WO2009115876A2

WO2009115876A2 - Process for producing sulphur dioxide, a thermochemical system comprising the process and its related apparatuses, use of carbon-based compounds to feed a process for producing sulphur dioxide and its related system

Info

Publication number: WO2009115876A2
Application number: PCT/IB2009/000246
Authority: WO
Inventors: Luca Patauner
Original assignee: Luca Patauner
Priority date: 2008-03-17
Filing date: 2009-02-13
Publication date: 2009-09-24
Also published as: EP2252548A2; ITBO20080172A1; WO2009115876A3

Abstract

The invention relates to a thermochemical process for producing sulphur dioxide, a thermochemical system comprising the thermochemical process and apparatuses for the implementation of the process and of the thermochemical system, as well as the use of carbon-based compounds in order to feed a thermochemical process for producing sulphur dioxide and its related system. The process comprises the steps for the collection of concentrated sulphuric acid (S) inside a thermochemical reactor (11) of a thermochemical apparatus for producing sulphur dioxide (10), for the heating of the concentrated sulphuric acid (S) until it boils. The peculiarity of the process is that of adding carbon-based compounds in the thermochemical reactor (11).

Description

PROCESS FOR PRODUCING SULPHUR DIOXIDE, A THERMOCHEMICAL SYSTEM COMPRISING THE PROCESS AND ITS RELATED APPARATUSES, USE OF CARBON-BASED COMPOUNDS TO FEED A PROCESS FOR PRODUCING SULPHUR DIOXIDE AND ITS RELATED SYSTEM

DESCRIPTION OF THE INVENTION:

The present invention relates to a thermochemical process for producing sulphur dioxide, a thermochemical system comprising the process, the system including in particular sulphuric anhydride as an intermediate product, as well as the apparatuses for the implementation of the process and of the thermochemical system.

Subject of the invention is also the use of carbon-based compounds to feed a thermochemical process for the production of sulphur dioxide and of a thermochemical system comprising the thermochemical process. Conceptually speaking, the invention can be interpreted as a system for the disposal and the recycling of waste constituted by carbon-based compounds, because the final products of some specific forms of application of the invention result hydrogen and carbon dioxide in proportional quantities for producing organic chemicals, particularly methanol.

The invention field of application regards all the thermochemical processes wherein it is necessary to dissociate the sulphuric acid in sulphur dioxide, in particular when the decomposition reaction is an intermediate product of a more complex thermochemical system. Among the numerous applicative versions of the invention, noteworthy is the gaseous hydrogen production field, methanol, organic compounds and the broader disposal and recycling of waste field, in particular reference to waste constituted by carbon-based compounds, that is organic carbonaceous waste, with particular reference to the disposal of biomasses in general, organic gelatines, various sludges and all those organic compounds with a high intrinsic water content, even up to the 70% of humidity.

There are numerous well-known processes for the dissociation of the sulphuric acid, that can occur in an electrolytic, thermal or thermochemical way. The reaction of decomposition of the sulphuric acid for obtaining sulphur dioxide by thermal way occurs according to the following equation: (1) 2 H₂SO₄ (iiq) → 2 H₂O (g_as) + 2 SO_{2 (gaS}) + O_{2 (gas)} ,

which is a highly endothermic reaction and occurs at high temperatures, normally higher than 800°C (typically between 850° and 1.00O⁰C), with separation of oxygen. Recent studies have identified catalysts that allow the said reaction to be occured under less drastic conditions, but anyway still far away from conditions which could permit its industrial exploitation and basically at the limit for the current standards of the chemical engineering.

Therefore, an evident limit of the well-known thermal processes is that they require a huge amount of energy for the decomposition of the sulphuric acid according to the reaction (1). This implies that the decomposition has to be supported by a large external supply of thermal energy.

Another well-known limit is the necessity of complex and expensive plants to support the reaction (1), due to the considerable temperatures that have to be reached and consequently the suitable materials, compatible with the intrinsic aggressive conditions.

