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Production mix technologyComment of decarboxylative cyclization of adipic acid (RER): decarboxylative cyclization of adipic acid technologyComment of formic acid production, methyl formate route (RER): The worldwide installed capacity for producing formic acid was about 330 000 t/a in 1988. Synthesis of formic acid by hydrolysis of methyl formate is based on a two-stage process: in the first stage, methanol is carbonylated with carbon monoxide; in the second stage, methyl formate is hydrolyzed to formic acid and methanol. The methanol is returned to the first stage. Although the carbonylation of methanol is relatively problem-free and has been carried out industrially for a long time, only recently has the hydrolysis of methyl formate been developed into an economically feasible process. The main problems are associated with work-up of the hydrolysis mixture. Because of the unfavorable position of the equilibrium, reesterification of methanol and formic acid to methyl formate occurs rapidly during the separation of unreacted methyl formate. Problems also arise in the selection of sufficiently corrosion-resistant materials Carbonylation of Methanol In the two processes mentioned, the first stage involves carbonylation of methanol in the liquid phase with carbon monoxide, in the presence of a basic catalyst: imageUrlTagReplacea0ec6e15-92c8-4d44-82bb-84e90e58b171 As a rule, the catalyst is sodium methoxide. Potassium methoxide has also been proposed as a catalyst; it is more soluble in methyl formate and gives a higher reaction rate. Although fairly high pressures were initially preferred, carbonylation is carried out in new plants at lower pressure. Under these conditions, reaction temperature and catalyst concentration must be increased to achieve acceptable conversion. According to published data, ca. 4.5 MPa, 80 °C, and 2.5 wt % sodium methoxide are employed. About 95 % carbon monoxide, but only about 30 % methanol, is converted under these circumstances. Nearly quantitative conversion of methanol to methyl formate can, nevertheless, be achieved by recycling the unreacted methanol. The carbonylation of methanol is an equilibrium reaction. The reaction rate can be raised by increasing the temperature, the carbon monoxide partial pressure, the catalyst concentration, and the interface between gas and liquid. To synthesize methyl formate, gas mixtures with a low proportion of carbon monoxide must first be concentrated. In a side reaction, sodium methoxide reacts with methyl formate to form sodium formate and dimethyl ether, and becomes inactivated. The substances used must be anhydrous; otherwise, sodium formate is precipitated to an increasing extent. Sodium formate is considerably less soluble in methyl formate than in methanol. The risk of encrustation and blockage due to precipitation of sodium formate can be reduced by adding poly(ethylene glycol). The carbon monoxide used must contain only a small amount of carbon dioxide; otherwise, the catalytically inactive carbonate is precipitated. Basic catalysts may reverse the reaction, and methyl formate decomposes into methanol and carbon monoxide. Therefore, undecomposed sodium methoxide in the methyl formate must be neutralized. Hydrolysis of Methyl Formate In the second stage, the methyl formate obtained is hydrolyzed: imageUrlTagReplace2ddc19c0-905f-42c3-b14c-e68332befec9 The equilibrium constant for methyl formate hydrolysis depends on the water: ester ratio. With a molar ratio of 1, the constant is 0.14, but with a water: methyl formate molar ratio of 15, it is 0.24. Because of the unfavorable position of this equilibrium, a large excess of either water or methyl formate must be used to obtain an economically worthwhile methyl formate conversion. If methyl formate and water are used in a molar ratio of 1 : 1, the conversion is only 30 %, but if the molar ratio of water to methyl formate is increased to 5 – 6, the conversion of methyl formate rises to 60 %. However, a dilute aqueous solution of formic acid is obtained this way, and excess water must be removed from the formic acid with the expenditure of as little energy as possible. Another way to overcome the unfavorable position of the equilibrium is to hydrolyze methyl formate in the presence of a tertiary amine, e.g., 1-(n-pentyl)imidazole. The base forms a salt-like compound with formic acid; therefore, the concentration of free formic acid decreases and the hydrolysis equilibrium is shifted in the direction of products. In a subsequent step formic acid can be distilled from the base without decomposition. A two-stage hydrolysis has been suggested, in which a water-soluble formamide is used in the second stage; this forms a salt-like compound with formic acid. It also shifts the equilibrium in the direction of formic acid. To keep undesirable reesterification as low as possible, the time of direct contact between methanol and formic acid must be as short as possible, and separation must be carried out at the lowest possible temperature. Introduction of methyl formate into the lower part of the column in which lower boiling methyl formate and methanol are separated from water and formic