Cashew shell
Cashew shell is what many people consider junk, but is becoming a new source of raw materials with many applications and could open up a market of hundreds of millions of dollars, positively contributing to the value chain of the cashew industry. Cashew oil and activated carbon can be produced from cashew shells with many applications for many high-tech industries.
Typically, from 1 ton of raw cashew nuts processing can be 68-75 kg of cashew shells and 25-30 kg of cashew kernels, which can produce around 15.4 kg of oil.
Cashew nuts are covered by two shells: a thin inner testa skin and a hard outer shell. The cashew kernel is surrounded by a hard shell that accounts for about 72% of real fruit’s weight. The kernel accounts for 28% of the real fruit's weight. Cashew shells are mainly composed of cardol and anacardic. Currently, cashew nuts are becoming a highly processed nut with the number reaching more than 3.5 million tons annually (according to Can Tho University Journal of Science - No. 42/2016). Cashew shells are waste products from the production and processing of cashew nuts. Although they were considered as serious damages to the environment before, with the development of science and technology, cashew shells were researched and applied to many new fields at present. Refined products from cashew shells are very diverse such as: refined oil, cardanol oil, charcoal, activated carbon and friction powder production, etc.
Fig.1 - Cashew shell after separated
Cashew nut shell oil (CNSL)
The hard shell of cashew nuts contains many Phenolic compounds that are inedible oil compounds - commonly known as cashew oil, with the scientific name CNSL. The essential oil liquid obtained from cashew shells contains 70% anacardic acids, 5% cardanol and 18% cardol. This is a highly toxic liquid. However it contains friction reducing and polymerizing properties that have many applications in the civil industry. Oil obtained from cashew shells can also be used to produce chemicals such as carnol and carnadol. The applications of this oil are very diverse, such as: friction powder, antioxidant, aircraft lubricant, paint, varnish, automobile brake pads, cement, fungicide and many other medicines.
After purchasing, cashew shells will be put into a press to get crude oil. Crude oil after the press tank will be processed through the filter to remove sediment, while the cashew shell residue (also known as cashew residue) will be molded into blocks for firing the furnace in brick tile kilns.
Cashew oil after the filter tank will be put into the reactors to split the water, the rest is oil refining that is put into the preheater to raise the temperature of the vacuum distillation and oil to produce cardanol. During the distillation process, refined oil at high temperature will turn into vapor and continue to condense into liquid at the bottom and then flow into the storage tank. The sediment of the cardanol oil will be produced as friction during the distillation process.
Cashew oil is commonly used to make high-quality adhesive materials, binder in seagoing vessel’s paint, and laminated and heat-resistant materials. It can also be used in the electrical and electronic industries, etc. Specifically as follows:
- Use cashew resin as a medicine: Cashew resin can be used to treat tinea versicolor, eczema, psoriasis, etc.
- Use cashew oil as a source of energy: Like gasoline, cashew oil is used as a burning fuel. However, unlike gasoline, there is little cashew oil and it is not popular. Therefore, its cost is very high.
- Use cashew oil to make oil paint: Nowadays, most of the anti-termite paints are mixed with cashew oil. Cashew oil helps prevent wood from being eaten by termites and is also durable over time, especially it is not harmful to health.
It is estimated that Vietnam exports more than 600,000 tons of cashew nut oil each year. Factories in Dong Nai province alone make up 60 percent of total cashew shell oil in Vietnam. Vietnam's cashew oil is qualified for export to the US. Large corporations can export about 10,000 tons of oil every month. The main markets of products from CNSL mostly go to China and South Korea.
“I think that Vietnam has many advantages to become a raw material center for cashew oil production in the world. The cashew nut shell oil will still be the main product due to its great potential. Therefore, we do not focus on Cardanol,” said F.T.E representative.
Considered a leading cashew nut producer of the world, Vietnam has numerous advantages in the cashew nut production industry. With a strategic position in Southeast Asia and a source of abundant raw materials from the cashew processing industry, Vietnam has advantages over Brazil and India, especially in terms of transportation costs. Therefore, the competitive advantage of the Vietnam cashew oil production industry is huge.
Fig.2 - CNSL pressed from cashew shells
Cashew nut shell charcoal
Cashew shells after pressing are used as fuel (coal) and activated carbon, or to make industrial plywood, etc. The residue of cashew shells will be molded into square blocks. Like coal, these blocks will be used as a fuel-mainly for brick kilns.