In order to industrially obtain gaseous hydrogen the most studied and established cycle up to now was the Sulphur-Iodine thermochemical one, which proves to be more advantageous than other well-known methods of the prior art for hydrogen production. For example, prior art methods include water electrolysis (overall yield of about 23%), hydrocarbons reforming or coal gasification, the letter showing yields little higher than the electrolysis system but onerous due to the need of separating hydrogen from other compounds derived from the involved reactions. Therefore there are a lot of patents/application concerning implementations and improvements of the aforementioned cycle, e.g. the Japanese documents JP2007/106656, JP2007/106656, JP2007/078817 and the Chinese document CNl 785796.

As It is well-known, the Sulphur-Iodine cycle makes use of the Bunsen reaction, which is exothermic and occurs spontaneously at temperatures in the range from 0° to 120°C:

(2) SO₂ (ga_s) + h (Hq) +2 H₂O (_gas) → H₂SO₄ (i_iq) + 2 HI (Hq).

The cycle goes on then according to the reaction of decomposition of the hydroiodic acid: (3) 2 HI (aq) H₂ (gas) + I₂ (gas),

which is slightly endothermic and occurs typically at temperatures between 300° and 500°C if it occurs as thermal pyrolysis. The temperatures are considerably lower working with electrochemical or catalyzed systems. Moreover, the use of such reaction in a thermochemical system involving the reaction of decomposition of the sulphuric acid (1) which, above mentioned, is a strongly endothermic reaction, confers to the Sulphur-Iodine cycle the same energetic problems and same disadvantages previously mentioned in relation to the thermochemical process.

In the acids purification field and in particular the purification of the sulphuric acid polluted by organic substances dissolved and/or suspended in it, the so-called "sulphur dioxide generator" process is well-known. In this process the sulphur dioxide is generated from the sulphuric acid or from the sulphuric anhydride and/or from a mixture of these two by means of various methodologies. Among the existing methodologies, there is the Hechenbleickner process, which is used exclusively for the recovery of the spent sulphuric acid. In this process the acid, that is polluted by organic compounds, is brought to temperatures over 200°C, so that the organic substances reacting with the acid behave as reducing agents, while the same sulphuric acid acts as oxidizing agent, and the result is the reduction reaction of sulphuric acid to sulphur dioxide. Therefore the sulphur dioxide is produced directly from the acid, which changes initially into water and sulphuric anhydride according to the reaction:

(4) H₂SO₄ → H₂O + SO₃

then the sulphuric anhydride, which is active towards the carbon-based compounds already present originally in the sulphuric acid to be purified, reacts with these compounds through the following oxidation reaction:

(5) 3 SO₃ + -(CH₂)- → 3 SO₂ + CO₂ + H₂O wherein with -(CH₂)- is meant natural and/or artificial generic organic compounds containing hydrogen and carbon, thus obtaining carbon dioxide. Carbon dioxide can also therefore obtained by carbon based compounds according to the overall oxidation reaction

(6.1) -(CH₂)- + 3 H₂SO₄ → 3 SO₂ + 4 H₂O + CO₂

which becomes, in the case of carbonaceous substances:

(6.2) C + 2 H₂SO₄ → 2 SO₂ + 2 H₂O + CO₂

This process of generation of the sulphur dioxide is nevertheless slow and moderately endothermic. In fact, such a process requires a limited external supply of energy because it makes use of the energy derived from the oxidation of the carbon compounds present in the sulphuric acid as pollutants. In order to be scaled up to the industrial process, such a process, due to the slowness of the reactions (6.1), (6.2) requires anyway the use of high temperatures.

Therefore, a first objective of the present invention is to provide a thermochemical process for producing sulphur dioxide, a thermochemical system including the thermochemical process and apparatuses for the implementation of the process and of the thermochemical system, which overall result of easy accomplishment, effective, reliable and economically feasible. A further objective of the invention is to provide the use of carbon-based compounds to feed a thermochemical process for the production of sulphur dioxide and a thermochemical system including the thermochemical process and its related apparatuses for the implementation of the process and of the system, which usefully allow also the disposal of wastes made of carbon-based compounds in a practical and ecological way, as the system in accordance with the invention, in one of its application form, allows the recycling of waste based on carbon compounds.

