WO2004035712A1

WO2004035712A1 - Removal of nitrogen compounds

Info

Publication number: WO2004035712A1
Application number: PCT/GB2003/004343
Authority: WO
Inventors: Peter John Herbert Carnell; Nicola Young
Original assignee: Johnson Matthey Plc
Priority date: 2002-10-16
Filing date: 2003-10-08
Publication date: 2004-04-29
Also published as: GB0224049D0; AU2003269258A1

Abstract

A process for the removal of basic nitrogen compounds from a hydrocarbon stream by contacting said stream with a cationic ion exchange resin or a salt thereof with a transition metal, said metal preferably being selected from copper, iron, manganese, cobalt and nickel.

Description

Removal of nitrogen compounds.

Hydrocarbon feedstocks, such as naphtha, contain a variety of impurties including organic sulphur and nitrogen compounds. In order to decrease these impurities to acceptable levels, it is commonplace to subject the feedstock to a hydrotreating step wherein the feedstock, in admixture with hydrogen, is passed at an elevated temperature over a bed of a suitable catalyst, such as a supported, sulphided, cobalt or nickel/molybdenum composition. The sulphur compounds are converted to hydrogen sulphide and the nitrogen compounds to ammonia. The mixture is then cooled and passed to a stripping column where the treated feedstock is separated as a liquid phase and the light components, including hydrogen, hydrogen sulphide and ammonia, are separated as a gaseous stream. The resultant treated feedstock stream typically has organic sulphur and organic nitrogen contents each in the range 0.2 to 0.5 ppm by weight. The treated hydrocarbon feedstock is then often subjected to catalytic reforming to increase the aromatics content of the hydrocarbon stream. The catalysts employed for catalytic reforming are often noble metals, such as platinum and/or rhenium on a suitable support. Generally the catalytic reforming catalyst is used in the form of a chloride and indeed it is often desirable to add chlorine compounds to maintain the reforming catalyst in the active state. The catalytic reforming reaction produces hydrogen and any residual nitrogen compounds in the feed will tend to be hydrogenated by the reforming catalyst to give ammonia, and likewise hydrogen chloride will be formed by reaction of the hydrogen with the catalyst. The hydrogen chloride and ammonia will tend to combine to form ammonium chloride and it has been found that this can lead to fouling and blockages in the catalytic reforming unit stabiliser section and hydrogen make-gas systems.

US 5,942,650 describes the removal of nitrogen compounds from an aromatic stream wherein a guard bed for the aromatic hydrocarbon stream comprising the nitrogen compounds is provided to contact the hydrocarbon stream with a selective adsorbent having an average pore size less than about 5.5 Angstroms to produce a treated feed stream essentially free of the nitrogen compound. The selective adsorbent is a molecular sieve selected from the group consisting of pore closed zeolite 4A, zeolite 4A, zeolite 5A, silicalite, F-silicalite, ZSM-5 and mixtures thereof.

US 4,985,139 describes the removal of heterocyclic N compounds from a petroleum fraction by distillation and extraction with an extractant consisting essentially of an aqueous solution of a lower carboxylic acid. The extractant complexes the basic heterocyclic nitrogen compound to produce a stream of petroleum crude oil or fraction thereof having a smaller content of heterocyclic nitrogen compounds and a stream comprising the lower carboxylic acid extractant with an increased quantity of basic heterocyclic nitrogen compounds. In US 4,521 ,299 the concentration of basic nitrogen compounds in hydrocarbonaceous feedstock fluids is reduced by contact with a solid particulate carbonaceous adsorbent/fuel material such as coal having active basic nitrogen complexing sites on the surface thereof.

EP-A-0278694 describes the removal of basic nitrogen compounds from solvent extracted oils using a solid polar acidic absorbent e.g. a silica-alumina, alumina or zeolite.

