**3. Unconventional application of** *Salix viminalis*

### **3.1 Fabrication of adsorbents and catalysts**

The above described proved efficiency in metal ion accumulation by *Salix viminalis* led to a novel concept of non-energetic use of the plant. In some earlier studies (Łukaszewicz & Wesołowski, 2008) authors have discovered that thermal treatment (oxygen free conditions) of dry *Salix viminalis* wood yields charcoals of a very original and potentially useful pore structure. Usually a two step procedure was applied:


The pore structure of such obtained charcoals is characteristic because of a very narrow pore size distribution function (PSD) i. e. only pores of not differentiated dimensions contribute to the total pore volume (figs 4, 5 and 6). The calculated dimensions of pores let to call such fabricated charcoals "nanoporous Carbon Molecular Sieves" (CMS).

Memon et al., claim that the application of biological metal-accumulators and metalhyperaccumulators for purification of soils and waters has several positive features like "low cost, generation of a recyclable metal-rich plant residue, applicability to a range of toxic metals and radionuclides, minimal environmental disturbance, elimination of secondary air or water-borne wastes, and public acceptance". The latter statement applies in full to *Salix viminalis*, too. Table 8 proves that Cd removal from soil is extraordinarily high (217 g/ha) if compared to other phytoaccumulators tested in the study (Porębska & Ostrowska, 1999). Also the concentration of the metal in dry *Salix viminalis* wood was very high (22.1 mg/kg) exceeding values found in our study

[t / ha]

Thlaspi caerulescens 2.93 12.1 35

Alyssum murale 1.32 33.7 43

Salix viminalis 10.00 22.1 217

Potato – tuber 14.77 3.2 47

Barley – straw 4.95 2.4 12

Barley – grain 3.14 0.70 2

White clover 3.52 1.14 4

Table 8. Estimated removal of Cd with the biomass. Selected data cited and translated after

The above described proved efficiency in metal ion accumulation by *Salix viminalis* led to a novel concept of non-energetic use of the plant. In some earlier studies (Łukaszewicz & Wesołowski, 2008) authors have discovered that thermal treatment (oxygen free conditions) of dry *Salix viminalis* wood yields charcoals of a very original and potentially useful pore


The pore structure of such obtained charcoals is characteristic because of a very narrow pore size distribution function (PSD) i. e. only pores of not differentiated dimensions contribute to the total pore volume (figs 4, 5 and 6). The calculated dimensions of pores let to call such


fabricated charcoals "nanoporous Carbon Molecular Sieves" (CMS).

Metal content [mg / kg] (dry weight)

Metal removal [g / ha]

Plant Biomass

Łukaszewicz et al., 2009.

Porębska & Ostrowska, 2009.

**3. Unconventional application of** *Salix viminalis*

structure. Usually a two step procedure was applied:

temperature ranging from 600 to 900 0C.

**3.1 Fabrication of adsorbents and catalysts** 

Fig. 4. Nitrogen adsorption isotherm at -196 0C for bare *Salix viminalis* wood finally carbonized at 700 0C. I type isotherm characteristic for the presence of nanopores.

Fig. 5. Nitrogen adsorption isotherm at -196 0C for activated *Salix viminalis* wood (phosphoric acid treatment) finally carbonized at 700 0C. I type isotherm characteristic for the presence of nanopores.

Energetic Willow (*Salix viminalis*) – Unconventional Applications 193

The described fabrication of CMSs does not exploit both unique features of *Salix viminalis* i. e. the unique ability of *Salix viminalis* biomass transformation into a CMS and the *Salix viminalis* ability to heavy metal ion accumulation. Both feature were exploited in the case of a series of hybrid carbon-metal oxide catalysts obtained according to the fabrication procedure proposed recently by Łukaszewicz et al., 2007. The novelty of the method consists in the exploitation of natural phenomenon of metal ion transportation in living plants for the introduction of a metal-based catalytic phase. Metal ions, after introduction to transport-responsible tissues in a living plant (*Salix viminalis*), are transported to the plant cells. The process was efficient since *Salix viminalis* was highly tolerant to the presence of heavy metal ions in its body. Freshly cut ca. 20 cm longs sections of a stem (rootless) of *Salix viminalis* were immersed (vertical alignment) in a water solution containing equimolar quantities of La(NO3)3 and Mn(NO3)2 (example concentrations: 0.001M, 0.01M, 0.1M). The stems were fresh enough to preserve intensive metal ion transport resulting in a gradual rise of the solution along the treated stems. A contrast dye was added to the solutions in some experiments to provide eye observation of the capillary rise of solutions along the treated stems. One the other hand, the length of stems was short enough to avoid differentiated distribution of metal ions in the stem what might be expected regarding some former tests (see figs 1 and 2). After the contact with La3+ and Mn2+ ion solutions, the metal saturated stems were dried, diminished and carbonized (600-800 °C, a two-step procedure) in an inert gas atmosphere (N2). The first carbonization let to expel volatile species and to transform the wood (lignin-cellulose matrix) into carbon matrix (CMS resembling), consisting mainly of C, O, N and H atoms (Gorska, 2009). The next heat treatment (1 h, N2 flow) at the temperature of 800 °C did not destroy already developed pore structure (preliminary carbonization) and, what is the most important, it enabled the transformation of introduced metal ions into the corresponding metal clusters. XPS and XRD analysis (Cyganiuk et al., 2010) proved that a complex oxide LaMnO3 was synthesized from introduced ions. SEM and HRTEM investigations proved that the provskite-type oxide is present in such obtained samples in form of inorganic nano-crystallites suspended in carbon matrix, which in general was an