Another objective of the present invention is to realize a thermochemical process for the production of sulphur dioxide and thermochemical systems including the thermochemical process, whose implementation apparatuses are simply feasible and require reduced price and space. A still further objective is to realize thermochemical systems, in particular hydrogen production systems, with low polluting emissions.

A still further objective is to realize thermochemical systems, in particular methanol production systems, which basically do not introduce in the atmosphere any polluting emission.

Another objective is to realize the production of hydrogen directly in the place of its possible use, thus avoiding the dangers associated to its transport, being the system even conveyable on dedicated means of transport.

Another objective is that the thermochemical process for producing sulphur dioxide and the thermochemical systems comprising the thermochemical process allow a self supporting system from energetic supply point of view.

A further objective concerns the fact that the aforesaid systems can be fed through the use of compounds and elements easily available on the territory, such as water and carbon- based compounds obtainable also by common town (solid) wastes. In order to achieve these objectives, subjects of the present invention are a thermochemical process for producing sulphur dioxide, a thermochemical system comprising the thermochemical process and apparatuses for the implementation of the process and of the thermochemical system, as well as the use of carbon-based compounds to feed a thermochemical process for producing sulphur dioxide and of a thermochemical system comprising the thermochemical process, according to the annexed claims which are integral part of the present description.

The core of the invention consists in having intuited that, unlike the traditional thermochemical processes for the dissociation of the sulphuric acid, the addition of carbon- based compounds to the concentrated sulphuric acid and then the respective use leads to obtain various and important advantages for the same thermochemical process and systems which use such processes, such as:

the combustion energy of the carbon-based compounds and the products extracted at the end of the process are used for the production of chemicals that can be profitably utilized, for instance in the industrial field, such as hydrogen and methanol, thus realizing a substantial recycling of the compounds themselves; when the carbon-based compounds, e.g. methanol, extracted at the end of the process are obtained simply from wastes, a substantial recycling of the waste itself would come off on the basis of what explained in the previous point; - they dissociate and recycle extremely well even carbon-based compounds highly rich in water, as for instance wet biomasses, sludges of various kinds, organic gelatines; they prove to be substantially self-sufficient from the energetic point of view, thus not requiring compatible thermal sources or plants, as they can sustain themselves just from the energetic point of view through the combustion of part of the generated carbon-based compounds and of those feeding the process; as industrial process, they work at relatively low temperatures, substantially not higher than 400-500°C, thus requesting economical plant that can be implemented with usual technical materials; the relatively low exercise temperatures, the substantial simplicity of realization and the autonomy from external thermal plants let the apparatuses according to the invention be feasible in places with limited room and resources, such as shelters and isolated research centres, little remote communities and further conveyable on adequate means of transport.

These considerations are likewise valid in the case of thermochemical systems comprising thermochemical processes for the sulphuric acid dissociation. It is specified that in the present document by the term concentrate sulphuric acid it is intended a solution having a concentration of sulphuric acid higher than 50%, preferably at least 80%.

Thereafter it is remarked that the voluntary addition of carbon-based compounds to the concentrated sulphuric acid implies the development of the aforementioned reaction (6.1) and/or (6.2), contrary to the traditional process of Hechenbleickner, usually applied to the recovery of exhausted sulphuric acid in all those cases in which organic and/or carbonaceous substances dispersed and/or in solution are previously present, whose the removal is wished. It is evident that, conceptually, is completely different to add intentionally carbon-based compounds to the concentrated sulphuric acid from carrying out the purification of organic and carbonaceous residuals compounds already present as undesired impurities in the sulphuric acid itself, as explained for instance in the document US 4053573. For instance, a significant difference consists in the fact that the process according to the invention has as starting material concentrated sulphuric acid, therefore in a completely different way from the well-known art which has spent sulphuric acid as starting material. Moreover, in the invention desired and selected carbon-based compounds can be also added in order to achieve determinate efficiency and functionality confirmations of the thermochemical systems according to the invention, compounds for instance chosen among wastes, although the thermochemical system in accordance with the invention works well and in efficient way with all kinds of carbon-based compounds, as it will be detailed thoroughly in the following.

