MANUFACTURING PLANT

Nicolò Del Ponte

Production history

The SAICI industrial complex was established with the aim of meeting the strong market demand at the time for rayon and cellulose through Italian-based production. The company was built on land acquired starting in 1937, whose expansion reached 5,300 hectares by 1942, in an area crossed by the Aussa and Corno rivers, important navigable routes for maritime transport [1].

At that time, Italy lacked sufficient forest resources to support such production, particularly coniferous trees, which were the traditional raw material for producing cellulose and artificial fibers and therefore had to be imported from northern regions. For this reason, a decision was made to cultivate an annual plant, namely giant reed (Arundo donax) [2], which led to the creation of an agro-industrial complex. This was later integrated with a poplar cultivation program, as well as attempts to use other types of wood such as various species of eucalyptus [3]. From an industrial perspective, the company later expanded by implementing a plant for the production of caprolactam, the raw material for lilion, and another for sulfuric acid to supply it, as well as introducing the production of semi-chemical pulp through a new monosulfite process [4].

The original production of textile cellulose from reed involved a modified bisulfite process developed by SNIA Viscosa [5], which, once expanded, reached a theoretical production of over 100,000 tons per year. This was achieved through the use of a plant for producing raw and bleached semi-chemical pulp, an electrochemical plant for producing chlorine, caustic soda, hypochlorite, and hydrochloric acid, and finally a thermoelectric power plant generating energy through the combustion of coal, fuel oil, and spent bisulfite liquor from cellulose cooking [6]. In addition, complementary facilities were built, such as one for producing chlorine dioxide and another for concentrating the spent liquor from cellulose production for combustion. The latter process took place in an evaporation plant where, by passing into a vacuum tank, it was also possible to recover the sulfur dioxide dissolved in the liquor for reuse in the main process.

Despite earlier attempts to revolutionize the plant-based raw material, the factory’s production ultimately consisted mainly of cellulose obtained from various imported hardwoods. Wood consumption amounted to around 700,000 stacked cubic meters per year, along with 80,000 tons of coal annually for steam production in the thermal power plant, and respectively 30,000 and 20,000 tons per year of pyrite and limestone, essential for the industrial process [7].

Type of Risk

Cellulose production

The production process began with transporting the raw plant material to a cutting facility, where it was debarked and reduced into chips, producing 90 tons per hour. This was followed by the cooking process, carried out in large digesters where, under specific temperatures and pressures, raw pulp was obtained through treatment with an acidic calcium bisulfite solution (from 1964, sodium sulfite was introduced for the production of semi-chemical pulp, followed by a refining phase). This process dissolved non-cellulosic substances, while the crude cellulose could be washed from the accompanying liquor (which would later be concentrated and burned) and subjected to mechanical (sorting) and chemical treatments, namely chlorination, purification, and bleaching, producing up to 35,000 tons per year of raw or bleached pulp [8].

It was precisely in these chemical treatments that caustic soda, chlorine, hydrochloric acid, sodium hypochlorite, and chlorine dioxide—produced directly at the plant—were used. Unlike the other compounds synthesized in the soda and chlorine production plant, chlorine dioxide was obtained by reacting sulfur dioxide with a sodium chlorate solution in the presence of sulfuric acid. Sulfur dioxide was required at various stages within the factory: primarily for cellulose production, but also for preparing calcium bisulfite liquor, semi-chemical pulp, and neutral sodium sulfite; it was produced through the roasting of pyrites.

At the end of all treatments, the cellulose was pressed into sheets and dried. These sheets were then cut into standard sizes to form bales ready for shipment for subsequent processing into textile fibers.

Soda and chlorine production

The plant was capable of producing 42,000 tons per year of electrolytic soda, 37,000 tons per year of liquid chlorine, and 12 million cubic meters of hydrogen (later used for caprolactam production) through the following reaction [9]:

2 NaCl (aq) + 2 H₂O (l) → 2 NaOH (aq) + Cl₂ (g) + H₂ (g)

In particular, this production was carried out using mercury flowing cathode cells, where the raw material was rock salt (mined sodium chloride) from Sicily, with an annual consumption of 70,000 tons. The strong direct electric current applied to the aqueous sodium chloride solution in the electrolysis cells enabled its decomposition, yielding the products listed above.