amorphous material with few graphite nano-crystallites (figs 7 an 8).

from data collected by Gorska, 2009.

Carbon 1 [SBET = 312 ± 9.5 m2/g] Carbon 2 [SBET = 358 ± 10.94 m2/g]

Temp [°C] Rs ΔRs Rs ΔRs 70 3.64 0.31 4.80 0.75 60 3.55 0.24 4.71 0.26 50 3.74 0.62 4.91 0.19 40 3.83 0.53 5.25 3.52 30 4.17 0.34 5.87 0.01

Table 9. Separation factors determined the separation of N2/CH4 binary gas mixtures. Separating medium – *Salix viminalis* originated carbons. Specific surface area SBET

determined by BET method from low temperature (-196 0C) nitrogen adsorption. Calculated

Fig. 6. Pore size distribution function (PSD) determined from low temperature (-1960C) nitrogen adsorption data by means of Hortvath-Kawazoe method (Horvath & Kawazoe, 1983).

The *Salix viminalis* originated CMSs proved their sieving properties in gas mixture separation to single components in chromatographic conditions (Gorska, 2009). For example table 9 contains separation coefficients determined for N2/CH4 binary gas mixture over two example Salix viminalis originated CMSs of similar surface area. The separation is of industrial importance since natural gas resources are often contaminated by nitrogen which high content may reduce commercial value of methane. The values are dramatically bigger than 1 at all investigated temperatures i. e. 30, 40, 50, 60 and 70 0C. It is to emphasize that separation is very efficient at highest temperature of 70 0C. It is particularly important regarding a potential application of such carbons as and adsorbing bed in a PSA (Pressure Swing Adsorption) installation. In the PSA method, the first step consists in the compression of a gas mixture to be separated in the adsorbing chamber (filled with CMS). Gas compression is an exothermal process leading to the warming of gases and carbon adsorbent what is an undesired phenomenon since separation at high temperature is generally much worse since PSA separation of air is very temperature sensitive (Japan EnviroChemicals Ltd., 2011).

Fig. 6. Pore size distribution function (PSD) determined from low temperature (-1960C) nitrogen adsorption data by means of Hortvath-Kawazoe method (Horvath & Kawazoe,

The *Salix viminalis* originated CMSs proved their sieving properties in gas mixture separation to single components in chromatographic conditions (Gorska, 2009). For example table 9 contains separation coefficients determined for N2/CH4 binary gas mixture over two example Salix viminalis originated CMSs of similar surface area. The separation is of industrial importance since natural gas resources are often contaminated by nitrogen which high content may reduce commercial value of methane. The values are dramatically bigger than 1 at all investigated temperatures i. e. 30, 40, 50, 60 and 70 0C. It is to emphasize that separation is very efficient at highest temperature of 70 0C. It is particularly important regarding a potential application of such carbons as and adsorbing bed in a PSA (Pressure Swing Adsorption) installation. In the PSA method, the first step consists in the compression of a gas mixture to be separated in the adsorbing chamber (filled with CMS). Gas compression is an exothermal process leading to the warming of gases and carbon adsorbent what is an undesired phenomenon since separation at high temperature is generally much worse since PSA separation of air is very temperature sensitive (Japan

1983).

EnviroChemicals Ltd., 2011).