The use of carbon-based compounds to feed a thermochemical process for sulphur dioxide production and a thermochemical system comprising the thermochemical process and its related apparatuses, in particular in the embodiment of a thermochemical system for hydrogen and/or methanol production, provides the following advantages compared to known incinerators of the art:

- either highly polluting compounds or potentially harmful substances, that can be dispersed in the surrounding environment, such as nitrogen oxides, dioxins, unburned compounds and nanoparticles, are not produced; unlike the traditional waste incinerators, a range of organic-based wastes with different humidity content and carbon content can be decomposed, in the waste incinerators the latter would comprise the qualitative and quantitative combustion efficiency with consequent operational diseconomy and environmental impact.

According to the invention and as to methanol production, it is possible to have a severe reduction of CO2 emissions in the surrounding atmosphere.

A peculiar aspect of the thermochemical process for producing sulphur dioxide in accordance with the invention is the addition of iodine/iodide and/or bromine/bromide systems to the sulphuric acid in decomposition. With such addition an acceleration of the reaction (6.1) and/or (6.2) is profitably achieved with a consequent significant reduction of the reaction times.

Another advantage peculiarity of the invention is the further addition, in the used sulphuric acid, of suitable catalysts for the decomposition of the sulphuric acid, whose efficacy varies with the concentration in combination with the presence of the iodine/iodide and/or bromine/bromide systems, there is a significant acceleration of the carbon-based compounds oxidation reaction (6.1) and/or (6.2).

Preferably, for energy benefits and with the objective of preventing the formation and consequent need of removal of the carbonaceous residuals, an important aspect of the invention foresees the completing of the oxidation reaction of the carbon-based compounds (6.1) and/or (6.2).

It is worthwhile to cite in the following of the document the use of the process of the invention in a cycle conventionally called NEW SYSTEM. This is a cycle which uses a part of the Sulphur-Iodine cycle to produce a mixture of carbon dioxide and hydrogen under definitely less aggressive and industrially economical conditions. The NEW SYSTEM is fed with carbon-based compounds of any kind, they can be natural e.g. biomasses or they can be synthetic e.g. such as wastes. It is based on the following reactions:

(6.1) -(CH₂)- + 3 H₂SO₄ → 3 SO₂ + 4 H₂O + CO₂

^Or (6.2) C + 2 H₂SO₄ → 2 SO₂ + 2 H₂O + CO₂

(2) SO₂ + 2 H₂O + 1₂ → H₂SO₄ + 2 HI

(3) 2 HI → H₂ + I₂

that can be summarized through the global reactions:

(7.1) -(CH₂)- + 2 H₂O → 3 H₂ + CO₂

(7.2) C + 2 H₂O → 2 H₂ + CO₂ with reference to the starting reactions (6.1) and (6.2).

The main advantage of the NEW SYSTEM, compared to the traditional Sulphur-Iodine cycle, is that the reaction (6.1) and/or the reaction (6.2) occur at temperatures lower than 400°C, in particular in the range from 200° to 400°C.

The products of the reaction (7.1) can be subsequently and conveniently used for the final production of methanol according to the reaction:

(8) 3 H₂ + CO₂ → CH₃OH + H₂O

By having the stoichiometric ponderal proportion of the reagents hydrogen and carbon dioxide appropriate for production of methanol. This implies profitably that, in this case of application of the system in accordance with the invention, there are no emissions and/or dispersions of carbon dioxide in the atmosphere, as this is entirely sequestrated thanks to the formation of the methanol.

