RU2538843C2 - Using solid waste-quicklime membrane treatment process to produce sodium hydroxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of a diluted solution of caustic soda using an ion-exchange technique. The method of producing a diluted solution of caustic soda from carbon dioxide formed from burning wastes, calcium hydroxide and sodium chloride, includes reacting salty water or acidic salty water with carbon dioxide and calcium hydroxide in a complex membrane system to obtain sodium carbonate. The obtained sodium carbonate is then reacted with calcium hydroxide to obtain sodium hydroxide. Energy from burning solid wastes is used to conduct the reaction between the sodium carbonate and calcium hydroxide.

EFFECT: invention provides more efficient production of Na₂CO₃ and NaOH using waste heat and enables to bind carbon dioxide gas and acidic gases.

13 cl, 5 dwg

Description

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

The use of heat generated during the burning of solid waste (or any available source of waste heat), salt water, acidic water and advanced technology using membranes and resins to produce soda ash Na ₂ CO ₃ and sodium hydroxide NaOH is proposed.

Slaked lime, calcium hydroxide Ca (OH) ₂ (from 500 to 1000 ppm (ppm)) is treated using a cation exchange system (strong or weak) to obtain sodium hydroxide (from 500 to 1000 ppm):

Ca (OH) ₂ + 2R-Na ⁺ → 2NaOH + R-Ca ⁺⁺

The present invention uses the classical equation according to which CO ₂ reacts with caustic soda NaOH to obtain a pure solution of sodium carbonate Na ₂ CO ₃ :

NaOH + CO ₂ → Na ₂ CO ₃

An important role is played by the presence of regenerating solutions (regenerants), such as salt water with a salt content of 6 to 12%, acidic water with an acidity> 8% (for example, HCl or H ₂ SO ₄ ), or combinations thereof, since they are used for regeneration of cation exchangers, so that:

$$\text{(one)}{\text{R-ca}}^{++}+\text{2NaCl}\to {\text{2R-Na}}^{+}+{\text{<figure-callout id="2" label="CaCl" filenames="00000006.png,00000007.png" state="{{state}}">CaCl</figure-callout>}}_{\text{2}}$$

$$\text{(2)}{\text{R-ca}}^{++}+\text{ÍÕ}\to \text{2R-H}+\text{ÑàÕ}$$

R-H + NaCl → R-Na ⁺ + HCl (acidic waste)

One aspect of the present invention provides for the bubbling reactor for bubbling acidic waste gases, where gases, such as HCl and SO ₂ , can be absorbed to obtain acidic solutions in such a way that:

HCl (gas) + H ₂ O → HCl (aq) is used to regenerate strong ion exchangers

SO ₂ (gas) + H ₂ O + O → H ₂ SO ₄ (aq.) Is used to regenerate strong ion exchangers.

Acidic waste can be combined with basic waste, such as waste from power plants, to produce a neutral product that can be safely discharged into the environment.

The resulting aqueous solution of sodium carbonate has a low concentration, namely from 0.05 to 0.5%, and should be concentrated to ~ 6%. The concentration process is performed using a reverse osmosis unit through which an aqueous solution of Na ₂ CO _{3 is} passed repeatedly until a final product concentration of 6% is reached. On an industrial scale, a concentration of 6% is low for the economical recovery of solids, which is the main obstacle to using membrane technology. The difficulty in moving liquids with a concentration above 6% when using existing membrane technology lies in the high pressure that destroys the membrane. Even when using recompression evaporation, approximately 1 MW is required to produce 1 ton of solid product. According to the present invention, the most obvious source of heat is the heat generated by burning solid waste, or from any other source of waste heat.

SUMMARY OF THE INVENTION

A description of how the invention solves a technical problem.

Solid waste, salt water waste and CO ₂ waste are significant problems that human society is facing all over the world. In the present invention, an attempt is made to reduce these three problems associated with waste into one industrial method for developing an environmentally friendly solution, while obtaining material benefits. An environmentally friendly solution is implemented through the large-scale elimination of various wastes mentioned above. The material benefits come from the sale of soda chemicals as by-products of the combined processes. In a sense, the production of NaOH using a membrane process for processing lime using waste heat (the WHQM process) is an alternative to the chlor-alkali cell process used worldwide to produce caustic NaOH soda. A significant problem of the process using a chlor-alkali cell is associated with the formation of chlorine, which is a toxic gas that requires safe storage. Obtaining caustic soda using the WHQM process is a chlorine-free process. The method is essentially based on advanced membrane technology systems for producing sodium hydroxide NaOH. Therefore, this method is significantly different from the chlor-alkali process associated with a high consumption of electric energy (i.e. 3000 kWh per ton of NaOH) for the conversion of NaCl to NaOH. In the present invention, there is a single by-product of CaCO ₃ , whereas when using the chlor-alkali method, it is necessary to work with hazardous gases such as chlorine and hydrogen.

