Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
2001-04-02
2002-10-08
Parsa, Jafar (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C210S150000, C210S620000, C210S660000, C210S670000
Reexamination Certificate
active
06462097
ABSTRACT:
The present invention concerns a process for the production of purified water and hydrocarbons from Fischer-Tropsch synthesis. This process makes it possible to eliminate the impurities present in the water produced during this synthesis, in particular water-soluble oxygenated compounds, as well as the metals generally produced by the catalyst used in the synthesis stage.
PRIOR ART
The Fischer-Tropsch synthesis is a process which simultaneously produces water and hydrocarbons. For example when the fossil resource under consideration is natural gas mainly constituted by methane, the global reaction can be written:
nCH4+n/2 O2→n(—CH2—)+n H2O (1)
The quantities of water co-produced are considerable. Thus an industrial unit producing 500,000 t distillates per year co-produces approximately 600,000 t water per year, i.e. approximately one barrel of water per barrel of hydrocarbons.
Fischer-Tropsch synthesis consists, in an initial stage, of transforming the fossil resource (for example natural gas, or a naphtha cut or a heavy petroleum cut, or coal) into synthesis gas, i.e. into a gaseous mixture containing carbon monoxide, carbon dioxide and hydrogen.
In the case of natural gas, gas production processes are generally used which involve synthesis by partial oxidation or steam reforming, or else by a combination of the two aforementioned technologies. When the fossil resource is coal, lignite, asphalts or residues of petroleum origin, gasification or partial oxidation processes are used to produce the synthesis gas.
In a second stage the synthesis gas is converted into water and hydrocarbons according to the reaction:
nCO+2n H2→n(—CH2—)+n H2O (2)
It is known that this reaction, which is strongly exothermic, is generally carried out in the presence of catalysts essentially comprising the metals iron or cobalt deposited on a support phase based on metal oxides such as aluminium, silicon or titanium oxide. Said catalysts are used in various types of reactors, for example multi-tubular isothermal reactors or fluidised bed reactors. In a preferred process, the said catalysts are used in suspension in a liquid phase made up of hydrocarbons (“slurry” technology).
In a third stage the hydrocarbons formed are converted partly by means of a hydro-isomerising hydro-cracking process carried out in the presence of a catalyst. Liquid hydrocarbon cuts, for example medium distillates, oils and gases are obtained, which contain slightly isomerised products to improve their properties during use: flow point for the gas-oil and kerosene cuts, viscosity index for lubricants.
The water co-produced with the hydrocarbons is partly recycled in the synthesis gas production section, in particular when the said synthesis gas is produced by steam-reforming, and partly rejected following sufficient treatments to bring it up to standard (e.g. conformity to the chemical oxygen demand). The expert knows that said water contains numerous water-soluble oxygenated compounds (e.g. alcohols, aldehydes, ketones, acids, esters, acetates, aldols etc.), traces of hydrocarbons as well as traces of heavy metals from the catalyst (e.g. from the iron or cobalt) in concentrations generally ranging from 10 parts per million (ppm) to 0.001 ppm. The oxygenated compounds and the metals present in this water give it an odour, a taste, and a potential toxicity incompatible with use for sanitary purposes or for consumption.
Apart from water, the Fischer-Tropsch process co-produces carbon dioxide (CO2) in a fairly large quantity. The CO2 co-produced, apart from that originating from the oven combustion gases, comes from the synthesis gas generation stage and the Fischer-Tropsch synthesis itself (reaction 2 above) and the carbon dioxide conversion reaction (Water Gas Shift, reaction 3 below), whose degree of advance depends in particular on the nature of the catalyst used for the hydrocarbon synthesis (reaction 2).
m CO+m H2O→m CO2+m H2 (3)
Part of the CO2 can be recycled to the synthesis gas production unit but, overall, all the oxygen present in the synthesis gas is found in the form of water or CO2 in the reaction products.
The expert also knows that the used waters can be effectively purified by a series of processes, some of which use adsorption on solids, and others biodegradation on dedicated strains of bacteria. The patent U.S. Pat. No. 5,569,790 describes a process for the purification of water used for washing a hydrocarbon charge involved in an ether production process. This purification is carried out by means of liquid-liquid contact with an amount of effluent arising from an etherification unit. In this process, the degree of purification of the water is limited, as the division of the impurities is carried out in favour of the aqueous phase. Moreover, such a process does not enable metals to be eliminated correctly.
The patent FR-2.772.373 describes a process for purification of a fluid, and in particular a process for the elimination of polar compounds contained in the washing water produced by an etherification unit. This process consists of bringing the fluid to be purified into contact with a vapour phase, to get rid of the majority of the impurities. The purification can be carried out by passing the fluid over a solid phase chosen to retain the impurities. The possibility of eliminating the oxygenated compounds and the metals simultaneously is neither described nor mentioned in this application.
SUMMARY OF THE INVENTION
The invention concerns a process for the production of purified water and hydrocarbons resulting from Fischer-Tropsch synthesis, comprising at least one stage of separation of the water and hydrocarbons formed during the Fischer-Tropsch synthesis, at least one stage of purification of the separated water by means of contact with at least one adsorbent selected from the group consisting of: the active carbons, clays which are hydrophobic or rendered hydrophobic, and zeolites which are hydrophobic or rendered hydrophobic. This process may in addition include a stripping stage before the purification by adsorption.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that by means of a simple technique involving adsorption on solids, it is possible to simultaneously eliminate oxygenated compounds, hydrocarbons and also the heavy metals present in the water co-produced with the hydrocarbons in the Fischer-Tropsch synthesis and thus to confer upon it usage properties compatible with use for sanitary purposes and, preferably for consumption.
It has also been found that water for consumption thus produced can possibly, after adjustment of its mineralisation, be gasified, partly using the CO2 resulting from at least one of the stages of the Fischer-Tropsch process.
The process according to the invention consists of separating the water formed from the hydrocarbons co-produced in the Fischer-Tropsch synthesis, possibly condensing this water after separation, then purifying said water by bringing it into contact with at least one adsorbent, selected from the group consisting of: the active carbons, clays which are hydrophobic or rendered hydrophobic, and zeolites which are hydrophobic or rendered hydrophobic. The clays or zeolites can be rendered hydrophobic by any means known to a man skilled in the art, e.g. by silicon grafting or dealumination.
The adsorbent according to the invention is preferably selected from the group consisting of: dealuminated zeolites with an Si/Al atomic ratio greater than or equal to ca. 20, silicalite, and clays which are hydrophobic or rendered hydrophobic. In a more preferred process the dealuminated zeolites in this group are either at least one dealuminated ZSM-5 zeolite, or at least one dealuminated Y zeolite, or a mixture of these two types of zeolite. In a highly preferred process, the adsorbent is a ZSM-5 zeolite with an Si/Al atomic ratio greater than or equal to ca. 20 or a dealuminated Y zeolite with an Si/Al atomic ratio greater than or equal to ca. 20 or a mixture of these zeolites with
Courty Philippe
Garibaldi Pierpaulo
Martino Germain
Institut Francais Du Petrole
Millen White Zelano & Branigan P.C.
Parsa Jafar
LandOfFree
Process for the production of purified water and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the production of purified water and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the production of purified water and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2965125