US4, 329,222 describes selectively rmoving basic nitrogen compounds from lube oils by mixing with a non-aqueous solution of anhydrous nonpolymeric Group IVb, Group Vb, Group Vlb, Group Vllb, the non-noble (iron group) metals of Group VIII, copper, zinc, cadmium, and mercury halides (except TiCl₄ or FeCI₃) or tetrafluoroborates, complexed with non-aqueous polar solvents under conditions of agitation and mild heating whereby the basic nitrogen compounds exchange with the polar solvent to complex with the above-recited metal halides and metal tetrafluoroborates.

The amount of residual nitrogen in the hydrotreated feedstock can also be decreased by increasing the temperature of the hydrotreating stage. However such increased temperature operation is economically unattractive.

In the present invention, the nitrogen compounds, which may be ammonia or organic nitrogen compounds such as amines or cyclic compounds such as pyridines, are removed by a separate absorption step.

Accordingly the present invention provides a process for the removal of basic nitrogen compounds from a hydrocarbon stream by contacting said stream with a cationic ion exchange resin or a salt thereof with a transition metal, said metal preferably being selected from copper, iron, manganese, cobalt and nickel.

The ion exchange resin is preferably a sulphonic acid functionalised resin, or a copper, iron, cobalt or nickel salt thereof, immobilised on a substrate such as a styrene or divinylbenzene polymer. Such ion exchange resins are well known and widely available.

The copper, iron, manganese, cobalt and nickel salts may be made by treating the cationic ion exchange resin with an aqueous solution of a suitable copper, iron, manganese, cobalt and nickel, for example a halide, sulphate, nitrate etc.

While the cationic ion exchange resin may effect removal of the nitrogen compounds by formation of an amide linkage, basic nitrogen compounds, particularly ammonia, amines and pyridines may be removed by metal salt-exchanged resins through formation of a complex.

The hydrocarbon stream may be a feedstock stream such as naphtha (e.g. containing hydrocarbons having 5 or more carbon atoms and a final atmospheric pressure boiling point of up to 204°C), middle distillate or atmospheric gas oil (e.g. having an atmospheric pressure boiling point range of 177°C to 343°C), vacuum gas oil (e.g. atmospheric pressure boiling point range 343°C to 566°C), or residuum (atmospheric pressure boiling point above 566°C), or a hydrocarbon stream produced from such a feedstock by e.g. catalytic reforming. The nature and amount of the impurities will depend on the feedstock, but the feedstock will generally contain significant amounts of organic sulphur and nitrogen compounds and may also contain metals such as vanadium and nickel. Such metals can also be removed by a hydrotreating process.

The hydrocarbon stream may be contacted with the ion exchange resin at any suitable pressure, preferably in the range 1 to 100 bar abs., and at temperatures from ambient to 250°C with the hydrocarbon stream in the gaseous or liquid state. The treatment with the ion exchange resin may be effected before or after any sulphur removal step, e.g. hydrotreatment and absorption of hydrogen sulphide or mercaptans. It is preferably effected after such a hydrotreating step.

The resin may be regenerated by washing with aqueous acid and optionally by treatment with a metal salt if the metal-exchanged resin is used. More than one bed of ion exchange resin may be provided so that regeneration or replacement of a first bed is carried out whilst a second bed is provided for basic nitrogen compound removal duty. Many suitable arrangements of absorbent beds to optimise the process throughput and lifetime of the beds are practised within industry and are known to the skilled person.

In particular the invention is applied to hydrocarbon streams supplied to a catalytic reforming process, so that the ion exchange resin can remove any ammonia present in such streams and hence the problem of the formation of ammonium chloride in the chloride-rich conditions of the catalytic reforming reaction and subsequent deposition of NH₄CI downstream is reduced or avoided. Preferably the treatment with ion-exchange resin is carried out prior to the stream entering the catalytic reformer so that level of basic nitrogen compounds in the reformer is reduced. However, because the strongly reducing conditions of the reformer may promote the formation of ammonia from any nitrogen compounds which are present in the reformer, it may be beneficial to treat the hydrocarbon stream exiting the reformer with the ion exchange resin according to the process of the invention to remove such ammonia or other basic nitrogen compounds present. Therefore the process of the invention may be applied either before or after a hydrocarbon processing step or both before and after if required.

