Alkali metals, such as sodium and potassium, can promote a tar cracking reac­tion. Catalysts, such as potassium carbonate and sodium carbonate, are effective in methane production and are available in most biomass ashes. Potassium, however, is well-known for agglomeration in fluidized beds. Studies on the effects of inorganic salts (MgC12, NaC1, FeSO4, and ZnC12) on the pyrolysis of cellulose have shown that MgCl2 does not change the overall pyrolysis but has some slight effects on gas production. For the other tested catalysts (NaC1, FeSO4, and ZnC12), an increase in char production was reported [49].

Municipal solid waste (MSW) management has become a major issue worldwide. Issues related to landfilling include: occupation of large areas, generation of green­house gases by digestion of the waste, generation of hazardous and refuse materials, etc. New recovery strategies to generate energy, such as incineration, have also given rise to many problems. In Europe, particularly in Germany, rotary kiln incinerators have been extensively studied and issues related to the high temperature have been reported: leaching of metals, emission of carcinogen compounds, emission of par­ticulate matter, etc. Pyrolysis has been identified as a promising avenue for MSW management: its lower operating temperature and absence of oxygen decrease the pollutant emissions as well as the cost of post-treating flue gases.

11.2.1.6 Municipal Biosolids

Waste water treatment is a critical process for our society: waste water contains dissolved organics and inorganics as well as suspended solids and microorganisms that must be eliminated before the water can be released into the environment or purified further to be drinkable. The recovered waste forms sewage sludge, which is difficult to recycle. When dried, contaminants such as heavy metals limit its po­tential applications. Currently, it is common practice to incinerate sewage sludge with the similar disadvantages to MSW incineration (see Sect. 11.2.1.9). However, incineration could be replaced by more efficient technologies, such as pyrolysis.

The cattle and poultry breeding are the vital branches of agriculture which overall pro­duction is closely associated with population and its living standards. Local demand on their production grows with the increase of the population density. Partly there­fore a shift toward larger farms which do not produce their own forage is observed recently in this sector; it made the manure disposal issue very important. Its mis­handling leads to bacteriological contamination of ground waters [17]. Meanwhile manure is a biomass and it can be used as a renewable energy source.

The manure composition can significantly vary depending on disposal technolo­gies, even if it is produced by the same group of animals. Therefore, determination of average composition of waste demands separate investigation. Here, for example, cow and chicken manure will be studied.

As described above, the flexibility and good generality combined with the ease of recovering the lignin and hemicellulose sugar streams make organosolv pre­treatment one of the most efficient pretreatment techniques. Its fundamentals and effective operation factors for improvement of the enzymatic hydrolysis have been well demonstrated in this literature. However, organosolv pretreatment still possesses several disadvantages [78] as below:

1. A higher cost that is associated with the handling and recovery of the organic solvent.

2. Pretreatment efficiency is still relatively low for softwood and similar feedstocks.

3. Its lignin product tends to be less water-soluble, which may limit its use in some applications.

4. Currently, there are few organosolv pretreatment operations on a commercial scale, and there are fewer commercial sources of organosolv lignin for further exploitation.

To resolve the above problems, further develop organosolv pretreatment technology, and consequently benefit the economics of the entire cellulosic bio-fuel production, we present the following recommendations:

1. Optimizing the effective factors of organosolv pretreatment on certain biomass materials, such as reaction time, temperature, catalyst concentration, biomass — to-solvent ratio, against the delignification and enhancement of sacharifaction by surface response design or orthogonal design.

2. Advancing the pretreatment process by (i) using cheaper and renewable medium; (ii) using highly efficient microwave-irradiation and ultrasonic techniques to re­place the common thermo heating and mechanical stirring methods [82]; (iii) employing two-phase heterogeneous medium; (iv) performing concentration op­eration with preheated aqueous organic fluids [65]; and (v) combining organosolv pretreatment with other methods to achieve higher delignification and hydrolysis efficiencies, especially for softwoods.

3. Improving the fundamental knowledge on the pretreatment technologies espe­cially for some recalcitrant biomasses (such as softwood).

4. Investigating new processes and products from the organosolv lignin and hemicellulose sugars derived from the organosolv process.

5. Conducting economic evaluation of the entire organosolv pretreatment.

6. Demonstrating organosolv-pretreatment technology on a pilot scale to obtain engineering data for industrial scale processing and sufficient refined products for characterization and exploitation.

