**2. Hydrothermal lignin: aromatic hydrocarbons from woody biomass**

### **2.1 Reducing molecular weight of lignin**

Lignin is one of main components of lignocellulosic biomass and a natural phenolic polymer with propyl-phenol groups. One big drawbacks of natural lignin in originally existing woody biomass is large molecular weight (because high molecular weight lignin has high viscosity or it is solid at room temperature and it has a complicated structure), and molecular weight reduction of lignin will provide many advantages in handling and processing as a chemical feedstock. In the paper [2], we proposed an environmental-friendly process for recovery of lignin from woody biomass, and it should have high efficiency with producing simple structure lignin, which is highly desired as a biorefinery feedstock. Here, the brief introduction of the process and the index of the operational parameters (how to know the optimum conditions) is summarized.

### **2.2 Experimental for hydrothermal lignin preparation**

In the paper [2], low-grade wood from Japanese cedar production was provided from a domestic wood manufacturer and had a lignin content of 44.6 wt% (the sample should be mainly bark of the Japanese cedar). The bark was crushed to have a coarse particle size of less than 5 mm. The elemental balance of the Japanese cedar *Resource Upgrading in Advanced Supercritical Fluid (Supercritical Fluid with Catalyst… DOI: http://dx.doi.org/10.5772/intechopen.89793*

### **Figure 2.**

ionic liquid as cosolvent: reduction of viscosity of ionic liquid solution [26], control of acidity and basicity of ionic liquid, solubility control of material in ionic liquid, separation of target molecule from ionic liquid into supercritical fluids, and so on. Our research group also progress the study of the separation of some components (biomass molecules or biomass refinery are targeted) from ionic liquid solution with supercritical carbon dioxide [27–30]. Here, we only briefly introduced some research results concerning biomass conversion into useful molecule in ionic liquid-

*Proposed process for liquid fuel production from protein-rich biomass by hydrothermal conversion together with*

In the conclusion of this chapter, we will conclude this chapter and mention

**2. Hydrothermal lignin: aromatic hydrocarbons from woody biomass**

Lignin is one of main components of lignocellulosic biomass and a natural phenolic polymer with propyl-phenol groups. One big drawbacks of natural lignin in originally existing woody biomass is large molecular weight (because high molecular weight lignin has high viscosity or it is solid at room temperature and it has a complicated structure), and molecular weight reduction of lignin will provide many advantages in handling and processing as a chemical feedstock. In the paper [2], we proposed an environmental-friendly process for recovery of lignin from woody biomass, and it should have high efficiency with producing simple structure lignin, which is highly desired as a biorefinery feedstock. Here, the brief introduction of the process and the index of the operational parameters (how to know the

In the paper [2], low-grade wood from Japanese cedar production was provided from a domestic wood manufacturer and had a lignin content of 44.6 wt% (the sample should be mainly bark of the Japanese cedar). The bark was crushed to have a coarse particle size of less than 5 mm. The elemental balance of the Japanese cedar

hydrothermal water mixture with additives (Section 4).

**2.1 Reducing molecular weight of lignin**

*Advanced Supercritical Fluids Technologies*

optimum conditions) is summarized.

**92**

**2.2 Experimental for hydrothermal lignin preparation**

outlook in this field.

**Figure 1.**

*"iso-conversion."*

*Coupled system of two batch reactors.*

was 49, 5.9, 0.1, 1, and 42.2 wt% for C, H, N, S, and O content, respectively. Ash content was 2 wt%.

A coupled system of two batch reactors was used (the photograph and schematic diagram of the reactor is shown in **Figure 2**, and its detail can be seen elsewhere [2]), and the sample was loaded into the upper reactor. The lower reactor was reservoir and used to recover hydrothermal extracts. The reservoir was maintained at a temperature of 473 K to inhibit the aggregation of lignin because lignin typically is melted into liquid phase at temperatures greater than 423 K in the presence of water [31]. Typically, a 7.5 g sample of bark (covered with stainless mesh) was loaded in the upper reactor along with 150 mL of pure water. After purging air inside the reactor, N2 gas was loaded. The upper reactor was heated up to 473–573 K. The pressure in the upper reactor (sample-loaded reactor) was close to the saturated pressure of water at the reaction temperature. After the desired treatment time, the valve between the two reactors was opened and the fractionated components in the reactor were recovered in the reservoir. The reservoir was then rapidly cooled with a water bath (ca. 10 min) and was then detached from the sample-loaded reactor. The residue in the upper (sample-loaded) reactor with the stainless mesh was weighed after drying at 333 K overnight. Connection lines between the two reactors were rinsed. The water-insoluble fraction among the recovered solutions was hydrothermal-soluble lignin (namely "hydrothermal lignin"). The soluble Klason lignin (hydrothermal lignin) was quantified, and the molecular characteristics (molecular weight with GPC and molecular structure with NMR) were evaluated.

