The present invention is directed to a process for removing iron containing particles.

Crude oils are a mixture of many substances which often are difficult to separate. Besides compounds consisting of hydrogen and carbon, crude oils can contain compounds further containing sulphur, nitrogen and/or oxygen. Additionally, sodium and potassium are usually present derived from saline water produced together with oil. Copper, zinc and iron are also often found. The presence and amount of these compounds differs from crude to crude.

The presence of iron has been found to be especially detrimental if the oil is to be catalytically converted as the iron itself tends to be catalytically active as well. Furthermore, it has been found that the presence of iron, especially iron sulphide, can cause asphaltenes to become extremely sticky.

US-A-5133851 describes that iron can be removed from hydrocarbon feeds with the help of a metal-selective membrane.

Membranes are less suitable for cleaning feedstock comprising a large amount of contaminants as it makes that the membranes become clogged relatively fast which requires the membranes to be cleaned relatively frequently which again causes the membranes to be out of operation for a relatively large part of the time. A filter has the advantage over membranes that it can be tailored to the size of the contaminants to be removed by adjusting the mesh size. It has now been found that a specific filter unit is surprisingly suitable for removing iron particles from hydrocarbon feed. A substantial amount of the iron particles is removed while the filter can be cleaned efficiently, i.e. to a high degree in a relatively short period of time, which reduces the time during which the filter is out of operation.

The present invention now relates to a process for removing iron containing particles from a hydrocarbon feed comprising iron containing particles by treating the feed in a filter unit comprising a perforated tube surrounded by hollow longitudinal projections comprising a filter having openings of at most 100 micrometer diameter in which the internal space of each of the hollow projections is in fluid communication with the inside of the perforated tube and which filter is regularly subjected to cleaning by treating each of the projections with cleaning fluid wherein the flow of cleaning fluid is opposite to the direction of normal flow.

The filter for use in the present invention is a filter having openings of at most 100 micrometer in which the internal space of each of the hollow projections is in fluid communication with the inside of the perforated tube. It has been found that iron particles can relatively easily be removed from such filter by treating each of the projections separately with cleaning fluid which flows in the direction which is opposite to the normal flow. A conventional filter unit generally consists of a surface which has to be treated in total during cleaning. However, only part of the total filter surface tends to be cleaned as the cleaning fluid is no longer effective if sufficient surface has become available through which the cleaning fluid can pass. The remainder of the surface area remains clogged. The filter unit of the present invention prevents this as it comprises separate hollow longitudinal projections which preferably are not in fluid communication with each other. This makes that each can be cleaned separately.

Besides the perforated tube and the hollow longitudinal projections, the filter unit for use in the present invention generally further comprises a container having a feed inlet, a filtrate outlet and a residue outlet. The perforated tube can be the feed inlet while it can contain the residue outlet. The container generally is a vessel or a tube.

The normal flow of the feed will be via the perforations of the perforated tube into the internal space of longitudinal projections where it is in contact with the filter. During cleaning of the filter, cleaning fluid passes from outside the filter into the internal space of the longitudinal projections. The iron particles which remained behind on the filter on the feed side, are removed via the retentate outlet. Generally, a limited number of projections are cleaned at the same time such that the remainder of the projections can continue filtering feed. The cleaning fluid can be made to flow in the direction opposite to the direction of normal flow by reducing the pressure in the part of the perforated tube which is in fluid communication with the projections to be cleaned. The reduction in pressure can comprise removing overpressure or actually reducing the pressure to below atmospheric. As the remainder of the filter unit generally is at substantially more than atmospheric pressure, it often suffices to lower the pressure of the retentate outlet to atmospheric pressure. - A -

The tube and the hollow projections are in fluid communication via the perforations in the tube. These perforations can have any shape suitable for the specific use such as slits and round openings. In many cases, round openings are preferred.

The further circumstances of use of the present invention determine the specific openings of the filter for use in a filter unit. The filter for use in the present invention has openings having a diameter of at most 100 micrometer. The absolute rating or cut-off point of a filter refers to the diameter of the largest particle which will pass through the filter. Filter media with an exact and consistent pore size or opening theoretically thus have an exact absolute rating. This does not usually apply in practice as pore size is not necessarily consistent with the actual open areas, and is further modified by the form of the filter element. The filter for use in the present invention has the mentioned opening size when measured in accordance with ISO 565 (1987) .

Preferably, the filter for use in the present invention has openings having a diameter of at most 100, more specifically at most 50, more specifically at most 40, and more specifically at most 30 micrometer. Depending on the percentage of iron to be removed and the particle size distribution of the iron particles, it can be preferred to apply a filter having openings having a diameter of at most 15 micrometer.

The effective filter surface area of a filter is the area through which fluid can actually pass. Filters using profiled wire, so-called wedge wire, have the advantage that they can be cleaned relatively easily but have the disadvantage that their effective surface area is relatively low, generally less than 5%. Filters using metal mesh tend to have a higher effective surface area. Therefore, it is preferred that the filter of the present invention comprises metal mesh. Preferably, the filter comprises at least 2 mesh layers. In this way, the mesh layers provide strength to each other. In a further preferred embodiment, the filter comprises at least 2 mesh layers which have been sintered together to provide a rigid and immobilized mesh structure which gives a sharp and fixed particle separation.

