Bioethanol production from wheat straw of the Kaliningrad region

Размещено на http://allbest.ru

УДК 663.534

Bioethanol production from wheat straw of the Kaliningrad region

Y. Zhukova, O. Mezenova

Introduction

Plant biomass is the world's most abundant renewable resource of energy. It can serve as a direct nourishment as well as a feedstock for chemical products like saccharides and aromatic species. Bioethanol has the potential to reduce the release of greenhouse gases that cause the global climate change. Commercial bioethanol is mainly produced by fermentation of monomeric sugars originated from starch.

Typical starch rich products are potatoes and crops like maize and grain. Figure 1.1 shows the annual world production of ethanol since 1975. The sharp increase of the world ethanol production since 2002 can be directly contributed to the development of the oil price. To meet the ever increasing demand of ethanol other potential feedstocks than starchy materials must be considered.

Fig. 1.1. World annual ethanol production [2]

Рис. 1.1. Ежегодное мировое производство этанола [2]

Lignocellulosic biomass is the only inexpensive resource that can be used for a sustainable production [1] of the large amount of liquid fuels needed in the transportation sector. Therefore numerous attempts to utilize biomass effectively have been undertaken in the past. In order to use plant biomass effectively the whole lignocellulosic structure has to be utilized.

Especially in the paper industry cellulose separating pulping processes, like the Kraft process [3], are well established. In this process wood chips are treated with a mixture of sodium hydroxide and sodium sulfide. The degradation products of the hemicellulose and the lignin are separated from the cellulose rich pulp and wasted or utilized for power generation [4].

In the 19th century French and Germen scientists developed a similar process to saccharify lignocellulose with concentrated sulfuric acid to monomeric sugars. Based on these findings Germany, the USA, and Russia established commercial saccharification plants at the beginning of the 20th century.

The high costs of ethanol from these plants were only affordable during times of war [3]. Due to the relative low price of oil during the middle of the 20th century ethanol from lignocellulosic biomass was no longer economically advantageous. With the constant rise of the oil price ethanol derived from plant polymers is getting back into focus.

Novel pretreatment processes of biomass promise to be more efficient than pretreatment with concentrated H₂S0₄. Despite new pretreatment techniques like alkaline treatment, steam pretreatment with S0₂ in bio-process technologies offer a promising prospective for the efficient conversion of biomass and recovery of ethanol [5]. It is widely acknowledged that the rate and extent of the enzymatic hydrolysis of lignocellulose substrates is influenced not only by the effectiveness of the enzymes but also by the chemical, physical and morphological characteristics of the heterogeneous lignocellulosic substrates [6]. Only the combination of both, effective pretreatment and enzymatic hydrolysis can bring the needed advances to make bioethanol derived from lignocellulose competitive to fossil fuels.

1. Fundamentals

1.1 Lignocellulosic Biomass

The major compounds of lignocellulosic materials are cellulose, hemicellulose, lignin, and extractives. The wood cells are composed of different layers, which differ from each other with respect to their structure and chemical composition. Basically, cellulose forms a skeleton which is surrounded by other substances functioning as matrix (hemicellulose) and encrusting (lignin) materials (compare Figure 1.1).

Cellulose, hemicellulose, and lignin are closely associated and covalent cross linkages have been suggested to occur between lignin and polysaccharides (lignin-carbohydrate complexes). The side-groups of the hemicellulose, arabinose, galactose, and 4-O-methylglucoronic acid are most frequently perceived as the connecting links to the lignin [7].

Fig. 1.1. Biomass, a composite material [8]

Рис. 1.1. Биомасса как сложный композиционный материал [8]

2. Materials and methods

2.1 Wheat straw

Wheat straw was purchased from a local animal feed supplier, the average composition is depicted in Table 1.1.

Table 1.1. Composition of wheat straw

Таблица 1.1. Состав пшеничной соломы

2.2 Experimental

2.2.1 Sequental LHW - Organosolv Process

In order to enhance the residence time of rye straw in the reaction zone and to achieve higher solid to liquid ratios, a fixed-bed reactor was designed.

