Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Halogenous component
Reexamination Certificate
2000-10-02
2003-07-08
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Halogenous component
C423S241000, C423S245100, C095S131000, C095S132000, C210S749000, C210S757000, C210S915000, C585S823000
Reexamination Certificate
active
06589494
ABSTRACT:
The present invention relates to a process for eliminating halogen-containing compounds, more particularly chlorine-containing compounds, contained in a gas or liquid.
In some industrial applications, halogen-containing compounds, in particular chlorine-containing compounds, contaminate a gas or liquid stream and have to be eliminated.
One illustrative example in the petroleum industry is the elimination of halogen-containing compounds, in particular chlorine-containing compounds, contained in the gas or liquid originating from catalytic reforming.
One aim of catalytic reforming is to produce hydrocarbons with an increased octane number. It has been established that the octane number of a hydrocarbon is higher if it is branched, cyclic or aromatic. Thus hydrocarbon cyclisation and aromatisation reactions are encouraged.
Normally, such hydrocarbon cyclisation and aromatisation reactions take place in the presence of heterogeneous chlorine-containing bimetallic catalysts. Such chlorine-containing catalysts are based on alumina and usually comprise platinum and another metal such as tin, rhenium or iridium. The presence of chlorine in said catalysts is important since, added to the alumina, it provides the system with overall acidity and contributes to re-dispersing the platinum over time, thus stabilising the catalytic activity of the catalyst.
However, adding chlorine is not a solution without disadvantages. Over time, chlorine clutes, in particular in the form of HCl. Such elution results firstly in the constant necessity to recharge the catalyst with chlorine. It also leads to the presence of HCl and other chlorine-containing compounds in gaseous and liquid effluents from catalytic reforming, which can lead to a corrosion problem in the facility and to the formation of other unwanted products which are deleterious to the operation of downstream units.
Catalytic reforming also produces hydrogen. When refining petroleum, hydrogen is a particularly precious product, in particular for use in hydrotreatments which are becoming ever more developed with the aim of environmental protection.
At the outlet from a conventional catalytic reforming process, which operates under a pressure of about 20 bars or more, the gaseous effluents are mainly composed of hydrogen, light hydrocarbons such as methane, ethane, etc., and generally contain traces of HCl and water. It is thus important to be able to eliminate all traces of HCl from such effluents, and then to recycle and use the purified hydrogen, still in the refinery.
Further, regenerative processes or new generation, have recently been developed and are expanding in that field. Such processes operate at a pressure of about 3 to 15 bars or less.
At the outlet from the regenerative catalytic reforming step, light hydrocarbons, traces of HCl and water, traces of unsaturated hydrocarbons such as ethylene, propylene, butene, butadiene etc. have been detected in addition to hydrogen. In the presence of chlorine and in contact with alumina, such unsaturated hydrocarbons are at least partially transformed into organochlorinated compounds which in turn, after many reactions with other organochlorinated compounds and/or unsaturated compounds, lead to the formation of high molecular weight oligomers known as green oils. Such green oils can cause blockages in the facility. Further, a significant drop in the service life of the adsorbent has been observed: in some cases, a drop of 4 to 5 times has been observed.
In that type of process, it is important to be able to eliminate all traces of HCl from such effluents in order to be able to recycle and thus use the purified hydrogen, and to reduce or prevent the formation of green oils.
The aim of the present invention is to provide an improved process for efficiently eliminating halogen-containing compounds in general, chlorine-containing compounds in particular, and HCl more particularly, contained in a gas or liquid.
A further aim of the present invention is to provide a process which uses a composition which will substantially reduce or prevent the formation of halogen-containing oligomers, in particular chlorine-containing oligomers known as green oils, downstream of regenerative reforming processes or new generation.
The invention achieves these aims in providing a process for eliminating halogen-containing compounds contained in a gas or a liquid.
Throughout the following text, the term “process for eliminating halogen-containing compounds” means “process for eliminating, reducing and/or preventing the formation of halogen-containing organic or inorganic compounds including higher weight oligomers”.
Thus the present invention provides a process for eliminating halogen-containing compounds contained in a gas or a liquid, characterized in that the gas or liquid is brought into contact with a composition based on an alumina and/or a hydrated alumina and at least one compound (A) comprising at least one metallic element selected from metals from groups VIII, IB and/or IIB of the periodic table, and in that the total metallic element(s) content is at most 45% by weight with respect to the total composition weight. More particularly, the complement by weight of the composition comprises in a major part alumina and/or a hydrated alumina.
Said composition is an adsorbent on which halogen-containing compounds, i.e. halogen-containing organic compounds and halogen-containing inorganic compounds, are retained by absorption. These halogen-containing compounds are eliminated from said gas or liquid under solely adsorption conditions, leading then to the entire purification of the gas or the liquid as no halogen-containing compounds (halogen-containing organic and inorganic compounds) are detected downstream the process. The process of the invention is implemented under reducing conditions, in the presence of hydrogen and/or hydrocarbon in the medium. By reducing conditions, we mean a medium substantially devoid of oxygen or any other oxidizing agent (i.e. less than 0.1% vol of O
2
or any other oxidizing agent). In case the process of the invention is carried out in the presence of a small amount of oxygen, oxygen will have no oxidizing power and no effect on the implementation of the process since halogens are adsorbed on the adsorbent composition. Oxygen, if there is some, comes from the contaminated gas or liquid. No oxygen is introduced into the process of the invention by external means.
Throughout the present text, the periodic table used is that from the “Supplement au Bulletin de la Société Chimique de France, No. 1, January 1966”.
The composition for the adsorption of halogen-containing compounds and used in the process of the present invention can be in the form of a powder, beads, extrudates, crushed material or monoliths.
The first essential constituent of the absorbent composition is alumina, a hydrated alumina or a mixture of an alumina and a hydrated alumina.
The starting alumina generally has a specific surface area of at least 5 m
2
/g, preferably at least 10 m
2
/g and more preferably at least 30 m
2
/g.
In the present invention, all of the specific surface areas indicated are surface areas measured using the BET method. This means the specific surface area determined by nitrogen adsorption in accordance with American standard ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in “The Journal of the American Chemical Society” 60, 309 (1938).
The starting alumina can also have a total pore volume (TPV) of at least 0.10 cm
3
/g, preferably at least 0.20 cm
3
/g, more preferably at least 0.25 cm
3
/g. This total pore volume is measured as follows: the values of the grain density and absolute density are determined: the grain (Dg) and absolute (Da) densities are measured using a picnometry method using mercury and helium respectively. The TPV is given by the formula:
[l/Dg]−[l/Da]
The processes for preparing the aluminas with the total pore volume and specific surface area characteristics necessary for carrying out the process of the invention ar
Institut Francais du Pe'trole
Millen White Zelano & Branigan
Nguyen Ngoc-Yen
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