acid, has also been suggested. This largely prevents reesterification because of the excess methyl formate present in the critical region of the column. Dehydration of the Hydrolysis Mixture Formic acid is marketed in concentrations exceeding 85 wt %; therefore, dehydration of the hydrolysis mixture is an important step in the production of formic acid from methyl formate. For dehydration, the azeotropic point must be overcome. The concentration of formic acid in the azeotropic mixture increases if distillation is carried out under pressure, but the higher boiling point at high pressure also increases the decomposition rate of formic acid. At the same time, the selection of sufficiently corrosion-resistant materials presents considerable problems. A number of entrainers have been proposed for azeotropic distillation. Reference: Gräfje, H., Körnig, W., Weitz, H.-M., Reiß, W.: Butanediols, Butenediol, and Butynediol, Chapter 1. In: Ullmann's Encyclopedia of Industrial Chemistry, Sev-enth Edition, 2004 Electronic Release (ed. Fiedler E., Grossmann G., Kersebohm D., Weiss G. and Witte C.). 7 th Electronic Release Edition. WileyInterScience, New York, Online-Version under: http://www.mrw.interscience.wiley.com/ueic/articles/a04_455/frame.html technologyComment of oxidation of butane (RER): The liquid-phase oxidation of hydrocarbons is an important process to produce acetic acid, formic acid or methyl acetate. About 43 kg of formic acid is produced per ton of acetic acid. Unreacted hydrocarbons, volatile neutral constituents, and water are separated first from the oxidation product. Formic acid is separated in the next column; azeotropic distillation is generally used for this purpose. The formic acid contains about 2 wt % acetic acid, 5 wt % water, and 3 wt % benzene. Formic acid with a content of about 98 wt % can be produced by further distillation. Reference: Gräfje, H., Körnig, W., Weitz, H.-M., Reiß, W.: Butanediols, Butenediol, and Butynediol, Chapter 1. In: Ullmann's Encyclopedia of Industrial Chemistry, Sev-enth Edition, 2004 Electronic Release (ed. Fiedler E., Grossmann G., Kersebohm D., Weiss G. and Witte C.). 7 th Electronic Release Edition. WileyInterScience, New York, Online-Version under: http://www.mrw.interscience.wiley.com/ueic/articles/a04_455/frame.html
technologyComment of gold mine operation and refining (SE): OPEN PIT MINING: The ore is mined in four steps: drilling, blasting, loading and hauling. In the case of a surface mine, a pattern of holes is drilled in the pit and filled with explosives. The explosives are detonated in order to break up the ground so large shovels or front-end loaders can load it into haul trucks. ORE AND WASTE HAULAGE: The haul trucks transport the ore to various areas for processing. The grade and type of ore determine the processing method used. Higher-grade ores are taken to a mill. Lower grade ores are taken to leach pads. Some ores may be stockpiled for later processing. HEAP LEACHING: The ore is crushed or placed directly on lined leach pads where a dilute cyanide solution is applied to the surface of the heap. The solution percolates down through the ore, where it leaches the gold and flows to a central collection location. The solution is recovered in this closed system. The pregnant leach solution is fed to electrowinning cells and undergoes the same steps as described below from Electro-winning. ORE PROCESSING: Milling: The ore is fed into a series of grinding mills where steel balls grind the ore to a fine slurry or powder. Oxidization and leaching: Some types of ore require further processing before gold is recovered. In this case, the slurry is pressure-oxidized in an autoclave before going to the leaching tanks or a dry powder is fed through a roaster in which it is oxidized using heat before being sent to the leaching tanks as a slurry. The slurry is thickened and runs through a series of leaching tanks. The gold in the slurry adheres to carbon in the tanks. Stripping: The carbon is then moved into a stripping vessel where the gold is removed from the carbon by pumping a hot caustic solution through the carbon. The carbon is later recycled. Electro-winning: The gold-bearing solution is pumped through electro-winning cells or through a zinc precipitation circuit where the gold is recovered from the solution. Smelting: The gold is then melted in a furnace at about 1’064°C and poured into moulds, creating doré bars. Doré bars are unrefined gold bullion bars containing between 60% and 95% gold. References: Newmont (2004) How gold is mined. Newmont. Retrieved from http://www.newmont.com/en/gold/howmined/index.asp technologyComment of primary lead production from concentrate (GLO): There are two basic pyrometallurgical processes available for the production of lead from lead or mixed lead-zinc-sulphide concentrates: sinter oxidation / blast furnace reduction route or Direct Smelting Reduction Processes. Both processes are followed by a refining step to produce the final product with the required purity, and may also be used for concentrates mixed with secondary raw materials. SINTER OXIDATION / BLAST FURNACE REDUCTION: The sinter oxidation / blast furnace reduction involves two steps: 1) A sintering