DE102019005628B9 - Process for the purification of sulphide-containing raw materials and the simultaneous extraction of elemental sulfur - Google Patents

Abstract

Process for the desulfurization of aqueous multiphase mixtures of water and sulfur-containing organic substances and non-water-soluble substances, characterized in that negatively charged sulfur in a reaction that takes place simultaneously in the aqueous and the non-aqueous phase, with the help of sulfur halides and bases to elementary Sulfur is reacted, which can be separated from the mixture as a solid.

Description

Sulfur-containing compounds are ubiquitous in nature. They occur in proteins, petroleum, natural gas and liquid manure, among other things. While sulfur is essential for plant growth and also for animals, it is harmful in petroleum and natural gas. When used thermally, sulfur compounds in crude oil or natural gas burn to form sulfur dioxide, which reacts with the moisture in the exhaust gases or the air to form sulphurous acid and then to sulfuric acid. Even if liquid manure is fermented in biogas plants and the gas produced is burned in gas engines to generate electricity, the sulfur and its compounds must be removed from the fuels before they can be burned. Catalytic hydrodesulphurisation is currently used for petroleum.

Usually, the volume and mass of the substances that have to be removed from the process with the sulfur are significantly greater than the amount of sulfur contained in the substance to be cleaned.

If the sulfur is removed at the beginning of the value chain before combustion or before the sulfur-containing raw materials are used, for example crude oil, natural gas or liquid manure, then the entire amount of raw material to be cleaned must be heated. In order to concentrate the diluted sulfur compounds in the raw material, the total amount of raw material must be brought to the process temperature of 300 ° C to 400 ° C in order to be able to generate the heat of separation, which is the same as the enthalpy of mixing. In addition, amine solution must be used to remove the sulfur, which has been reduced to hydrogen sulfide, from the raw material. Another disadvantage of the process is that the hydrodesulfurization takes place on a fixed bed reactor, which naturally loses its catalytic properties over time and has to be replaced. Heating the entire amount of raw material to 300 ° C to 400 ° C just to be able to separate three or four percent sulfur is very energy-consuming and therefore expensive.

To remove sulfur from natural gas, it is known to bind carbon dioxide and hydrogen sulfide together with a base such as N-methyl-pyrrolidone (Purisol process) in a high-boiling solvent. For physical separation, for example the sulfinol process, a high-boiling polar organic liquid that contains some water is used. The sulfinol process uses a mixture of diisopropanolamine (DIPA), tetrahydrothiophenol dioxide (sulfolane) and water as the solvent. The hydrogen sulfide from the natural gas is converted into sulfur under high heat with oxygen.

To this day, attempts have been made to improve the above process. Here is an example of the US 6,207,047 B1 , U.S. 6,153,087 A , U.S. 5,055,175 A , U.S. 4,801,362A , U.S. 4,797,137 A , U.S. 4,246,966 A , US 2008/001643 A1 as well as the US 10,112,171 B2 referenced.

In the DE 1618745 B it is also described that the performance of catalysts used for hydrodesulfurization can be improved if they are treated with disulfur dichloride. It is also described that the service life of the catalysts treated with disulfur dichloride and their performance can be improved if they are treated with hydrogen chloride before and after the treatment with disulfur dichloride.

In the EP 0 414 170 B1 it is disclosed that it is possible to remove hydrogen sulfide from petroleum or natural gas using aldehydes. However, ten-fold excesses of aldehyde are necessary for the process described.

It is also known that it is possible to improve their performance and stability by treating known catalysts with disulfur dichloride, as is set out in two further US patents. In the US 9,944,961 B2 this happens with sulfide-oxidizing bacteria in the presence of oxygen. the US 8,986,638 B2 suggests catalytic oxidation of sulfide, mono- and / or dihydrogen sulfide using a chelate complex.

Another known possibility is to remove the sulfur from the exhaust gas after burning sulfur-containing fuels. In scrubbers, which filter the sulfur from the fuel or heavy oil from the exhaust gas after combustion, calcium sulfate is produced and discharged from the process, causing the substances to be discharged to be increased by a factor of 4.25. The process is only profitable because the calcium sulphate produced can be processed as gypsum in the construction industry.

The object of the present invention was to eliminate the disadvantages of the prior art, in particular to avoid the accumulation of large amounts of products to be discharged with the sulfur. Furthermore, the energy input required for desulfurization should be as low as possible. In addition, the desulfurization should be able to manage without the use of catalysts if possible.

