BR102013022095A2 - process for obtaining hydrogen sulfide from the reduction of calcium sulfate and the decomposition of calcium sulfide with magnesium chloride - Google Patents

Abstract

process for obtaining hydrogen sulfide from the reduction of calcium sulfate and decomposition of calcium sulfide with magnesium chloride process for the generation of hydrogen sulfide from the reduction of calcium sulfate and decomposition of calcium sulfide formed with magnesium chloride composed of the following operations: reduction of calcium sulfate with coal, where the case4.2h2o compound contained in calcium sulfate is converted to solid calcium sulfide and resulting in a carbon dioxide rich gas; reaction between the solid cas and an aqueous solution of magnesium chloride, leading to the obtainment of a hydrogen sulfide-rich gas stream, an aqueous suspension composed of calcium chloride and magnesium hydroxide. from that gas stream the sulfides or sulfates of interest such as sodium sulfide can be obtained

Description

DESCRIPTIVE REPORT

Process for obtaining hydrogen sulfide from CALCIUM SULPHATE REDUCTION AND MAGNESIUM CHLORIDE SULPHIDE DECOMPOSITION Field of application [001] This innovation belongs to the field of the chemical and mineral metallurgy industry, more specifically a original process for obtaining hydrogen sulfide using reduced calcium sulfate as a sulfur source and making use of magnesium chloride as an agent that promotes the generation of hydrogen sulfide for later conversion into a sulfide or sulfated end product of interest.

History of the Innovation Hydrogen sulfide is the chemical compound with the formula H2S. It is a colorless gas with a foul odor characteristic of rotten egg, heavier than air, very poisonous, corrosive, flammable and explosive. Hydrogen sulfide often results from bacterial decomposition of organic matter in the absence of oxygen, as in water and sewage swamps, this process is commonly known as anaerobic digestion. H2S also occurs in volcanic gases, natural gas, and some water wells. The human body produces small amounts of H2S and uses it as a signaling molecule.

Dissolved in water, it is a weak inorganic acid. With strong bases, forms salts and sulfides. In an acidic solution, hydrogen sulfide is a moderate reducing agent and plays an important role in traditional qualitative analyzes, where metals such as insoluble sulfides precipitate. And a gas widely used in the petrochemical industry.

Hydrogen sulfide is very flammable and its self-ignition temperature is 260 ° C, while the low explosive limit is around 4.3% in air (by volume). H2S (34.08 g / mol) is slightly heavier than air (28.8 g / mol), it condenses in liquid form at a temperature of -62 ° C and is partially soluble in water and organic compounds. Solubility in water at 20 ° C is 3850 mg / L (0.385%). Solubility in organic substances is generally higher than in water. Solubility in ethyl ether is 2.1%, while in hydrocarbons it is around 1.2%.

Commonly, solubility decreases by about 2.5% for each degree of temperature increase.

[006] In the industrial segments, the origin of H2S is generally known to come from chemical removal and / or acid gas scrubbing processes, effluent treatment systems, fermentations, acid leaks, etc. H2S generation occurs in several segments and its toxic action in humans has been known since the eighteenth century, however, after so many years, there are still cases of poisoning even with large numbers of deaths. On the other hand, aggressiveness is also assessed in contact with industrial materials and equipment, most often resulting in deterioration or fracture of ferrous materials with catastrophic consequences.

[007] Hydrogen sulfide is a central participant in the sulfur cycle of the biochemical sulfur cycle on earth. In the absence of oxygen, sulfur-reducing and sulfate-reducing bacteria get energy from hydrogen or the oxidation of organic molecules by reducing elemental sulfur or sulfate to hydrogen sulfide. Other bacteria release hydrogen sulfide from sulfur-containing amino acids.

