Sulfuric acid - Ryusan (English spelling)

Japanese: 硫酸 - りゅうさん（英語表記）sulfuric acid

Chemical formula: _H2SO4 , formula _weight : 98.1. It refers to the pure substance with the composition _H2SO4 or its aqueous _solution , but it is usually the aqueous solution. It is one of the most important strong acids in industry. Usually, an aqueous solution with a concentration of 90% or more is called concentrated sulfuric acid, and one with a concentration of less than 90% is called dilute sulfuric acid. Currently, most sulfuric acid produced in Japan is synthesized by the contact method (described below), in which impurities are thoroughly removed from the raw material sulfur dioxide before it is oxidized over a catalyst with air (to protect the catalyst). As a result, the product is of extremely high purity, and commercially available products usually have a concentration of 96%, a density of 1.84g/ ^cm3 , and 18mol/ ^dm3 . Oleum is made by dissolving sulfur trioxide in concentrated sulfuric acid.

[Kenichi Morinaga and Katsunori Nakahara]

history

Sulfur and alum have been known since ancient times, so sulfuric acid may have been used in some form, but the manufacturing method first appeared in history around the 8th century, when the Arab Geber (Jabir bin Hayyan) is said to have made it by dry distilling alum. Around the 15th century, it was discovered that sulfur trioxide could be obtained by burning sulfur with saltpeter, and in the 18th century, a factory was built in England that burned this mixture in a glass vessel to produce sulfuric acid in the vessel. Later, a lead chamber was used instead of glass, and the sulfur combustion furnace was separated from the lead chamber. In the 19th century, improvements were made, and cheap pyrite came to be used instead of sulfur, nitrogen oxides were recovered in the Gay-Lussac Tower (1827), and denitrification of the recovered nitrate-containing sulfuric acid (sulfuric acid containing nitrogen oxide) was carried out in the Glover Tower (1859), and the basic lead chamber type sulfuric acid manufacturing method was completed. It further developed into the so-called tower type manufacturing method that does not use a lead chamber (1909), and the nitric acid type manufacturing method was completed. However, these methods are no longer used today, as they have been replaced by contact methods. In 1831, it was discovered that sulfur trioxide could be produced from sulfur dioxide and oxygen using platinum asbestos as a catalyst, but industrialization was delayed because the catalytic ability of platinum was easily lost due to impurities. Later, industrialization was successful in England using refined sulfur dioxide (1881), and large-scale industrialization progressed toward the beginning of the 20th century with the development of the dye industry. In 1924, vanadium catalysts were invented, and they developed rapidly due to their advantages of being cheaper and less susceptible to poisoning than platinum. Currently, contact sulfuric acid manufacturing methods using vanadium catalysts are mainstream, and nitric acid manufacturing methods are no longer used at all. In Japan, the lead-chamber method was adopted at the Osaka Mint in 1872 (Meiji 5) because it was necessary for smelting gold and silver bullion, and the contact method was first used at the Hiratsuka Gunpowder Factory in 1905 (Meiji 38).

[Kenichi Morinaga and Katsunori Nakahara]

Manufacturing method

Dissolving sulfur trioxide in water produces sulfuric acid. In the laboratory, sulfur trioxide can be produced by decomposing iron(III) sulfate hydrate, oleum, or sodium disulfate by heating.

Industrial sulfuric acid manufacturing methods are broadly divided into two types: the nitric acid manufacturing method, in which sulfur dioxide is generated by burning sulfur or sulfide ores, and then nitrogen oxide gas is mixed in as a catalyst to cause an oxidation reaction to produce sulfuric acid, and the contact manufacturing method, in which thoroughly purified and dried sulfur dioxide is heated to over 400°C and catalytically oxidized with a catalyst such as vanadium oxide (V) to produce sulfuric acid from the resulting sulfur trioxide. Both methods are the same up to the point of producing sulfur dioxide.

Sulfur dioxide is produced by roasting sulfur or pyrite in excess air in a roasting furnace. There are various types of roasting furnaces, including sulfur furnaces and fluidized bed roasting furnaces. In addition, smelting waste gas (roaster gas from ores produced during the smelting of copper, zinc, lead, etc.) has a relatively low concentration of sulfur dioxide, but the amount is large and causes smoke pollution problems, so research has been conducted into how to utilize it and it is used as a raw material for sulfuric acid production. In ores with high contents of ore dust, arsenic, selenium, etc., there is a risk that these oxides will sublimate and be mixed into the gas emitted from the roasting furnace. In particular, in the contact type, the raw gas needs to be purified, and this is done using cooling, washing, and electrostatic precipitators. Please refer to Figure B for the contact type sulfuric acid production process.