Surprisingly, it has been shown that it is possible to quantitatively remove organic sulfur compounds and also hydrogen sulfide from natural gas, petroleum, petroleum products and also biogas, hereinafter referred to as raw material, by using a chemical reaction, the sulfur contained in the raw materials is oxidized to elemental sulfur with a theoretical oxidation number of less than one, whereby the necessary enthalpy of reaction occurs through the simultaneous addition of bases and sulfur halides. The reaction takes place quantitatively at pH values between 4 and 7, preferably between 5 and 6, particularly preferably at pH 5.5. To set the preferred pH, it is advantageous to add base and sulfur halide simultaneously to the raw material to be cleaned. For this it makes sense to move the raw material mechanically. This can be done by stirring or by trickling or spraying.

In the laboratory, the solution to be desulphurized, which contains hydrogen sulphide or a mercaptan or an aminosulphuric acid or a sulfur-containing protein, is stirred vigorously, for example with a propeller stirrer or a magnetic stir bar.

If, for example, a liquid mercaptan that is not soluble in water is reacted, then during the entire reaction time it must be stirred so vigorously that an unstable emulsion or suspension is formed. If the two phases are present next to one another with a sharp, clearly visible dividing line, then the reaction does not take place or takes place only partially or too slowly.

It is therefore preferable to use a homogenizer instead of the other agitators. Homogenizers are offered by Bosch for the kitchen area or by IKA for laboratories. Disulfur dichloride is added dropwise to the stirred or homogenized liquid. The pH of the liquid drops due to the hydrochloric acid that is formed. When the pH falls below 5.5, 1 molar sodium hydroxide solution is added dropwise. The sodium hydroxide solution is added in such a way that approximately 15 ml of a 1 molar sodium hydroxide solution are added to 1 g of added disulfur dichloride. The exact amount varies with the original that is to be desulfurized. A yellow precipitate of sulfur forms, which can be separated off. The unpleasant smell of the sulfur compounds has disappeared.

The removal of hydrogen sulfide and organic sulfides from crude oil or natural gas can in particular take place by using disulfur dichloride or other sulfur halides and bases as reagents in a multiphase reaction.

The usual mixture of crude oil and natural gas, which is obtained from secondary production, is pumped together with the production water. Hydrogen sulfide and organic sulfides are dissolved both in the water phase and in the hydrophobic phase.

To remove the unwanted sulfur in the oil phase, most of the water is separated off in a settling tank by skimming off the oil phase on top. This process has been known for many years. The amount of feed water emulsified in the oil is sufficient to carry out the reaction in a separate stirred tank, which is then followed again in the process by a settling tank in which the elemental sulfur formed settles.

The removal of gaseous sulfur compounds of negatively charged sulfur, such as hydrogen sulfide or low molecular weight mercaptans or low molecular weight thioethers from natural gas, is possible with gas scrubbers. Gas scrubbers are currently used around the world to remove unwanted substances from gases. If sulfur halide, preferably disulphur dichloride or another sulfur chloride or a mixture of sulfur halides, is atomized into the gas stream to be cleaned, and then the necessary base is sprayed into the gas stream or into the aqueous phase, in order to achieve a slightly acidic pH of in the washer in the aqueous phase 5 to 6, the process according to the invention can also be used to remove undesired sulfur compounds from gaseous product streams. The process according to the invention then takes place in the gas scrubber, in which intimate contact is established between the product gas to be purified and the two components for sulfur removal. It is irrelevant how the gas scrubber is constructed in detail, only an intimate contact of the liquid aqueous phase with the gaseous hydrophobic product phase is important. It is possible to use gas scrubbers in which the gaseous product phase has to pass through a packing of trickles. The aqueous phase, which usually trickles from top to bottom in these gas scrubbers, also functions as a transport medium to remove the precipitated sulfur from the gas scrubber. If the gaseous product phase, which may already contain the sulfur halide, is distributed in gaseous form in a continuous aqueous phase and rises in the form of bubbles in the continuous aqueous medium to the surface, then the resulting elemental sulfur can be collected on the ground and removed from there.

One of the advantages of the process according to the invention is that the desulphurisation takes place without catalysts. Therefore no expensive apparatus is necessary and no expensive catalysts can be poisoned and made unusable. The invention shows that it is unnecessary to use the base for the Desulfurization of liquids that contain sulfur in oxidation states -1 or -2 by adding sulfur compounds in oxidation states +1, +2 or higher as a catalyst carrier in the reaction vessel. As a result of the neutralization reaction with a base, either on the catalyst support or in solution, the heat of reaction is so great that the reaction proceeds completely and stoichiometrically even if the sulfur is removed with the addition of oxygen: H ₂ S + S ₂ Cl ₂ + 2 NaOH → 3S + 2HCl + 2 NaOH → 3S + 2 NaCl + 2 H ₂ O or instead of NaOH, other alkali, alkaline earth or earth metal hydoxides. It is important that the metal halides formed are formed with a high heat of reaction and have a distinct to very good solubility in water and, at the same time, poor solubility in organic liquids.