The cleaning fluid can be any fluid known to be suitable to someone skilled in the art. A cleaning fluid which is especially preferred is filtrate of the present process. The use of filtrate for cleaning the filter by which the filtrate has been obtained, is called back- flush operation. It is especially advantageous to use filtrate because it makes that no additional compounds are introduced. This allows easy operation and reduced risk of contamination. Filters for use in the present invention can be obtained from the company Filtrex s.r.l., Italy. A filter which has been found to be especially suitable is the filter known as the Automatic Counterwash Refining (ACR) filter which is commercially available from this company. Any feed containing iron particles can in principle be used in the process of the present invention. The iron particles will generally comprise iron sulphide and/or iron oxide. It is especially preferred to treat feed containing asphaltenes besides iron particles. These feeds are especially difficult to clean. Examples of such feeds are natural gas condensates and residues. Residue is the oil fraction which is left after lighter compounds are removed. It is preferred that the amount of gas in the feed is less than 5 %wt, based on total amount of feed, more preferably less than 1 %wt, more preferably less than 0.5 %wt, more preferably less than 0.2 %wt, more preferably less than 0.1 %wt . Most preferably, the hydrocarbon feed does not contain gas.

The amount of iron in the hydrocarbon feed generally is at least 20 parts per million by weight (ppmw) , more specifically at least 25 ppmw, more specifically at least 30 ppmw, more specifically at least 35 ppmw, most specifically at least 40 ppmw, weight amount of iron on feed.

Further, the hydrocarbon feed to be contacted with the filter preferably is at a pressure of less than 20 bar, more specifically less than 15 bar, more specifically less than 10 bar and most specifically less than 8 bar. The temperature of the feed can vary over a wide range. The temperature can be up to 350 ⁰ C, more specifically up to and including 300 ⁰ C, more specifically up to and including 300 ⁰ C. The temperature generally will be at least 150 ⁰ C, more specifically at least 170 ⁰ C, most specifically at least 200 ⁰ C.

Residues generally are feeds of which at least 90% by weight boils above 300 ⁰ C, more specifically at least 95% by weight. It has been found that the process of the present invention can remove both iron containing particles and asphaltenic particles from such feeds. For this application, it is preferred that the filter has openings of at most 40 micrometer, more specifically at most 30 micrometer, more specifically at most 25 micrometer.

Natural gas condensates are the fractions of natural gas which condense from raw natural gas when the temperature is reduced to below the hydrocarbon dew point of the raw gas. Compounds generally present in natural gas condensates are hydrogen sulphide, mercaptans, carbon dioxide, alkanes containing of from 2 to 12 carbon atoms, more specifically of from 2 to 8 carbon atoms, cyclohexane, benzene, toluene, xylenes and ethylbenzene . In addition, natural gas condensates tend to comprise iron sulphide and mercury sulphide. It has now surprisingly been found that mercury sulphides can be removed together with iron sulphide by subjecting the natural gas condensates to a filtering process according to the present invention. This is very advantageous as mercury sulphide tends to be difficult to remove. Therefore, the present invention further relates to a process which comprises separating iron sulphide and mercury sulphide from natural gas condensate comprising iron sulphide, mercury sulphide and hydrocarbons containing of from 2 to 12 carbon atoms, which process comprises subjecting the condensate to a filtration process according to the present invention. For this application, it is preferred that the filter has openings of at most 40 micrometer, more specifically at most 30 micrometer, more specifically at most 25 micrometer.

The filtrate obtained by the process of the present invention is especially suitable to be converted further with the help of a catalyst. Therefore, the present invention further relates to a process in which the filtrate is contacted with catalyst at elevated temperature and pressure, preferably a temperature of from 200 to 450 ⁰ C and a pressure of from 10 to 100 bar, more preferably at a hydrogen partial pressure of from 5 to 50 bar. The invention will be described in more detail and by means of non-limiting examples, with reference to the Figures, wherein

Figure 1 schematically shows a cross-section of a filter unit suitable for use in the present invention. The cross section is perpendicular to the longitudinal projections and the perforated tube. The filter unit comprises a perforated tube 1 surrounded by hollow longitudinal projections 3 comprising filter 2. The longitudinal projections 3 are surrounded by a further tube 4 having an outlet 7 for removing the filtrate. The longitudinal projections 3 are in fluid communication with tube 1 via openings 8. During normal operation, the pressure in the perforated tube 1 is higher than the pressure in space 5 formed by the outside of the longitudinal projections and the further tube 4. This makes that feed flows from the perforated tube into the projections 3, and filtrate flows to space 5 and from there to outlet 7. The filter 2 can be cleaned by decreasing the pressure in the part of the perforated tube which is in fluid communication with the projections to be cleaned. This can for example be done with the help of a conduit 6 which can rotate around the longitudinal axis of perforated tube 1 such that all projections can be treated. During cleaning of the projections in question, the projections 3 are in fluid communication with conduit 6 while the pressure in conduit 6 is lower than the pressure in the space 5. This makes that filtrate flows from space 5 into projection 3 and then into conduit 6. Residue accumulated on filter 2 is thereby removed and flows via conduit 6 to a residue outlet connected therewith.