Process for recovering and purifying biological sulfur for the production of sulfuric acid
Patent Information
- Application Number
- PCT/BR2026/050136
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2026-03-24
- Filing Date
- 2026-03-24
- Publication Date
- 2026-10-01
Abstract
Description
[0001] PROCESS FOR RECOVERING AND PURIFYING BIOLOGICAL SULFUR FOR THE PRODUCTION OF SULFURIC ACID FIELD OF THE INVENTION
[0002]
[0001] The present invention relates to the area of chemical processes applied to the treatment and purification of sulfurous materials of biological origin. More specifically, the invention relates to chemical recovery and purification technologies, meeting industrial and agricultural demands for sulfurous products with lower impurity content.
[0003] BACKGROUND OF THE INVENTION
[0004]
[0002] In recent years, the production of elemental sulfur by biological means has gained prominence as a sustainable alternative to conventional processes, which use intensive chemical processes and generate aggressive waste. However, sulfur obtained in biological processes contains undesirable contaminants, including sodium, which can compromise subsequent applications, especially in the production of sulfuric acid. Therefore, the need for a purification process that eliminates these contaminants without altering the hydrophilic characteristics of sulfur has become pressing in the technical and industrial literature.
[0005]
[0003] The current state of the art reveals that, despite advances in obtaining biological sulfur, the purification processes applied do not achieve satisfactory levels of sodium elimination, resulting in products with purity below that required for applications in highly demanding sectors, such as sulfuric acid production. Conventional processes use precipitation processes or oxidative techniques that end up altering the nature of the sulfur, affecting its dispersion in aqueous medium and reducing its added value. Thus, there is a need for a process that maintains the structure of biological sulfur, preserving its essential physical and chemical characteristics.
[0006]
[0004] Several international and national patent documents, including applications CN101972596A, JP2008529947A and US5017280A, address processes for recovering and purifying sulfur from chemical or mineral sources. These documents, however, focus on sulfur recovery through reactions involving waste gases or oxidative extractions of residues, without considering the challenges inherent in purifying sulfur of biological origin, which presents a complex matrix with daily parameter variations.
[0007]
[0005] In particular, document CN101972596A describes a method for using waste sulfur dioxide gases in the formation of sulfite compounds, which differs substantially from the present approach dealing with the purification of biological sulfur. The methodology applied in the aforementioned patent application does not address the removal of ionic contaminants, especially sodium, which is critically necessary for the use of biological sulfur in valorization processes, such as the production of sulfuric acid.
[0008]
[0006] Application JP2008529947A discloses a method for the production of sulfur oxides involving vacuum and gaseous contact conditions. The use of extraction techniques under low pressure conditions, although effective for reduced levels of impurities, does not achieve the desired efficiency when applied to biological sulfur, whose matrix has a heterogeneous character.
[0009]
[0007] The method described in US patent application 5017280A is based on oxidative reactions for the removal of sulfur and metals from solid waste, presenting operational complexity and high energy demand. Furthermore, the reactive conditions used in this process are not compatible with maintaining the hydrophilic nature of biological sulfur, which is one of the main attractions for its use as a fertilizer and input for the production of sulfuric acid.
[0010]
[0008] The inefficiency of conventional biological sulfur purification processes is directly related to the difficulty in achieving a degree of purity that allows the reduction of sodium content to levels below 10 ppm. Sodium, present in varying concentrations due to factors in the biological process, has a negative effect on neutralization reactions when sulfur is used in the production of sulfuric acid, generating problems of corrosion and low catalytic activity.
[0011]
[0009] Studies conducted by various research groups highlight that the behavior of biological sulfur in aqueous media is sensitive to the presence of ionic contaminants, especially sodium, which interferes with the stability and dispersion of sulfur. The variability of biological sulfur parameters, such as concentration and particle size, requires a robust and adaptable purification process that does not depend on individual analyses of each batch, but is effective across a spectrum of operational variations.
[0012]
[0010] The technical challenge lies in the need to develop a process capable of efficiently removing sodium without employing reagents or conditions that modify the morphology and fundamental properties of biological sulfur. Processes that use multiple filtration or decantation stages prove to be costly and technically complicated, generating the need for a simplified and economically viable procedure.
[0013]
[0011] To achieve the desired level of purity, some processes employ additional washing steps or solvent treatments, which can lead to the loss of sulfur or the introduction of other contaminants. Such techniques are not considered suitable for biological sulfur due to its nature and the sensitivity of its structure in aqueous media.