The use of various types of nitrogen bases is also possible: H ₂ S + S ₂ Cl ₂ + 2 NH ₄ OH → 3S + 2HCI + 2 NH ₄ OH → 3S + 2 NH ₄ Cl + 2 H ₂ O

The use of amines is also possible, but energetically not so strongly preferred: H ₂ S + S ₂ Cl ₂ + 2 R ₁ R ₂ -NH + 2H ₂ O → 3S + 2HCI + 2 R ₁ R ₂ -NH ₂ OH → 3S + 2 R ₁ R ₂ -NH ₂ Cl + 2 H ₂ O

The removal of sulfur from thioethers is done according to the following gross equation: (CH ₃ ) ₂ S + S ₂ Cl ₂ + 2 NaOH → 3S + 2 (CH ₃ ) Cl + 2 NaOH → 3S + 2 NaCl + 2 CH ₄ + 2 H ₂ O

Another reaction is also possible in parallel: (CH ₃ ) ₂ S + S ₂ Cl ₂ + 2 NaOH → 3S + 2 (CH ₃ ) OH + 2 NaCl

In general it can be formulated: R ₁ R ₂ S + S ₂ Cl ₂ + 2 NaOH → 3S + R ₁₀ H + R ₂ OH + 2 NaCl

In all of the above equations, R ₁ and R _{2 are} either an alkyl radical, an aryl radical or a hydrogen atom. The alkyl radical or the aryl radical can be substituted in one or more places. The two alkyl or aryl radicals do not have to be identical and it is also possible for an alkyl and an aryl radical or an alkyl radical and a hydrogen atom or an aryl radical and a hydrogen atom to be bonded to a sulfur atom.

The other bases mentioned above can also be used.

The reaction produces elemental sulfur, which can be removed from the raw material as a solid.

Instead of disulfur dichloride, other sulfur halides can also be used, for example sulfur dichloride. However, the use of sulfur dichloride is associated with high administrative costs, since sulfur dichloride is a precursor for the synthesis of mustard gas.

The sulfur bromides are not stable enough to be used as raw material for the desulfurization process. Sulfur iodide, also called iodine sulfur, is a solid compound. Because of these properties, the use of liquid sulfur chlorides is preferred.

It is advantageous to establish intimate contact between the two phases. Intimate contact and thus a short process duration mean that the necessary apparatus can be built smaller than with a reaction procedure in which the contact between the phases is carried out by an anchor stirrer, namely when the phases are carried out by a propeller stirrer or, particularly preferably, by a homogenizer be brought into contact. It is particularly advantageous if the oxidation component, usually the disulfur dichloride, is metered directly into the homogenizer. If the pH regulating component, i.e. the base, is then dosed directly into the same homogenizer, the desulphurisation can be carried out in a very small space and is therefore also suitable for the desulphurisation of crude oil and raw gases on production platforms.

A large contact area is necessary for complete and rapid conversion of the sulfur compounds with the oxidizing agent to elemental sulfur. The large contact area is produced by bringing the water-insoluble phase, which contains the oxidizing agent sulfur halide, into intimate contact with the aqueous phase, for example by stirring.

To achieve a large contact area between the hydrophilic phase and the hydrophobic phase, it can be helpful to add other substances to the reaction mixture in addition to the base and the oxidizing agent, for example the disulfur dichloride. On the one hand, these can be substances that reduce the surface tension between the two phases in such a way that the phases can be better distributed within one another with less energy expenditure. On the other hand, these can be substances that the Stabilize the phase boundary between the two phases or substances that cause both.

It can therefore be advantageous to allow the process according to the invention to take place on trickle bodies which themselves do not take part in the reaction, that is to say have no catalytic effect.

Usually, surfactants are used both to reduce the surface tension and to stabilize the phase boundaries. All chlorine-stable surfactants can be used as surfactants, such as, for example, end-group-capped surfactants, such as, for example, end-group-capped ethylene-butylene glycol block polymers or end-group-capped alkyl-ethylene oxide-propylene oxide or end-group-capped ethylene oxide-butylene oxide surfactants. The latter have been on the market for many years ^{under the name Plurafac ®.}

The use of anionic or cationic surfactants is also possible. Both the known alkylarylsulfonic acids and the benzalkonium chlorides or didecyldimethylammonium chlorides, which are only to be mentioned here as examples, can multiply the size of the interfaces between a hydrophilic phase and a hydrophobic phase and thus multiply the reaction rate of the chemical reaction.

