, and with many yields higher.

These processes are usually carried out with a upward flow of catalyst particles but it a number of drawbacks result, due to the fact that the gases present tend to rise, while the catalyst particles, because of their mass, resist upward movement. As a result, the C / O ratio from the flow rate C of catalyst to the flow rate O of feed to be treated is generally between 3 and 7, in reactors current, and usually close to 5.

More specifically, in an upflow reactor, the catalyst particles tend to descend and these are the cracked charge, vaporized, and the gas training (in English, "lift gas") that support and drive the catalyst bed. It is therefore not possible to freely increase the flow rate C of the catalyst, without risking unduly slowing the rise of catalyst particles. Obviously, such a problem does not arise with a downflow reactor.

These limitations of upflow reactors (so-called still risers or, in English, "risers") from the prior art, are particularly evident in the case of cracking of charges with a high nitrogen content basic. Among the basic nitrogen compounds present in the load, we will notably mention the pyridine, quinoline, acridine, phenanthridine, hydroxyquinoline, hydroxypyridine and their derivatives alkylated. With such loads, the drop in the rate of conversion can reach up to 15 points compared to a normal charge. It is known, in fact, that nitrogen basic attaches to the active catalyst sites, which are acidic sites, and thus alters the properties catalyst catalysts.

In addition, in upward flow reactors produces an accumulation of particles in the vicinity of reactor walls, resulting in overcracking hydrocarbons at this level, resulting in the formation of coke and hydrogen, instead of the products to high octane number sought, while in the center of reactor, where fewer particles are present, we obtains an insufficient conversion of the load.

Furthermore, if, overall, the grains of catalyst rise in the reactor, some of they can go down locally. This phenomenon, known under the English name of "back-mixing", also results in a local drop in conversion, since the grains which descend are partially disabled and have less effect on the load only the grains that rise. This phenomenon is all the more annoying as the C / O ratio previously mentioned is lower.

To overcome these drawbacks, which make it very difficult and uneconomical the catalytic cracking of fillers with high basic nitrogen content it has been proposed to carry out hydrotreating of the charges, which has for effect of reducing their basic nitrogen content, but which requires high pressures and temperatures, and which is therefore expensive.

It has also been proposed to use absorbents solids or solvents immiscible with the filler, for remove basic compounds, but such a process is long and expensive.

The same is true of load treatments with acid additives to neutralize nitrogen compounds basic, so we prefer to use cracking catalysts, usable in processes FCC, which are resistant to basic nitrogen (see Nitrogen Resistance of FCC Catalysts, by J. Scherzer and D.P. McArthur, communication presented at "Katalistiks 7th Annual Cat Cracking Symposium ", Venice, Italy, 12-13 May 1986).

It’s this type of downflow FCC process, using a compound-resistant cracking catalyst basic nitrogen, which the present invention is concerned with and it aims to allow cracking in good conditions of hydrocarbon charges containing more than 350 p.p.m. by weight of basic nitrogen, the nitrogen content basic up to 1300 p.p.m. by weight, even more.

The invention also aims to remove or limit, in such a process, the wall effects of the reactor and the back-movements of the particles of catalyst.

• un réacteur, dans lequel la charge à traiter et le lit fluidisé du catalyseur se déplacent, de façon connue en soi, à co-courant et de haut en bas dans le réacteur ;
• des particules d'un catalyseur qui, à l'état d'équilibre, adsorbe à 150°C, sous une pression de 5mbars, une quantité de pyridine inférieure à 250 micromoles/g et, de préférence, inférieure à 50 micromoles/g, et dont la rétention de pyridine, après chauffage à 350°C sous vide, n'excède pas 20%.

The Applicant has established that such an advantageous result can be obtained by using jointly:

• a reactor, in which the charge to be treated and the fluidized bed of the catalyst move, in a manner known per se, cocurrently and up and down in the reactor;
• particles of a catalyst which, at steady state, adsorbs at 150 ° C, under a pressure of 5 mbar, an amount of pyridine less than 250 micromoles / g and, preferably, less than 50 micromoles / g, and whose retention of pyridine, after heating to 350 ° C. under vacuum, does not exceed 20%.