The experimental setup is illustrated in Figure 2.1.

The solid fraction was retained in the reactor with a sinter plate. The solid loading in the reactor at the beginning of the reaction amounted approximately 17 g. To achieve high solid concentrations the straw was intensively compressed with a metal stick. Water was pumped through the solid biomass with an HPLC pump. Different flow rates between 1 and 10 g/min were investigated.

The pressure of the system was regulated with a spring loaded back pressure regulator.

The oven could be heated up to temperatures around 210°C. Temperatures were measured at the entrance and the exit of the column and in the oven. As a solvent was used water/ethanol-mixture with different ethanol concentrations. The reactor was heated to the temperature 165 or 180°C.

The fraction extracted at the reactor temperature, which are dissolved in the solvent, came out from the reactor with the flowing solvent.

Fig. 2.1. Fixed-bed reactor laboratory scale (V = 50 mL)

Рис. 2.1. Биореактор с фиксированной твердой фазой лабораторный (V=50 мл)

When the process was finished, the reactor was cooled down and weighted. The solids were taken out and weighted.

2.2.2 Enzymatic hydrolysis

The solid residues (0.1 g) of the sequential LHW - Organosolv pretreatment were suspended in 10 mL universal buffer and enzymes were added. At temperatures around 50°C the samples were incubated in a termo stirrer for 72 hours.

The final sugar concentrations were determined with assay kits for glucose D-Glucose HK kit, Megazyme.

2.2.3 Ethanol fermentation

The glucose fermentation was spent in the laboratory installation represented in Figure 2.2.

Fig. 2.2. Laboratory installation for glucose fermentation in ethanol

Рис. 2.2. Лабораторная установка для ферментации глюкозы в этанол

First water of 40°C (104°F) was poured into the fermenter. Then sugar was added and mixed well until completely dissolved. Then Alcotec 48 was added and stirred for one minute. Was left to ferment in 20-30°C (68-86°F), optimum is 25°C (77°F) for 5 days.

3. Results and discussion

The environmentally friendly technology for producing bioethanol from wheat straw as its complex processing of hydrothermal treatment, organosolv (ethanol-water mixture), enzymatic hydrolysis and fermentation of glucose was studied.

We also studied the technical-chemical properties of wheat straw, which represents the plant biomass, whose main components are cellulose, hemicellulose and lignin.

The most concentrated extract comes out after 15 - 20 minutes of the LHW-process (Fig. 3.1).

Fig. 3.1. Concentration of xylose in dependence on time

Рис. 3.1. Концентрация ксилозы в зависимости от времени

Optimum parameters of the process of hydrothermal treatment of wheat straw, which are temperature of 210°C and pressure 40 bar, make more efficient to allocate the structure of hemicellulose from wheat straw at 84% (Fig. 3.2).

Fig. 3.2. Xylose removal

Рис. 3.2. Извлечение ксилозы

The process of post-processing of wheat straw with a mixture of ethanol-water. An optimum parameters of the process (temperature of 180°C, pressure 30 bar, the concentration of a ethanol-water mixture of 75%), which help set the pattern of a small amount of wheat straw hemicellulose (about 5%), remaining in the plant biomass after the hydrothermal treatment, and lignin (Figure 3.3).

Fig. 3.3. Glylose removal

Рис. 3.3. Извлечение глюкозы

The process of enzymatic hydrolysis of cellulose after the hydrothermal treatment and processing of organic solvent. Revealed an inhibitory effect of lignin on cellulolytic enzymes. The process of fermentation of glucose formed after the enzymatic hydrolysis of cellulose. Fermentation was subjected to 72% glucose.

Figure 3.4 shows the process flow diagram for the production of ethanol from biomass. Whereas the fermentation of the major sugars in lignocellulosic biomass, glucose and xylose, and the separation of the ethanol/water mixture is state of the art, the hydrolysis of biomass to monomeric sugars is an active field of research.

