Method for preparing raw materials for glass production

CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 1 PROCESS FOR PREPARING RAW MATERIALS FOR THE MANUFACTURE OF GLASS The invention relates to a method for preparing some of the materials 1o that can be used to manufacture glass.

In the context of the present invention, the term “raw materials” is understood to mean all the materials, vitrifiable materials, natural ores or synthesized products, materials resulting from recycling of the cullet type, etc., which may enter into the composition which feeds a furnace. glassmaker.

Likewise, the term “glass” is understood to mean glass in the broad sense, that is to say encompassing any material with a vitreous, glass-ceramic or ceramic matrix.

The term "manufacture" includes the essential melting step of the raw materials and possibly all the subsequent / additional steps aimed at refining / conditioning the molten glass with a view to its final shaping, in particular in the form of flat glass 20 (glazing), hollow glass (flasks, bottles), of glass in the form of mineral wool (glass or rock) used for its thermal or sound insulation properties or even possibly of glass in the form of so-called textile threads used in reinforcement.

The invention is particularly interested in the raw materials 2s necessary for manufacturing glasses having a significant alkali content, in particular sodium, for example glasses of the silico-soda-lime type used to make flat glass.

The raw material currently most frequently used to provide sodium or potassium is sodium carbonate Na2CO3 or potassium carbonate IC2CO3, a choice which is not devoid of drawbacks.

In fact, on the one hand, this compound provides only sodium as a constituent element of glass, all the carbonaceous part decomposing in the form of releases of CO 2 during melting. On the other hand, it is an expensive raw material, compared to the others, because it is a synthetic product, obtained by the Solvay process from sodium chloride and CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 2 limestone, a process requiring a certain number of manufacturing steps and not very energy efficient.

This is the reason why it has been proposed to use .as sodium source not a carbonate but a silicate, optionally in the form of a mixed silicate of alkalis (Na) and alkaline earth (Ca) that we prepare beforehand. The use of this type of intermediate product has the advantage of bringing together several of the constituents of the glass, of eliminating the decarbonation phase, and of reducing the CO 2 emissions from the melting furnace.

It also makes it possible to accelerate the melting of the raw materials as a whole, and to promote their homogenization during melting, as indicated, for example, in patents FR-1 211 098 and FR-1 469 109.

However, this route poses the problem of manufacturing this silicate.

A first method of synthesis has been described in patent WO-00/46161: it involves converting a halide, for example NaCl, and silica to silicate at high temperature, the thermal input being supplied to the using submerged burners.

Combustion by submerged burners was already known, for example from patents US-3,627,504, US-3,260,587 or US-4,539,034, to ensure the melting of vitrifiable materials to make glass.

Using this technology in the different context of the synthesis of silicates, therefore upstream of the actual manufacture of the 2o glass, indeed brings many advantages: this combustion mode causes strong turbulence within the materials during the reaction. , strong convection movements around the flames or gas jets of the submerged burners, which promotes very efficient mixing of the reagents.

In addition, the submerged burners provide heat directly where it is needed, 2s in the mass of the products being reacted. It is also an environmentally friendly combustion method.

For more details on the different reactions involved, reference may be made to the previously mentioned patent WO-00/46161.

The direct conversion of NaCl and silica done in this way is therefore very attractive in more than one way.

However, it turned out that this direct conversion was difficult to implement on a large scale.

The aim of the invention is therefore to develop another type of silicate manufacture, which can retain the advantages of the technique described above, while being easier to use on an industrial scale.

Incidentally, CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 3 we will try to ensure that this new type of manufacturing is as respectful as possible of the environment and takes into account / optimizes all the products of reaction involved other than silicates, silicates whose production remains the primary objective of the present invention.

s The invention firstly relates to a process for the manufacture of compounds based on alkali silicates, such as Na, K and / or alkaline earth metals, such as Ca, Mg, and / or rare earths such as Ce, optionally in the form of mixed silicates combining at least two of these elements.

This process involves 1o (i) a conversion reaction (1) of halides, in particular chlorides, of said alkalis and / or of said alkaline earth metals and / or of said rare earths, into corresponding sulphates, (ü) a conversion reaction (2 ) of said sulphates with silica to corresponding silicates, the thermal input necessary for this conversion being provided, at least in part, by a combustion reaction (3) using one or a plurality of submerged burners.

The process according to the invention can also include only step (ü) according to reaction (2).

We understand here under the term "silica" any compound containing 2o predominantly silica (silicon oxide) SiO2, even if it may also contain other elements, other minority compounds, which is particularly the case. when using natural materials such as sand.