• une étape d'alimentation en particules de catalyseur, au moins en partie régénéré, de la partie supérieure de la zone réactionnelle ;
• une étape d'introduction et de pulvérisation de la charge à traiter dans la partie supérieure de la zone réactionnelle, au-dessous de la zone d'alimentation en catalyseur ;
• une étape de circulation en contact mutuel, dans la zone réactionnelle, du catalyseur et de la charge à traiter, dans des conditions propres à permettre le craquage de la charge ;
• une étape de séparation, à la partie inférieure de la zone réactionnelle, du catalyseur désactivé et des produits de la réaction de craquage ;
• une étape de strippage du catalyseur désactivé ;
• une étape de régénération d'une partie au moins du catalyseur désactivé strippé, dans une zone de régénération ;
• une étape de recyclage du catalyseur régénéré à la partie supérieure de la zone réactionnelle ;
• et une étape de transfert des produits de craquage de la charge hydrocarbonée vers une zone de séparation de ces produits ;

   ce procédé étant caractérisé en ce que la charge et le catalyseur circulent de haut en bas et à co-courant dans la zone tubulaire et en ce que l'on utilise un catalyseur, qui, à l'état d'équilibre , à 150 °C, sous une pression de 5 mbars, adsorbe une quantité de pyridine inférieure à 250 micromoles/g et, de préférence, inférieure à 50 micromoles/g, et dont la rétention de pyridine, après chauffage à 350°C sous vide, n'excède pas 20 % et, de préférence, 10 %, de la quantité adsorbée à 150°C.The subject of the invention is therefore a process for catalytic cracking in a fluidized bed of a hydrocarbon feedstock, in particular a feedstock with a high content of basic nitrogen compounds, in a tubular reaction zone, this process comprising:

• a step of feeding catalyst particles, at least partly regenerated, to the upper part of the reaction zone;
• a step of introducing and spraying the feed to be treated into the upper part of the reaction zone, below the catalyst supply zone;
• a step of circulation in mutual contact, in the reaction zone, of the catalyst and of the feed to be treated, under conditions suitable for allowing cracking of the feed;
• a step of separation, at the bottom of the reaction zone, of the deactivated catalyst and the products of the cracking reaction;
• a step of stripping the deactivated catalyst;
• a step of regenerating at least part of the stripped deactivated catalyst, in a regeneration zone;
• a step of recycling the regenerated catalyst at the top of the reaction zone;
• and a step of transferring the cracked products from the hydrocarbon charge to a zone for separating these products;

this process being characterized in that the charge and the catalyst circulate from top to bottom and co-current in the tubular zone and in that a catalyst is used, which, at steady state, at 150 ° C, under a pressure of 5 mbar, adsorbs a quantity of pyridine less than 250 micromoles / g and, preferably, less than 50 micromoles / g, and whose retention of pyridine, after heating to 350 ° C. under vacuum, n ' not exceed 20% and preferably 10% of the amount adsorbed at 150 ° C.

As will be seen below, the process according to the invention has the advantage of lending itself to cracking in good nitrogen load conditions, on the one hand, because the low acidity of the catalyst, which reduces its activity, is offset by the increase in reaction temperature, made possible by use of a downflow reactor and by lowering the resulting reaction time, and, on the other hand, because that increasing the reaction temperature allows shift towards desorption the adsorption-desorption balance basic molecules at the acid sites of the catalyst.

Indeed, in a downflow reactor (called still "downer" or "dropper"), the speed of movement catalyst particles grow from top to bottom in the reactor, as the cracking reaction progresses, and, at the exit of the reaction zone, it is practically equal to that of gases and of the order of 25 m / s, and therefore much more important than in a mode with upward flow.

The flow rate of catalyst used may advantageously be increased, which will increase the number of active sites. The ratio of the mass of catalyst present in the hydrocarbon mass reactor may, in particular, advantageously be greater than 5 and, from preferably between 7 and 15.

The new catalyst used could, for example, include a limited amount of alumina (s), not exceeding not 30% by weight, at least one zeolite, in an amount representing 15 to 40% by weight, the balance to 100% which may consist of kaolin, a basic clay or weakly acidic, such as sepiolite and vermiculite, a silica-based binder and optionally a metal trap such as for example a metal oxide.

One form of implementation of the invention will be described below, with reference to the single figure of attached drawing, which is a diagram of the apparatus used.