The methanol is a good fuel, thus it acts as energetic carrier and is one of the main bases of the industrial organic chemistry, because practically all the organic compounds can be obtained from it.

The NEW SYSTEM is therefore an excellent starting system for transforming and recycling integrally the energy and the mass of the carbon-based compounds that are introduced and transformed through the reaction just written. Therefore the present system is a strong innovative method to contribute to the correct and appropriate management of the carbon cycle.

Further objectives, features and advantages of the present invention will appear clear from the following detailed description of some embodiments of the present invention, given for illustrative and non limitative purposes with reference to the annexed figures wherein:

Figure 1 represents a schematic view of a favourite preferred embodiment of an apparatus realization which implements a thermochemical process for sulphur dioxide production in accordance with the invention; Figure 2 represents a schematic view of an apparatus realization which implements a thermochemical system in accordance with the invention, specifically a system for producing hydrogen.

Figure 1 illustrates a preferred embodiment which implements a thermochemical process for producing sulphur dioxide or an apparatus for producing sulphur dioxide, indicated as a whole with 10, which comprises a thermochemical reactor 11 wherein the concentrated sulphuric acid S is contained. The reactor 11 is equipped with feeding means 12 for the introduction in its interior of carbon-based compounds and reaction accelerators. The feeding means 12 are such as to guarantee the perfect seal of the reactor 11 at the reacting gases outlet in its interior during the feeding operation of the said compounds, for instance a feeding system with sealed rotating cells. Preferably, in the bottom of the reactor

11 residuals R extraction means 14 are provided, for instance a sealed extraction screw for

-the continuous extraction of the residuals R without any gas present in the reactor, such screw being able to run through the said extraction means 14. The residuals R develop by sedimentation and precipitation on the reactor 11 bottom; these are various solid compounds remaining from the development of the thermochemical reactions in its interior.

Heat transfer means 13 for heating the acid S are associated to the reactor 11 and, above it, cooling means 15 for the reaction accelerators condensing. Above the reactor 11 there are extraction and recovery means of the reaction gases 16 to recover the gases coming from the reaction that take place in the apparatus 10, for instance a reactor for producing sulphites.

The functioning of the apparatus 10 as well as the thermochemical process for producing sulphur dioxide by it implemented is hereafter described. Initially the concentrated sulphuric acid S is collected inside of the thermochemical reactor 11, to which reaction accelerators are added, specifically sulphuric acid decomposition catalysts. The heat transfer means 13 heat the concentrated sulphuric acid S until it boils, that is a temperature of about 250-340⁰C. Thereafter the carbon-based compounds are added through feeding means 12 and further reaction accelerators. It is advantageous to remove periodically the residuals R present in the reactor 11 , and this can profitably be carried out continuously. The residuals removal allows an efficient and regular working of the thermochemical apparatus 10 over the time. When such removal occurs in a continuous way, one can avoid to stop the reactor in order to start the removal process, thus giving the apparatus 10 a better productivity and profitability.

The aforesaid additions are important peculiarities of the thermochemical process for sulphur dioxide production in accordance with the invention, allowing numerous and significant benefits to be achieved in comparison to the processes of the state of the art.

The addition of carbon-based compounds makes sure that in the reactor 11 the reaction (6.1) and/or the reaction (6.2) occur, that allows profitably the production of sulphur dioxide at process temperatures substantially not higher than 400°C, therefore considerably less than about 800°C as carried out in the state of the art. The invention therefore allows a big exercise inexpensiveness and a considerable realization simplification and inexpensiveness of the apparatus 10 which carries out the process in accordance with the invention.

Important benefits follow when the further reaction accelerators consist of iodine/iodide and/or bromine/bromide systems, because these systems strongly accelerate the process with respect to the case wherein these accelerators are not present.