The term “submerged burners” is understood here to mean burners configured so that the “flames” they generate or the combustion gases resulting from these flames 2s develop in the reactor where the conversion takes place, within the same. of the mass of materials being processed. Generally, they are arranged so as to be flush with or slightly protruding from the side walls or the floor of the reactor used (we are talking about flames here, even if they are not strictly speaking the same "flames" as those. produced by 3o overhead burners, for simplicity).

The process described above is an improvement of the process described in patent WO-00/46161, in that it divides into two distinct stages the overall reaction involving a halide (such as NaCl) and silica to produce a silicate.

In the present invention, there is thus an intermediate step CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 4 consisting of going through the manufacture of a sulfate.

The industrial feasibility is greatly improved: one thus avoids having to thermally break, at very high temperature, a halide of the NaCl type, which tended to cause a certain volatilization of NaCl in the furnace where the reaction was carried out. with silica.

On the contrary, in the invention, step (1) of converting the halide into sulfate is easier to carry out, can be carried out at a relatively lower temperature and under operating conditions already mastered in the chemical industry. Step (2) of converting the sulphate into silicate by submerged burners makes it possible to obtain the desired product with all the advantages of submerged burners mentioned in the preamble of the present application.

To illustrate these two steps, with a view to manufacturing sodium silicate, the invention therefore proposes in particular the following successive steps (i) 2 NaCl + H2S04 - ~ Na2S04 + 2 HCI ~ s (ü) Na2S04 + x Si02 - ~ ( SiOa) X - Na20 + S02 / S03 For this second reaction, the value of x can vary, an example is in particular x = 2.

This text will return later on the interest / valorization of the reagents / reaction products involved in these reactions, in addition to NaCl, Si02 and 2o silicate (SiO ~), ~ - Na20.

The efficiency of the burners at all levels (quality of the mixture, excellent heat transfer) means that the conversion according to reaction (2) is greatly favored, and this without necessarily having to reach extremely high temperatures. .

2s Another advantage of submerged burners is the following: they allow the introduction of liquid / solid fuels in the same way as vitrifiable raw materials.

In fact, this leads to obtaining high redoxes of the molten silicate, which is favorable to the decomposition reaction of the sulphates.

The oxidizer chosen to feed the burner (s) submerged) in the 3o reaction (2) can simply be air.

Preferably, however, preference is given to an oxidizer in the form of air enriched with oxygen, and even in the form substantially of oxygen alone.

A high concentration of oxygen is advantageous for various reasons: the volume of combustion fumes is thus reduced, which is favorable in terms of energy and avoids any risk of CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 excessive fluidization of the materials in the course of the reaction which can cause projections on the superstructures, the vault of the reactor where the conversion takes place.

In addition, the "flames" obtained are shorter, more emissive, which allows a faster transfer of their energy to the materials undergoing fusion / conversion.

Regarding the choice of fuel for the submerged burner (s), three ways are possible, alternative or cumulative: one can choose a liquid fuel, gaseous or in solid form.

If it is at least partially in gaseous form, it can directly feed the submerged burners. If it is in liquid, solid form, it can be brought near the submerged burners.

As gaseous fuel, mention may be made of natural gas (mainly methane), propane, hydrogen, or any other hydrocarbon and / or sulfur compound.

1s As solid or liquid fuel, there may be mentioned any compound predominantly in carbon and / or hydrocarbon and / or sulfur form (including sulfur and carbon): as in the previous case, it may be by-products of petroleum industry (heavy fuel oil, bitumens). It can also be polymer-based materials that we will be able to recycle (any material called 2o plastic, tire, ...), and even sand soiled with hydrocarbon, which will also provide both silica and fuel, which is an ingenious way to deal with the problem of cleaning up beaches after oil spills, for example.

In fact, a particularly original characteristic of the present invention is that it is possible to use, if desired, fuels containing sulfur, or even pure sulfur.

Traces of sulfur are found in all vulcanized polymers (tires), they are also found in by-products of the petroleum industry, and the invention allows them to be valued in an interesting way: in fact, the sulfur contained in the fuel provided to make the 3o combustion reaction (3) will oxidize.

Now, in a manner known in the chemical / petroleum industry, it is possible to transform these sulfur oxides (SO2 and / or SOs) into sulfuric acid, by recovering them in the fumes and by treating them appropriately.

We then have two choices (alternative or cumulative in fact, in particular depending on the quantity of H2S04 produced, which closely depends on the level of S CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 6 chosen in the fuel. ): either HZSO4 is valued as a reagent widely used in the chemical industry, independently of the process according to the invention, or it is re-used in the process of the invention.