[Kenichi Morinaga and Katsunori Nakahara]

Nitric acid sulfuric acid manufacturing method

In the past, the lead-chamber method was used, with several lead chambers placed between the Glover and Gay-Lussac towers, but today only a few Petersen towers, a tower-type production method that does not use lead chambers, are in operation. The resulting nitrosyl hydrogen sulfate is hydrolyzed to produce nitrous acid and sulfuric acid. In the actual reaction, it is believed that most of the oxidation reaction of sulfur dioxide takes place in the nitrosyl hydrogen sulfate. See Figure A for the reaction of sulfuric acid production using the nitric acid method. The resulting sulfuric acid has a low concentration (less than 80%), so it is used for fertilizer production, etc.

The contact sulfuric acid manufacturing method has higher purity and concentration than the nitric acid method, and is suitable for producing refined sulfuric acid and fuming sulfuric acid. Since impurities contained in the roaster gas weaken the effect of the catalyst and shorten its lifespan, the focus is on gas purification. The dust-removed gas is cooled, washed with dilute sulfuric acid, dried with concentrated sulfuric acid, and then introduced into a converter where an oxidation reaction occurs using _vanadium oxide (V) ( _V2O5 - _K2SO4 - _SiO2 _system ) catalyst. Sulfur dioxide is almost completely oxidized to sulfur trioxide.

_2SO2 + _O2 - → _2SO3
If sulfur trioxide is directly absorbed into water, it will come into contact with water vapor and produce a sulfuric acid mist, making it difficult to recover the sulfur trioxide. Since sulfuric acid has the lowest vapor pressure at a concentration of 98.3%, sulfur trioxide is absorbed into 98% sulfuric acid to produce fuming sulfuric acid or 100% sulfuric acid, the concentration of which is adjusted with dilute sulfuric acid and water from the gas absorption tower, and some of it is used as a product and some is recycled and used to absorb sulfur trioxide.

[Kenichi Morinaga and Katsunori Nakahara]

nature

Pure sulfuric acid is a colorless, viscous oily liquid. When a small amount of water is added, its specific gravity increases, but when a large amount of water is added, it gradually decreases (see table for changes in specific gravity of sulfuric acid). It dissolves many inorganic and organic substances, and when heated, it begins to decompose at 290°C, generating sulfur trioxide ( _SO3) . 98.3% sulfuric acid is an azeotropic mixture with a maximum boiling point of 338°C. When concentrated sulfuric acid is mixed with water, a large amount of heat is generated. The heat generated increases with the concentration of sulfuric acid, with the calorific value per kilogram being 39 kcal at 61.25%, 193 kcal for pure sulfuric acid, and 486 kcal for 100% sulfur trioxide. It forms hydrates with water, such as monohydrate (colorless, melting point 8.6°C, boiling point 290°C) and dihydrate (colorless, melting point -39°C, boiling point 167°C). See Figure C for the phase diagram (melting point) of sulfuric acid.

Sulfuric acid not only bonds strongly with water, but also has a dehydrating effect, removing hydrogen and oxygen atoms from various compounds in a ratio of _H2O . This action liberates carbon from many organic substances. For example, pouring concentrated sulfuric acid onto carbohydrates such as sugar will cause them to generate heat and decompose, leaving only carbon behind. In addition, because it is highly hygroscopic, it is used as a drying agent by placing it in a desiccator. Sulfuric acid is a dibasic acid, and its aqueous solution ionizes in two stages, making it highly acidic.

_H2SO4H ⁺ ⁺ _HSO4-
_HSO4 ^- H ⁺ ⁺ _SO42-
In dilute solutions, the first stage of ionization is complete, but the second stage ionization constant is 0.02 (18°C). The degree of ionization is 51% at 1N and 59% at 0.1N, making it a slightly weaker acid than hydrochloric acid and nitric acid. Dilute sulfuric acid reacts with zinc and iron to generate hydrogen, but does not react with copper or silver. Concentrated sulfuric acid has an oxidizing effect, and hot concentrated sulfuric acid in particular oxidizes metals that do not dissolve in dilute sulfuric acid (except gold and platinum), as well as carbon and sulfur. Concentrated sulfuric acid and fuming sulfuric acid react with organic matter to produce sulfonic acid, and mixtures with concentrated nitric acid (mixed acids) are used to nitrate organic compounds. Its effect on iron and lead is unique. Iron is used in transport tanks because concentrated sulfuric acid creates an insoluble film that protects the inside (passive state). On the other hand, lead is insoluble in dilute sulfuric acid (75% or less), but dissolves in concentrated sulfuric acid, especially at higher temperatures. Sulfates include normal _salts _M2SO4 and acid salts _MHSO4 . Most sulfates are soluble in water, but sulfates of alkaline earth metals and lead salts are poorly soluble.