It has been further noticed that the sulphuric acid decomposition catalysts use, whose efficacy varies according to the concentration and the contemporaneous presence of the iodine/iodide and/or bromine/bromide systems, allows a significant acceleration of the oxidation reaction of the carbon-based compounds (6.1) and/or (6.2). In particular, excellent results are achieved with the addition in the reactor 11 , in appropriate proportion, of a iodine/iodide system when in the sulphuric acid, combined or singularly, iron-based catalysts, Pt/Rh/Ru/Pd systems and particularly vanadium V₂O₅ in homogeneous phase are previously added. With reference to Figure 2, a preferred embodiment of an apparatus which implements a thermochemical system comprising the thermochemical process in accordance with the invention is shown. Such preferred embodiment, concerns specifically a thermochemical apparatus for hydrogen and methanol production, indicated as a whole with 20. The apparatus 20 comprises the following listed elements of apparatus 10, with analogous associations and functions: thermochemical reactor 11 containing sulphuric acid S, feeding means 12, heat transfer means 13, residuals R extraction means 14. Associated to the reactor 11 , means of implementation of an sulphur dioxide oxidation reaction and reaction products separation 21 are provided, particularly according to the Bunsen reaction 2 and associated to means of chemo-physical separation of the various compounds of the reaction 2, for instance a distillation column, particularly of the type "reactive with filling". Further associated to the reactor 11, particularly on the upper part, means of generation of hydrogen gas 22, e.g. a catalyzed decomposition system. Advantageously, recirculation means of the reaction fluids 23 are provided which are associated to exit openings for the said means of generation of hydrogen gas 22, e.g. recirculation pumps with forced input connected to the said exit openings directed inside the apparatus 20, in particular inside of the implementation means 21 and particularly at the side of the distillation column, which is "reactive with filling" type 21.

The described preferred embodiment of the thermochemical system of the invention includes, just representatively, one of the possible implementations of the NEW SYSTEM previously illustrated. The functioning of the thermochemical apparatus for hydrogen production 20, as well as the thermochemical system for hydrogen production implemented by it, is hereafter described. Initially the functioning and the implementation of the thermochemical system occur in the same way, as seen above in connection with the thermochemical process for sulphuric acid production in accordance with the invention and all the previous remarks on this process are equally valid. In brief, the concentrated sulphuric acid S, inside the thermochemical reactor 11, additivated with sulphuric acid decomposition catalysts, is heated until its substantial decomposition. Carbon-based compounds and the further reaction accelerators, such as iodine/iodide and/or bromine/bromide systems, in particular iodine/iodide systems are then added. The addition of carbon-based compounds makes sure that in the reactor 11 the reaction (6.1) and/or the reaction (6.2) take place, which allows sulphur dioxide, steam, carbon dioxide and residuals R to be advantageously produced.

The gases and steam generated pass afterwards inside the implementation means of the sulphur dioxide oxidation reaction 21, where they come in contact with a mixed solution of water, iodine and iodide and react according to reaction 2. Subsequently, or simultaneously in the example wherein the implementation means of oxidation reaction of the sulphur dioxide are constituted by a distillation column 21, be it of the filling or plate type, the reactants and the reaction products 2 undergo a fractionation. In particular, the sulphuric acid come back to the reactor 11 because its high boiling point is not reached in the column 21 and therefore comes down again by gravity, while the hydroiodic acid moves towards the means of generation of the hydrogen gases 22, as it has a boiling point lower than the temperatures present in the column 21, wherein it is advantageously dissociated into hydrogen and iodine according to reaction 3. The generated hydrogen comes out from the generation means 22 together with the carbon dioxide, while the iodine comes back inside the thermochemical apparatus 20, particularly through a lateral surface of the reactive distillation column 21, where it reacts again according to reaction 2. Any carbon-based compound, both organic such as gelatines, sludges, plastics and carbonaceous such as peat, anthracites, lignite, graphite, etc. even at particularly high humidity, allows the reactions (6.1) and (6.2) with the consequent (7.1) and (7.2) to be efficiently carried out, as the diversity of chemical composition of the carbon-based compounds does not affect the final products of the aforementioned reactions, but only their ponderal relation and the amount of generated waste R. At the most, small amounts of low boiling hydrocarbons can be generated, which can be advantageously recovered and put back in the cycle through the recirculation means of the reaction fluids 23.