The described fabrication of CMSs does not exploit both unique features of *Salix viminalis* i. e. the unique ability of *Salix viminalis* biomass transformation into a CMS and the *Salix viminalis* ability to heavy metal ion accumulation. Both feature were exploited in the case of a series of hybrid carbon-metal oxide catalysts obtained according to the fabrication procedure proposed recently by Łukaszewicz et al., 2007. The novelty of the method consists in the exploitation of natural phenomenon of metal ion transportation in living plants for the introduction of a metal-based catalytic phase. Metal ions, after introduction to transport-responsible tissues in a living plant (*Salix viminalis*), are transported to the plant cells. The process was efficient since *Salix viminalis* was highly tolerant to the presence of heavy metal ions in its body. Freshly cut ca. 20 cm longs sections of a stem (rootless) of *Salix viminalis* were immersed (vertical alignment) in a water solution containing equimolar quantities of La(NO3)3 and Mn(NO3)2 (example concentrations: 0.001M, 0.01M, 0.1M). The stems were fresh enough to preserve intensive metal ion transport resulting in a gradual rise of the solution along the treated stems. A contrast dye was added to the solutions in some experiments to provide eye observation of the capillary rise of solutions along the treated stems. One the other hand, the length of stems was short enough to avoid differentiated distribution of metal ions in the stem what might be expected regarding some former tests (see figs 1 and 2). After the contact with La3+ and Mn2+ ion solutions, the metal saturated stems were dried, diminished and carbonized (600-800 °C, a two-step procedure) in an inert gas atmosphere (N2). The first carbonization let to expel volatile species and to transform the wood (lignin-cellulose matrix) into carbon matrix (CMS resembling), consisting mainly of C, O, N and H atoms (Gorska, 2009). The next heat treatment (1 h, N2 flow) at the temperature of 800 °C did not destroy already developed pore structure (preliminary carbonization) and, what is the most important, it enabled the transformation of introduced metal ions into the corresponding metal clusters. XPS and XRD analysis (Cyganiuk et al., 2010) proved that a complex oxide LaMnO3 was synthesized from introduced ions. SEM and HRTEM investigations proved that the provskite-type oxide is present in such obtained samples in form of inorganic nano-crystallites suspended in carbon matrix, which in general was an amorphous material with few graphite nano-crystallites (figs 7 an 8).


Table 9. Separation factors determined the separation of N2/CH4 binary gas mixtures. Separating medium – *Salix viminalis* originated carbons. Specific surface area SBET determined by BET method from low temperature (-196 0C) nitrogen adsorption. Calculated from data collected by Gorska, 2009.

Energetic Willow (*Salix viminalis*) – Unconventional Applications 195

Fig. 8. HRTEM image of a LaMnO3 crystallite embedded in the carbon matrix. Crystalline

domains (graphite crystallites) visible in the amorphous carbon matrix.

Fig. 7. HRTEM image of a LaMnO3 crystallite embedded in the carbon matrix.

Fig. 7. HRTEM image of a LaMnO3 crystallite embedded in the carbon matrix.

Fig. 8. HRTEM image of a LaMnO3 crystallite embedded in the carbon matrix. Crystalline domains (graphite crystallites) visible in the amorphous carbon matrix.

Energetic Willow (*Salix viminalis*) – Unconventional Applications 197

Fig. 11. SEM and SEM-EDS/EDX analysis of hybrid C/Ti catalysts obtained from *Salix viminalis*: a – SEM micrograph, b –distribution of oxygen atoms determined by SEM-EDS/EDX, c - distribution of titanium atoms determined by SEM-EDS/EDX, d – elemental

Such obtained hybrid materials were tested as catalysts for n-butanol conversion to a 4-

2 RCH2OH → 2 RCHO → RCOR The catalysts exhibited very good catalytic performance despite very low concentration of the active component i. e. a perovskite-type oxide LaMnO3 (atomic content below 1%). The noticed high activity i. e. yield and selectivity (Cyganiuk et al., 2010) resulted from very high

Similarly, titanium and cerium based hybrid materials were obtained by exploitation of metal ion transportation in living parts of Salix viminalis (ca. 20 cm long stem sections). Figs 10 and 11 depict uniform distribution of Ce and Ti atoms in a carbon matrixes. Their occurrence is accompanied by oxygen atoms however the latter are a usual constituent of carbon matrixes and can not be exclusively associated with Ce and Ti in the form of metal oxides. Elemental analysis data definitely prove (figs 10 and 11) that Ce and Ti are present in investigated hybrid

analysis of the hybrid material.

heptanone according to the reaction:

dispersion of the active phase understood as:



Fig. 9. Identical distribution of Mn (left) and La (right) atoms in hybrid C/LaMnO3 catalyst.

Fig. 10. SEM and SEM-EDS/EDX analysis of hybrid C/Ce catalysts obtained from *Salix viminalis*: a – SEM micrograph, b –distribution of oxygen atoms determined by SEM-EDS/EDX, c - distribution of cerium atoms determined by SEM-EDS/EDX, d – elemental analysis of the hybrid material.

Fig. 9. Identical distribution of Mn (left) and La (right) atoms in hybrid C/LaMnO3 catalyst.

Fig. 10. SEM and SEM-EDS/EDX analysis of hybrid C/Ce catalysts obtained from *Salix viminalis*: a – SEM micrograph, b –distribution of oxygen atoms determined by SEM-EDS/EDX, c - distribution of cerium atoms determined by SEM-EDS/EDX, d – elemental

analysis of the hybrid material.