[0014]
[0012] The design of conventional purification processes often ignores the fact that biological sulfur has a smaller particle size and a much more homogeneous dispersion in water, characteristics that represent competitive advantages for its use, but which also impose technical challenges for the selective removal of sodium. Current technology does not offer solutions that reconcile these aspects without compromising the integrity of the final product.
[0015]
[0013] In addition to the problem related to sodium removal, there is also the difficulty of maintaining process continuity without the need for frequent reanalysis of the biological sulfur composition. Existing processes do not account for the intraday variation dynamics of the product, resulting in the operation of systems that may not adapt quickly to changes in raw material parameters.
[0016]
[0014] In several case studies, it has been observed that sodium impurities directly interfere with the efficiency of subsequent acid neutralization processes. This fact has motivated the search for processes that can, through a single treatment stage, reduce the concentration of sodium ions without resorting to multiple correction cycles.
[0017]
[0015] Technical literature indicates that integrating dissolution and filtration processes can offer a significant advantage in the purification of biological sulfur. However, the processes known to date do not implement an acid addition step under controlled conditions that would allow the elimination of contaminants without altering the properties of the sulfur dispersed in the aqueous solution.
[0018]
[0016] Another relevant aspect is the need to apply the treatment in stirred reactors, ensuring homogeneity in the mixture and facilitating the neutralization reaction. The use of reactors without an adequate stirring system can cause the formation of zones with uneven concentrations of reagents, compromising the efficiency of the purification of biological sulfur.
[0019]
[0017] Environmental and economic concerns also underpin the need for a purification process that operates with minimal generation of secondary waste. Inadequate disposal of byproducts from conventional processes can result in negative environmental impacts, reinforcing the importance of an integrated and sustainable biological sulfur recovery system.
[0018] Finally, the absence of a single procedure that effectively combines dissolution, controlled acid addition, and multi-stage filtration separation characterizes the gap to be filled.
[0020] OBJECTIVES OF THE INVENTION
[0021]
[0019] The present invention has as its primary objective to provide an integrated process for the recovery of elemental sulfur, specifically sulfur originating from biological processes, efficiently eliminating contaminants such as sodium. This objective aims to guarantee a final product with adequate purity for applications in the chemical and agricultural industries, preserving its original characteristics, especially its hydrophilic nature.
[0022]
[0020] A second objective is to enable the continuous operation of biological sulfur processing, allowing the treatment to be carried out in stirred reactors that promote the homogeneity of the mixture and the efficiency of the acid neutralization reaction. In this way, the aim is to reduce operating costs and minimize the processing time for each batch, ensuring the competitiveness of the process.
[0023]
[0021] Finally, the invention seeks to eliminate the need for multiple reprocessing steps, using a single integrated sequence of dissolution, acidification, and filtration to separate the purified sulfur from soluble contaminants. This objective ensures that the process is economically viable and environmentally sustainable, promoting a final product suitable for the manufacture of sulfuric acid with a sodium content of less than 10 ppm.
[0024] SUMMARY OF THE INVENTION
[0025]
[0022] The present invention discloses a process for recovering and purifying biological sulfur for the production of sulfuric acid, comprising the following steps:
[0026] a. to receive a centrifuged paste cake of biological sulfur;
[0027] b. Dissolve the aforementioned cake in water, preferably demineralized water, forming a suspension;
[0028] c. transfer the suspension to a reactor;
[0029] d. Gradually add a strong acid to the suspension, while stirring, controlling the pH to ensure it exceeds the titration inflection point; and e. Subject the suspension resulting from step D to at least one pressure filtration step to separate a liquid phase containing soluble contaminants and a solid phase containing sulfur;
[0030] f. perform one or more additional steps of dissolving the solid phase in water followed by further filtration under pressure; and
[0031] g. obtaining purified sulfur with a sodium content of less than 10 ppm.
[0023] The strong acid is preferably sulfuric acid.
[0032]
[0024] The addition of acid is carried out with controlled stirring, temperature and pH, until the alkalinity is neutralized and ionic contaminants are solubilized.
[0033]
[0025] The process comprises one or more filtration stages.
[0034]
[0026] In the first filtration stage, the liquid phase containing sodium ions is removed, and in a subsequent stage, remaining contaminants are removed.