The use of the reactive distillation column 21 allows to unify in a single body the functions necessary to the Bunsen reaction 2 and those of separation and recirculation of the sulphuric acid and of the iodine inside of the thermochemical apparatus 20, thus forming an highly pure hydroiodic acid, which will be subsequently dissociated into hydrogen and iodine in the hydrogen separation means 22. Advantageously, this solution allows a considerable plant engineering simplification of the thermochemical apparatus 20, providing numerous benefits in terms of costs and size otherwise necessary. It is important that the humidity present in the carbon-based compounds which feed the reactor 11 is sufficient to satisfy the stoichiometry of the global reactions (7.1) and/or (7.2), otherwise it is sufficient to implement in the system the step of introducing an amount of water to satisfy the aforesaid stoichiometry. This step can be advantageously carried out in the recirculation means of the reaction fluids 23 with the help of measuring and dosage tools appropriately associated to the apparatus 20.

In order to obtain an excellent functioning of the system 20 it is important that the reactions (6.1) and (6.2) and consequently (7.1) and (7.2) are fully completed for energetic reasons and for limiting the residuals R, obtainable with the permanency of the reagents under the just now described conditions for a suitable time.

Moreover, in the case of sole presence of reaction (7.1), the completion is a necessary condition to come to the reaction (8) with the correct required stoichiometry. This methanol production occurs through well-known methods of conversion of the carbon dioxide and of the gaseous hydrogen to methanol associated to the thermochemical apparatus 20, in particular to an exit of the means of generation of hydrogen gases 22, these means of conversion implementing well-known processes according to reaction (8), as for instance the processes developed by ICI, BASF, LURGI. It is clear that numerous configurations are possible, for the people in the field, for the thermochemical process for producing sulphur dioxide, for the thermochemical system comprising the thermochemical process, as well as for the apparatuses for the implementation of the process and of the thermochemical system in accordance with the present invention, as it is clear that in its practical realization the forms of the illustrated and described details can be different, and the same could be substituted by technically equivalent elements and procedures.

For instance, an apparatus which implements a thermochemical system comprising the thermochemical process for producing sulphur dioxide in accordance with the invention, e.g. a thermochemical apparatus for producing hydrogen and methanol as illustrated in figure 2, could advantageously present, associated to the reactor of the apparatus and to the related heating means, means for the use of the products of reaction (7.1) and/or (7.2) and/or (8) to feed, even integrally, the heating means of the reactor. Advantageously, the system proves to be self-sufficient and does not need external energy sources.

Claims

1. Thermochemical process for sulphur dioxide production, comprising the following steps:

collecting concentrated sulphuric acid (S) inside a thermochemical reactor (11) of a thermochemical apparatus for sulphur dioxide production (10), heating the concentrated sulphuric acid (S) substantially until it boils, characterized by the step of adding carbon-based compounds in the thermochemical reactor (11)

2. Process according to claim 1, wherein in the thermochemical reactor (11) iodine/iodide systems are added to the sulphuric acid (S)

3. Process according to claim 1 and/or 2 wherein bromine/bromide systems are added to the sulphuric acid (S) in the thermochemical reactor (11).

4. Process according to any one of claims 1-3, wherein decomposition catalysts of the sulphuric acid are added in the thermochemical reactor (11) to the sulphuric acid (S).

5. Process according to the claim 4, wherein the decomposition catalysts comprise iron-based catalysts, Pt/Rh/Ru/Pd systems or their mixtures.

6. Process according to claim 4 or 5, characterized by the fact that the aforesaid catalysts comprise vanadium V₂O₅.

7. Process according to any one of claims 1-6 wherein the carbon-based compounds are reacted inside the reactor (11) until the completeness of the following reactions (6.1. and 6.2)

• -(CH₂)- + 3 H₂SO₄ → 3 SO₂ + 4 H₂O + CO₂ (6.1)

• C + 2 H₂SO₄ → 2 SO₂ + 2 H₂O + CO₂ (6.2)

8. Process according to anyone of claims 1-7, wherein the residuals (R) present in the reactor (11) after the step of heating are periodically removed .