Part of the chlorine and hydrogen produced during electrolysis was then used to produce hydrochloric acid and sodium hypochlorite, while excess chlorine was dried and liquefied to be sold on the European market.

Caprolactam production

Alongside the large market for cellulose-based artificial fibers, there was also significant growth in fully synthetic fibers obtained through chemical synthesis. Following the success of SNIA Viscosa’s polyamide fiber, lilion, it was decided to establish in Torviscosa a facility to produce its necessary raw material: caprolactam. This decision was also supported by the possibility of using hydrogen recovered from the plant’s electrolysis facilities producing soda and chlorine. The caprolactam production process involved the use of hydrogen and toluene, a widely available and low-cost product of the petroleum industry, leading to a production capacity of over 10,000 tons per year.

Specifically, the production steps included the oxidation of toluene with air in the presence of a catalyst to form benzoic acid (from which benzaldehyde was also recovered by rectification), followed by catalytic hydrogenation to hexahydrobenzoic acid and its reaction with nitrosylsulfuric acid to obtain a caprolactam solution. This solution was then neutralized with ammonia, and the caprolactam was extracted and distilled. Once purified, it was ready for market, along with other by-products such as ammonium sulfate (usable as a nitrogen fertilizer), benzoic acid, and nitrous compounds [10].

Among the raw materials required for the various steps were therefore toluene, ammonia, and sulfuric acid [11]. The latter was produced in Torviscosa in a plant annexed to the caprolactam facility, which used sulfur from pyrites and also included a plant for producing oleum (a mixture of sulfur trioxide in sulfuric acid, also used as an alternative in caprolactam production).

1. Cfr. Mareno Settimo, Torviscosa 1940. Progetti e realizzazioni, speranze e fallimenti, truffe e soprusi nel nome dell’autarchia. Torviscosa, Gruppo Consiliare Mareno Settimo, 2020, p. 135.
2. Cfr. Franco Marinotti, Il problema della cellulosa nobile italiana: la realizzazione di Torre di Zuino. «La chimica», XV (1939), n. 2, pp.74-77.
3. Cfr. SNIA Viscosa, Gruppo SNIA Viscosa. Milano, Istituto grafico Bertieri, 1949.
4. Cfr. Torviscosa. Saici Snia Viscosa. Milano, Pan, 1967.
5. Cfr. Archivio Storico SNIA (d’ora in oi ASS), fasc. 107, brevetto n. 344761 «Procedimento di preparazione di cellulosa di grande purezza per raion e per esplosivi (nitro cellulosa) a partire da steli e foglie di piante annuali in particolare da steli e foglie di canna comune (Arundo donax) e di cascami agricoli». Vedi anche Settimo, Torviscosa1940 cit, p. 45.
6. Cfr. Archivio Storico Comune di Torviscosa (d’ora in poi ASCT), Controllo ambientale, Stabilimenti industriali: osservanza delle norme in materia di edilità, b. 1, fasc. 2, «Relazione tecnica sui cicli di lavorazione degli stabilimenti di Torviscosa», 1° dicembre 1976.
7. ASS, Santamaria, Business plan Torviscosa, 1973.
8. ASCT, Controllo ambientale, Stabilimenti industriali: osservanza delle norme in materia di edilità, b. 1, fasc. 2, «Relazione tecnica sui cicli di lavorazione degli stabilimenti di Torviscosa», 1° dicembre 1976.
9. Ibidem.
10. Ibidem.
11. ASCT, Controllo ambientale, Stabilimenti industriali: osservanza delle norme in materia di edilità, b. 1, fasc. 3, Lettera del 13 dicembre 1976.