[008] Hydrogen sulfide has wide applications in industry, hence the interest in obtaining it. It can be used in the production of organic thio compounds, as various organosulfur compounds are produced using hydrogen sulfide. These include methanethiol, ethanethiol and thioglycolic acid. Also in the production of alkali metal sulphides, where, after combination with alkali metal bases, hydrogen sulphide converts to alkaline hydrosulphides such as sodium hydrosulphide and sodium sulphide which are used in the degradation of biopolymers such as as in the processes of leather depilation and pulp delignification by the Kraft process. In analytical chemistry, hydrogen sulfide has been important for well over a century in qualitative inorganic analysis of metal ions. In these analyzes, heavy metal and nonmetal ions are precipitated from the solution upon exposure to H2S. The components of the resulting precipitate redissolve with some selectivity. H2S also has application as a precursor for metal sulfides, as many metal ions react with hydrogen sulfide giving the corresponding metal sulfides. This conversion is widely exploited, for example, in hydrogen sulfide-contaminated gases or waters that can be cleaned with metal sulfides. In flotation concentration of metal ores, mineral powders are often treated with hydrogen sulfide to improve separation. In addition, metal parts are sometimes hydrogen sulfide passivated, such as catalysts used in hydrodesulfurization are routinely hydrogen passivated, and the behavior of metal catalysts used in other parts of a refinery is also modified with hydrogen sulfide. Other hydrogen sulfide applications include its use to separate deuterium oxide, or heavy water, from normal water via the Girdler sulfide process.

One of the major products obtainable from H2S is sodium sulfide, a compound whose main application is in the kraft papermaking process. This compound is also used as a tanner for animal skins, bleach in the textile industry, as a desulphurizer and chlorinator, as well as a flotation collector in the mining industry, a preservative in food and detergent manufacturing, among other applications.

Based on this fact and thinking about the continuous development of the products, an innovation is proposed, sometimes claiming the privileges of its protection for its novelty and inventive activity, as explained below. Therefore, it is proposed a process to obtain hydrogen sulfide from calcium sulfate, abundant material as a byproduct of several processes of the chemical and mineral metallurgical industries, characterized by the following operations: 1) reduction of calcium sulfate with coal, where calcium sulfate is converted to solid calcium sulfide and carbon dioxide; 2) reaction between calcium sulfide and an aqueous solution of magnesium chloride, leading to the obtainment of aqueous calcium chloride and magnesium hydroxide and hydrogen sulfide.

From then on, it is also proposed to obtain sodium sulfide using the hydrogen sulfide generated in the above process, contemplating the following steps: 1) absorption with aqueous sodium hydroxide solution of sodium sulfide. hydrogen formed in the same H2S generation step, resulting in the formation of an aqueous sodium acid sulfide solution; 2) neutralizing the NaHS solution with sodium hydroxide solution, generating an aqueous sodium sulfide solution; 3) evaporation of sodium sulfide solution, resulting in solid Na2S.

[012] The main advantage of the proposed process is the use of calcium sulfate (CaSC> 4.2H20), abundant material as a result of industrial activities and processes. Thus, the so-called phosphogypsum - a byproduct of phosphoric acid manufacture - or calcium sulfate from any acid or lime effluent neutralization operation can be employed.

State-of-the-art analysis In European patent EP1103521 a process for obtaining dehydrated sodium sulfide (98% Na2S) is described by mixing an aqueous solution containing Na2S and a water-immiscible organic solvent such as as xylol, in which the mixture is heated to about 10 ° C to 20 ° C below its boiling point, followed by progressive heating to a temperature of the order of 10 ° C to 20 ° C above and after the boiling point. azeotropic vacuum distillation. Such a process has as its main drawback the need to start from a solution containing the sodium sulfide itself in advance.

[014] In another patent, CN1067225, a process for the manufacture of sodium sulphide by reducing mirabilite (Na2SC> 4) with carbon in the presence of barite is disclosed. The fact that the process requires the use of barite as an additional source of sulfur is a serious disadvantage.

The process disclosed in GB826023 is based on the reduction of sodium sulfate with hydrogen in which 2% to 4% of an alkali metal carbonate (L12CO3 or K2CO3) is used as catalyst for the reduction reaction. . A serious drawback of this process is the long reduction time required to obtain yields compatible with that of an industrial process.

List of Figures [016] Figure 1 shows a typical sequence of unitary operations inherent to the proposed innovation, illustrating the interaction between the operations that make up the innovative process including the production of hydrogen sulfide (H2S) and sodium sulfide (Na2S). .

Detailed Description of the Innovation [017] Given the shortcomings presented in the art, a process is proposed as an innovation that begins with the intimate mix between calcium sulfate and a solid, preferably carbon-based, reducing agent in an environment of reduction. Reduction is carried out in a controlled environment, preferably for rotary horizontal shafts, where heating is provided by combustion of a heat source, maintaining the temperature in the range of 600 ° C to 1200 ° C, with a residence time of 1:00 to 3:00. The amount of carbon used in the reduction is calculated to meet the following stoichiometric balance of the reduction reaction: [018] Normally, an excess carbon of about 10% to 30% above the stoichiometric value is worked on.