In fact, the reaction (1) for converting the halides into sulphates advantageously uses sulfuric acid: there is also a “loop” process, where the combustion product of reaction (2) is used as a reagent, a once transformed, in reaction (1).

There is another way, alternative or cumulative with the previous one, to manufacture H2SO4 from the process according to the invention: the reaction (2) for converting sulphate into silicate also produces sulfur oxides SO2 and / or 1o S03.

It is therefore also possible to recover these sulfur oxides, and to subject them to a reaction of conversion into sulfuric acid.

As in the previous case, this sulfuric acid can be re-used as a reagent in reaction (1) and / or it can be upgraded as a reagent for the chemical industry.

In fact, if the fuel contains a significant amount of sulfur, these two reactions of converting sulfur oxides to sulfuric acid can produce more, and even significantly more, sulfuric acid than is necessary for the reaction (1 ) conversion of halides to sulphates, which enhances the process according to the invention as a whole.

There is another reaction product in the process of the invention which is valuable 2o in the chemical industry in particular, it is hydrochloric acid HCl, produced during reaction (1) for converting halides into sulphates, when the halide in question is a chloride of the NaCl type.

It can of course be treated as an effluent, which can be neutralized with calcium carbonate CaG03, which amounts to manufacturing CaCh, which can be used for example for snow clearing roads.

We can also consider HGl as a basic chemical widely used in the chemical industry (just like H2S04), and extract it from the fumes to establish an industrial production chain of HCI.

It is then advantageous to install the device for carrying out this reaction (1) in the site of the chemical industry ayanfi need of this type of chlorinated products.

A first outlet for the silicates produced according to the invention relates to the glass industry: they can replace, at least in part, the traditional raw materials providing alkalines or rare earths, with, especially as regards sodium , an at least partial substitution CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 7 of Na2CO3 by Na20- (Si02) X.

The silicates of the invention can therefore be used to supply a glass furnace.

It may be necessary to subject a treatment step of the granulation type to the silicate formed according to the invention before introduction into the glass furnace.

The glass furnace can be of traditional design (for example electric melting furnace by submerged electrodes, furnace with overhead burners operating with lateral regenerators, loop furnace, and any type of furnace known in the glass industry thus including furnaces with burners. submerged), possibly with a design and mode of operation slightly adapted to a melting process without carbonate or with less carbonate than for standard melts.

It should be noted that certain silicates other than sodium silicate are also very advantageous to manufacture according to the invention.

Thus, the invention makes it possible to manufacture potassium silicate from KCl, which is, economically Is at least, very advantageous as a starting material carrying Si and K for making so-called “mixed alkali” glasses, ie. i.e. containing both Na and K.

These glasses are used in particular to make touch screens, television screen glasses, glasses for a plasma display panel ("Plasma Display Panel").

2o Likewise, the invention makes it possible to manufacture more economically special glasses containing additives for which the chlorides are less expensive than the oxides. This is the case with rare earths such as cerium: the presence of cerium oxide conferring anti-UV properties on glasses, and rare earths of this type are also used in the composition of special glasses with high elastic modulus for discs. hard. The invention thus makes it possible to have a starting material carrying Si and Ce, cerium silicate, at a moderate cost.

A second outlet for the silicates produced according to the invention (apart from being used as raw materials for a glass furnace), more particularly sodium silicate, concerns the detergents industry; sodium silicate frequently entering 3o in the composition of laundry / detergents.

A third outlet for the silicates (and optionally the chlorinated derivatives) formed according to the invention relates to the preparation of particular silicas, commonly referred to by the term “precipitated silicas” entering, for example, in the composition of concretes.

It is in fact possible to carry out an acid attack CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 8 of the silicates formed according to the invention, advantageously with sulfuric acid, so as to precipitate silica under form of particles having a particular particle size: the particle size targeted is generally nanometric (1 to 100 nm for example).

s To carry out the reaction (1) for converting the halides into sulphates, it is possible to use a reactor known in the chemical industry under the term Mannheim furnace.

To carry out the reaction (2) for converting the sulphates into silicates, it is possible to use, as described in patent WO-00/46161, a reactor 1o equipped with burners) submerged) and at least one introduction means silica and / or sulphates below the level of the molten materials, in particular in the form of one or more endless screw charging machines. The same is preferably true for the solid or liquid fuels optionally used, such as the carbon and / or hydrocarbon and / or sulfur compounds (including sulfur and carbon) mentioned above.

