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Preparation of iron compounds by hydrothermal conversionRelated Patent Categories: Chemical Apparatus And Process Disinfecting, Deodorizing, Preserving, Or Sterilizing, Chemical Reactor, Including Plural Reaction Stages, And Means Providing Discrete Sequential Reaction Stages; E.g., Train, Etc., Plural Solid, Extended Surface, Fluid Contact Reaction Stages Each Containing; E.g., Inert Raschig Rings, Particulate Sorbent, Particulate Or Monolithic Catalyst, Etc.Preparation of iron compounds by hydrothermal conversion description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070189937, Preparation of iron compounds by hydrothermal conversion. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICTIONS [0001] This application is a divisional of U.S. application Ser. No. 10/642,893, filed Aug. 18, 2003, which claims priority to European Patent Application No. 02078407.0, filed Aug. 16, 2002. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a process for the hydrothermal conversion of a solid starting iron compound selected from the group consisting of iron oxides, iron hydroxides, iron oxyhydroxides, and mixtures thereof into a solid product iron compound, the solid product iron compound having different physical, chemical, and/or structural properties from the solid starting iron compound. [0004] 2. Prior Art [0005] It is known from the prior art to convert goethite (alpha-FeOOH) into hematite (alpha-Fe.sub.2O.sub.3) in a suspension under hydrothermal conditions. Romanian Patent Application RO 86979 discloses this conversion using an autoclave and temperatures of about 210.degree. C. The same conversion, but now in the presence of potassium carbonate using temperatures between 180 and 210.degree. C. and pressures between 16 and 20 atm., is disclosed in RO 100113. [0006] In order to minimize operational costs and to maximize energy conservation, it would be desirable to conduct the hydrothermal conversion of iron oxides, iron hydroxides, and iron oxyhydroxides in a continuous mode. [0007] However, as will be explained below, processes involving suspensions are not easy to conduct continuously, mainly due to segregation and sedimentation. [0008] Suspensions consist of a continuous phase, i.e. a liquid, and a dispersed phase, i.e. solid particles. Suspensions can be homogeneous or heterogeneous. In this specification, homogeneous suspensions are defined as suspensions having a constant volume fraction of the continuous phase throughout the whole system. Suspensions without such a constant volume fraction of the continuous phase are referred to as heterogeneous. In these heterogeneous systems there are concentration gradients of the dispersed phase. [0009] Suspensions can separate into a fraction with a higher volume fraction of the continuous phase and a fraction with a lower volume fraction of the continuous phase. Within this specification this phenomenon is referred to as segregation. Segregation can occur by the action of various forces, for instance centrifugal forces or gravity. Sedimentation is a form of segregation where the dispersed phase settles by gravity. [0010] When a sediment is formed, part of the flow region within a reactor is blocked by a stagnant solid, reducing the volume available for free flow. With constant mass flux, the suspension will have to move through a smaller area, resulting in higher velocities of the continuous phase. This results in even more segregation and a non-ideal residence time distribution of the dispersed phase in the reactor. [0011] The conversion of solid particles in a suspension can be performed continuously in traditional pipe reactors or cascade reactors, provided that the starting particles easily form a stable homogeneous suspension, e.g., a sol or a gel, and are of a more or less uniform particle size. Even then limitations in the Solids to Liquid Ratio (SLR) may occur due to the rheological behavior of the homogeneous suspension. High energy input, e.g., high-shear mixing, can alleviate these difficulties if the suspensions exhibit shear-thinning behaviour. [0012] Unfortunately, readily available iron oxides, iron hydroxides, and iron oxyhydroxides are not easily suspendable and/or do not form stable homogeneous suspensions, neither at high solids to liquid ratios nor at low ones. This is due either to their large particle size (say >0.1 micron) and/or to their chemical incompatibility with the liquid, making segregation of the particles from the liquid very likely. This means that the particles will show a tendency to form a sediment layer, resulting in an uncontrolled and non-ideal residence time distribution in the reactor, thereby hindering the conversion. This situation may be further aggravated when dealing with starting particles of different sizes. [0013] Contrary to the case of the stable homogeneous suspensions described above, where high shear can assist in homogenisation and reduction of the viscosity, unstable suspensions tend to segregate even faster when a high energy input is added to the system. Therefore, good mixing throughout the whole reactor and avoiding any dead or non-mixing zones is preferred to avoid non-ideal residence time distributions and to promote efficient conversion of the starting particles. [0014] Alternatively, expensive chemicals need to be added in order to stabilise and disperse the suspension and to prevent segregation. [0015] It has now been found that solid starting iron compounds selected from the group consisting of iron oxides, iron hydroxides, iron oxyhydroxides, and mixtures thereof can be converted continuously, even at high Solids to Liquid Ratios (SLR), in one or a series of separate vessels without an unacceptable level of segregation. Using high Solids to Liquid Ratios enables the use of relatively compact equipment and offers low operational costs and energy consumption. SUMMARY OF THE INVENTION [0016] The invention relates to a process for the conversion of a solid starting iron compound selected from the group consisting of iron oxides, iron hydroxides, iron oxyhydroxides, and mixtures thereof into a solid product iron compound, the solid product iron compound having different physical, chemical, and/or structural properties from the solid starting iron compound, which process comprises the steps of: [0017] a) dispersing the solid starting iron compound in a liquid thus forming a suspension, and [0018] b) feeding the suspension continuously though one or more agitated conversion vessel(s), in which vessel(s) the solid starting iron compound is converted into the solid product iron compound under hydrothermal conditions. [0019] Other embodiments of the invention include reaction conditions, characteristics of the suspension, suspension flow and forms of iron, all of which will be hereinafter described in detail. BRIEF DESCRIPTION OF THE DRAWING [0020] FIG. 1 shows a schematic layout of a plant for carrying out the present invention. DETAILED DESCRIPTION OF THE INVENTION [0021] The invention relates to the conversion of one solid iron compound into another solid iron compound. It does not relate to, e.g., a precipitation process in which a dissolved iron compound is converted into a solid iron compound, or a digestion process in which a solid iron compound is dissolved. Continue reading about Preparation of iron compounds by hydrothermal conversion... Full patent description for Preparation of iron compounds by hydrothermal conversion Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Preparation of iron compounds by hydrothermal conversion patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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