Chemistry of inorganic compounds – Halogen or compound thereof – Elemental halogen
Reexamination Certificate
2001-01-12
2003-01-28
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Elemental halogen
C423S633000, C423S493000, C423S148000
Reexamination Certificate
active
06511646
ABSTRACT:
This invention relates to a process for producing chlorine and metal oxides from metal chlorides.
Whilst the process applies to any metal chloride which is oxidisable to chlorine and the corresponding metal oxide, it is particularly applicable to iron chloride.
Several industrial processes, such as the production of titanium dioxide from titanium tetrachloride resulting from the direct chlorination of titaniferous ores, generate large quantities of by-product iron chloride. Disposal of this iron chloride poses potential environmental problems and represents an economic loss of the chlorine.
Depending on the chlorination process, the iron chloride may be present as ferrous chloride, ferric chloride or a mixture of the two.
There have been many attempts to produce an economic process to overcome this problem and these are well summarised in U.S. Pat. No. 4,994,255.
A common step in these processes is the reaction of ferric chloride in the vapour phase with oxygen, i.e.
2FeCl
3
+1.5O
2
→Fe
2
O
3
+3 Cl
2
At low temperature (600° C.) where the thermodynamics of this reaction are favourable, the rate is slow and a catalyst is needed and at higher temperatures (800° C.-900° C.) where the rate is practical, the thermodynamics are unfavourable and the reaction is far from complete.
As a result, particularly when operating at such higher temperatures, the gaseous reaction products contain a relatively high proportion of ferric chloride which needs to be separated from the chlorine.
GB-A-2019376 describes a way of achieving this separation by cooling the gaseous product to cause the ferric chloride to condense out onto iron oxide particles. However, in the arrangement shown, there will be a tendency for the ferric chloride to deposit on the cooling coils in the condenser vessel.
A further problem of the reaction is that there is a tendency for the iron oxide to build-up on the reactor walls and associated equipment.
According to one aspect of the invention, there is provided a process for producing chlorine and iron oxide comprising treating ferric chloride in the vapour phase with oxygen at a temperature of 700 to 900° C. in a fluidised bed reactor, continuously recirculating a portion of the bed material from the reactor back to the reactor, condensing unreacted ferric chloride in the gas stream by cooling iron oxide particles below the condensation point of ferric chloride and injecting said particles into the gas stream whereby ferric chloride condenses on the surface of the iron oxide particles and the particles are carried by the gas stream to a separator, the separated coated iron oxide particles being recycled to the condensation step or the reaction step.
The problem of unwanted ferric chloride deposition is avoided because the ferric chloride does not come into contact with the cooling coils as it does in GB 2019376. Thus a greater amount of unreacted ferric chloride (and hence a lower percentage conversion) can be tolerated. The process can, therefore, be operated at a higher temperature where the kinetics are more favourable and a catalyst is not necessary.
The condensing step is preferably carried out in a fluidised bed condenser as described in EP-A-467441 U.S. Pat. No. 5,205,350).
According to a preferred feature of this invention, the ratio between the recirculation rate of solid material and the feed rate of ferric chloride is at least 10:1. This high ratio provides a scrubbing action which prevents oxide build-up on the equipment.
The chlorination processes previously mentioned are conventionally carried out in a fluidised bed made up of the ore and carbon in the form of coke.
The gaseous products from the process (at 700-1100° C.), in the case of a titanium ore such as ilmenite, consist mainly of titanium tetrachloride and iron chloride. The iron chloride may be in the ferrous and/or ferric form, the amount of each present being dependent on the conditions in the chlorination reaction. In addition, finely divided solids, mainly carbon and unreacted titanium dioxide, are elutriated from the fluidised bed and carried in the gas stream. Thus after appropriate separation of the titanium tetrachloride, a residue, herein referred to as chlorination dust, is left consisting typically of circa 70% iron chloride, 20% carbon, and 5% titanium dioxide, the remainder being small amounts of various chlorides and oxides of other metals such as aluminum, magnesium, manganese etc.
Great difficulties are associated with oxidising chlorination dust. To oxidise ferrous chloride in the vapour phase, high temperatures have to be used because of its low volatility and, hence, large amounts of energy have to be added.
The problems are intensified by the elutriated material. The separation of these impurities from the iron chloride is impracticable before the oxidation step and the resultant iron oxide is contaminated.
Moreover, the carbon will react with added oxygen in preference to the oxidation of iron chloride producing an excessive amount of carbon dioxide which dilutes the recovered chlorine to an extent that it is unsuitable for further use without an expensive separation step. Furthermore the energy released provides difficulties in the downstream process and is costly to remove.
The problems due to the presence of carbon and the other impurities will be relevant even if the iron chloride is present in the ferric form.
The problem of the carbon is ignored in many of the prior art processes. In EP-A-165543 the carbon content of the dust is controlled relative to the amount of iron chloride and in U.S. Pat. No. 4,994,255, the carbon is removed in a separate step.
An attempt to solve the problems is, however, made in GB-A-1517264. In the disclosed process ferrous chloride is reacted with sufficient oxygen to form ferric oxide and ferric chloride but insufficient to liberate any substantial amount of chlorine, the gaseous products, after separation of solid material, being treated to the conventional oxidation process.
Although this reference mentions the problem of excess carbon dioxide, it does not solve this problem as the final gas product contains nearly equal amounts of chlorine and carbon dioxide.
According to a further aspect of the present invention, there is provided a process for treating chloination dust comprising reacting the dust with chlorine in a recirculating fluidised bed to convert ferrous chloride to ferric chloride, separating the solids from the gaseous products, and passing the gaseous product to an oxidation reactor to oxidise the ferric chloride to chlorine and iron oxide.
By operating in this manner, a final gaseous product containing only circa 22% carbon dioxide can be achieved.
The residual solids containing the major amount of the carbon and the unreacted titanium dioxide can be returned for further treatment in the chlorination process.
According to a preferred feature, the temperature necessary for the reaction is achieved by burning a minor proportion of the carbon in the dust.
According to a third aspect of the invention, there is provided a process for producing chlorine and iron oxide from material containing ferrous chloride comprising reacting the material with chlorine in a recirculating fluidised bed to convert the ferrous chloride to ferric chloride, separating the gaseous ferric chloride from any residual solids, reacting the gaseous ferric chloride with oxygen at a temperature of circa 700 to 900° C. in a fluidised bed reactor, continuously recirculating a portion of the bed material from the reactor back to the reactor, condensing unreacted ferric chloride in the gas stream by cooling iron oxide particles below the condensation point of ferric chloride, and injecting said particles into the gas stream whereby ferric chloride condenses on the surface of the iron oxide particles and the particles are carried by the gas stream to a separator, the separated coated iron oxide particles being recycled to the condensation step or the reaction step.
According to a fourth aspect of the invention, there is provided a process for producing
Bennett Brian
Conduit Martin
Davidson John Frank
Davidson Peter John
Fallon Neil
Brown Ron D.
Nguyen Ngoc-Yen
Stolle Russ R.
Tioxide Group Services Limited
Whewell Christopher J.
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