[019] The gas resulting from the reduction is directed to a washing operation, aiming at its use in carbonation, while the solid material - CaS, goes to the hydrogen sulfide generation phase - H2S, which is the core of the innovation proposed here. .

[020] This step is performed in a stirred reactor, promoting contact between the reducing CaS and an aqueous magnesium chloride solution containing 10% to 30% (w / w) MgCE, preferably 20%, at a temperature in the range of 50 ° C to 70 ° C, preferably 60 ° C. The residence time should be in the range of 60min to 180min, preferably 120min, needed to promote the desired reaction. The following main reaction occurs at this stage, resulting in an aqueous calcium chloride pulp (CaCl2) and magnesium hydroxide - Mg (OH) 2 - in suspension, as well as hydrogen sulfide (H2S): [021] The pulp of Mg (OH) 2 suspended in the calcium chloride (CaCfi) solution feeds the carbonation step described below, while the -H2S gas goes through a condensation step to reduce moisture and is then absorbed into a sodium hydroxide solution.

[022] Carbonation occurs in a reactor which promotes the bubbling of the CO2 gas from the reduction step within the Mg (OH) 2 pulp suspended in the calcium chloride solution. The temperature is set in the range from 40 ° C to 60 ° C, preferably 50 ° C, and the residence time is about 3 hours. Thus, the following reaction is promoted, whose main product is an aqueous magnesium chloride pulp (MgCh) and a calcium carbonate pulp (CaCCE): [023] CaCCh + MgCh pulp undergoes a thickening operation, whose lower flow feeds a solid / liquid separation step. The upper flow of the thickening and the liquid phase of separation proceed to a storage tank, generating a solution containing essentially magnesium chloride (MgCb). Such a solution, together with a small replacement of MgCb, returns to the H2S generation stage, thus representing a circulating load of the present innovation. In turn, the centrifuged solid has a high CaCC content> 3, above 90%, and is an important by-product of the process described herein.

[024] Hydrogen sulfide (H2S) resulting from the reaction between CaS and MgCh undergoes an indirect condensation operation with water, in which the amount of water is regulated to provide a gas temperature in the range of 30 ° C to 40 ° C, preferably 35 ° C.

Then, this gaseous stream, with a content of about 98% H2S, is absorbed in an aqueous sodium hydroxide solution with a concentration of 40% to 50% w / w NaOH, resulting in the formation of a solution. aqueous sodium sulfide acid (NaHS) according to the following stoichiometric balance: [026] Such a solution proceeds to an almost instantaneously neutralizing step again with 50% sodium hydroxide solution ( w / w) - which results in an aqueous sodium sulfide solution according to the following reaction: The temperature in this step is maintained in the range of 70 ° C to 90 ° C, preferably.

The sodium sulfide solution feeds an evaporation step, which takes place in the temperature range of 135 ° C to 145 ° C. The saturated solution resulting from this evaporation feeds a scaler, providing the obtaining of scaled sodium sulfide, the end product of the present innovation. This material according to the operating conditions described above has a content of about 50% (w / w) Na 2 S.