oxidative roast to remove sulphur with production of PbO; and 2) Blast furnace reduction of the sinter product. The objective of sintering lead concentrates is to remove as much sulphur as possible from the galena and the accompanying iron, zinc, and copper sulphides, while producing lump agglomerate with appropriate properties for subsequent reduction in the blast furnace (a type of a shaft furnace). As raw material feed, lead concentrates are blended with recycled sinter fines, secondary material and other process materials and pelletised in rotating drums. Pellets are fed onto sinter machine and ignited. The burning pellets are conveyed over a series of wind-boxes through which air is blown. Sulphur is oxidised to sulphur dioxide and the reaction generates enough heat to fuse and agglomerate the pellets. Sinter is charged to the blast furnace with metallurgical coke. Air and/or oxygen enriched air is injected and reacts with the coke to produce carbon monoxide. This generates sufficient heat to melt the charge. The gangue content of the furnace charge combines with the added fluxes or reagents to form a slag. For smelting bulk lead-zinc-concentrates and secondary material, frequently the Imperial Smelting Furnace is used. Here, hot sinter and pre-heated coke as well as hot briquettes are charged. Hot air is injected. The reduction of the metal oxides not only produces lead and slag but also zinc, which is volatile at the furnace operating temperature and passes out of the ISF with the furnace off-gases. The gases also contain some cadmium and lead. The furnace gases pass through a splash condenser in which a shower of molten lead quenches them and the metals are absorbed into the liquid lead, the zinc is refined by distillation. DIRECT SMELTING REDUCTION: The Direct Smelting Reduction Process does not carry out the sintering stage separately. Lead sulphide concentrates and secondary materials are charged directly to a furnace and are then melted and oxidised. Sulphur dioxide is formed and is collected, cleaned and converted to sulphuric acid. Carbon (coke or gas) and fluxing agents are added to the molten charge and lead oxide is reduced to lead, a slag is formed. Some zinc and cadmium are “fumed” off in the furnace, their oxides are captured in the abatement plant and recovered. Several processes are used for direct smelting of lead concentrates and some secondary material to produce crude lead and slag. Bath smelting processes are used: the ISA Smelt/Ausmelt furnaces (sometimes in combination with blast furnaces), Kaldo (TBRC) and QSL integrated processes are used in EU and Worldwide. The Kivcet integrated process is also used and is a flash smelting process. The ISA Smelt/Ausmelt furnaces and the QSL take moist, pelletised feed and the Kaldo and Kivcet use dried feed. REFINING: Lead bullion may contain varying amounts of copper, silver, bismuth, antimony, arsenic and tin. Lead recovered from secondary sources may contain similar impurities, but generally antimony and calcium dominate. There are two methods of refining crude lead: electrolytic refining and pyrometallurgical refining. Electrolytic refining uses anodes of de-copperised lead bullion and starter cathodes of pure lead. This is a high-cost process and is used infrequently. A pyrometallurgical refinery consists of a series of kettles, which are indirectly heated by oil or gas. Over a series of separation processes impurities and metal values are separated from the lead bouillon. Overall waste: The production of metals is related to the generation of several by-products, residues and wastes, which are also listed in the European Waste Catalogue (Council Decision 94/3/EEC). The ISF or direct smelting furnaces also are significant sources of solid slag. This slag has been subjected to high temperatures and generally contains low levels of leachable metals, consequently it may be used in construction. Solid residues also arise as the result of the treatment of liquid effluents. The main waste stream is gypsum waste (CaSO4) and metal hydroxides that are produced at the wastewater neutralisation plant. These wastes are considered to be a cross-media effect of these treatment techniques but many are recycled to pyrometallurgical process to recover the metals. Dust or sludge from the treatment of gases are used as raw materials for the production of other metals such as Ge, Ga, In and As, etc or can be returned to the smelter or into the leach circuit for the recovery of lead and zinc. Hg/Se residues arise at the pre-treatment of mercury or selenium streams from the gas cleaning stage. This solid waste stream amounts to approximately 40 - 120 t/y in a typical plant. Hg and Se can be recovered from these residues depending on the market for these metals. Overall emissions: The main emissions to air from zinc and lead production are sulphur dioxide, other sulphur compounds and acid mists; nitrogen oxides and other nitrogen compounds, metals and their compounds; dust; VOC and dioxins. Other pollutants are considered to be of negligible importance for the industry, partly because they are not present in the production process and partly because they are immediately neutralised (e.g. chlorine) or occur in very low concentrations. Emissions are to a large extent bound to dust (except cadmium, arsenic and mercury that can be present in the vapour phase). Metals and their compounds and materials in suspension are the main pollutants emitted to water. The metals concerned are Zn, Cd, Pb, Hg, Se, Cu, Ni, As, Co and Cr. Other significant substances are fluorides, chlorides and sulphates. Wastewater from the gas cleaning of the smelter and fluid-bed roasting stages are the most important sources. References: Sutherland C. A., Milner E. F., Kerby R. C., Teindl H. and Melin A. (1997) Lead. In: Ullmann's encyclopedia of industrial chemistry (ed. Anonymous). 