[0035]
[0027] The process comprises, after neutralization, a purification step in two or more stages operated in countercurrent flow in which:
[0036] • The sulfur cake is resuspended with the filtrate from a subsequent stage; and
[0037] • New water is preferably added in the final stage.
[0038]
[0028] The process comprises, after neutralization, a multi-stage purification step operated in concurrent mode, in which each stage comprises resuspension of the cake with fresh water followed by pressure filtration.
[0039]
[0029] The process comprises, after neutralization, a single-stage purification step, in which:
[0040] • Filtration and washing of the sulfur cake occur simultaneously; and
[0041] • Washing is done with fresh water.
[0042]
[0030] The process integrates the stages of dissolution, acidification and filtration in a continuous or batch production line.
[0043]
[0031] The agitation speed, which occurs in step D, is between moderate and strong.
[0044]
[0032] The agitation is continuous.
[0045]
[0033] Agitation is carried out by a three-blade stirrer or a vibrating stirrer.
[0046]
[0034] The received paste cake comprises between 40 and 60% solids.
[0047] DETAILED DESCRIPTION OF THE INVENTION
[0048]
[0035] In the context of the present invention, "titration inflection point" means the geometric moment at which the titration curve changes concavity, corresponding to the maximum pH variation with respect to the volume of the titrant.
[0049]
[0036] Initially, biological sulfur comes from a biological process, appearing as a paste-like cake containing approximately 40 to 60% solids by weight, in which elemental sulfur is partially in colloidal form along with salts and other contaminants. Due to the inherent variability of the biological process, the parameters of biological sulfur, such as concentration and particle size, can vary daily, requiring a robust purification process. The proposed process begins after receiving the paste-like cake containing the biological sulfur, which is the concentrated solid fraction.
[0050]
[0037] Next, the paste cake is dissolved in water, preferably demineralized water, ensuring the homogeneity of the mixture and facilitating the subsequent reaction with the acid. At this stage, the ratio between the amount of water and the cake is defined in order to optimize the agitation of the mixture and the neutralization reaction. The reaction is carried out in a suitable mixing tank, which ensures the complete dispersion of the particles and the stability of the suspension.
[0051]
[0038] During the acidification reaction, a slight exothermicity occurs, which is controlled by the reactor's agitation system, allowing the released energy to be distributed uniformly in the suspension. This thermal control is fundamental to avoid overheating that could compromise the stability of the product. The system has sensors that continuously monitor the temperature and pH, which must be maintained between 5.0 and 7.0.
[0052]
[0039] After the acid addition step and consequent pH neutralization of the suspension, the biological sulfur purification process can be conducted using different configurations, including filtration steps and optionally washing of the paste cake or dissolution, with the aim of removing soluble contaminants, especially sodium ions, to levels below 10 ppm. In the filtration step, the liquid phase, containing the dissolved contaminants, is separated from the solid phase rich in elemental sulfur.
[0053]
[0040] In a multi-stage embodiment operated in countercurrent mode, the sulfur cake obtained in the filtration stage is resuspended using the filtrate from a subsequent stage, and then filtered again. In this configuration, fresh water is preferably introduced only in the last stage of the system, flowing in the opposite direction to the displacement of the solid phase. This arrangement allows for greater efficiency in contaminant removal with lower fresh water consumption and less liquid effluent generation, while maintaining the integrity of the biological sulfur throughout the stages.
[0054]
[0041] In one embodiment, the process can be carried out in concurrent mode, in which the sulfur cake is subjected to two or more successive stages, each comprising resuspension with fresh water followed by filtration. This configuration has the advantage of operational simplification and a reduction in the number of stages required, implying lower investment in equipment (CAPEX), although with a higher relative consumption of water when compared to the countercurrent regime.
[0055]
[0042] In one embodiment, the purification process is carried out in a single stage, in which the filtration of the suspension and the washing of the sulfur cake occur simultaneously, using fresh water. This configuration allows obtaining purified sulfur with a sodium content of less than 10 ppm in a single step, significantly reducing the complexity of the process.
[0056]
[0043] Single-stage operation offers additional advantages, including lower overall water consumption, reduced liquid effluent generation, lower capital (CAPEX) and operating (OPEX) costs, as well as greater operational simplicity and robustness, making the process particularly suitable for continuous or batch-scale industrial implementation.