The device shown comprises a reactor downflow tubular 1, or "downer", supplied at its upper part, from an enclosure 2, which is concentric, in regenerated catalyst particles. A valve 3, intended to regulate the mass ratio of catalyst to the charge mass to be treated in the reactor, is interposed between reactor 1 and enclosure 2. Above this valve there is a line 4, fitted with a valve 5, supplying the reactor 1 in the hydrocarbon charge to be treated, preheated by in a manner known per se. This charge is sprayed into fines droplets by injectors at the top from reactor 1, towards the bottom of it, to come to mix with the catalyst particles, on contact from which the cracking reaction takes place. As we will see below, these particles have been brought to a temperature suitable for cracking by the operation of regeneration of spent catalyst. The particles of catalyst and the charge to be treated therefore flow from high below, co-current, in reactor 1.

At the base of this, the catalyst particles spent discharge into a stripping chamber 6, provided with its base of a diffuser 7, supplied with water vapor by a line 8.

Also at the base of reactor 1, above enclosure 6, leads to a line 9, through which the cracked products and hydrocarbons from strippers are evacuated to a separation column 10. Before reaching this column 10, the gases evacuated by line 9 can optionally be soaked with a hydrocarbon or water vapor, introduced through the line 11 in row 9.

The stripped catalyst particles are removed by gravity of the enclosure 6, by an inclined conduit 22, towards an ascending column 12, in which they are routed upwards, towards a regenerator 13, using of a carrier gas, diffused at 14 at the base of the column 12, from line 15.

Column 12 opens into regenerator 13 below a ballistic separator 16, which ensures the separation of the catalyst particles and the carrier gas. The catalyst particles are then regenerated, in a manner known per se, in the regenerator, by combustion coke that has deposited on their surface and remaining hydrocarbons, using a draft or of oxygen brought by line 17 to diffuser 18.

The regenerated catalyst particles are removed by gravity through conduit 19 towards the enclosure 2, without thermal losses.

At the top of the regenerator 13, the gases from combustion are discharged to cyclones 23, which separate the fines, recycled through line 20 towards the regenerator, and the gases, evacuated by line 21.

Many variations of such a device can naturally be designed by those skilled in the art for the implementation of the method of the invention.

The following examples, which have no character limitative, illustrate this implementation.

Example 1

Three catalytic cracking tests were carried out using two hydrocarbon charges described below. Type of load processed A (low nitrogen) B (very nitrogenous) - density (° API) 17.7 18.5 - sulfur (% by weight) 2.42 0.9 - hydrogen (% by weight) 11.6 11.95 - Conradson carbon (% by weight) 1.92 1.08 - basic nitrogen (ppm) 350 1015 - PT 50% TBP (° C) 470 475 - vanadium (ppm) 1.5 1.0 - nickel (ppm) 1.1 1.9

During these three tests, the load A was cracked according to the traditional cracking process in mode ascending (Trial 1). Load B has been processed at once according to the traditional cracking process (Test 2) and according to the method according to the invention (Test 3). The cracking catalyst in tests 1 and 2 is the same and classic. It is an acid catalyst as can be get it from the manufacturers GRACE DANISON, AKZO, ENGELHARD, chosen from the family of designated products by the trade names SPECTRA, RESOC, OCTACAT, RESIDCAT, ORION, XP (GRACE), ADVANCE, OCTAVISION, VISION (AKZO) PRECISION, DIMENSION (ENGELHARD), which have in common to have a pyridine adsorption capacity in the state equilibrium greater than 250 micromoles / g at 150 ° C, under a pressure of 5 mbar. In test 3, the catalyst used is that described according to the invention.

The operating conditions were as follows: Test 1 2 3 Catalyst injection temperature (° C) 750 748 733 Charge injection temperature (° C) 233 250 250 Reactor outlet temperature (° C) 520 530 540 C / O report 4.9 5.4 7.8