5th edition on CD-ROM Edition. Wiley & Sons, London. IPPC (2001) Integrated Pollution Prevention and Control (IPPC); Reference Document on Best Available Techniques in the Non Ferrous Metals Industries. European Commission. Retrieved from http://www.jrc.es/pub/english.cgi/ 0/733169 technologyComment of primary zinc production from concentrate (RoW): The technological representativeness of this dataset is considered to be high as smelting methods for zinc are consistent in all regions. Refined zinc produced pyro-metallurgically represents less than 5% of global zinc production and less than 2% of this dataset. Electrometallurgical Smelting The main unit processes for electrometallurgical zinc smelting are roasting, leaching, purification, electrolysis, and melting. In both electrometallurgical and pyro-metallurgical zinc production routes, the first step is to remove the sulfur from the concentrate. Roasting or sintering achieves this. The concentrate is heated in a furnace with operating temperature above 900 °C (exothermic, autogenous process) to convert the zinc sulfide to calcine (zinc oxide). Simultaneously, sulfur reacts with oxygen to produce sulfur dioxide, which is subsequently converted to sulfuric acid in acid plants, usually located with zinc-smelting facilities. During the leaching process, the calcine is dissolved in dilute sulfuric acid solution (re-circulated back from the electrolysis cells) to produce aqueous zinc sulfate solution. The iron impurities dissolve as well and are precipitated out as jarosite or goethite in the presence of calcine and possibly ammonia. Jarosite and goethite are usually disposed of in tailing ponds. Adding zinc dust to the zinc sulfate solution facilitates purification. The purification of leachate leads to precipitation of cadmium, copper, and cobalt as metals. In electrolysis, the purified solution is electrolyzed between lead alloy anodes and aluminum cathodes. The high-purity zinc deposited on aluminum cathodes is stripped off, dried, melted, and cast into SHG zinc ingots (99.99 % zinc). Pyro-metallurgical Smelting The pyro-metallurgical smelting process is based on the reduction of zinc and lead oxides into metal with carbon in an imperial smelting furnace. The sinter, along with pre-heated coke, is charged from the top of the furnace and injected from below with pre-heated air. This ensures that temperature in the center of the furnace remains in the range of 1000-1500 °C. The coke is converted to carbon monoxide, and zinc and lead oxides are reduced to metallic zinc and lead. The liquid lead bullion is collected at the bottom of the furnace along with other metal impurities (copper, silver, and gold). Zinc in vapor form is collected from the top of the furnace along with other gases. Zinc vapor is then condensed into liquid zinc. The lead and cadmium impurities in zinc bullion are removed through a distillation process. The imperial smelting process is an energy-intensive process and produces zinc of lower purity than the electrometallurgical process. technologyComment of treatment of electronics scrap, metals recovery in copper smelter (SE, RoW): Conversion of Copper in a Kaldo Converter and treatment in converter aisle. technologyComment of treatment of scrap lead acid battery, remelting (RoW): The referred operation uses a shaft furnace with post combustion, which is the usual technology for secondary smelters. technologyComment of treatment of scrap lead acid battery, remelting (RER): The referred operation uses a shaft furnace with post combustion, which is the usual technology for secondary smelters. Typically this technology produces 5000 t / a sulphuric acid (15% concentration), 25’000 t lead bullion (98% Pb), 1200 t / a slags (1% Pb) and 3000 t / a raw lead matte (10% Pb) to be shipped to primary smelters. Overall Pb yield is typically 98.8% at the plant level and 99.8% after reworking the matte. The operation treats junk batteries and plates but also lead cable sheathing, drosses and sludges, leaded glass and balancing weights. From this feed it manufactures mainly antimonial lead up to 10% Sb, calcium-aluminium lead alloys with or without tin and soft lead with low and high copper content. All these products are the result of a refining and alloying step to meet the compliance with the designations desired. The following by products are reused in the process: fine dust, slag, and sulfuric acid. References: Quirijnen L. (1999) How to implement efficient local lead-acid battery recycling. In: Journal of Power Sources, 78(1-2), pp. 267-269.