16.3.2.1 Liquid Hot Water (LHW)

Hot-water pretreatment changes the structure of lignocellulose and solubilizes the hemicellulose, thus keeping cellulose amenable for cellulolytic enzymic action [18, 29]. LHW penetrates inside the lignocellulose matrix and degrades hemicel — lulose into xylose and other accessory sugars with the least generation of inhibitors [17]. The required pressure was applied at high temperatures (160-240 °C) for the cell wall degradation [29]. Laser et al. [30] reported 80 % xylan recovery from SB after hot-water pretreatment (170-230 °C, 1-46 min) which showed 90 % ethanol conversion after simultaneous saccharification and fermentation (SSF).

16.3.2.2 Autohydrolysis

Autohydrolysis is a process that involves the use of steam with or without explosion, based on the selective depolymerization of hemicelluloses from SB/SL [14]. The hydrolysis of acetyl groups generates acetic acid, and hemicelluloses breakdown into its monomeric constituents. Mechanically, a quick reduction of pressure (0.69­4.83 MPa) at high temperature (160-260 °C) provokes an explosive decompression of lignocellulosic material effectively releasing hemicellulosic sugars, preserving the physical-chemical properties of the cellulose [14].

During autohydrolysis, due to depolymerization and repolymerization reactions lignin moieties are redistributed on the fiber surface promoting an enhancement of the pore size and surface area of SB/SL. Hemicellulose is solubilized under high temperature and short residence time (270 °C, 1 min) or lower temperature and longer residence time (190 °C, 10 min) [15, 31]. Dekker and Wallis [32] performed auto hydrolysis of SB at 200 °C for 4 min and observed 90 % solubilization of hemicellulose. The pretreated bagasse enzymatically hydrolysed, revealed 80 % saccharification after 24 h.

The presence of phospholipids in feedstocks is a serious concern to the biodiesel in­dustry. This is basically due to their emulsifying properties and their negative impact on cold soak filtration times and consequently cold weather fuel performance. When phospholipids are present in the biodiesel alkaline transesterification production pro­cess they complicate phase separation of products as they lead to the formation of emulsions which are hard to break. This situation can be detrimental to downstream processing by ion-exchange resin, processing yield, and final product quality. Also, phospholipids pose many problems for the storage and processing of the crude oil, therefore must be removed from oil during refining by a process known as degumming [42,43].

Lipids obtained by screw pressing (mechanical extruding) and solvent extraction are termed “crude oils” which form deposits or gums upon storage. The chem­ical nature of these gums consists mainly of phosphatides which entrain oil and meal particles which are formed when the oil absorbs water. Under such conditions gums become oil-insoluble (hydrated phosphatides) which can be readily removed by filtration.

Accordingly, hydrating the gums and removing the hydrated gums before storing the oil can prevent the formation of gum deposits; such treatment is called water degumming. Other ingredients, including FFAs, hydrocarbons, ketones, tocopherols, glycolipids, phytosterols, phospholipids, proteins, pigments, and resins, which are oil-soluble or form stable colloidal suspensions in the oil are normally removed from vegetable oils by chemical or physical refining processes which involve the use of phosphoric acid, citric acid, or other degumming substances [44, 47, 48].

Degumming process plays a critical role in the physical refining process of edible oils. Traditional degumming processes, including use of membranes [49], chelating agents [50], enzymes [42, 51, 52], water degumming, acid treatment, and TOP degumming (water degummed oil is heated up to 90-105° C, thoroughly mixed with degumming acid, mixed with dilute caustic and then separated, and washed with water) or “total degumming process,” [45, 46] cannot all guarantee the achievement of low phosphorus contents required for physical refining. Such methods are not always optimally suited for all oil qualities because of the high content of non — hydratable phospholipids [53].

The vegetable oil refining industry has also recently experienced the use of free microbial enzymes for degumming of plant oils. Phospholipase A1 (Lecitase Ul­tra, Novozymes) and Phospholipase C (Purifine, Verenium) are the most prominent enzymes which already have found real industrial applications in oil degumming [42, 51]. Phospholipase A1 catalyzes the hydrolysis of fatty acyl groups at the sn — 1 position of phospholipids to form 1-Lyso-phospholipids and a free fatty acid in the first stage, and glycerophospholipids and a free fatty acid in the second hydrol­ysis stage. The formed 1-Lyso-phopholipids and glycerophospholipids have both increased hydrophilic characteristics which can be easily washed out of oil with mild-acidic water solution.