[0057]
[0044] Regardless of the configuration adopted, the filtration systems employed are selected in order to guarantee solid-liquid separation efficiency between 45 and 75%, enabling the removal of fine particles and dissolved contaminants, and ensuring that the purified sulfur meets the specifications required for its use in the production of sulfuric acid.
[0058]
[0045] The process is carried out in stirred reactors equipped with a digital control panel, allowing adjustment of operational variables such as stirring speed, acid dosage, reaction time, and temperature, in order to optimize each stage of the process. Automation and monitoring of reactive conditions reduce the possibility of operational errors and ensure the consistency of results, regardless of initial variations in biological sulfur.
[0059]
[0046] The reaction condition is maintained by means of controls that continuously monitor the pH of the mixture, using sensors installed in the reactor. Real-time pH measurement allows the addition of acid to be stopped at the exact moment the desired neutralization is reached, preventing over-acidification that could lead to sulfur degradation. These monitoring devices are essential for the safety and efficiency of the process.
[0060]
[0047] Another important aspect lies in the integration of the purification process with the continuous production of biological sulfur. The proposed system allows biological sulfur, immediately after its extraction and centrifugation, to be sent for purification treatment, establishing an integrated production line that reduces losses and increases operational efficiency. This integration minimizes the need for intermediate storage and avoids impacts resulting from material stagnation.
[0061]
[0048] The modularity of the process allows its adaptation to both small-capacity units and large processing centers. In larger industrial plants, biological sulfur can be transferred to a centralized purification plant, where the dissolution, acidification, and filtration steps are carried out continuously, optimizing resource use and reducing operating costs. Modular flexibility is one of the innovative features of the invention.
[0062]
[0049] During the acid addition reaction, the dynamics of the biological sulfur particles are intensified by agitation, which facilitates the interaction between the reagents and improves the efficiency of contaminant removal. This phenomenon also contributes to the homogeneous dispersion of the acid, avoiding zones with high concentrations that could compromise the quality of the sulfur. Agitation, therefore, plays a fundamental role in the dissolution step.
[0063]
[0050] The use of sulfuric acid as a neutralizing agent is preferred because, in addition to adjusting the pH, this acid does not introduce other corrosive ions, as occurs with hydrochloric acid. The choice of sulfuric acid allows the final product, purified sulfur, to maintain ideal characteristics for the subsequent production of sulfuric acid, promoting an integrated production cycle. The chemical reaction involved is simple, but highly suitable for the treatment of biological sulfur.
[0064]
[0051] The process time control is rigorously defined, encompassing everything from initial dissolution to final filtration, completed in a period not exceeding a few hours. The speed of the process is a key differentiator, allowing for the rapid reintegration of purified sulfur into the sulfuric acid industry's production line. This time efficiency contributes to reduced operating costs and increased production speed.
[0065]
[0052] Operational aspects, such as pressure and temperature, do not require extreme adjustments. The temperature will be controlled by the steam supply to the system, while the pressure is ambient. The operational simplicity allows the process to be implemented in various industrial facilities without the need for highly specialized equipment or complex infrastructure. This robust character makes the process applicable on a large scale.
[0066]
[0053] Process variables, such as the concentration of added acid and the ratio of water to biological sulfur, are predefined based on experimental studies and can be adjusted according to the specific characteristics of each raw material load. This operational flexibility is fundamental to adapting to the natural variations in biological sulfur production, always guaranteeing the obtaining of a final product with the desired parameters, especially a sodium content of less than 10 ppm, which does not cause excessive corrosion of the equipment.
[0054] The acid concentration should be between 0.5 and 5 N. While the water concentration depends on the tests performed on the suspension, to obtain a final product with a sodium content below 10 ppm.
[0067]
[0055] The filtration stage, after each dissolution cycle, uses devices capable of retaining micrometer-sized particles, ensuring that the collected sulfur has high purity. The technology of the filters employed allows for the recovery of almost all of the sulfur, minimizing waste and contributing to the sustainability of the process.
[0068]
[0056] The final product, purified sulfur, is then stored under controlled conditions in appropriate tanks for later use in the production of sulfuric acid or in other industrial processes. Storage is carried out in a contamination-free environment, where temperature and humidity are constantly monitored to preserve the quality of the sulfur. This step ensures the stability of the product until its final use.
[0069]
[0057] The purification of biological sulfur, as described, eliminates the main technical challenges related to the presence of ionic contaminants, demonstrating that the process is capable of achieving the purity levels required by the market. The reduction of sodium ions, achieved through the controlled addition of acid and subsequent filtration, is the differentiating factor of the invention.