[Kenichi Morinaga and Katsunori Nakahara]

Applications

The consumption of sulfuric acid has traditionally been said to be a barometer of the level of a country's chemical industry, and its uses are so wide that it is no exaggeration to say that there is no product that is not related to sulfuric acid. In Japan, approximately 6.38 million tons were produced in 2013 on a 100% conversion basis. Domestic demand for sulfuric acid is 16% for fertilizer, 11% for fiber, 27% for inorganic chemicals, and 46% for other uses (2013).

Its uses are classified as follows:

(1) Products that use sulfuric acid directly as a raw material and contain sulfuric acid in the product: Ammonium sulfate, superphosphate, metallic sulfates such as sodium and potassium, alum, and dimethyl sulfate.

(2) Products that utilize the chemical reactivity of sulfuric acid but do not contain sulfuric acid: wet phosphoric acid, hydrochloric acid, acetic acid, copper and other metal smelting, phenol, synthetic fibers such as nylon and vinylon, various dyes and intermediates.

(3) Oxidation promoters: aldehydes, quinones, organic sulfides, etc.

(4) Generation of hydrogen as a reduction agent.

(5) Nitration auxiliaries: Nitrobenzene, nitrocellulose, TNT and other explosives.

(6) Use of dehydration: Production of ether from alcohol, gas drying.

(7) Applications of acidity: Production of halogens, etc.

(8) Applications of corrosive properties: Removing rust from iron, brass, bronze, and silver.

(9) Catalysts: Production of various esters such as acetate esters.

(10) For refining or cleaning: Petroleum refining, cleaning of oils and fats.

(11) Others: For storage batteries, disinfectants, insecticides, preservatives, chemical analysis reagents.

Concentrated sulfuric acid has a strong dehydrating and corrosive effect, so be careful not to let it come into contact with your skin or clothing. If it does get on your skin or clothing, wash it off with a large amount of water or dilute ammonia water. Even dilute sulfuric acid will fall apart if left on clothing. The permissible concentration for the human body as vapor is 1 mg/m ³ .

[Kenichi Morinaga and Katsunori Nakahara]

Nitric acid-based sulfuric acid production reaction (Fig. A)
©Shogakukan ">

Nitric acid-based sulfuric acid production reaction (Fig. A)

Contact sulfuric acid production process (Fig. B)
©Shogakukan ">

Contact sulfuric acid production process (Fig. B)

Phase diagram of sulfuric acid (melting point) [Figure C]
©Shogakukan ">

Phase diagram of sulfuric acid (melting point) [Figure C]

Change in specific gravity of sulfuric acid [Table]
©Shogakukan ">

Change in specific gravity of sulfuric acid [Table]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

化学式H₂SO₄、式量98.1。組成H₂SO₄の純物質あるいはその水溶液をいうが、普通は水溶液をさすことが多い。工業上もっとも重要な強酸の一つ。通常、水溶液濃度が90％以上のものを濃硫酸といい、90％未満の濃度のものを希硫酸といっている。現在、日本で生産されている硫酸はほとんどが接触法（後述）によって合成されたもので、原料とする二酸化硫黄の不純物を十分に除去してから（触媒の保護のため）触媒上で空気酸化を行う。そのため得られるものはきわめて純度が高いものであり、市販品は濃度96％、密度1.84g/cm³、18mol/dm³のものが普通である。濃硫酸にさらに三酸化硫黄(いおう)を溶かしたものが発煙硫酸である。

