Desiccant - Desi Pak Bentonite Clay

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Bentonite clay is an abundant and naturally-occurring mineral that results from the weathering and sedimentation of volcanic ash deposits. Its principal ingredient is calcium montmorillonite, a highly adsorbent, chemically inert and non-corrosive substance. When mined from the ground, then processed and dried into the form of free-flowing granules, bentonite clay attracts and binds water vapor readily within its complex and highly layered structure, making it a highly effective desiccant.

Silica gel is a synthetic material, a highly porous form of amorphous silicon dioxide that is typically produced in the form of transparent beads, about 2-3 mm in size. Silica gel adsorbs water vapor in an internal network of random, intersecting channels of various diameters. Silica gel is manufactured on a large scale through a multi-step chemical process. The current primary global source for silica gel is China, so silica gel desiccants are generally shipped worldwide in bulk or individual package form.

Packaging engineers responsible for ensuring the quality and shelf life of packaged products face a range of considerations when it comes to sourcing the desiccant that is right for their applications.  Desi Pak bentonite clay desiccants are used to protect products from moisture damage during shipping or storage such as:

• automobile parts
• aviation
• canned and bottle foods and drinks
• foods
• electronics
• electronic components (example: surface mount devices, integrated circuits, circuit boards, capacitors and resistors) used in dry pak per JEDEC J-STD-033
• engines
• textiles
• leather goods
• metals
• machinery

In terms of their capabilities and performance as desiccants, bentonite clay and silica gel have numerous similarities. Both are highly adsorbent materials. This means that even at full water vapor capacity, both remain dry and free-flowing, without any apparent change in size, shape or texture. And, both of these desiccants can be “reactivated” by oven-drying them to remove retained water vapor between uses.

They are also quite similar in terms of “unit” weight and relative adsorption performance. Desiccants are measured in “units” according to military and industry specifications including MIL-D-3464 (U.S), DIN 55473 (Germany) and AFNOR NF H00-321 (France). The MIL and DIN specifications define a unit as the amount of desiccant that will, at a temperature of 25° C, adsorb 3 g of water vapor at 20% relative humidity and 6 g of water vapor at 40% relative humidity. By this standard, a unit of bentonite clay desiccant weighs about 33 grams, while a unit of silica gel weighs about 26 grams. Both will adsorb water vapor equivalent to between 30 and 40 percent of their unit weight. (Note: the AFNOR NF H00-321 specification defines a desiccant unit with 100 g moisture adsorption.)

Although the adsorption properties of bentonite clay and silica gel desiccants are comparable on a unit for-unit basis, tests show that bentonite clay offers higher adsorption capacity in the most common and relevant package conditions. The adsorption capacity of bentonite is substantial at low humidity levels and increases with increasing relative humidity. Silica gel behaves similarly, but becomes even more adsorbent at higher levels of relative humidity. At these higher humidity levels, its very high rate of adsorption can, at times, make silica gel more difficult to handle.

• It is abundant and naturally occurring.
• Once mined, its production and processing require no chemical processing and use no chemical additives or solvents.
• Its carbon footprint is small: only a comparatively modest amount of energy is consumed by the equipment required to mine, extrude, dry, and sort bentonite clay for packaging. Clariant is continuously working to reduce the amount of energy consumed even further. For example, through the use of sun drying.
• The global availability of bentonite clay assures an uninterrupted supply, while numerous sites for regional production worldwide reduce the carbon footprint associated with transporting this desiccant to market anywhere in the world.

Clariant manufactures a complete line of bentonite clay desiccants, trade-named Desi Pak. All Desi Pak ingredients are sourced by Clariant. The process begins with the exploration needed to identify and acquire top-grade bentonite clay deposits, through to the mining (extraction) process, and even to the reclamation/restoration process for areas where our mining is complete. Our commitment to ecological sustainability is clear: Clariant will restore and recultivate all bentonite mining areas to an equal or better state than when our operations began.

Following extraction at some 40 bentonite mining sites globally, bentonite clay is transported to one of the three Clariant production facilities that produce Desi Pak desiccants to meet demanding internal and global standards of quality.

Though bentonite clay is abundant and readily available, Clariant selects and uses only top grades of bentonite clay that meet demanding adsorption requirements. After locating these top-grade deposits, Clariant manages all aspects of mining and processing this mineral into desiccants at numerous sites worldwide.

Generally, desiccant-quality bentonite clay is found in deposits that are in the top about 40 feet (10 m) of the earth’s crust. To obtain the mineral, Clariant conducts surface mining operations that expose and extract the mineral. When the deposit is exhausted, Clariant manages the reclamation and recultivation of the mined site to its own high environmental and ecological sustainability standards.

After mining, bentonite clay is transported to a Clariant desiccant processing facility. There, the bentonites is processed into a high-performance desiccant material. It is put through a mechanical process of extrusion, dried to a suitable moisture content and then graded (by screening) into finely granulated material of uniform size, ready for packaging.

The production of silica gel desiccant involves a far more complex, multi-step process. The process begins with a raw material, sand, plus sodium carbonate, a chemical feedstock. These are combined in an energy intensive furnace or hydrothermal process, followed by additional processing, to produce an intermediate material—sodium silicate. The sodium silicate is then combined with sulfuric acid in a reaction vessel to produce sodium sulfate and amorphous silica gel. Following removal of the sodium sulfate and process effluent and subsequent extensive washing, the remaining silica gel is ready for processing into desiccant material. It is washed down with water to a desired conductivity level, heat dried to a moisture content of 3% or less, and then graded prior to packaging.