[0070]
[0058] The process also stands out for its simple operation, which does not require the use of catalysts or additional reagents that could complicate the reaction. The absence of catalysts reduces costs and simplifies the system structure, contributing to the robustness and reliability of the process. The integrated approach of dissolution, acidification, and filtration minimizes the number of steps, making the procedure efficient and easy to implement.
[0071]
[0059] The reaction, characterized as slightly exothermic, is monitored in real time by means of sensors that check the pH, temperature and acid concentration, ensuring that the operating parameters remain within ideal limits. This dynamic control allows for immediate adjustments, increasing the safety and efficiency of the process, and enabling the standardization of the final product, regardless of variations in the raw material.
[0072]
[0060] All equipment used in the process was selected based on its compatibility with corrosive agents and its ease of cleaning, aiming for continuous and safe operation. Agitated reactors, dissolution tanks, and high-precision filters make up the installation, which can be implemented in common industrial spaces without the need for complex structural adaptations. The robustness of the components ensures the durability and operational reliability of the system.
[0061] The integration of the process with the existing production system allows for parallel operation without interruption or the need for large investments in infrastructure. This integration provides synergy between the production of biological sulfur and its purification, generating a continuous cycle that maximizes productivity and minimizes losses. The automation of the system contributes to the standardization and reproducibility of the results obtained.
[0073]
[0062] Finally, the presented process fills a gap in the technical literature by offering a unique solution for the recovery and purification of biological sulfur, preserving its essential characteristics and ensuring a high-purity end product. The process not only overcomes the challenges related to sodium removal but also adapts to the variations inherent in biological sulfur, being economically viable and operationally simple. In this way, the invention demonstrates its potential to transform the way biological sulfur is treated and used in industry.
Claims
CLAIMS 1. Process for the recovery and purification of biological sulfur for the production of sulfuric acid, characterized by comprising the following sequential steps: a. to obtain a paste-like cake of biological sulfur; b. Dissolve the aforementioned cake in water, preferably demineralized water, forming a suspension; c. transfer the suspension to a reactor; d. Gradually add a strong acid to the suspension, while stirring, controlling the pH to ensure it exceeds the titration inflection point; and e. Subject the suspension resulting from step D to at least one pressure filtration step to separate a liquid phase containing soluble contaminants and a solid phase containing sulfur; f. perform one or more additional steps of dissolving the solid phase in water followed by further filtration under pressure; and g. obtain purified sulfur with a sodium content of less than 10 ppm.
2. Process according to claim 1, characterized in that the strong acid is preferably sulfuric acid.
3. A process, according to any of the preceding claims, characterized in that the addition of acid is carried out with controlled agitation, temperature, and pH, until the alkalinity is neutralized and ionic contaminants are solubilized.
4. A process, according to any of the preceding claims, characterized in that it comprises one or more filtration stages.
5. Process according to claim 4, characterized in that, in a first filtration stage, the liquid phase containing sodium ions is removed, and, in a subsequent stage, remaining contaminants are removed.
6. A process, according to any of the preceding claims, characterized by comprising, after neutralization, a multi-stage purification step operated in countercurrent flow, in which: • The sulfur cake is resuspended with the filtrate from a subsequent stage; and • New water is preferably added in the final stage.
7. A process, according to any of the preceding claims, characterized by comprising, after neutralization, a multi-stage purification step operated concurrently, in which each stage comprises resuspension of the cake with fresh water followed by filtration.
8. A process, according to any of the preceding claims, characterized by comprising, after neutralization, a single-stage purification step in which: • Filtration and washing of the sulfur cake occur simultaneously; and • Washing is done with fresh water.
9. A process, according to any of the preceding claims, characterized by integrating the steps of acidification, filtration, and washing in a continuous or batch production line.
10. Process, according to any of the preceding claims, characterized in that the neutralization reaction time is between 15 and 60 minutes.
11. Process, according to any of the preceding claims, characterized in that the agitation speed, which occurs in step D, is between moderate and strong.
12. Process according to claim 11, characterized in that the agitation is continuous.
13. Process, according to claims 11 and 12, characterized in that the agitation is carried out by a three-blade agitator or a vibrating agitator.
14. Process, according to claim 1, characterized in that the resulting paste cake comprises between 40 and 60% solids.