Microwave heating for sustainable valorization of almond hull towards high-added-value chemicals

• Microwave (MW) treatment promotes homogeneous heating compared to conventional methods, thus increasing the recovery of high-added-value compounds and leading to a considerably lower amount of both by-products and side reactions. Therefore, the main goal of this work is to valorize almond hull (AH) via microwave (MW)-assisted radiation (0–200 W, 0–300 psi, 100–190 °C, 10–40 min). In this context, two different pathways were evaluated. Firstly, the transformation of AH into levulinic acid (LA), one of the major bio-based chemicals obtained from lignocellulosic biomass. The so-called almond hull extractives-free biomass (AH-EFB) led to the best results after using both Lewis (AlCl3⋅6 H2O, 1 mol/L, 87 % molar yield) and Brønsted (p-toluenesulfonic (p-TsOH), 0.25 mol/L, 91 % molar yield) acids, at 190 °C for 20 min. This latter not only provides a sustainable system in contrast to mineral acids such as H2SO4 or HCl, but also the possibility of being recovered and recycled for further transformations. In a parallel secondary experiment, the recovery of biologically active compounds (BACs) was studied separately. For this purpose, antioxidant assays and phenolic profiling were carried out, which demonstrated that MW was more efficient than traditional methods (i.e. soaking) based on obtained values in terms of scavenging activity and polyphenols. Overall, this valorization approach involves most of the Green Chemistry principles, thus contributing to the development of almond biorefineries.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Industriell bioteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Industrial Biotechnology (hsv//eng)

NATURVETENSKAP  -- Kemi -- Organisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Organic Chemistry (hsv//eng)

Keyword

Almond hull

Bioactive compounds

Green processing

Levulinic acid

Microwave radiation

Aluminum chloride

Bioactivity

Microwave heating

Organic acids

Recovery

Sustainable chemistry

Added-value chemicals

Conventional methods

High added-value compounds

Microwave treatment

Microwave-heating

Valorisation

Microwaves

antioxidant

bioassay

chemical analysis

chemical compound

heating

sustainability

transformation

valorization

Publication and Content Type

ref (subject category)

art (subject category)