technologyComment of manganese production (RER): The metal is won by electrolysis (25%) and electrothermic processes (75%). ELECTROLYSIS OF AQUEOUS MANGANESE SALTS The production of manganese metal by the electrolysis of aqueous manganese salts requires at first a milling of the manganese ore. Milling increases the active surface and ensures sufficient reactivity in both the reduction and the subsequent leaching steps. After milling the manganese ore is fed to a rotary kiln where the reduction and calcination takes place. This process is carried out at about 850 - 1000 ºC in a reducing atmosphere. As a reducing agent, several carbon sources can be used e.g. anthracite, coal, charcoal and hydrocarbon oil or natural gas. The cal-cined ore needs to be cooled below 100 ºC to avoid a further re-oxidation. The subsequent leaching process is carried out with recycled electrolyte, mainly sulphuric acid. After leaching and filtration the iron content is removed from the solution by oxidative precipitation and the nickel and cobalt are removed by sulphide precipitation. The purified electrolyte is then treated with SO2 in order to ensure plating of γ-Mn during electrolysis. Electrolysis is carried out in diaphragm cells. The cathode is normally made of stainless steel or titanium. For the anode lead-calcium or lead-silver alloy can be used. After an appropriate reaction time the cathodes are removed from the electrolysis bath. The manganese that is deposited on the cathode starter-sheet is stripped off mechanically and then washed and dried. The metal is crushed to produce metal flakes or powder or granulated, depending on the end use. ELECTROTHERMAL DECOMPOSITION OF MANGANESE ORES The electrothermal process is the second important process to produce manganese metal in an industrial scale. The electrothermal process takes place as a multistage process. In the first stage manganese ore is smelted with only a small amount of reductant in order to reduce mostly the iron oxide. This produces a low-grade ferro-manganese and a slag that is rich in Mn-oxide. The slag is then smelted in the second stage with silicon to produce silicomanganese. The molten silicomanganese can be treated with liquid slag from the fist stage to obtain relatively pure manganese metal. For the last step a ladle or shaking ladle can be used. The manganese metal produced by the electrothermal process contains up to 98% of Mn. Overall emissions and waste: Emissions to air consist of dust and fume emissions from smelting, hard metal and carbide production; Other emissions to air are ammonia (NH3), acid fume (HCl), hydrogen fluoride (HF), VOC and heavy metals. Effluents are composed of overflow water from wet scrubbing systems, wastewater from slag and metal granulation, and blow down from cooling water cycles. Waste includes dust, fume, sludge and slag. References: Wellbeloved D. B., Craven P. M. and Waudby J. W. (1997) Manganese and Manganese Alloys. In: Ullmann's encyclopedia of industrial chemistry (ed. Anonymous). 5th edition on CD-ROM Edition. Wiley & Sons, London. IPPC (2001) Integrated Pollution Prevention and Control (IPPC); Reference Document on Best Available Techniques in the Non Ferrous Metals Industries. European Commission. Retrieved from http://www.jrc.es/pub/english.cgi/ 0/733169 technologyComment of manganese production (RoW): The metal is won by electrolysis (assumption: 25%) and electrothermic processes (assumption: 75%). No detailed information available, mainly based on rough estimates. technologyComment of treatment of non-Fe-Co-metals, from used Li-ion battery, hydrometallurgical processing (GLO): The technique SX-EW is used mainly for oxide ores and supergene sulphide ores (i.e. ores not containing iron). It is assumed to be used for the treatment of the non-Fe-Co-metals fraction. The process includes a leaching stage followed by cementation or electro-winning. A general description of the process steps is given below. In the dump leaching step, copper is recovered from large quantities (millions of tonnes) of strip oxide ores with a very low grade. Dilute sulphuric acid is trickled through the material. Once the process starts it continues naturally if water and air are circulated through the heap. The time required is typically measured in years. Sulphur dioxide is emitted during such operations. Soluble copper is then recovered from drainage tunnels and ponds. Copper recovery rates vary from 30% to 70%. Cconsiderable amounts of sulphuric acid and leaching agents emit into water and air. No figures are currently available on the dimension of such emissions. After the solvent-solvent extraction, considerable amounts of leaching residues remain, which consist of undissolved minerals and the remainders of leaching chemicals. In the solution cleaning step occur precipitation of impurities and filtration or selective enrichment of copper by solvent extraction or ion exchange. The solvent extraction process comprises two steps: selective extraction of copper from an aqueous leach solution into an organic phase (extraction circuit) and the re-extraction or stripping of the copper into dilute sulphuric acid to give a solution suitable for electro winning (stripping circuit). In the separation step occurs precipitation of copper metal or copper compounds such as Cu2O, CuS, CuCl, CuI, CuCN, or CuSO4 • 5 H2O (crystallisation) Waste: Like in the pyrometallurgical step, considerable quantities of solid residuals are generated, which are mostly recycled within the process or sent to other specialists to recover any precious metals. Final residues generally comprise hydroxide filter cakes (iron hydroxide, 60% water, cat I industrial waste).
technologyComment of adipic acid production (RER, RoW): This dataset models the production of adipic acid by nitric acid oxidation of a mixture of cyclohexanol and cyclohexanone, which is obtained by oxidation of cyclohexane. Abatement of N2O emissions is assumed to reduce the emissions by 80%. Essentially all production of adipic acid is derived from the nitric acid oxidation of a mixture of cyclohexanone – cyclohexanol (KA mixture). The reactor, controlled at 60 – 80 °C and 0.1 – 0.4 MPa, is charged with the recycled nitric acid stream, the KA feed material, and makeup acid containing 50 – 60 % nitric acid and copper – vanadium catalyst. The reaction is very exothermic (6.280 MJ/kg). Adipic acid is obtained with a yield greater than 90%. Nitrogen oxides, carbon dioxide, and some lower dicarboxylic acids are the major by-products, as well as oxidation products arising from impurities in the KA intermediate. The nitric acid oxidation step produces three major waste streams: an off-gas containing oxides of nitrogen and CO2, water containing traces of nitric acid and organics from the water removal column; and a dibasic acid purge stream containing adipic, glutaric and succinic acids. The production of adipic acid can be represented by the following simplified reaction formula: 0.733 C6H12O + 0.367 C6H10O + 2 HNO3 -> C6H10O4 + N2O + 2 H2O + 7.23 H2 References: Althaus H.-J., Chudacoff M., Hischier R., Jungbluth N., Osses M. and Primas A. (2007) Life Cycle Inventories of Chemicals. ecoinvent report No. 8, v2.0. EMPA Dübendorf, Swiss Centre for Life Cycle Inventories, Dübendorf, CH.