［守永健一・中原勝儼］

歴史

硫黄やミョウバンは古くから知られていたから、硫酸もなんらかの形で用いられたかもしれないが、その製法が歴史に初めて登場したのは8世紀ごろで、アラビア人ゲーベル（ジャービル・ビン・ハイヤーン）がミョウバンを乾留してつくったと伝えられている。15世紀ごろ硫黄を硝石とともに燃やして三酸化硫黄が得られることがわかり、18世紀にはイギリスで、ガラス器を用いてこの混合物を燃焼、器内で硫酸を製造する工場がつくられた。その後、ガラスのかわりに鉛室が用いられ、硫黄の燃焼炉が鉛室から分離された。19世紀になると改良が進み、硫黄のかわりに安価な硫化鉄鉱が用いられるようになり、ゲイ・リュサック塔で窒素酸化物が回収され（1827）、グラバー塔で回収含硝硫酸（酸化窒素を含む硫酸）の脱硝が行われるようになり（1859）、鉛室式硫酸製造法の基本ができあがった。さらに、鉛室を用いない、いわゆる塔式製造法へと発展し（1909）、硝酸式製造法が完成した。しかし、これらの方法は現在では接触式にとってかわられており、行われていない。1831年、白金石綿を触媒として二酸化硫黄と酸素から三酸化硫黄を生成することがみつけられたが、不純物により白金の触媒能が失われやすいため工業化は遅れた。その後、精製した二酸化硫黄を用いてイギリスで工業化に成功し（1881）、染料工業の発展とともに20世紀の初めごろ大規模な工業化が進んだ。1924年バナジウム触媒が発明され、白金に比べて安価、毒作用を受けにくい利点のため急速に発達し、現在ではバナジウム触媒を用いる接触式硫酸製造法が主流となっており、硝酸式製造法はすべて行われなくなっている。日本では1872年（明治5）金銀地金の製錬に必要なため大阪造幣寮で鉛室式が採用され、接触式は1905年（明治38）平塚火薬製造所で初めて用いられた。

［守永健一・中原勝儼］

製造法

三酸化硫黄を水に溶かすと硫酸が得られる。三酸化硫黄の製造は、実験室的には硫酸鉄(Ⅲ)水和物、発煙硫酸、二硫酸ナトリウムなどを加熱分解する方法が用いられる。

　工業的硫酸製造法は、硫黄、硫化鉱などを燃焼させて二酸化硫黄を発生させ、一種の触媒として酸化窒素の気体を混ぜ、酸化反応をおこして硫酸を得る硝酸式製造法と、十分に精製・乾燥した二酸化硫黄を400℃以上に加熱して、酸化バナジウム(Ⅴ)などの触媒による接触酸化を行って得た三酸化硫黄から硫酸をつくる接触式製造法とに大別される。いずれの方法においても二酸化硫黄の製造までは共通である。

　二酸化硫黄の発生には、焙焼(ばいしょう)炉を用いて硫黄、硫化鉄鉱を過剰の空気中で焙焼する。焙焼炉には硫黄炉、流動焙焼炉など、いろいろな形式がある。また、製錬廃ガス（銅、亜鉛、鉛などの製錬に際して発生する鉱石の焙焼炉ガス）も、二酸化硫黄の濃度は比較的低いが量が多く煙害問題をおこすので、その利用法が研究され、硫酸製造の原料として使われている。焙焼炉から出るガス中には、鉱塵(こうじん)やヒ素、セレンなどの含有量の高い鉱石ではこれらの酸化物が昇華して混入するおそれがある。とくに接触式では原料ガスの精製が必要であり、冷却、洗浄、電気集塵装置などを用いて精製が行われる。接触式硫酸製造工程については図Bを参照されたい。

［守永健一・中原勝儼］

硝酸式硫酸製造法

以前は、グラバー塔とゲイ・リュサック塔の間に数個の鉛室を配置した鉛室式が行われたが、現在では鉛室を用いない塔式製造法のペターゼン塔式がわずかに操業されているだけである。生成した硫酸水素ニトロシルが加水分解されて、亜硝酸と硫酸を生成する。実際の反応では、二酸化硫黄の酸化反応の大部分は硫酸水素ニトロシル中で進むものと考えられている。硝酸式硫酸製造の反応については図Aを参照されたい。得られる硫酸は濃度が低い（80％以下）ため、肥料の製造用などに使われる。

　接触式硫酸製造法は、硝酸式に比べて純度や濃度が高く、精製硫酸や発煙硫酸の製造に適している。焙焼炉ガス中に含まれる不純物は、触媒の効果を弱め寿命を短くするので、とくにガスの精製に重点を置き、除塵したガスを冷却して希硫酸で洗浄し、濃硫酸で乾燥したのち転化器に導き、酸化バナジウム(Ⅴ)（V₂O₅-K₂SO₄-SiO₂系）触媒により酸化反応をおこさせる。二酸化硫黄はほとんど完全に三酸化硫黄に酸化される。