Produce charcoal and activated carbon-making from cashew nut shell: After being extracted oiled, cashew residue is dried and burned by a heat transfer system to form charcoal. Cashew shell charcoal will then be put into a smokeless coal furnace, then continue to be heated at a temperature of about 850 degrees Celsius until activated carbon is created.
In general, up to now, activated carbon produced from cashew shells is often of low quality but its production costs are high, so it is still not economically feasible. Therefore, the application of activated carbon of cashew shells has not been fully exploited.
Cashew testa skin
Cashew nut shell is a thin brown shell surrounding the cashew nut, accounting for 18% to 3% of the cashew nut's weight (According to the study "The importance of the cashew nut" - Oliveira N. F., Leal R. S., Dantas T. N. C. ). Cashew shells are often known by people through salted roasted cashews with testa skin. In the process of producing cashew nuts, the cashew shell is often considered a waste product (except for salt-roasted cashew nuts with testa skin).
Although testa is a waste product, it still contains some nutrients, specifically about 11% protein and 8% fat. According to a study written by Mac Xuan Hoa published in Journal of Food Science and Technology (2018), the content of polyphenol compounds and TPC (antioxidant compounds) in testa skin is even higher than those in green tea and dark chocolate. Testa skin, therefore, has wide applications in life, including:
- The role of testa in the production of salted roasted cashew nuts: Testa helps protect the cashew nut from dusts and limit salt from entering the cashew nut during the toasting process. Cashew nuts with testa skin are also cheaper than peeled cashew nuts because the peeling step is removed in the production process . In addition, after packaging, testa also helps protect the cashew nuts from air and temperature outside, help them retain their crispy and increase their storage time.
- Use as fuel: Testa was not used in other fields before. Nowadays, testa skin is also used as fuel similar to cashew shells in the cashew production process. Although testa is flammable, it burns out quickly.
- Use testa in the production process for animal feed: Testa skin is widely used in the animal feed processing industry thanks to the nutrient content in the testa.
- Use testa in the production process for fertilizer: Testa is used as an ingredient in organic fertilizer thanks to their porosity and humus creation. According to "Research on composting process from cashew testa" written by Phan Thi Thanh Thuy and Nguyen Van Viet published in Journal of Science and Technology No. 6/2017, testa skin is considered one of the most promising new raw materials for composting, which is effective and cost-effective.
- Use testa in the medical field: cashew testa is used to prevent tartar, tooth decay. Testa contain many strong anti-ìmlamatory ingredients that help break down the structure of tartar, thereby helping to remove tartar.
- Use testa in the chemical industry: According to a research written by Mac Xuan Hoa, cashew testa is a potential new low-cost material to extract polyphenol compounds (antioxidant compounds).
- Use testa in the pigment industry: cashew testa has wide applications in the pigment industry thanks to their low price, abundant raw material sources and good coloring ability. Powder from cashew testa is used to produce dyes, pigments etc.
Despite its many applications, can cashew testa be edible for humans? There is currently no official research regarding this issue. Some people still eat cashew nuts with testa. The testa has a harsh taste and is a bit difficult to swallow. Thus, testa are recommended not to be eaten directly.
Cashew wood
Many areas of cashew trees are cut down each year because they are old or are sawed by garden owners to convert crops. Cashew wood is often purchased by cashew processing facilities as fuel for cashew processing. However, besides its traditional use as fuel, cashew wood is becoming a new dominant source of raw materials in the production of household wooden furniture such as shelves, cabinets, tables and chairs, etc.
Fig.3 - Cashew wood
Cashew wood is a moderately hard wood with a bright reddish pink tone, the figure often has a shape same as a mountain or striped pattern. Cashew wood in nature is soft, light, brightly colored and suitable for all products such as tables, chairs, beds, cabinets. , joinery boards and raw materials for the production of artificial boards (suitable as raw materials for the production of joinery boards). Compared to other types of wood, cashew wood has a quite competitive price because of the abundant and stable source of raw materials. The characteristics of cashew trees are that they are usually only harvested for about 15 years, then they are often cut down to plant new trees. According to the General Statistics Office, 294.9 thousand hectares of Vietnam's total cashew growing area in 2019, this is a very abundant source of raw materials for the cashew wood industry.
Cashew wood is often sawed into cylindrical sections, then cut into planks to facilitate the processing process. Next, the cashew planks are cut into pieces with many different specifications and placed in a pressure tank to soak with chemicals at the appropriate rate for preventing termites. After soaked for a specified period of time, the wood pieces will be dried until it reaches the appropriate quality and moisture. Finally, cashew wood is quality tested, classified and packaged into bales according to a closed process that meets export standards, being ready for shipment.
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