Fig. 11. SEM and SEM-EDS/EDX analysis of hybrid C/Ti catalysts obtained from *Salix viminalis*: a – SEM micrograph, b –distribution of oxygen atoms determined by SEM-EDS/EDX, c - distribution of titanium atoms determined by SEM-EDS/EDX, d – elemental analysis of the hybrid material.

Such obtained hybrid materials were tested as catalysts for n-butanol conversion to a 4 heptanone according to the reaction:

### 2 RCH2OH → 2 RCHO → RCOR

The catalysts exhibited very good catalytic performance despite very low concentration of the active component i. e. a perovskite-type oxide LaMnO3 (atomic content below 1%). The noticed high activity i. e. yield and selectivity (Cyganiuk et al., 2010) resulted from very high dispersion of the active phase understood as:


Similarly, titanium and cerium based hybrid materials were obtained by exploitation of metal ion transportation in living parts of Salix viminalis (ca. 20 cm long stem sections). Figs 10 and 11 depict uniform distribution of Ce and Ti atoms in a carbon matrixes. Their occurrence is accompanied by oxygen atoms however the latter are a usual constituent of carbon matrixes and can not be exclusively associated with Ce and Ti in the form of metal oxides. Elemental analysis data definitely prove (figs 10 and 11) that Ce and Ti are present in investigated hybrid

Energetic Willow (*Salix viminalis*) – Unconventional Applications 199

Free radicals play important role in the functioning of human organism (Grajek, 2007). However, their presence may be the reason of oxidative stress. The stress often results from disrupted balance between peroxidants and antioxidants in an organism. It is proven that high activity of free radicals and prolonged influence of oxidative stress are responsible for pathogenesis of nearly 100 diseases (Wolski, 2007) including Alzheimer and Parkinson diseases (Bartosz, 2008; Fitak & Grzegorczyk-Jaźwińska, 1999). During ageing oxidative damages in cells become more frequent with parallel reduction the activity of antioxidative enzymes. The situation becomes worse due to UV irradiation, environmental pollution, permanent mental stress and bad nutrition habits. Oxygen being the base of human existence is mainly available in it triplet form O2\*\*. The electron configuration results in moderate chemical activity in contrast to other forms like (O2\*)-, HO2\* and OH\*. The latter form is considered as the most reactive. Proper enzymes ensure control over 98-99% of all oxygen in a human body. However, the remaining amount of oxygen may undergo transformation (Fenton reaction, Haber-Weiss reaction) into the most reactive forms i. e. oxygen derivatives being free radicals. Daily up to 10 thousand DNA oxygen-related damages occur in a human body. The damages may be repaired by some specific enzymes but the introduction of antioxidants should reduce the threat. Therefore everyday diet has to be supplemented by natural antioxidants. Antioxidation properties of polyphenols may




Such positive chemical features of polyphenols turns peoples attention towards intensive search for sources of them and the development of methods of polyphenols separation from their natural matrixes for further enrichment of some products like pharmaceuticals, food, cosmetics etc. This way of thinking involves investigations on appropriate plants i. e. candidates for a subsequent chemical treatment like polyphenol extraction. According to some extended studies (Makowska-Wąs & Janeczko, 2004) polyphenols occur in many plants and plant originated products like herbs, needles of coniferous plants, algae, green tea leaves, eucalyptus wood, byproducts of olive, wine, yeast production. It is obvious that chemical exploitation of one source plant yields a limited number of polyphenols and search for other polyphenols needs a selection and a proper treatment of another source plants. It has to be stated that the polyphenol content in source plants is very differentiated but also very low. Table 10 informs about the antioxidant activity determined for 100 g of example fruits and vegetables. The highest activity is noticed for pure vitamins and synthetic antioxidants. However, the mentioned products owe their antioxidative activity not only due to the presence of polyphenols since other type of

next oxygen radical stabilizes as chinone like structure (fig. 12)

Fe2+ ions and yielding dangerous hydroxyl radical OH,

stimulating the formation of free radicals.

**3.3 Polyphenols and other antioxidants** 

involve the three general mechanisms:

antioxidants may be present, too.

samples and their presence result only from the performed fabrication procedure. The elements are relatively rare and have not been found in the samples of non-impregnated but carbonized *Salix viminalis* wood. Also in this case the atomic content of the metals is very low i. e. definitely below 1% despite of the concentration of impregnating solution. Thus, the proposed exploitation of metal ion transport in living parts of *Salix viminalis* ensures rather low level of impregnation but of very high dispersion. The Ti and Ce containing hybrid materials were tested as catalysts, too. Both materials despite of the same properties of carbon component of them, exhibited dramatically different catalytic activity:


The differences must by attributed to different catalytic properties of the active components of the hybrid materials i. e. to Ce and Ti derivatives (mixed oxides) which presence was proved by XRD, XPS and HRTEM measurements.