Phospholipase C cleaves the phosphoric acid ester bondage in phospholipids molecules to form di-glycerides and phosphoryl alcohols. The formed phospho — ryl alcohols are hydrophilic molecules which can also be washed easily with water to obtain degummed oils [22].

Both enzymes, Phospholipase A1 and Phospholipase C have been applied at industrial scales in the oil refining industry; however, because of their costs are still not widely used in the oil industry. Similarly, the costs related to the use of both enzymes in degumming of oils feedstocks are economically unaffordable in the biodiesel industry.

It has been demonstrated that the immobilized enzymes, TransZyme and Es — terZyme, both developed by TransBiodiesel, are capable of transesterifying phospho­lipids and methanol to form biodiesel and glycerophospholipids, thereby allowing the use of crude plant oils in the biodiesel production process. While the formed glycerophospholipids are of hydrophilic characteristics, they accumulate in the glyc — erol/water phase and thereby facilitating the biodiesel downstream processing as well as increasing the biodiesel production yield by 1-2 %.

Jing Dai and Armando G. McDonald

Abstract In this study, the target product was the generation of sugars from woody biomass that can be the substrate for conversion into value-added chemicals, such as polyhydroxyalkanoates, lactic acid, succinic acid, etc. In order to release sugars from wood economically, wood needs to be pretreated to enhance the enzymatic hydroly­sis of cellulose and hemicelluloses. The primary goal of this study was to determine the optimal condition to obtain fermentable monosaccharides from hydrolysates of hybrid poplar by a hot-water pretreatment (150-210 °C, 0-30 min). The pretreat­ment conditions were optimized using a response surface methodology (RSM) on a 23 full central composites design was performed by varying on temperature, reac­tion time, and solid loading. After pretreatment, the solid residue was subsequently treated with a cellulase preparation, and released sugars were quantified by HPLC. The total sugar yield was applied as response variable to the RSM. The optimal pretreatment condition for producing sugars was 200 °C, 18 min, and 20 % solid loading.

Keywords Hybrid poplar ■ Hot-water pretreatment ■ Enzymatic hydrolysis ■ Sugars ■ Response surface methodology

9.1 Introduction

Lignocellulosic biomass includes a wide range of carbon-rich resources, which can be utilized as feedstock for production of many industrial products ranging from lumber, paper, chemicals, biofuels, and value-added biodegradable polymers [1]. The technique for conversion of lignocellulosic biomass to fuel ethanol has been well developed. Cellulosic ethanol, however, has economic barriers to overcome to be economically competitive [2, 3]. Therefore, upgrading the conversion of cel — lulosic biomass to higher value products such as polyhydroxyalkanoates (PHA)

A. G. McDonald (H) ■ J. Dai

Renewable Materials Program, Department of Forest, Rangeland and Fire Sciences, University of Idaho, Moscow, Idaho 83844-1132, USA e-mail: armandm@uidaho. edu

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_9, © Springer-Verlag Berlin Heidelberg 2013 would gain better commercial value compared to cellulosic ethanol. The cost of the carbon substrate reportedly contributes more than 40 % of the production cost of PHA [4-6]. The use of inexpensive renewable agricultural materials such as woody biomass as feed stocks could be a tremendous advantage to the economics of PHAs production.

Hybrid poplar, as a short rotation fast growing wood species with low lignin content, has been highlighted as a good biomass resource for fuel and chemi­cal production [7, 8]. Xylose is the main constituent of hardwood hemicellulose (acetyl-4-omethylglucuronoxylan). Recently, studies showed that xylose can be obtained via a pretreatment process using dilute sulfuric acid (H2SO4) [9, 10]. Cellulose in wood is present as a semi-crystalline polymer and is comprised of glucose building blocks linked by P-o-4 linkages which can be cleaved by acids or enzymes. The major proportion of cellulose exists in the crystalline form. How­ever, cellulose is more susceptible to degradation in its amorphous form [11]. Thus, breaking down cellulose crystalline structure to make it more accessible to cellulase enzymes usually requires pretreatment with heat, long reaction time, and addition of catalysts [8]. Lignin as a bonding component in wood is an in­hibitor for hydrolysis or further fermentation process [11]. A pretreatment process can not only depolymerize lignin structure, but also remove some lignin in wood [12, 13]. Enzymatic hydrolysis is the most common method for converting woody biomass to sugars. Compared with acid hydrolysis, enzymatic hydrolysis yields no fermentation inhibitors such as furfural and it does not need neutralization and detoxification [2]. The only disadvantage of enzymatic hydrolysis is longer reaction times required for releasing the sugars. However, enzymatic hydrolysis is a better choice if further fermentation or bioconversions are required to produce value-added chemicals.