Fig. 3.4. Process flow diagram of the synthesis of bioethanol

Рис. 3.4. Схема синтеза биоэтанола

This work was a part of a diploma thesis done by the graduate of the Department of Food biotechnology. In cooperation with the Technical University of Hamburg (Germany) an effective method for the conversion of lignocellulosic biomass to ethanol should be developed. The specifications were an environmentally friendly process, which uses the combined power of LHW (Liquid Hot Water pretreatment) and enzymatic treatment to saccharify a model substrate, which is largely available in Russia. Wheat straw is an abundant biomass in Russia and was therefore selected as model substrate.

biomass ethanol glucose fermentation

Bibliography

1. B. Yang and C. Wyman. Pretreatment: the key to unlocking low-cost cellulosic ethanol. Biofuels Bioproducts and Biorefining, 2(2):26-40, 2008.

2. F. Licht. World ethanol production, 1975-2005, earth policy institute. http://www. earth-policy, org, 2006.

3. D. Osteroth. Holzverzuckerung - Ein historischer Ruckblick. Chemie fur Labor und Betneb, 39:165-169, 1988.

4. G. Garrote, H. Dominguez, and J. Parajo. Hydrothermal processing of lignocellulosic materials. Holz als Roh- wad Werkstoff, 57:191-202, 1999.

5. С. S. Gong, N. J. Cao, J. Du, and G. T. Tsao. Ethanol production from renewable resources. Advances in Biochemical Engineering/ Biotechnology, 65:207-241, 1999.

6. R. Chandra, R. Bura, W. Mabee, A. Berlin, X. Pan, and J. Saddler. Substrate pretreatment: The key to effective enzymatic hydrolysis of ligniocellulosics? Advances in Biochemical Engineering / Biotechnology, 108:67-93, 2007.

7. D. Fengel and G. Wegener. Wood : chemistry, ultrastructure, reactions. De Gruyter, 1984.

8. W. G. Hopkins. Introduction to Plant Physiology. John Wiley & Sons, Inc., New York, 1999.

Annotation

УДК 663.534

Bioethanol production from wheat straw of the Kaliningrad region. Y. Zhukova, O. Mezenova

New pretreatment methods were developed for separating hemicellulose, cellulose, and lignin from biomass for their efficient use in the thermo-chemical conversion of each component. One method is basically a two-step process. Biomass treated in hot water at 180 °C was extracted in a flowing stream of water/ethanol mixture under 40 bar at 210 °C.

Through the hot water treatment, hemicellulose in biomass was successfully recovered as saccharides, leaving lignin and cellulose as a solid. Through the sequential extraction by the water/ethanol solvent, lignin was depolymerized into the water/ ethanol-soluble compounds and the residual cellulose was partly dehydrated. The proposed methods were expected to be new routes for converting low-grade resources into valuable chemicals.

Keywords: bioconversion, lignin removal, LHW, enzymatic hydrolysis, fixed-bed reactor, pretreatment, organosolv, fermentation

Аннотация

Технология биоэтанола из пшеничной соломы Калининградского региона. Ю. А. Жукова, О. Я. Мезенова

Новые методы предварительной обработки были разработаны для разделения гемицеллюлозы, целлюлозы и лигнина из биомассы для их эффективного использования в процессе термохимической биоконверсии каждого компонента. Один из методов состоит из двух этапов. Биомасса подвергается гидротермальной обработке при температуре 180°С, затем обработке органическим растворителем под давлением 40 бар при температуре 210°C.

Благодаря гидротермальной обработке гемицеллюлозы извлекаются из биомассы в виде сахаров, оставив лигнин и целлюлозу в качестве твердого остатка. Благодаря последующей обработке смесью этанол-вода, лигнин деполимеризуется в соединения, растворимые в смеси этанол-вода, а оставшаяся целлюлоза частично обезвоживается. Предложенные методы, как ожидается, станут новыми путями для преобразования низкокачественных ресурсов в ценные химические вещества.

Ключевые слова: биоконверсия, извлечение лигнина, гидротермальная обработка, ферментативный гидролиз, реактор, предварительная обработка, обработка органическим растворителем, ферментация

Размещено на Allbest.ru