In summary, the proposed hybrid catalysts fabrication method is basing on two important and exclusive features of *Salix viminalis*:


The originality of the above presented concept let to submit patent applications (Łukaszewicz et al., 2006; Łukaszewicz et al., 2007).

### **3.2 Dry distillation of** *Salix viminalis* **wood**

Fabrication of charcoals from *Salix viminalis* consists in the a heat treatment of the biomass in oxygen free conditions. In fact this process can be also called dry distillation w wood. However, usually distillation is run aiming at the collection of volatile products which evolve during heat treatment. Looking at charcoal fabrication (described above) from such a point view authors has decided to cool down (liquefaction) volatiles leaving heating zone of stove along with the stream of inert gas (nitrogen) passing through the stove. The condensate in form of a dark brown viscous liquid was collected in a glass beaker and subsequently subjected to several analysis. We assumed that the condensate is a mixture of numerous organic compound as in the case of wood tar obtained by dry distillation of other sorts of wood i. e. pine (Egenberg et al., 2002).

At the beginning we assumed that the collected tar must contain phenols and polyphenols which are created during thermolysis of lignin (de Wild et al., 2010). *Salix viminalis* wood contains ca. 20-24 % (by weight) of lignin in dry mass of wood (Mleczek et al., 2010). The distillate called biooil was subjected to some separation measures like extraction to isolate several fractions containing polyphenols. Polyphenols are a precious group of compounds mainly because of their antioxidant properties.

### **3.3 Polyphenols and other antioxidants**

198 Sustainable Growth and Applications in Renewable Energy Sources

samples and their presence result only from the performed fabrication procedure. The elements are relatively rare and have not been found in the samples of non-impregnated but carbonized *Salix viminalis* wood. Also in this case the atomic content of the metals is very low i. e. definitely below 1% despite of the concentration of impregnating solution. Thus, the proposed exploitation of metal ion transport in living parts of *Salix viminalis* ensures rather low level of impregnation but of very high dispersion. The Ti and Ce containing hybrid materials were tested as catalysts, too. Both materials despite of the same properties of carbon



The differences must by attributed to different catalytic properties of the active components of the hybrid materials i. e. to Ce and Ti derivatives (mixed oxides) which presence was

In summary, the proposed hybrid catalysts fabrication method is basing on two important



The originality of the above presented concept let to submit patent applications

Fabrication of charcoals from *Salix viminalis* consists in the a heat treatment of the biomass in oxygen free conditions. In fact this process can be also called dry distillation w wood. However, usually distillation is run aiming at the collection of volatile products which evolve during heat treatment. Looking at charcoal fabrication (described above) from such a point view authors has decided to cool down (liquefaction) volatiles leaving heating zone of stove along with the stream of inert gas (nitrogen) passing through the stove. The condensate in form of a dark brown viscous liquid was collected in a glass beaker and subsequently subjected to several analysis. We assumed that the condensate is a mixture of numerous organic compound as in the case of wood tar obtained by dry distillation of other

At the beginning we assumed that the collected tar must contain phenols and polyphenols which are created during thermolysis of lignin (de Wild et al., 2010). *Salix viminalis* wood contains ca. 20-24 % (by weight) of lignin in dry mass of wood (Mleczek et al., 2010). The distillate called biooil was subjected to some separation measures like extraction to isolate several fractions containing polyphenols. Polyphenols are a precious group of compounds

component of them, exhibited dramatically different catalytic activity:

of a complete plant (single rod cut into 20 cm long pieces),

55% selectivity at 460 0C),

ca. 75% selectivity at 460 0C).

and exclusive features of *Salix viminalis*:

and shrinkage did not occur.

(Łukaszewicz et al., 2006; Łukaszewicz et al., 2007).

**3.2 Dry distillation of** *Salix viminalis* **wood** 

sorts of wood i. e. pine (Egenberg et al., 2002).

mainly because of their antioxidant properties.

proved by XRD, XPS and HRTEM measurements.

Free radicals play important role in the functioning of human organism (Grajek, 2007). However, their presence may be the reason of oxidative stress. The stress often results from disrupted balance between peroxidants and antioxidants in an organism. It is proven that high activity of free radicals and prolonged influence of oxidative stress are responsible for pathogenesis of nearly 100 diseases (Wolski, 2007) including Alzheimer and Parkinson diseases (Bartosz, 2008; Fitak & Grzegorczyk-Jaźwińska, 1999). During ageing oxidative damages in cells become more frequent with parallel reduction the activity of antioxidative enzymes. The situation becomes worse due to UV irradiation, environmental pollution, permanent mental stress and bad nutrition habits. Oxygen being the base of human existence is mainly available in it triplet form O2 \*\*. The electron configuration results in moderate chemical activity in contrast to other forms like (O2\*)-, HO2\* and OH\*. The latter form is considered as the most reactive. Proper enzymes ensure control over 98-99% of all oxygen in a human body. However, the remaining amount of oxygen may undergo transformation (Fenton reaction, Haber-Weiss reaction) into the most reactive forms i. e. oxygen derivatives being free radicals. Daily up to 10 thousand DNA oxygen-related damages occur in a human body. The damages may be repaired by some specific enzymes but the introduction of antioxidants should reduce the threat. Therefore everyday diet has to be supplemented by natural antioxidants. Antioxidation properties of polyphenols may involve the three general mechanisms:


Such positive chemical features of polyphenols turns peoples attention towards intensive search for sources of them and the development of methods of polyphenols separation from their natural matrixes for further enrichment of some products like pharmaceuticals, food, cosmetics etc. This way of thinking involves investigations on appropriate plants i. e. candidates for a subsequent chemical treatment like polyphenol extraction. According to some extended studies (Makowska-Wąs & Janeczko, 2004) polyphenols occur in many plants and plant originated products like herbs, needles of coniferous plants, algae, green tea leaves, eucalyptus wood, byproducts of olive, wine, yeast production. It is obvious that chemical exploitation of one source plant yields a limited number of polyphenols and search for other polyphenols needs a selection and a proper treatment of another source plants. It has to be stated that the polyphenol content in source plants is very differentiated but also very low. Table 10 informs about the antioxidant activity determined for 100 g of example fruits and vegetables. The highest activity is noticed for pure vitamins and synthetic antioxidants. However, the mentioned products owe their antioxidative activity not only due to the presence of polyphenols since other type of antioxidants may be present, too.

Energetic Willow (*Salix viminalis*) – Unconventional Applications 201

Red Grapes 1350 Red Cabbage 1000

Broccoli Flowers 500

Spinach 500

Tomato 300

Green Beans 175

Green Cabbage 150

Lima Beans 1055

Red Beans 11459 Blueberries 3300

Raisins 5900

Ascorbate 442 000

Witamin E 201 000

Table 10. Antioxidant activity of selected food products, vitamins and synthetic

**TE – TRILOX Equivalent** 

antioxidants. Selected points cited after (Prakash et al., 2010).

Trilox 400 000

BHT 395 000

**Substance Antioxidant activity** 

Wheat Bran 4620

Wheat Flour (refined) 600

Green Grapes 400

**Food produkt Antioxidant activity** 

**[TE/100 g]** 

**[TE/100 g]** 

TRILOX

Fig. 12. Oxygen based free radical reaction with a polyphenol.

Obviously the above list is not closed and other natural and synthetic products may be addend and therefore search for other effective products is fully justified. Authors attention has turned towards chemical processing of some easily accessible and renewal resources. Our primary idea was to involve chemical processing not limited to the separation of already existing polyphenols (a passive approach) but also on treatments that transform original matter of low polyphenol content into a new product of high polyphenol concentration (active approach). Such a concept focused our attention on *Salix viminalis* again due to its inexpensiveness, renewal cultivation and high content of lignin which thermal treatment releases polyphenols. As the matter of fact *Salix viminalis* as a living plant contains some amounts of different polypneols like flavonoides (flavanols, flavones, flavonones, flawonone dimers, chalcones), phenolic acids, lignans, catechin and its derivatives as well as tannins (procyanidins, prodelfinidins) being derivatives of flavan-3-ols. Particular *Salix* species differ much regarding the total content of polypheneols (Nyman & Julkunen-Tiitto, 2005) and their type (Landucci et al., 2003).

For example *Salix caprea* contains variety of flavonoids and the lack of lignans (Pohjamo et al., 2002). Contrastly, for *Salix viminalis* characteristic are relatively low concentrations of flavonoids (Harborne & Baxter, 1999), moderate concentrations of lignans (Pohjamo et al., 2003) and high concentrations of tannins (Nikitina & Orazov, 2001).

Fig. 12. Oxygen based free radical reaction with a polyphenol.

2003) and high concentrations of tannins (Nikitina & Orazov, 2001).

2003).

Obviously the above list is not closed and other natural and synthetic products may be addend and therefore search for other effective products is fully justified. Authors attention has turned towards chemical processing of some easily accessible and renewal resources. Our primary idea was to involve chemical processing not limited to the separation of already existing polyphenols (a passive approach) but also on treatments that transform original matter of low polyphenol content into a new product of high polyphenol concentration (active approach). Such a concept focused our attention on *Salix viminalis* again due to its inexpensiveness, renewal cultivation and high content of lignin which thermal treatment releases polyphenols. As the matter of fact *Salix viminalis* as a living plant contains some amounts of different polypneols like flavonoides (flavanols, flavones, flavonones, flawonone dimers, chalcones), phenolic acids, lignans, catechin and its derivatives as well as tannins (procyanidins, prodelfinidins) being derivatives of flavan-3-ols. Particular *Salix* species differ much regarding the total content of polypheneols (Nyman & Julkunen-Tiitto, 2005) and their type (Landucci et al.,

For example *Salix caprea* contains variety of flavonoids and the lack of lignans (Pohjamo et al., 2002). Contrastly, for *Salix viminalis* characteristic are relatively low concentrations of flavonoids (Harborne & Baxter, 1999), moderate concentrations of lignans (Pohjamo et al.,


Table 10. Antioxidant activity of selected food products, vitamins and synthetic antioxidants. Selected points cited after (Prakash et al., 2010).

