Sodium silicate: Production route
Furnace glass or pressure cooker: two ways to make it
What this tab covers How it is made: the main production routes or, for product families, the main product types and technologies, compared on share of supply, inputs per tonne, plant scale, yield, co-products and unit cost.Two routes make sodium silicate. The furnace route melts sand and soda ash into glass, which is dissolved or sold solid; it suits high-ratio neutral grades and large volumes. The hydrothermal route dissolves sand directly in caustic soda in an autoclave at about 150-200 C; it uses less heat and suits alkaline, lower-ratio grades, but depends on caustic soda prices. Metasilicates and powdered grades are made by further processing. Choice depends on the relative cost of soda ash, caustic soda and fuel.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| Furnace route (soda ash plus sand) | majority of world capacity (indicative) | about 0.77 t sand, 0.40 t soda ash, about 4-6 GJ natural gas per t glass at ratio 3.3 (indicative) | furnaces of 50-200 kt/yr (indicative) | near 100% on silica | CO2 from soda ash about 0.17 t per t glass | soda ash about $120-160/t of glass at $300-400/t soda ash (indicative) |
| Hydrothermal route (caustic soda plus sand) | minority (indicative) | about 0.3 t NaOH (100%) and 0.7 t sand per t solids at lower ratios (indicative) | 10-100 kt/yr (indicative) | high; limited to ratio about 2.5-2.8 (indicative) | none material | caustic dominated; competitive when caustic is in surplus (indicative) |
| Solid and specialty grades (powder, metasilicate, granular) | small (indicative) | solution plus drying energy | small | high | none | drying adds cost (indicative) |
How each route works
Furnace route (soda ash plus sand)Sand and soda ash are melted in a regenerative tank furnace similar to a glass furnace. The glass is tapped, cooled into lumps, then dissolved under steam pressure. Most large producers (PQ, Qemetica, BASF, Nippon Chemical) run furnaces.
Lowest cost for neutral grades; high-temperature fuel use and process CO2.
Stoichiometry; indicative Hydrothermal route (caustic soda plus sand)Ground sand is reacted with 30-50% caustic soda in a pressure vessel. No glass is made, so no high-temperature melting is needed. Common where caustic soda is cheap, for example next to chlor-alkali plants.
Low energy and no process CO2 on site; depends on caustic soda and its electricity footprint.
Indicative Solid and specialty grades (powder, metasilicate, granular)Solutions are spray-dried or the glass is ground to powder; sodium metasilicate is crystallised from low-ratio solutions for industrial cleaners and detergents.
Higher value; extra energy.
Indicative Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.