DETAILED DESCRIPTION OF THE INVENTION AND A BRIEF DESCRIPTION OF THE GRAPHIC MATERIALS

Heat from solid waste incineration (or from any other source of waste heat) can be used, as discussed in patent document PCT / IB2008 / 002020. The mechanism for producing NaOH corresponds to the same scheme as the preparation of NaHCO ₃ , as shown in FIG.

Bubbler design: acidic exhaust gases can be bubbled under pressure to dissolve acidic gas in seawater or river water to form an acidic liquid that can be used to regenerate strong or weak ion exchangers.

Ion exchange system: you can use a solution of calcium hydroxide Ca (OH) ₂ (for example, ~ 0.5-1 g / l) to obtain a diluted solution of caustic soda with a concentration of 1000 ppm

Schematic of the reactor: carbon dioxide gas is bubbled into the reactor through caustic NaOH to form a dilute solution of sodium carbonate Na ₂ CO ₃ (for example, 700 ppm Na ₂ CO ₃ in 300 ppm NaOH). The latter is then subjected to additional filtration to remove mechanical impurities, and then served on the installation of reverse osmosis. The low concentrated solution should be converted and concentrated to obtain a higher concentrated aqueous solution of sodium carbonate Na ₂ CO ₃ (for example, 2400 ppm Na ₂ CO ₃ in 1000 ppm NaOH) by passing it through a reverse osmosis unit.

The reverse osmosis (RO) installation contains RO cartridges cascaded with CO ₂ -NaOH reactors between them. The goal is to maintain NaOH concentrations below 300 ppm. as the concentration of Na ₂ CO ₃ increases, that is, maintaining a pH of ~ 11.

On figa, 3B and 3C presents the data of mass analysis of the whole process.

A block diagram of an ion exchange reverse osmosis unit is shown in FIG. 2. The process is carried out until a 6% solution of Na ₂ CO _{3 is} obtained (not to powdered soda ash). At this stage, a solution of Na ₂ CO ₃ (i.e. a 6% solution) upon evaporation using available waste heat will produce dry soda ash. However, when processing a 3.5% solution of Na ₂ CO ₃ with a solution of Ca (OH) ₂ , the reaction proceeds:

Na ₂ CO ₃ + Ca (OH) ₂ → 2NaOH + CaCO ₃ ↓

In the table (see Fig. 3A, 3B and 3C), which shows the experimental results, it is shown that for the formation of 13 kg of NaOH and 16 kg of CaCO _3, 24 kg of Ca (OH) ₂ and ~ 20 kg of NaCl are consumed. In terms of evaporation efficiency, 1 MWh of thermal energy is required to produce 1 ton of dry NaOH. If thermal energy is available in the form of waste heat, a fine of 1 MWh will not be required.

From the WHQM process described in PCT / 1B2008 / 002020, the waste heat provided by the solid waste treatment unit can turn water into steam at a temperature of 120 to 150 ° C. in a steam boiler located above the solid waste incinerator. Steam can be used to convert a 7% sodium hydroxide solution to a 50% solution by evaporating half the volume of the solution or by evaporating it before turning it into dry sodium hydroxide. The ion exchange resins used in this process are regenerated either from treated seawater or from the resulting salt water. In the above scheme, if the concentration of C salt in salt water is> 10%, then a complex membrane and a heat exchange system are not required. If the salt concentration in salt water is 6% <C <9%, then a complex membrane is not required, and the heat exchange system can be used to increase the salt water concentration to 10%, or, if it is cheaper, to bring the C concentration to 10% add NaCl. If only seawater is available and the exhaust gases contain acidic gases such as hydrogen chloride and sulfur dioxide, then such gases can be bubbled with seawater under pressure to produce acidic seawater suitable for ion exchange processes. Acidic seawater can be used as a regenerant to remove calcium and magnesium ions in the case of using seawater to rinse the regenerated ion-exchange resins and turn them into the form of Na ⁺ . One of the important aspects related to this method is the circulation of reverse osmosis permeate, which saves on the production of clean water and the supply of chemicals. At the same time, production wastes, such as calcium chloride and magnesium chloride, can be diluted with pure water obtained using an integrated membrane and heat exchange system, and returned to the sea without harming the marine environment. The volume of drinking water produced at this stage is poorly assessed and depends on the state maximum permissible level of Ca ⁺⁺ , Mg ⁺⁺ salts after dilution.