[029] The nature and scope of the present innovation can be better understood from the following examples, which contemplate the overall process of (i) hydrogen sulfide generation and (ii) sodium sulfide production. It should be noted that such examples are illustrative only and should not be construed as limiting the process developed. EXAMPLE 1 - The sequence of operations of this example is as shown in Figure 1. A batch of 1840kg 98% pure calcium sulfate (98% CaSO4.2E20) and 330kg green petroleum coke are homogenized in a rotating drum. and feed a horizontal rotary kiln heated by the combustion of natural gas, which gives a temperature of 900 ° C in the central portion of the oven and 350 ° C at the outlet. The slope and rotational speed of the furnace provide a residence time of the calcium sulfate / coal mixture of about 2 hours. From this operation, 770kg of a 96% CaS solid product and 3600m3 of a gas containing 24% CO2, 45% N2 and 30% water vapor are recovered, all expressed as a volumetric percentage. The gas passes through a scrubber whose temperature is set at 60 ° C at the outlet through the passage of a cooling water stream and is directed to the carbonation step. The 770kg CaS rich solid product is mixed with 4300 liters of a 20% (w / w) aqueous solution of MgCl 3 in a reactor maintained at 60 ° C. After about 2 hours of reaction, 5500kg of a pulp with 21% aqueous solution of CaCl2 and 11% Mg (OH) 2 is recovered, as well as 375 m3 of a gas containing 87% (by volume) H2S and the remaining water vapor. Such gas passes through a condenser whose temperature is maintained at 35 ° C, which provides 280 m3 of a gas with 98% H2S. The 5500kg of the magnesium hydroxide and calcium chloride pulp proceed to the carbonation step, in which 2700 m3 of the reduction gas is bubbled at a temperature of 50 ° C for about 3 hours. From this operation, 6080kg of a pulp with 18% CaC03 in suspension and the remaining of an aqueous solution with about 20% MgCfi are collected. Such, the pulp is thickened, and the resulting underflow is subjected to a centrifugation operation, from which a solid material with 1180kg and 90% by weight of CaIXE is recovered, which material can be sold as a byproduct. The overflow of the weighing and the liquid centrifugation phase are mixed in a tank, together with a 54 liter make-up of a 20% magnesium chloride solution, resulting in 4300 L of MgCl2 solution which returns to the step. H2S generation, previously described. In turn, the 280m3 of H2S-rich gas feeds an absorption tower, where they react in a very short time with 560 liters of a 50% (w / w) caustic soda (NaOH) solution at 80 ° C. This reaction results in 1230kg of an aqueous solution of sodium sulfide acid fetus - NaHS - which is almost instantaneously neutralized with 830kg of a 50% (w / w) sodium hydroxide solution, resulting in 2080kg of an aqueous sodium sulfide solution with 40% (w / w) Na2S. This solution is evaporated at 140 ° C in a forced circulation evaporator whose resulting saturated solution feeds a scaler. The flake product, with a total mass of 1670kg and 50% humidity, is the final product of interest for the present innovation. The values of the main technical indices of this example are shown in Table 1.

Material Mass or Volume Purity Calcium Sulphate 1840kg 98% CaS04.2H20 Carbon Source 330kg 85% C

Solid CaS 770kg 96% CaS CO2-rich gas (1) 3600 m3 24% CO2 (volume) Recycling MgCF 4300 L 20% MgCE (w / w) Pulp CaCl2 / Mg (OH) 2 5500kg 21% CaCh (mass) Pulp CaC03 / MgCl2 6080kg 18% CaC03 (mass) By-product CaC03 (2) 1180kg 90% CaC03 (w / w) H2S rich gas (3) 280 m3 98% H2S

Na3S 2080kg Aqueous Solution 40% Na3S (w / w) Final Product Na3S 1670kg 50% Moisture (w / w) Table 1 - Main Technical Indexes of Example 1 (1) - Calcium Sulphate Reduction Gas (2) - after thickening and centrifugation (3) - after washing / condensation EXAMPLE 2 - As in the previous example, the sequence of operations in this example is shown in Figure 1. The reduction is performed with 1250kg of 98% calcium sulfate. purity (98% CaSO4 FEO) and 305kg charcoal under similar temperature and residence conditions as in the previous example. After performing the same sequence of operations as described in Example 1, 790kg of calcium carbonate (90.8% CaCO3) and 1100kg of Na3S were recovered in scales with about 50% humidity. The key technical index values for this example are shown in Table 2.

Material Mass or Volume Purity Feed (1250kg sulfate 98% CaSO ^ EEO calcium) Feed (carbon) 305kg 61% C

Solid CaS 535kg 95% CaS CO2-rich gas (1) 2500 m3 23% CO2 (volume) Recycling MgCfi 2900 L 20% MgCE (w / w) Pulp CaCl2 / Mg (OH) 2 3700kg 22% CaCl2 (mass) Pulp CaCOa / MgCb 4050kg 17% CaC03 (mass) By-product CaC03 (2) 790kg 91% CaC03 (w / w) H2S rich gas (3) 187 m3 98% H2S

Na3S 1390kg aqueous solution 40% Na3S (w / w) End product Na2S 790kg 50% humidity (w / w) Table 2 - Main technical indices of example 2 (1) - gas resulting from calcium sulfate reduction (2) - after thickening and centrifugation (3) - after washing / condensation [030] In both examples presented the operations were performed batchwise. However, it is obvious to any person skilled in the art that such operations can be performed continuously, with obvious benefits to the entire process described.