As a result of the molecular characteristics, the hydrothermal lignin obtained from bark of Japanese cedar by hydrothermal extraction at 523 K under the saturated pressure of water, 3.98 MPa, about was mainly 6-mer (about 1 kDa of mean molecular weight) with syringyl-rich structure [2].

### **2.3 Dimensionless severity number**

The kinetic study for lignin recovery (how much percentage of Klason lignin can be recovered based on the Klason lignin in the raw material, the bark of Japanese cedar) was performed, and severity factor was used for consideration of the effect of reaction temperature and reaction time. The severity factor, *R*<sup>o</sup> [min], is defined as below:

*Advanced Supercritical Fluids Technologies*

$$R\_o = \exp\left(\frac{T - T\_r}{\alpha}\right)t\tag{1}$$

Eq. (5) shows that the dimensionless severity number (*k*<sup>r</sup>*R*o) is also the function of *t* and *T* as well as severity factor (*R*o) as shown in Eq. (1). While *R*<sup>o</sup> varies a wide range of values and the optimum *R*<sup>o</sup> for the target reaction is not easy to estimate, meaningful transitional change should occur at the range of 0.1 to 10 for the dimensionless severity number *k*<sup>r</sup>*R*o, as reported here and in the literatures [2, 32, 33]. Therefore, the dimensionless severity number (*k*<sup>r</sup>*R*o) is quite useful, and the severity analysis using *k*<sup>r</sup>*R*<sup>o</sup> can be adopted to various type of the reactions. Our research group is going to study on utilization of the dimensionless severity number (*k*<sup>r</sup>*R*o) for various kind of reactions and its application and usefulness with a variety

*Resource Upgrading in Advanced Supercritical Fluid (Supercritical Fluid with Catalyst…*

**3. Protein hydrolysis and amino acid degradation: low temperature catalytic hydrothermal cracking (LT-CHTC) for liquid fuel**

Based on the concept of "sustainable development goals (SDGs)" by UN and "circular economy" by EU, waste materials (by-product of main activity) must be used in effective and useful application and ideally must be back to primary resource production. In our daily life, huge amount of food waste generates and its utilization/valorization is still insufficient. This situation is not only for food waste (including house waste, municipal waste, sewage sludge, which are by-product of our daily life) but also agricultural by-product. One of the big problems of these wastes is to contain high amount of water, which is hard to exclude from the wastes. Water inside the waste (namely wet biomass) assists to cultivate fungi, and some of the wet biomass wastes are easy to rot with a bad odor and toxic component formation. Even with huge amount of energy loss, the large part of the wet wastes is forcedly burned to eliminate without effective utilization as energy or thermal

Microalgae, which has fast grow rate with CO2 stabilization through photosynthesis and attracts much attention as renewable resource, is also wet biomass as the same as daily-life wastes with containing a large amount of water mentioned above. The total difference of microalgae from the waste wet biomass is that cultivation and harvesting of microalgae can be controlled to level not only for yield but also composition. Thus, microalgae is a primary and industrial renewable resource. However, problem related to water is to be solved as well as wet biomass waste. Sub and supercritical water technologies enable water (also in the wet biomass)

to eliminate from the structure of the biomass and to use for hydrolysis of the natural polymer in the biomass as reactant. As mentioned above, supercritical water plays the important role in the CHTC for producing olefinic hydrocarbon from lipid and free fatty acid, as solvent and reactant. But, for feeding lipid into the process, extraction of the lipid from microalgae must be done. Typical lipid extraction processes from microalgae are solvent extraction and mechanical press, both of which require dry to improve lipid yield before the extraction. Also, in iso-

conversion concept, the residue of the extraction of lipid (protein and carbohydrate are main components) will be treated by anaerobic fermentation to form small molecules such as organic acids. Advantage of the biochemical process is high selectivity, but disadvantage is low reaction rate. For the purpose of liquid fuels production, broad product distribution in the range of small molecular weight is acceptable. Or rather, rapid transformation process has to be necessary for the residue conversion of the residual biomass containing protein and carbohydrate.

of the examples will be reported in near future.