Where a step of hydrotreating stage is employed, the hydrotreating catalyst will depend on the nature of the feedstock and on the impurities to be removed. Examples of suitable hydrotreating catalysts are compositions comprising a sulphided composition containing cobalt and/or nickel plus tungsten and/or molybdenum, e.g. cobalt molybdate or tungstate or nickel molybdate or tungstate, on a support which is often alumina. The catalyst often also contains a phosphorus component. Examples of hydrotreating catalysts are described in US 4014821 , US 4392985, US 4500424, US 4885594, and US 5246569. The hydrotreating conditions will depend upon the nature of the hydrocarbon feedstock and the nature and amount of impurities and on the catalyst employed. Generally the hydrotreating will be effected under superatmospheric pressure, e.g. 5 to 150 bar abs., and at a temperature in the range 300°C to 500°C with a hydrogen to hydrocarbon ratio of 50 to 2000 litres of hydrogen (at STP) per litre of hydrocarbon liquid (at STP). The feedstock and hydrotreating conditions are preferably such that the feedstock/hydrogen mixture is a single, i.e. gaseous, phase under the hydrotreating conditions, although a mixed phase system may alternatively be employed.

By employing a nitrogen removal step separate from hydrotreating, the hydrotreating conditions do not have to be so severe as those giving rise to mercaptan formation. Preferably the treatment of the feedstock with the ion exchange resin is effected prior to hydrotreating and is effective to reduce the organic nitrogen content to below 0.2 ppm by weight, and preferably to below 0.1 ppm by weight, and in particular to below 0.05 ppm by weight. As a result the hydrotreating temperature may be below 350°C.

Alternatively the hydrotreating may be effected, preferably at a temperature below 350°C, prior to treatment with the ion exchange resin. Again, as a result of the separate nitrogen compound removal step, the hydrotreating conditions do not have to be so severe as to give rise to mercaptan formation.

The invention will be demonstrated in the following Examples.

Examplel 60 ml (36g) of Amberlyst™ A15 ion exchange resin (0.4-0.5mm spheres) was charged to a borosilicate glass reactor (20mm internal diameter), the bed being supported on a 2cm depth of glass wool. The resin was used 'as received' and was not pretreated. The feedstock, 100ppm pyridine in n-heptane, was pumped into the bottom of the reactor at a flow rate of 300ml/hr and the feed flowed upwards through the static bed of resin at atmospheric pressure and ambient temperature (25 °C) The pyridine content retained in the heptane exiting the bed was monitored by gas chromatography with a flame ionisation detector. This run was continued for 155.5hrs during which time the level of pyridine in the effluent was always below the limit of detection of the GC method (<1 ppm). The adsorbed nitrogen content on the inlet of the discharged bed was then measured as 3.7 %w/v using a LECO 932 nitrogen analyser. Example 2

Example 1 was repeated using accelerated test conditions in which the bed volume was reduced to 30ml of A15 resin and the concentration of pyridine in the feedstock was raised to lOOOppm. The experiment was continued for a total of 12.5 hours during which time the level of pyridine in the effluent heptane was always retained below the limit of detection. The calculated loading of nitrogen on the bed was 4.2%w/w.

Claims

1. A process for the removal of basic nitrogen compounds from a hydrocarbon stream by contacting said stream with a cationic ion exchange resin or a salt thereof with a transition metal.

2. A process as claimed in claim 1 , wherein said transition metal is selected from the group consisting of copper, iron, manganese, cobalt and nickel.

3. A process according to claim 1 or claim 2, wherein the hydrocarbon stream is hydrotreated, before or after treatment with the ion exchange resin.

4. A process according to any one of claims 1 to 3, wherein the hydrocarbon stream is subjected to catalytic reforming after treatment with the ion exchange resin.