Hot-water pretreatment with controlled pH has been shown to improve enzymatic digestibility of lignocellulosic biomass [2,14]. Acetic acid and other organic acids are released from the hemicelluloses, which help autocatalyze hemicellulose hydrolysis and disrupt cellulose and lignin structure. Unlike the anaerobic fermentation for cellulosic ethanol production, organic acids, such as acetic acid, are not considered as inhibitors during PHA biosynthesis but used as carbon source for PHA production

[6] . The pH of the pretreatment liquor needs to be between 4 and 7 to minimize decomposition of sugars [2]. For the purpose of scale-up or industrial production, determining the optimal pretreatment conditions by using statistical approach is important. The experimental design works for variety of species, chemical reagents, temperature, and reactor features.

The aim of this study was to find optimal conditions to obtain total sugars (mainly glucose and xylose) by enzymatic hydrolysis via a hot-water pretreat­ment. A response surface methodology (RSM) was chosen to determine the optimal pretreatment conditions for sugar concentrations in enzymatic hydrolysates. Re­action time, temperature, and solid loading were the three variables tested in this design.

The chemical composition of the gasification product strongly depends on the type of gasifier. Different reactors have been used to perform the gasification process. The different types of reactors can be categorized based on the specifics of the solid transportation in the reactor or the means by which the gasifying agent is introduced to them. The main characteristics, advantages, and limitations of the most widely used gasifiers are summarized in Table 10.3.

Pressure influences the equilibrium reactions and therefore affects the volatile prod­ucts composition: the condensable (bio-oil) and non-condensable gases. It has also been shown that pressure can promote other gas-solid reactions involving moisture, hydrogen, carbon dioxide and possibly other gaseous species. The mechanisms in­volved remain unclear, but chemical reactions such as the Boudouard reaction are suspected:

C(S) + CO2g ^ 2CO(g) (11.2)

Moisture, which is inevitably present during biomass pyrolysis, has also been shown to influence the volatile yield and composition [43]. These reactions are characterized by fast kinetics only under specific conditions: they generally occur in pressurized gasification and under high temperatures, while pyrolysis is typically performed at milder temperatures.

The solids will not be significantly influenced by pressure if an inert gas is em­ployed [44,45]. Experimentation is still the best method to characterize the effect of pressure on the pyrolysis products since it is specific to the biomass feedstock used.

Figure 12.7 and Table 12.2 represent the experimental and calculated data of investigation of the plasma gasification of biomass using wood waste as the example.

Feedstock consumption was determined by differences of mass streams of major elements (carbon, hydrogen, oxygen, and nitrogen) assuming that ash content and the nitrogen content in wood are negligibly small. The fuel element composition was determined by mean values of flow rates of carbon, hydrogen, and oxygen of fuel for two intervals. The lower heating value (LHV) was estimated by this composition (by formula for an estimation of heating value of biomass [92]).

The mode of wood plasma gasification was observed on the interval 9:43-16:30. About 606.34 kg of wood was processed during this period according to the estimates, and actually about 609.98 kg of wood was loaded into the reactor in the course of the experiment. That validates the technique of experimental data processing.

The experimental results were compared with calculations for two regimes with constant air plasma flow rate and powers of plasma torches (see Table 12.2). The comparison showed that the data agreed well for the chemical energy yields and are satisfactory for syngas composition.

Calculations were carried out assuming adiabatic process and thermodynamic equilibrium of gasification products composition. On these modes, the composition of raw materials which matches to wood with moisture of 8-10 % also had been

determined. Well data agreement on the chemical energy yields was explained by the fact that the air plasma flow rate was more than stoichiometric in 2.8-3.0 times. It led to a considerable shortening of a reduction zone, therefore heat losses did not significantly affect syngas composition. More considerable difference in composition is caused by high methane stability and water-gas shift reaction at weak reaction rates and branch pipe sampling zones. As a whole, comparison results confirm usability of equilibrium approach for the estimation of plasma gasification key parameters.