technologyComment of pig iron production (RER): Typical blast furnace process
technologyComment of processing of anode slime from electrorefining of copper, anode (GLO): Based on typical current technology. Anode slime treatment by pressure leaching and top blown rotary converter. Production of Silver by Möbius Electrolysis, Gold by Wohlwill electrolysis, copper telluride cement and crude selenium to further processing. technologyComment of selenium production (RER, RoW): Production from selenium is based on simplified roasting process with sodium carbonate. The inventory is based on stoechiometric calculations, according to the following equations: 2 X-Se + 2 Na2CO3 + 3 CO2 -> 2 Na2O4Se + 2 CO2 + 2 X (with X = compounds that were connected to Se - e.g. Cu2, CuAg, ....) 2 Na2O4Se + 4 HCl -> 2 H2O3Se + 4 NaCl + O2 2 H2O3Se + 2 SO2 -> 2 Se + 2 H2SO4 + O2 A surplus input of 25% is assumed. The air emissions occurring from the process are estimated to 0.2% of the raw material input. The remaining amount of unreacted raw materials is assumed to leave the production process to 95% as a solid waste and to 5% in the wastewater. Further it is assumed that this wastewater is treated in an internal wastewater plant. The carbonate is dissolved in the water and not shown anymore in the dataset. Sodium and chloride are assumed to be neutralized within the waste water treatment plant, leading to emissions of Cl- and Na+ in the water outflow. Sodium dioxide will be reacted into sulphuric acid and therefore leads to emissions of SO42- in the water outflow.
technologyComment of magnesium production, electrolysis (RoW, IL): Electrochemical processes to make magnesium are based on salts containing chloride which can be found naturally or are transformed from other raw materials like serpentine, magnesite, bischofite or carnallite. The magnesium chloride salts are dried with various processes in order to receive anhydrous MgCl2. The raw material for magnesium production in this activity is an anhydrous carnallite (MgCl2-KCl). In the process, KCl represents the electrolyte. In the course of the MgCl2 decomposition, the KCl content increases until the (spent) electrolyte is partly pumped out and replaced with new carnallite. Finally, two by-products are produced: liquefied chlorine (Cl2) and KCl-rich salt (70% KCl). Magnesium oxide (MgO) is formed as an impurity during dehydration. Concerning the CO2/CO equilibrium in the calcination process, there are numerous reactions that take place in the chlorination chambers and the carbon can be consumed by reaction with MgO, air, water, sulfates and other impurities. Theoretically, the predominant reactions are those in which carbon dioxide is formed. Thus, it is assumed that the carbon is entirely converted to CO2. The CO2 emissions from graphite anode consumption are expected to contribute less than 1 % of the overall emissions and are neglected in the module. In practice, the off gases are not released to the atmosphere as is, as they are treated in wet alkali scrubbers. That is that some of the CO2 (be it from the reaction or from the ambient dilution air) is converted to calcium carbonate. The input of petroleum coke contributes less than 1 % to the overall GWP results and is excluded from this datasets for reasons of confidentiality. technologyComment of magnesium production, pidgeon process (CN): The Pidgeon process includes the following process steps: calcination, grinding & mixing, briquetting, reducion and refining. Coal as energy source is only used in for the calcination process. For other process steps, coke oven, semi coke oven, producer or natural gas are used. The use of these fuels is calculated according to the weighted average in terms of annual magnesium output per fuel. The production of producer (coal) gas is included in this module. A main influencing factor for the emissions from fuel combustion is the composition of the fuel itself. Due to the different origins of the fuel gases used in the Pidgeon process, the composition of the gases varies considerably. For semi coke and coke oven gas, a large variation in gas composition can be observed. As the data base for these compositions is restricted to few measurements, no statistical average can be determined.