The results collated below show the harmful effect of basic nitrogen on the conversion (Test 2 compared to Test 1) and that the device according to the invention allows, from a highly nitrogenous load (containing 1015 ppm by weight basic nitrogen), to obtain a better conversion of the charge into liquefied petroleum gas, i.e. the cut (C3 + C4) plus more light thinner gasoline, as well as an appreciable reduction in the deposit of coke on the catalyst ("delta coke"), with consequently, a better stability of the catalyst and a decrease in addition of fresh catalyst (Test 3 compared to 2). Test 1 2 3 Dry gases (% by weight) 4.1 4.0 4.0 Section C3 + C4 (% by weight) 13.4 10.0 12.1 Essence (% by weight) 41.4 38.1 41.2 Light thinner (% by weight) 18.9 19.1 18.7 Heavy thinner (% by weight) 17.3 23.7 17.4 Coke (% by weight) 4.9 5.1 6.6 220 ° C conversion (% by weight) 63.8 57.2 63.9 Conversion 350 ° C (% by weight) (C3 + C4 + Petrol + light thinner) 73.7 67.2 72.0 Delta coke (% by weight) 1.00 0.94 0.84

Example 2

Three catalytic cracking tests were carried out on the nitrogenous feed B described above and according to the "Downer" process as described in the attached figure. During these tests, the characteristics of the catalyst according to the invention were as follows: Test 1 2 3 Catalyst AT B VS Amount of pyridine adsorbed at 150 ° C (micromole / g) 550 200 45 Retention of pyridine after heating at 350 ° C under vacuum (%) 40 20 10 The operating conditions were as follows: Catalyst injection temperature (° C) 737 733 720 Charge injection temperature (° C) 250 250 250 Reactor outlet temperature (° C) 530 540 550 C / O report 6.2 7.8 11.5

The results collated below show the advantage of reducing the acidity of the cracking catalyst to maximize the conversion of the nitrogenous charge by operating in accordance with the invention. Test 4 5 6 Dry gases (% by weight) 3.8 4.0 4.2 Section C3 + C4 (% by weight) 10.8 12.1 14.3 Essence (% by weight) 39.1 41.2 43.8 Light thinner (% by weight) 20.7 18.7 17.4 Heavy thinner (% by weight) 20.0 17.4 11.8 Coke (% by weight) 5.6 6.6 8.5 220 ° C conversion (% by weight) 59.3 63.9 70.8 350 ° C conversion (C3 + C4 + petrol + light thinner) 70.6 72.0 75.5 Delta coke (% by weight) 0.90 0.84 0.74

Claims (5)

1. A process for the fluid catalytic cracking of a hydrocarbon charge, in particular a charge with a high content of basic nitrogen compounds, in a tubular reaction zone, said process comprising a stage for feeding at least partly regenerated catalyst particles to the upper portion of the reaction zone, a stage for introducing and atomising the charge to be treated into the upper portion of the reaction zone below the catalyst feed zone, a stage for co-current circulation and mutual contact of the catalyst and the charge to be treated in the reaction zone, under conditions suitable for allowing the cracking of the charge, a stage for separating the spent catalyst and the products of the cracking reaction in the lower portion of the reaction zone, a stage for stripping the spent catalyst, a stage for regenerating at least one portion of the stripped spent catalyst in a regeneration zone, a stage for recycling the regenerated catalyst in the upper portion of the reaction zone, and a stage for transferring the products of the cracking of the hydrocarbon charge to a zone for separation of these products,
      said process being characterised in that the charge and the catalyst circulate from the top downwards and co-concurrently into the tubular zone, and in that a catalyst is used which, in a state of equilibrium, at 150°C and at a pressure of 5 mbar, adsorbs a quantity of pyridine which is lower than 250 micromoles/g, preferably lower than 50 micromoles/g, and the pyridine retention after heating to 350°C under vacuum does not exceed 20 %, preferably 10 %, of the quantity adsorbed at 150°C.
2. A process according to claim 1, characterised in that the ratio of the mass of the catalyst to the mass of the hydrocarbon charge is higher than 5 and, preferably, between 7 and 15.
3. A process according to claim 1 or claim 2, characterised in that at the outlet from the reaction zone the speed of movement of the catalyst particles is substantially equal to that of the gases.
4. A process according to any one of claims 1 to 3, characterised in that at the outlet from the reaction zone the speed of movement of the catalyst particles is of the order of 25 m/s.
5. A process according to any one of claims 1 to 4, characterised in that the catalyst comprises, in % by weight, at least 30 % of alumina, between 15 and 40 % of at least one zeolite, the remainder to make up 100 % being composed at least partly of a diluent chosen from the group comprising kaolin, basic or weakly acid clays, such as sepiolite and vermiculite, a silica-based binder and, optionally, a metal trap.

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