Energetic Willow (*Salix viminalis*) – Unconventional Applications 203

Fig. 15. Structures of three phenolic alcohols being monomers in lignin: A – p-cumarol

Fig. 14. Pattern structure of lignin.

alcohol, B – coniferyl alcohol, C – synapine alcohol.

The concentration of polyphenols in *Salix viminalis* depends also on the season of the year. t maximal concentration of flavonoids is reached during blossom while tannins concentration is highest in Autumn (Nikitina & Orazov, 2001). Long exposure of *Salix viminalis* to sunshine (UV radiation) additionally increases the content of compounds capable to neutralization of free radicals (flavonoids, phenolic acids, proantocyanidynes) and reduces the content of salicylic acid and its derivatives (Tegelberg & Julkunen-Titto, 2001). Thus, a proper cultivation of *Salix viminalis* and well planned collection of polyphenols by extractive methods may result in a better efficiency of the whole attempt. However, as mentioned earlier, the total contents of polyphenols is relatively low and therefore the mass of isolated antioxidants in relation to the mass of raw material is dramatically low. Thus, the contemporary chemical technology should not only rely on the Nature's productivity but also search for more effective methods of polyphenols fabrication instead of collection. The heat-treatment of *Salix vimanlis* wood yields three basic products (charcoal, biooil, biogas) but yield of each depends on heating rate as depicted in fig. 13).

As mentioned biooil formation is a result of lignin pyrolysis. Lignin is biopolymer (fig. 14) consisting of some characteristic units i. e. p-cumarol alcohol, coniferyl alcohol, synapine alcohol (fig. 15.) bonded by various organic bridges. Thus, the bonds may break at different point yielding a huge number of organic compounds including polyphenols. Volatile products evolve during heat-treatment with unequal intensity (fig. 16). The most intensive collection of liquid condensate is possible in the temperature range of 260-380 °C).

Fig. 13. Typical products of biomass pyrolysis. The influence of process conditions (heating rate, temperature) on yield of particular products.

The concentration of polyphenols in *Salix viminalis* depends also on the season of the year. t maximal concentration of flavonoids is reached during blossom while tannins concentration is highest in Autumn (Nikitina & Orazov, 2001). Long exposure of *Salix viminalis* to sunshine (UV radiation) additionally increases the content of compounds capable to neutralization of free radicals (flavonoids, phenolic acids, proantocyanidynes) and reduces the content of salicylic acid and its derivatives (Tegelberg & Julkunen-Titto, 2001). Thus, a proper cultivation of *Salix viminalis* and well planned collection of polyphenols by extractive methods may result in a better efficiency of the whole attempt. However, as mentioned earlier, the total contents of polyphenols is relatively low and therefore the mass of isolated antioxidants in relation to the mass of raw material is dramatically low. Thus, the contemporary chemical technology should not only rely on the Nature's productivity but also search for more effective methods of polyphenols fabrication instead of collection. The heat-treatment of *Salix vimanlis* wood yields three basic products (charcoal, biooil, biogas) but yield of each depends on heating rate as

As mentioned biooil formation is a result of lignin pyrolysis. Lignin is biopolymer (fig. 14) consisting of some characteristic units i. e. p-cumarol alcohol, coniferyl alcohol, synapine alcohol (fig. 15.) bonded by various organic bridges. Thus, the bonds may break at different point yielding a huge number of organic compounds including polyphenols. Volatile products evolve during heat-treatment with unequal intensity (fig. 16). The most intensive collection of liquid condensate is possible in the temperature

Fig. 13. Typical products of biomass pyrolysis. The influence of process conditions (heating

rate, temperature) on yield of particular products.

depicted in fig. 13).

range of 260-380 °C).

Fig. 14. Pattern structure of lignin.

Fig. 15. Structures of three phenolic alcohols being monomers in lignin: A – p-cumarol alcohol, B – coniferyl alcohol, C – synapine alcohol.