technologyComment of chlor-alkali electrolysis, diaphragm cell (RER, RoW): In the diaphragm process, all reactions take place in only one cell. A diaphragm is used to separate the feed brine (anolyte) and the chlorine formed at the anode from the sodium hydroxide containing solution (catholyte) and the hydrogen formed at the cathode. Without the diaphragm being present during electrolysis, chlorine and hydrogen would form an explosive mixture and sodium hydroxide and chlorine would react to form sodium hypochlorite (NaOCl). Diaphragms used to be made from asbestos but up-todate technology allows for asbestos-free polymer-based diaphragms. Purified brine is fed to the anode compartment and percolates through the diaphragm into the cathode compartment. The percolation rate is controlled by a difference in liquid level between both compartments. At the anodes (metal oxide coated titanium), chlorine gas is formed which is collected and directed to further processing. Cathodes, where water decomposition takes place, are made of activated carbon steel. Catholyte leaving the cell, also called cell liquor, is a mixture of 10-12 wt.-% sodium hydroxide and 15-17 wt.-% sodium chloride in water. This solution is usually evaporated to 50 wt.-% NaOH. In this process, simultaneously most of the salt is removed by precipitation to a final residual of 1 wt.-%. The resulting salt is typically recirculated to brine preparation. The advantage of diaphragm cells is that the quality requirements for the brine and the electrical energy consumption are low. Disadvantageous are the high amount of thermal energy necessary for sodium hydroxide concentration and the comparably low quality of the produced sodium hydroxide and chlorine. References: Euro Chlor (2013) An Eco-profile and Environmental Product Declaration of the European Chlor-Alkali Industry, Chlorine (The chlor-alkali process). technologyComment of chlor-alkali electrolysis, membrane cell (CA-QC, RER, RoW): In the membrane cell process, the anode and cathode compartments are separated by a perfluoropolymer cation-exchange membrane that selectively transmits sodium ions but suppresses the migration of hydroxyl ions (OH-) from the catholyte into the anolyte. Saturated brine flows through the anode compartment, where chlorine gas is produced at the anode. The electric field in the electrolysis cell causes hydrated sodium ions to migrate through the membrane into the cathode compartment. The cathode compartment is fed with diluted sodium hydroxide solution. Water is electrolysed at the cathode releasing gaseous hydrogen and hydroxyl ions, which combine with the sodium ions and thus increase the concentration of sodium hydroxide in the catholyte. Typically, the outlet concentration of sodium hydroxide is around 32 wt.-%. A part of the product stream is diluted with demineralised water to about 30 wt.-% and used as catholyte inlet. In some units, a more diluted 23 wt.-% NaOH solution is produced. In these cases, the inlet concentration is adjusted to 20-21 wt.-%. Usually the NaOH solution is evaporated to the marketable concentration of 50 wt.-% using steam. Depleted brine leaving the anode compartment is saturated with chlorine and is therefore sent to a dechlorination unit to recover the dissolved chlorine before it is resaturated with salt for recirculation. The advantages of the membrane cell technique are the very high purity of the sodium hydroxide solution produced and the comparably low energy demand. Disadvantages comprise the high requirements on brine purity, the need for sodium hydroxide evaporation to increase concentration, and the comparably high oxygen content in the produced chlorine. In general, multiple cell elements are combined into a single unit, called electrolyser, of whom the design can be either monopolar or bipolar. In a monopolar electrolyser, the anodes and cathodes of the cells are connected electrically in parallel, whereas in the bipolar design, they are connected in series. Therefore, monopolar electrolysers require high current and low voltage, whereas bipolar electrolysers require low current and high voltage. Since bipolar systems allow higher current densities inside the cells, investment and operating costs are usually lower than for monopolar systems. References: Euro Chlor (2013) An Eco-profile and Environmental Product Declaration of the European Chlor-Alkali Industry, Chlorine (The chlor-alkali process). technologyComment of chlor-alkali electrolysis, mercury cell (RER, RoW): The mercury cell process comprises an electrolysis cell and a decomposer. Purified and saturated brine (25-28 wt.-% NaCl in water) is fed to the electrolysis cell on top of a film of mercury (Hg) flowing down the inclined base of the cell. The base of the cell is connected to the negative pole of a direct current supply forming the cathode of the cell. Anodes consisting of titanium coated with oxides of ruthenium and titanium are placed in the brine without touching the mercury film. At the anodes, chlorine gas is formed which is collected and directed to further processing. Due to a high overpotential of hydrogen at the mercury electrode, no gaseous hydrogen is formed; instead, sodium is produced and dissolved in the mercury as an amalgam (mercury alloy). The liquid amalgam is removed from the electrolytic cell and fed to a decomposer, where it reacts with demineralised water in the presence of a graphite-based catalyst to form sodium hydroxide solution and hydrogen. The sodium-free mercury is recirculated back into the cell. Cooling of hydrogen is essential to remove any water and mercury. The sodium hydroxide solution is very pure, almost free from chloride contamination and has usually a concentration of 50 %. Further treatment comprises cooling and removal of catalyst and mercury traces by centrifuges or filters. Advantages of the mercury cell process are the high quality of chlorine and the high concentration and purity of sodium hydroxide solution produced. The consumption of electric energy for electrolysis is, however, higher than for the other techniques and a high purity of the feed brine is required. Inherently, the use of mercury gives rise to environmental releases of mercury. References: Euro Chlor (2013) An Eco-profile and Environmental Product Declaration of the European Chlor-Alkali Industry, Chlorine (The chlor-alkali process).