[031] This innovation is not limited to the representations commented upon or illustrated here but should be understood in its broad scope. Many modifications and other representations of the innovation will come to mind of one skilled in the art to which this innovation belongs, having the benefit of the teaching presented in the previous descriptions and accompanying drawings. Further, it is to be understood that innovation is not limited to the specific form disclosed, and that modifications and other forms are understood to be included within the scope of the appended claims. Although specific terms are used here, they are used only in a generic and descriptive manner and not for purposes of limitation.

Claims (2)

1) Process for the generation of hydrogen sulfide from calcium sulfate reduction characterized in that said generation is promoted by the reaction of calcium sulfide with magnesium chloride, comprising the following operations: a) reduction (1) of the raw material rich in high temperature calcium sulfate, in which the CaSO4 fCO compound is converted to solid calcium sulfide (CaS) and carbon dioxide (CO2); followed by b) reaction (2) between calcium sulfide and an aqueous solution of magnesium chloride (MgCC), providing a gas stream rich in hydrogen sulfide (H2S) and a calcium chloride pulp - CaCb - and magnesium hydroxide - Mg (OH) 2 wherein the reducing agent may be one of: petroleum coke, charcoal, metallurgical coke or any other type of solid coal-based reducing agent or another reducing agent such as gases hydrogen and carbon monoxide; wherein the reduction (1) of sulphate sulphate occurs within a temperature range of 600 ° C to 1200 ° C, preferably 900 ° C; wherein the residence time of the calcium sulphate / coal mixture in the reduction step (l) is red 3h, preferably 2h; The aqueous solution employed for the conversion (2) of calcium sulfide (CaS) to calcium chloride (CaCh) and the generation of hydrogen sulfide (H2S) contains from 10% to 30% by weight of MgCh, preferably 20%. % (w / w) MgCO 3; the step (2) of conversion of calcium sulfide (CaS) to calcium chloride (CaCC) and generation of hydrogen sulfide (H2S) is carried out in the temperature range of 50 ° C to 70 ° C, preferably 60 ° C. ° C; whereas the conversion (2) of calcium sulfide (CaS) into calcium chloride (CaCC) and hydrogen sulfide generation (H2S) occurs at a residence time in the CaS / MgCb solution reactor from 60min to 180min, preferably 120min; Process for obtaining sodium sulphide from the hydrogen sulphide generated according to claim 1, characterized in that it comprises the following operations: a) a carbonation operation (3) with the COi-rich gas stream from the reduction (1). ) calcium sulfate, regenerating magnesium chloride, which is recirculated, and calcium carbonate (Ca-CO3), which, after thickening and solid / liquid separation, is an important by-product of the process of the present innovation; (b) H2S-rich gas passes through an absorption step (4) in a vertical tower, where it comes into contact with an aqueous solution of sodium hydroxide (NaOH), generating a solution of sodium acid sulfide (NaHS). which feeds c) a neutralization step (5), again with aqueous caustic soda (NaOH) solution, generating an aqueous sodium sulfide solution (Na2S), which solution is subjected to d) a final evaporation step (5 ), leading to a saturated Na2S-based solution, which feeds a flake, resulting in solid sodium sulfide and the carbonation step (3) of the CaCl2 / Mg (OH) 2 pulp is carried out with the gas. rich in carbon dioxide from the calcium sulphate reduction step (1); wherein the carbonation step (3) of the CaCl2 / Mg (OH) 2 pulp occurs in the temperature range of 40 ° C to 60 ° C, preferably 50 ° C; wherein the residence time of the CaCl2 / Mg (OH) 2 pulp in the carbonation step (3) is 1 hr 4h, preferably 3h; The absorption step (4) of the H2S-rich gas from the conversion (2) of calcium sulfide (CaS) to calcium chloride (CaCf) and hydrogen sulfide generation is carried out with aqueous caustic soda solution. with a concentration of 40% to 50% w / w NaOH, preferably 50% w / w NaOH; wherein the neutralizing step (5) of the sodium acid sulfide (NaHS) solution from the absorption step (4) is carried out at a temperature of 70 ° C to 90 ° C, preferably 80 ° C; wherein the evaporation (6) of the aqueous Na 2 S solution occurs at a temperature in the range of from 135 ° C to 145 ° C, preferably 140 ° C.