Examples of intended use and other industrial uses

The WHQM process is most convenient for industries that emit salt water (that is, water with a salt content of 6 to 16%) and that do not have sources of waste heat and CO ₂ . However, this process can also be carried out in industry in plants that emit a limited amount of CO ₂ , where the combined amounts from the industrial plant and the solid waste processing plant can be used to remove CO ₂ and produce caustic soda. The solid waste processing method can be applied on an industrial scale, where solid waste incineration can be used to form CO ₂ , salt water and heat for the WHQM process. This method can also be adapted for the emission of acidic-containing exhaust gases that can be used to regenerate ion exchangers.

Advantages achieved include binding of CO ₂ and acid gases (i.e., HCl and SO ₂ ). The first of these is known to cause global warming, while the latter lead to acid rain in remote regions.

Claims (13)

1. A method of obtaining a dilute solution of caustic soda from carbon dioxide generated by the combustion of solid waste, calcium hydroxide and sodium chloride by means of an ion exchange process in which salt water or acidic salt water are reacted with carbon dioxide (CO ₂ ) and calcium hydroxide in a complex membrane system to produce sodium carbonate, then the resulting sodium carbonate is reacted with calcium hydroxide to produce sodium hydroxide, in which to conduct the reaction between sodium carbonate Riya and calcium hydroxide use the energy from burning solid waste. 2. The method according to claim 1, in which the sodium carbonate solution is concentrated to 6-7% by repeated reverse osmosis and bubbling acidic CO ₂ , and the resulting concentrated solution is treated by heating to obtain solid sodium carbonate. 3. The method according to claim 1, in which the sodium carbonate solution is concentrated to 6-7% by repeated reverse osmosis and bubbling acidic CO ₂ , and the resulting concentrated sodium carbonate solution is reacted with calcium hydroxide to obtain a 6-7% sodium hydroxide solution NaOH . 4. The method according to claim 1, wherein said acidic saline solution is obtained by acidifying salt water with an acidic exhaust gas containing HCl or SO ₂ . 5. The method according to claim 1, wherein said sodium carbonate solution is converted into a solution with a concentration of 50% or into solid NaOH. 6. The method according to p. 1, in which salt water is sea water. 7. The method according to claim 1, wherein said calcium hydroxide solution has a concentration of 0.5 g / L. 8. The method according to claim 1, in which the initial concentration of the output caustic soda is 1000 ppm 9. The method according to claim 1, wherein said sodium carbonate solution has a concentration of approximately 700 ppm, caustic soda is obtained with a concentration of approximately 300 ppm. NaOH, said sodium carbonate solution is concentrated to a concentration of approximately 2400 ppm, the initial concentration of the caustic soda is approximately 1000 ppm. 10. The method according to claim 1, in which the concentration of caustic soda is maintained below 300 ppm. with an increase in the concentration of sodium carbonate introduced. 11. Installation for implementing the method according to any one of paragraphs. 1-7, including elements (i) - (iv):
(i) a bubbler providing pressure bubbling of acidic off-gases to dissolve the acid gas in salt water to form an acid solution that is used in the ion exchange system (ii);
(ii) an ion exchange system into which a calcium hydroxide solution is introduced to produce caustic soda (NaOH);
(iii) a bubbler reactor for sparging carbon dioxide gas through caustic soda NaOH to form a dilute sodium carbonate solution;
(iv) a reverse osmosis plant combined with cascaded reactors carbon dioxide - caustic soda. 12. The apparatus of claim 11, wherein the bubbler reactor (iii) further comprises a filtration system for removing impurity particles before introducing said solution into the reverse osmosis unit (iv). 13. The apparatus of claim 11 or 12, wherein the bubbler reactor (iii) further comprises means for controlling the pH of the reaction solution.

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