Energetic Willow (*Salix viminalis*) – Unconventional Applications 205



The determination of the composition of the two preliminary extracts A and B has a certain chemical value but more important is to confirm if the extract theoretically consisting of antioxidant species can exhibit efficient antioxidant activity, what is the main motivation for this research. The absence of such activity could question the whole research attempt which from early beginning was focused on a practical aspects i. e. on the applicability of all products of the dry *Salix viminalis* wood pyrolysis. The preliminary hypothesis was confirmed by the performed controlled oxidation tests (fig. 17). It is visible that the addition of 1000 ppm of a commercial antioxidant i. e. BHT protects the test substance DBS for ca. 50 hours. After this time one observes increasing concentration of some oxidation products in the reaction chamber. In the same experimental conditions pure DBS undergoes instant oxidation without any significant protection time. The addition of the biooil extract B in the same proportion of 1000 ppm extends threefold the protection time. Thus, DBS was protected nearly for one week despite sever experimental conditions. It has to be stated that the protection times for much lower temperatures like

lignin,

heterocyclic compounds.

room temperature must by very long.

Fig. 17. Restraining of DBS oxidation by means of extract B and BHT.

Fig. 16. The intensity of liquid condensate yield (biooil) at different temperatures.

The such collected fraction was considered as a raw biooil subsequently subjected to separation (extraction, chromatography) procedures and chemical characterization. Several instrumental methods were applied: gas chromatography GC-MS (Autosystem XL - MS Turbomass), nuclear magnetic resonance 1H and 13C NMR (700 MHz Bruker Avance) and infrared spectroscopy FT-IR (Perkin Elmer Spectrum 2000). Additionally the isolated fractions were tested as antioxidants according to ASTM 4871 standard (www.astm.org/Standards/D5770.htm, 2011). The latter procedure consists in the oxidation of a standard substance DBS (dibuthyl sebacate) in liquid phase at relatively severe conditions (150 0C, constant flow of air 100 cm3/min). The oxidation may proceed in the presence (1000 ppm) of different protective antioxidants including separated fractions of raw biooil of *Salix viminalis* origin (dry distillation) and some commercially distributed antioxidants like BHT (2,6-di-tert-buthyl-p-cresol, buthyl hydroxy toluene, buthylated hydroxy toluene). BHT is widely used for the protection and stabilization of cosmetics and food products. The most promising results were achieved so far for two extracts called A and B (ethyl ether and dichloromethane extracts respectively).

The results of a complex analysis (GC-MS, NMR, FTIR, UV-VIS) of both extracts confirm that:


Fig. 16. The intensity of liquid condensate yield (biooil) at different temperatures.

and B (ethyl ether and dichloromethane extracts respectively).

that:

properties,

The such collected fraction was considered as a raw biooil subsequently subjected to separation (extraction, chromatography) procedures and chemical characterization. Several instrumental methods were applied: gas chromatography GC-MS (Autosystem XL - MS Turbomass), nuclear magnetic resonance 1H and 13C NMR (700 MHz Bruker Avance) and infrared spectroscopy FT-IR (Perkin Elmer Spectrum 2000). Additionally the isolated fractions were tested as antioxidants according to ASTM 4871 standard (www.astm.org/Standards/D5770.htm, 2011). The latter procedure consists in the oxidation of a standard substance DBS (dibuthyl sebacate) in liquid phase at relatively severe conditions (150 0C, constant flow of air 100 cm3/min). The oxidation may proceed in the presence (1000 ppm) of different protective antioxidants including separated fractions of raw biooil of *Salix viminalis* origin (dry distillation) and some commercially distributed antioxidants like BHT (2,6-di-tert-buthyl-p-cresol, buthyl hydroxy toluene, buthylated hydroxy toluene). BHT is widely used for the protection and stabilization of cosmetics and food products. The most promising results were achieved so far for two extracts called A

The results of a complex analysis (GC-MS, NMR, FTIR, UV-VIS) of both extracts confirm



The determination of the composition of the two preliminary extracts A and B has a certain chemical value but more important is to confirm if the extract theoretically consisting of antioxidant species can exhibit efficient antioxidant activity, what is the main motivation for this research. The absence of such activity could question the whole research attempt which from early beginning was focused on a practical aspects i. e. on the applicability of all products of the dry *Salix viminalis* wood pyrolysis. The preliminary hypothesis was confirmed by the performed controlled oxidation tests (fig. 17). It is visible that the addition of 1000 ppm of a commercial antioxidant i. e. BHT protects the test substance DBS for ca. 50 hours. After this time one observes increasing concentration of some oxidation products in the reaction chamber. In the same experimental conditions pure DBS undergoes instant oxidation without any significant protection time. The addition of the biooil extract B in the same proportion of 1000 ppm extends threefold the protection time. Thus, DBS was protected nearly for one week despite sever experimental conditions. It has to be stated that the protection times for much lower temperatures like room temperature must by very long.

Fig. 17. Restraining of DBS oxidation by means of extract B and BHT.

Energetic Willow (*Salix viminalis*) – Unconventional Applications 207

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