*DOI: http://dx.doi.org/10.5772/intechopen.89793*

**3.1 How to convert protein-rich biomass into liquid fuels**

**production**

purposes.

**95**

where *T* [K] is reaction temperature,*T*<sup>r</sup> [K] is the reference temperature (here is 373 K), *t* [min] is reaction time, and*ω*is the function of activation energy,*Ea* [kJ mol�<sup>1</sup> ], gas constant, *R* = 8.314 J mol�<sup>1</sup> K�<sup>1</sup> , and *T*r, as shown in the following equation.

$$\rho = \frac{R \bullet T\_r^2}{E\_a} \tag{2}$$

According to the derivation of the severity model, lignin recovery (*LR*) can be calculated by the next equation.

$$\text{Lignin\\_recovery} \ (LR)[wt96] = \{1 - \exp(-k\_r \bullet R\_o)\} \times 100 \tag{3}$$

where *k*<sup>r</sup> is the rate constants in min�<sup>1</sup> at reference temperature *T*<sup>r</sup> (373 K), as described in the following equation:

$$k\_r = k\_o \exp\left(-\frac{E\_a}{RT\_r}\right) \tag{4}$$

where *k*<sup>o</sup> [min�<sup>1</sup> ] is pre-exponential factor of the reference rate constant.

By fitting the equations to the experimental data (as shown in **Figure 3**), all the kinetic parameters were decided as to be 135 kJ mol�<sup>1</sup> for *<sup>E</sup>*<sup>a</sup> and 6.8 � <sup>10</sup>�<sup>5</sup> min�<sup>1</sup> for *k*r. The experimental data at the most severe condition (*k*r�*R*<sup>o</sup> value is over 1, and these data were obtained at 573 K for 10 min) were far from the calculated value, and the reason why the data are not fitted with the calculated value is because the cellulose in the bark was carbonized and the remained Klason lignin in the residue was estimated to be high.

As shown in **Figure 3**, lignin solubilization (lignin recovery) in hydrothermal water drastically changed between 0.1 < *k*r�*R*<sup>o</sup> value <10. The similar trend was seen in the previous reports [2, 32, 33]. From Eqs. (1), (2), and (4), the dimensionless severity number (*k*r�*R*o) is written by the below equation:

$$k\_r \bullet R\_o = k\_o \bullet t \bullet \exp\left(\frac{\mathcal{E}\_a(T - 2T\_r)}{R \bullet T\_r}\right) \tag{5}$$

**Figure 3.** *Dimensionless severity number for lignin recovery from bark of Japanese cedar (473–573 K for 3–40 min).* *Resource Upgrading in Advanced Supercritical Fluid (Supercritical Fluid with Catalyst… DOI: http://dx.doi.org/10.5772/intechopen.89793*

Eq. (5) shows that the dimensionless severity number (*k*<sup>r</sup>*R*o) is also the function of *t* and *T* as well as severity factor (*R*o) as shown in Eq. (1). While *R*<sup>o</sup> varies a wide range of values and the optimum *R*<sup>o</sup> for the target reaction is not easy to estimate, meaningful transitional change should occur at the range of 0.1 to 10 for the dimensionless severity number *k*<sup>r</sup>*R*o, as reported here and in the literatures [2, 32, 33]. Therefore, the dimensionless severity number (*k*<sup>r</sup>*R*o) is quite useful, and the severity analysis using *k*<sup>r</sup>*R*<sup>o</sup> can be adopted to various type of the reactions. Our research group is going to study on utilization of the dimensionless severity number (*k*<sup>r</sup>*R*o) for various kind of reactions and its application and usefulness with a variety of the examples will be reported in near future.