It is thus possible to introduce directly into the mass of the products in the course of melting / reaction at least those of the starting reagents capable of vaporizing before having time to react.

To optimize the entire process in terms of energy, we can 2o recover the heat from the fumes from the submerged burner reactor used for the reaction (2) and use it to contribute to the thermal input necessary for the reaction (1) in the Mannheim type furnace.

The process according to the invention described above therefore has many advantages, among which 2s> a reduction in CO2 emissions in glass furnaces which replace all or part of the sodium carbonate with sodium silicate, a lower energy consumption of these ovens because the decarbonation reactions are reduced or eliminated,> upgrading of the halogen of the starting halide, in particular in the HCl form when it is a chloride, > a possibility of running the process in a loop, with re-use of the manufactured H2SO4 by-product,> a possibility of recovering sulfur derivatives as fuel.

The invention will be detailed below with the aid of non-limiting examples, and in CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 9 using a FIG. 1 O FIG. 1: a diagram of a preferred variant of the method according to the invention, operating in a loop.

The two examples according to the invention both relate to the manufacture of sodium silicate from sodium chloride and sulfuric acid, according to the variant illustrated in FIG. 1.

Let us take again in detail the reaction process, in three main stages, represented in the form of a loop in figure 1: the aim of the two examples is to manufacture 1000 kg of sodium silicate of formula Na20- (Si02) 2, i.e. 5489 1o moles.

The yields of the reactions involved are considered to be 100%.

1 - Synthesis of sodium sulfate 2 NaCl + H2S04 ~ Na2S04 + 2 HCl quantity in moles 2 x 5489 5489 5489 2 x 5489 quantity in kg 642 538 779 401 1s This step is carried out in a Mannheim furnace in a known manner.

2- S rLnthesis of sodium silicate in an immersed burner Na2S04 + 2 Si02 - ~ Na20- (SiO ~) a + S02 / S03 quantity in moles 5489 2 x 5489 5489 5489 quantity in kg 779 660 1000 2o This synthesis is carried out in a submerged burner furnace, such as that described in patent WO-00146161.

3 Combustion reaction providing the energy necessary for the synthesis of silicate (estimated here at 2042 kWh / tonne of silicate) For a fuel containing carbon chains of type 2s CHX formula, and sulfur, the combustion reactions are (3) CH , ~ + (1 + x / 4) 02 ~ C02 + x / 2 H20 S + O2 - ~ S02 Depending on the sulfur content of the fuel, the combustion reaction releases more or less S02 in the flue gases which go s' add to the SOx 3o produced by the synthesis of the silicate itself.

We denote by “y” the number of moles of SO2 coming from the combustion.

4 and 4 '- conversion of sulfur oxides into sulfuric acid SO2 / SO3' ~ H2SO4 quantity in moles 5489 + y 5489 + y CA 02462677 2004-04-O1 WO 03/031357 PCT / FR02 / 03398 5489 moles of H2S0 ~ are reintroduced in the synthesis of sodium sulfate (1).

The remaining “y” moles can be recovered outside this synthesis loop.

EXAMPLE 1 This example uses, for step (3), 100 ° 1 ° fuel in the form of sulfur (originating in particular from the desulphurization of petroleum products in a refinery).

Its lower calorific value (PCI) is 2584 kWh / tonne of sulfur.

Reaction (2) requires 2,042 kWh, or 790 kg of sulfur (24,688 moles of 1o S).

The combustion of this sulfur produces y = 24688 moles of SO2.

In addition to the 5,489 moles self-supplying the mouth with H2SO4, we therefore obtain 24,688 additional moles of H2SO4, or 2420 kg which can be recovered outside the loop.

1s EXAMPLE 2 This example uses for step (3) a fuel in the form of heavy fuel oil No. 2 with 4% sulfur.

Its PCI is around 10,930 kWh / t.

We therefore need 187 kg of this fuel to produce one tonne of silicate.

2o We will therefore burn 7.5 kg of sulfur from this fuel, or 234 moles, releasing y = 234 moles of SO2.

We therefore obtain 234 moles, or 23 kg of H2SO4 recoverable outside the loop.

It can therefore be seen that depending on the choice of fuel, the excess 2s sulfuric acid that can be obtained with respect to what is necessary for reaction (1) varies greatly.

All intermediate solutions, with the combination of fuel oil and sulfur, or even the use of vulcanized tires, are possible, which allows the combustion to be best adjusted (3) according to the type of fuel most available and / or the amount of sulfuric acid that we want to produce.