A chemical process captures and convert hydrogen sulfide (H.sub.2S) gas into elemental sulfur, polysulfide, sulfur dioxide and/or sulfuric acid while regenerating sodium hydroxide capture agent for further use in an initial H.sub.2S capture step. Processing may include initial sodium hydroxide scrubbing of gas streams containing H.sub.2S, electrochemical regeneration of the sodium hydroxide from sodium hydrosulfide or sodium sulfide, recovery of sulfur and/or sulfur dioxide from the electrochemical processing, and production of sulfuric acid from such sulfur and/or sulfur dioxide.

A chemical process captures and convert hydrogen sulfide (H.sub.2S) gas into elemental sulfur, polysulfide, sulfur dioxide and/or sulfuric acid while regenerating sodium hydroxide capture agent for further use in an initial H.sub.2S capture step. Processing may include initial sodium hydroxide scrubbing of gas streams containing H.sub.2S, electrochemical regeneration of the sodium hydroxide from sodium hydrosulfide or sodium sulfide, recovery of sulfur and/or sulfur dioxide from the electrochemical processing, and production of sulfuric acid from such sulfur and/or sulfur dioxide.

In this disclosure, a process of recycling acid, base and the salt reagents required in the Li recovery process is introduced. A membrane electrolysis cell which incorporates an oxygen depolarized cathode is implemented to generate the required chemicals onsite. The system can utilize a portion of the salar brine or other lithium-containing brine or solid waste to generate hydrochloric or sulfuric acid, sodium hydroxide and carbonate salts. Simultaneous generation of acid and base allows for taking advantage of both chemicals during the conventional Li recovery from brines and mineral rocks. The desalinated water can also be used for the washing steps on the recovery process or returned into the evaporation ponds. The method also can be used for the direct conversion of lithium salts to the high value LiOH product. The method does not produce any solid effluent which makes it easy-to-adopt for use in existing industrial Li recovery plants.

A process for producing a purified aqueous lithium (sulfate) solution including: processing a lithium-containing raw material to produce a crude aqueous solution containing lithium sulfate; contacting the crude solution with an organic medium, in an extraction step to produce a lithium-loaded organic medium and a raffinate; stripping said lithium-loaded organic medium by means of an aqueous acid stripping solution (e.g., sulfuric acid), to extract the lithium cations from the lithium-loaded medium, to produce: the purified aqueous lithium (sulfate) solution and a stripped organic medium; separating the purified lithium solution from the stripped organic medium; recycling the stripped organic medium to the extraction step, the organic medium including the stripped organic medium; subjecting the raffinate to electrolysis to produce: an alkali (sodium) hydroxide solution contaminated with lithium and a sulfuric acid stream; and recycling the alkali hydroxide and sulfuric acid streams for use within the process.

Apparatus for producing alkali hydroxide and method for operating apparatus for producing alkali hydroxide are provided. A cooling chamber through which a coolant can pass is constructed by placing a separation wall in a cathode chamber on a side opposite to an ion-exchange membrane, and a flow rate adjuster, such as manual valves, which can adjust the supply flow rate of the coolant is placed in each unit cell. The electrolytic temperature of each unit cell is regulated at an optimum operating temperature depending on the current density by adjusting the flow rate of the coolant without individually adjusting the flow rate of salt water supplied to the unit cell or the concentration of the salt water.

Apparatus for producing alkali hydroxide and method for operating apparatus for producing alkali hydroxide are provided. A cooling chamber through which a coolant can pass is constructed by placing a separation wall in a cathode chamber on a side opposite to an ion-exchange membrane, and a flow rate adjuster, such as manual valves, which can adjust the supply flow rate of the coolant is placed in each unit cell. The electrolytic temperature of each unit cell is regulated at an optimum operating temperature depending on the current density by adjusting the flow rate of the coolant without individually adjusting the flow rate of salt water supplied to the unit cell or the concentration of the salt water.

There are provided methods for preparing lithium carbonate. For example, such methods can comprise reacting an aqueous composition comprising lithium hydroxide with CO.sub.2 by sparging the CO.sub.2 the said composition, thereby obtaining a precipitate comprising the lithium carbonate. The methods can also comprise inserting at least a portion of the precipitate into a clarifier and obtaining a supernatant comprising lithium bicarbonate and a solid comprising the lithium carbonate, separating the solid from the supernatant; and heating the supernatant at a desired temperature so as to at least partially convert the lithium bicarbonate into lithium carbonate.

There are provided methods for preparing lithium carbonate. For example, such methods can comprise reacting an aqueous composition comprising lithium hydroxide with CO.sub.2 by sparging the CO.sub.2 the said composition, thereby obtaining a precipitate comprising the lithium carbonate. The methods can also comprise inserting at least a portion of the precipitate into a clarifier and obtaining a supernatant comprising lithium bicarbonate and a solid comprising the lithium carbonate, separating the solid from the supernatant; and heating the supernatant at a desired temperature so as to at least partially convert the lithium bicarbonate into lithium carbonate.

Methods of forming pyrazines from reactants derived from a plant of the Nicotiana species, including receiving an aqueous reactant solution including at least one tobacco-derived cellulosic sugar and at least one tobacco-derived amino acid, heating the reactant solution to a reactant temperature and holding the reactant solution at the reactant temperature for a reactant time to produce a reactant product including at least one tobacco-derived pyrazine, and isolating the at least one tobacco-derived pyrazine from the reactant product. Tobacco products incorporating the tobacco-derived pyrazines are also provided.

Methods of forming pyrazines from reactants derived from a plant of the Nicotiana species, including receiving an aqueous reactant solution including at least one tobacco-derived cellulosic sugar and at least one tobacco-derived amino acid, heating the reactant solution to a reactant temperature and holding the reactant solution at the reactant temperature for a reactant time to produce a reactant product including at least one tobacco-derived pyrazine, and isolating the at least one tobacco-derived pyrazine from the reactant product. Tobacco products incorporating the tobacco-derived pyrazines are also provided.