9. Process according to claim 8, wherein the periodical removal of the residuals (R) is carried out in a continuous way.

10. Thermochemical system for carrying out the thermochemical process for sulphur dioxide production according to any one of the claim 1-9 and implemented in a thermochemical apparatus (20), wherein said system comprises a thermochemical reactor (11) and implementation means (21) of the following global reaction (7.1, 7.2)

• -(CH₂)- + 2 H₂O → 3 H₂ + CO₂ (7.1)

• C + 2H₂O → 2 H₂ + CO₂ (7.2) by means of oxidation of the sulphur dioxide, that occurs inside of the apparatus (20).

11. System according to claim 10, wherein said system produces hydrogen.

12. System according to claim 10 or 11, wherein a sufficient amount of water is added inside of the apparatus (20) to satisfy the appropriate stoichiometry of the global reaction (7.1, 7.2).

• -(CH₂)- + 2 H₂O → 3 H₂ + CO₂ (7.1)

• C + 2H₂O → 2 H₂ + CO₂ (7.2)

13. System according to claim 12, wherein the addition of water is carried out inside the implementation means of a sulphur dioxide oxidation reaction, in particular inside a reactive distillation column (21).

14. System, according to anyone of claims 11 to 13, characterized by the fact of producing methanol.

15. System according to anyone of claims 10 to 14, wherein the global reaction (7.1, 7.2) is completed with the permanency of the reagents inside the apparatus (20).

16. Apparatus for the implementation of the thermochemical process for sulphur dioxide production according to anyone of the claims from 1 to 9

17. Apparatus for the implementation of the thermochemical process according to anyone of the claims from 10 to 15, comprising: a thermochemical reactor (11) containing sulphuric acid (S), feeding means (12) associated to the reactor (11) for feeding compounds in its interior heat transfer means (13) associated to the reactor (11) for its heating, - implementation means of a sulphur dioxide oxidation reaction and reaction products separation (21), associated with the reactor (11) for the development of the oxidation reaction (2), wherein the aforesaid implementation means of a sulphur dioxide oxidation reaction and reaction products separation (21) are integrated in a single body.

18. Apparatus, according to claim 17, wherein the implementation means comprise a distillation column (21), in particular of type "reactive with filling".

19. Apparatus according to claim 17 or 18, wherein the extraction means (14) of residuals (R) are associated with the reactor (11) in order to remove the residuals

(R) from the interior of the reactor (11).

20. Apparatus according to anyone of the claims from 17 to 19, wherein the generation means of hydrogen gases (22) are associated to the reactor (11) for the generation of hydrogen gas .

21. Apparatus, according to claim 20, wherein the recirculation means of the reaction fluids (23) are associated to exit openings of the said hydrogen gas generation means (22).

22. Apparatus, according to anyone of the claims from 17 to 21, wherein the fact that it comprises an apparatus for hydrogen production.

23. Apparatus according to claim 22, wherein conversion means of the carbon dioxide and of the gaseous hydrogen into methanol are associated to the generation means of hydrogen gases (22) for the methanol generation, in particular at one exit of the same generation means (22).

24. Apparatus, according to anyone of the claims from 17 to 23, wherein means for the use of the reaction products (7.1) and/or (7.2) and/or (8) are associated with the reactor (11) and with the heating means of the apparatus (13) to feed the aforesaid heating means (13).

25. Use of carbon-based compounds to feed a thermochemical process for producing sulphur dioxide and related apparatus (10).

26. Use of carbon-based compounds to feed a thermochemical system carrying out a thermochemical sulphur dioxide production process and comprising an apparatus (20), wherein said thermochemical system is for the hydrogen production and any organic compound from it generated.