technologyComment of silicon production, electronics grade (DE, RoW): In practice, EG-silicon is a product from complex chemical production plants. The conventional route for production of EG-silicon comprises three process steps: 1) the MG-silicon is converted into a gas, either trichlorosilane (SiHCl3) or silane (SiH4), 2) this gas is purified by means of distillation, 3) silicon in solid form is deposited in a Siemens reactor. Reference: Jungbluth N., Stucki M, and Frischknecht R. (2009) Photovoltaics. In Dones, R. (Ed.) et al., Sachbilanzen von Energiesystemen: Grundlagen für den ökologischen Vergleich von Energiesystemen und den Einbezug von Energiesystemen in Ökobilanzen für die Schweiz. ecoinvent report No. 6-XII, Swiss Centre for Life Cycle Inventories, Dübendorf, CH, 2009.
technologyComment of epoxy resin production, liquid (RER): Commercial epoxy resin can be produced by reacting bisphenol-A and epichlorohydrin in presence of a base catalyst (here represented by sodium hydroxide) (Guichon Valves n.d. and Pham and Marks 2005). Epoxy resins are in liquid form if n is from 0 to 1. When n is larger than 1 the resin in solid (Licare and Swanson, 2011). As the product here representes epoxy resin in liquid form, n is set to 1. 2C15H16O2 + 3C3H5ClO + 3NaOH -> C39H44O7 + 3Na+ + 3Cl- + 3H2O Pham, H.Q. and Marks, M.J. 2005. Epoxy Resins. In Ullmann's Encyclopedia of Industrial Chemistry, Electronic Release, Vol.13, pp.155-244. Wiley-VCH, Weinheim. Guichon Valves, n.d. Epoxy resins – Manufacturing process of Epoxy resins. Retrieved from: http://guichon-valves.com/faqs/epoxy-resins-manufacturing-process-of-epoxy-resins/, accessed 13th February 2017 For more information on the model please refer to the dedicate ecoinvent report, access it in the Report section of ecoQuery (http://www.ecoinvent.org/login-databases.html) The process is carried out in a reactor where a solution of sodium hydroxide is added (20 to 40% concentration). The product is brought to boiling temperature and a solvent is added. Solvents are not included in the inventory as it is assumed that solvents are closed-loop recycled. The unreacted epichlorohydrin is collected and recycled back into the system. The epoxy resin in then washed; this gives the final product in liquid form. Epoxy resin can also be produced in solid form. To do so, curing with, for example secondary amines, is necessary. Epoxy resins can have different characteristics, these depend on additional products that can be added to the liquid resin. The required characteristics depend on the final use of the product (Guichon Valves n.d.) This inventory representing production of a particular chemical compound is at least partially based on a generic model on the production of chemicals. The data generated by this model have been improved by compound-specific data when available. The model on production of chemicals is using specific industry or literature data wherever possible and more generic data on chemical production processes to fill compound-specific data gaps when necessary. The basic principles of the model have been published in literature (Hischier 2005, Establishing Life Cycle Inventories of Chemicals Based on Differing Data Availability). The model has been updated and extended with newly available data from the chemical industry. In the model, unreacted fractions are treated in a waste treatment process, and emissions reported are after a waste treatment process that is included in the scope of this dataset. For volatile reactants, a small level of evaporation is assumed. Solvents and catalysts are mostly recycled in closed-loop systems within the scope of the dataset and reported flows are for losses from this system. The main source of information for the values for heat, electricity, water (process and cooling), nitrogen, chemical factory is industry data from Gendorf. The values are a 5-year average of data (2011 - 2015) published by the Gendorf factory (Gendorf, 2016, Umwelterklärung, www.gendorf.de), (Gendorf, 2015, Umwelterklärung, www.gendorf.de), (Gendorf, 2014, Umwelterklärung, www.gendorf.de). The Gendorf factory is based in Germany, it produces a wide range of chemical substances. The factory produced 1657400 tonnes of chemical substances in the year 2015 (Gendorf, 2016, Umwelterklärung, www.gendorf.de) and 740000 tonnes of intermediate products. Reference(s): Hischier, R. (2005) Establishing Life Cycle Inventories of Chemicals Based on Differing Data Availability (9 pp). The International Journal of Life Cycle Assessment, Volume 10, Issue 1, pp 59–67. 10.1065/lca2004.10.181.7 Gendorf (2016) Umwelterklärung 2015, Werk Gendorf Industriepark, www.gendorf.de Licari, J.J. and Swanson, D.W. 2011. Chemistry, Formulation, and Properties of Adhesives. In Adhesives Technology for Electronic Applications (Second Edition), 2011
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