The use of amines can therefore be particularly preferred because the amine salts formed accumulate at the phase boundary and thus improve the distribution of the aqueous and the hydrophobic phase in one another. It can therefore be particularly advantageous to use amines as bases in the same reaction in addition to alkali, alkaline earth or earth metal hydroxides. The amines added in addition to the metal hydroxides replace the nonionic or anionic surfactants or quaternary ammonium compounds in this variant.

The precipitated sulfur is a raw material that can be sold or used yourself. Sulfur is an essential element that must be used as a fertilizer to promote plant growth and thus ensure a good harvest. Another application is in pharmacy and medicine. A third in the steel industry as an alloying element for special steels. Half of the sulfur extracted worldwide is used in agriculture. The demand in China and India is increasing the most.

It can be advantageous to discharge only a third of the sulfur produced from the process and to convert the majority of two thirds back into disulfur dichloride, which is then reintroduced into the process. This process management is a preferred variant. The conversion of elemental sulfur to disulfur dichloride is known per se. The production of disulfur dichloride from the elemental sulfur produced in the reaction is advantageous in that it saves transport routes and the sulfur chlorides produced do not have to be precisely defined chemically. If, instead of a pure disulfur dichloride, a mixture of disulfur dichloride and sulfur dichloride is produced on the company premises, this mixture of different sulfur chlorides can be used again for desulfurization without further purification or separation of the components. This can reduce the reaction volume, container volumes and transport volumes without the need to use sulfur dichloride.

Embodiments:

Example 1:

50 g of distilled water are added to 100 g of heavy oil with a sulfur content of three and a half percent in a 500 ml Erlenmeyer flask. Both substances are heated together to up to 70 ° C until the heavy oil is liquid. Then a pH measuring chain is immersed in the solution.

The two liquids are stirred with a magnetic stir bar. The resulting emulsion is adjusted to pH 9 with 1N sodium hydroxide solution. Disulfur dichloride is added dropwise from a burette to the emulsion. The pH value drops to pH 6 to 5 or even lower. The pH value is kept at 5.5 to 6 by adding further sodium hydroxide solution drop by drop.

14 to 15 g of disulfur dichloride and 220 ml of 1N sodium hydroxide solution are used for the titration.

Seven grams of elemental sulfur precipitate and can be filtered off. The sulfur obtained can be used as raw material.

After the aqueous phase has settled, the sulfur-free oil can be decanted off.

Example 2:

250 ml of fresh cattle manure with a dry weight of 50 g and a sulfur content of 0.35 percent are placed in an Erlenmeyer flask. The pH of the manure is 6.7. 1.4 to 1.5 g of disulfur dichloride are slowly added dropwise with stirring. At the same time, the pH value is stabilized at pH 6.5 to 7 with 1N sodium hydroxide solution.

1.4 g of elemental sulfur are deposited and 22 ml of 1N sodium hydroxide solution are consumed.

If the suspension is fermented in a biogas plant, the biogas obtained is free of sulfur compounds. The precipitated sulfur remains in the suspension and can be used as fertilizer.

Claims (13)

Process for the desulfurization of aqueous multiphase mixtures of water and sulfur-containing organic substances and non-water-soluble substances, characterized in that negatively charged sulfur in a reaction that takes place simultaneously in the aqueous and the non-aqueous phase, with the help of sulfur halides and bases to elementary Sulfur is reacted, which can be separated from the mixture as a solid. Procedure according to Claim 1 , characterized in that the pH value in the reaction mixture is regulated between the values 4 and 7 with the aid of the added base. Procedure according to Claim 2 , characterized in that the pH value in the reaction mixture is regulated between the values 5 and 6 with the aid of the added base. Method according to one of the Claims 1 until 3 , characterized in that the aqueous and the non-aqueous phase, in particular with a stirrer or a homogenizer, are mixed. Method according to one of the Claims 1 until 4th , characterized in that an alkali, an alkaline earth or an earth metal hydroxide is used as the base. Procedure according to Claim 5 , characterized in that sodium hydroxide is used as the base. Procedure according to Claim 5 , distinguished by the fact that slaked lime is used as the base. Method according to one of the Claims 1 until 4th , characterized in that a nitrogen base from the group of aliphatic and / or aromatic amines is used as the base. Method according to one of the Claims 1 until 8th , characterized in that it is carried out in a gas scrubber. Method according to one of the Claims 1 until 9 , characterized in that a surfactant is also added. Method according to one of the Claims 1 until 10 , characterized in that disulfur dichloride is used as the sulfur halide. Method according to one of the Claims 1 until 10 , characterized in that sulfur dichloride is used as the sulfur halide. Method according to one of the Claims 1 until 12th , characterized in that part of the elemental sulfur produced is converted directly back into sulfur halide, which is then fed back directly to the reaction without being worked up.