　　2SO₂＋O₂―→2SO₃
三酸化硫黄を直接に水に吸収させると、水蒸気に触れて硫酸の霧を生じ、三酸化硫黄の回収が困難となる。硫酸は濃度98.3％で蒸気圧が最低となるので、三酸化硫黄を98％硫酸に吸収させて発煙硫酸や100％硫酸をつくり、これをガス吸収塔からの希硫酸や水で濃度を調節し、一部を製品とし、一部は循環させて三酸化硫黄の吸収用に用いる。

［守永健一・中原勝儼］

性質

純硫酸は無色、粘性のある油状液体である。少量の水が加わると比重はかえって増加するが、多量の水が加わるとしだいに減少する（硫酸の比重変化については表を参照されたい）。多くの無機・有機物を溶かし、熱すれば290℃で分解し始め、三酸化硫黄SO₃を発生する。98.3％硫酸は共沸混合物で最高沸点338℃を示す。濃硫酸を水と混ぜると多量の熱を発生する。発生熱は硫酸の濃度が増すにつれて大きくなり、1キログラム当りの発熱量は61.25％のとき39キロカロリー、純硫酸では193キロカロリー、100％三酸化硫黄で486キロカロリーである。水との間に一水和物（無色、融点8.6℃、沸点290℃）や二水和物（無色、融点－39℃、沸点167℃）などの水和物をつくる。硫酸の状態図（融点）については図Cを参照されたい。

　硫酸は水と激しく結合するだけでなく、種々の化合物中の水素原子と酸素原子をH₂Oの割合で奪う、いわゆる脱水作用がある。多くの有機物はこの作用により炭素を遊離する。たとえば、砂糖などの炭水化物に濃硫酸を注ぐと激しく発熱して分解し、炭素のみを残す。また、吸湿性が強いので、デシケーターに入れて乾燥剤として用いられる。硫酸は二塩基酸で、水溶液は二段階に電離して強酸性を示す。

　　H₂SO₄H⁺＋HSO₄^-
　　HSO₄^-H⁺＋SO₄^2-
希薄溶液で第一段の電離は完全に進行するが、第二段の電離定数は0.02（18℃）である。電離度は1規定で51％、0.1規定で59％であり、酸としては塩酸、硝酸よりやや弱い。希硫酸は亜鉛、鉄などと反応して水素を発生するが、銅、銀などとは反応しない。濃硫酸は酸化作用があり、とくに熱濃硫酸は希硫酸に溶けない金属（金、白金以外）のほか、炭素、硫黄を酸化する。濃硫酸や発煙硫酸は有機物と反応してスルホン酸をつくり、濃硝酸との混合物（混酸）は有機化合物のニトロ化に使われる。鉄と鉛に対する作用は特異的である。鉄は濃硫酸により不溶性の皮膜をつくって内部が保護される（不動態）ので、輸送用タンクに用いられる。一方、鉛は希硫酸（75％以下）に不溶だが濃硫酸に溶け、とくに温度が高いほどその傾向が強い。硫酸塩には正塩M₂SO₄と酸性塩MHSO₄がある。硫酸塩の多くは水に溶けるが、アルカリ土類金属の硫酸塩や鉛塩などは難溶性である。

［守永健一・中原勝儼］

用途

硫酸の消費量は、従来一国の化学工業水準のバロメーターといわれるほどで、その用途は広く、硫酸に関係のない製品はないといってもいいすぎではない。日本では2013年に100％換算で約638万トン製造されている。また、硫酸の国内需要は肥料16％、繊維11％、無機薬品27％、その他46％となっている（2013）。

　その用途は次のように分類される。

(1)硫酸を直接の原料として用い、製品中に硫酸分を含むもの　硫酸アンモニウム、過リン酸石灰、ナトリウムやカリウムなどの金属の硫酸塩、ミョウバン、硫酸ジメチル。

(2)硫酸の化学反応性を利用するが、製品中に硫酸分を含まないもの　湿式リン酸、塩酸、酢酸、銅などの金属製錬、フェノール、ナイロンやビニロンなどの合成繊維、各種の染料および中間物。

(3)酸化助剤用　アルデヒド、キノン、有機硫化物など。

(4)還元助剤用　水素の発生。

(5)ニトロ化助剤用　ニトロベンゼン、ニトロセルロース、TNTその他の火薬。

(6)脱水性の利用　アルコールからのエーテル製造、ガス乾燥。

(7)酸性の応用　ハロゲンなどの製造。

(8)侵食性の応用　鉄・黄銅・青銅・銀のさび落とし。

(9)触媒　酢酸エステルなど各種エステルの製造。

(10)精製または洗浄用　石油精製、油脂の洗浄。

(11)その他　蓄電池用、殺菌剤、殺虫剤、防腐剤、化学分析試薬。