ETHANOL PRODUCTION FROM YAM (DIOSCOREA SPP) PEELS

Abstract

This work is concerned mainly with the production of ethanol from yam (Dioscorea spp) peels. The yam tubers were bought from Eke Oko Market, in Orumba North L.G.A. Anambra State. The tubers were peeled and the peels washed, milled & weighed. To 1000 g of the powdered wort, distilled water was added, mashed & filtered. Yeast & malt were added to the filtered wort and allowed to stand for three days for fermentation. The fermented wort was distilled to collect a colourless liquid as the distillate. This distillate was neutral to litmus test, soluble in water, forms esters with acetic acid and positive to lucas test showing it to be a primary alcohol-ethanol.

CHAPTER ONE

INTRODUCTION

Background of the study

Yams (Dioscorea spp) of the family Dioscoreaceae are members of the flowering plant. They are monocots, related to palms, grasses and orchids. Most yam species grow in the tropics and subtropics area with fairly heavy total annual rainfall, but with a definite day season. During the rainy season, they produced one or more underground tubers to store food and water through the dry season the tubers are thickened stems. Most yam plant have small flower with one plant having only male or female flower (Kay, 1987).

The tubers of most species of yam are poisonous to humans. The cultivation of most yams is very labour intensive. Cultivated yams generally do not produce seed and so tubers or pieces of tuber must be planted in prepared soil, most often in wounds to grow new plants.

Yams are nutritious food, providing carbohydrate, some protein, and mineral like phosphorus and potassium besides the use as food, yams have been symbolically associated with culture and ritualism in some parts of Africa, Asia and Latin Americas.

According to Ogbuka (2005) Ethanol can be produced from starch containing substances like maize, cassava and yam. Ethanol is a monohydric alcohol that is colourless and flammable, it is a 2 –carbon alcohol with molecular formula CH3 CH2 OH, its empirical formula is C2H6O. An alternative notation is CH3CH2 OH which indicates that the carbon of a methyl group (CH3) is attached to the carbon of an ethylene group (CH2-) which is attached to the oxygen of a hydroxyl group (OH). Ethanol is a colourless liquid that burns with a smokeless blue flame. It has a choking smell and a boiling point of 780c. They are characterized by the possessing of hydroxyl group (OH) as their functional group. Alcohols can be classified as primary, secondary and tertiary. The primary alcohols have only one or no alkyl group attached to the hydroxyl bonded carbon atom, the secondary alcohol contain two alkyl group attached to the hydroxyl bonded carbon atom while the tertiary alcohol contains three alkyl groups but no hydrogen attached to the hydroxyl- bonded carbon atom while the tertiary alcohol contains three alkyl groups but no hydrogen attached to the hydroxyl-bonded carbon atoms:

According to West et.al (2007) ethanol is a principle fuel that can be used as petrol substitute for vehicles. It is a renewable energy source produced mainly by sugar fermentation process. It is used in preservation of specimen, food e.t.c and even as a raw material in the manufacturing of chemicals and pharmaceuticals like trichloromethane

Statement of the Problems

Alcohol has been known to be produced from fossil like maize, cassava, even yam tuber but there is still need to search for other sources considering the usefulness of ethanol source, hence the need for this study. Furthermore, yam peel are regarded as waste after using the main yam tuber, therefore there is need to source for alcohol in this peel which either are throw away. This study will also reduce environmental pollution which is caused by the yam peel.

  • Objectives of the Study

Objectives of this study include:

  • To extract ethanol from yam peel
  • To carry out qualitative test on the produced ethanol

Significant of the Study

The knowledge from this study will help in creating awareness to the government as well as the society at large on the need to grow more yams. Finally this study will also help the society to know that ethanol is not just present in the yam tuber alone but also in the peels (yam peels)

Scope of Study

This study is concerned with the production of ethanol using yam peel which involves

  • Collection and identification of the sample
  • Preparation of the sample
  • Production of ethanol from the sample
  • Qualitative tests on the produced ethanol.

 

CHAPTER TWO

LITERATURE REVIEW

2.1   Origin and History of Yam

Yam (Dioscorea spp) is an annual perennial tuber bearing and climbing plant belonging to the family of Diocerecaea. Some species of yam originated from Africa before spreading to other parts of world while some originated from Asia and have spread to Africa (Halm et.al, 1987).

Today, yams are grown widely throughout the tropics and they have a large biological diversity including more than 60 species worldwide (Burkill, 1960; coursey, 1967) but only six species are widely cultivated in west and central Africa. The cultivated species are D. alata, D. bulbifera, D. dumetorum, D. esculenta, D. cayenensis and D. rotundata. Wild types also exist and may be used as food after undergoing processing during the hunger season (Tetteh and Saakwa, 1994).

2.2   Description of Yam

Yams are monocots, related to lilies and grasses. Native of Africa and Asia, yam tubers vary in size. It can grow up to 1.5 meters (4.9 feet) in length and weight up to 7.6 to 15.2cm (3.0 to 6.0 inch) high. The vegetable have a rough skin which is difficult to peel, but which suffers after heating.

2.3   Taxonomy of Yam

Yams are members of the flowering plant genus Dioscorea

Kingdom    :   Plantae

Division   :   Magnoliophyta

Class   :  liliopsida

Order     :   Dioscoreales

Family  :  Dioscoreaceae

Genus     :   Dioscorea

2.4 Harvesting of Yam

Yam in West Africa are typically harvested by hand using sticks, spades or diggers (linus opera, 2003) Wood-based tools are preferred to metallic tools as they are less likely to damage the fragile tubers; however, wood tools need frequent replacement. Yam harvesting is labour intensive and physically demanding. It involves studying, bending, squatting and sometime sitting on the ground depending the size of mound, size of tuber or depth of tuber penetration. Care must be taken to avoid damage of tuber because damaged tubers do not store well and spoil rapidly.

2.5   Nutritional Composition of Yam

Yam tuber is the most economically utilized part of the yam plant. Its chemical composition varies with species. It may vary down to the environmental condition of the places cultivated (onwuene, 1978). Yam is essentially starchy food. Its greatest single component water accounting for about 65.85% of the fresh weight. Carbohydrate on the other hand is the major component most of its species contain carbohydrates which are mainly starch. i.e annylopetic branched chain existing in the cells in form of starch granules (Uguru, 1993), sugar and protein are only in a quantity of about 2.3 respectively, with protein being mainly sulphur containing amino-acid most of which are caused of the tuber is chilled (Puiseglore, 1976).

TABLE 1: Chemical composition of yam

(D. rotundata) (white yam)

Component        % Composition

Energy           112kg

Moisture         70.2

Protein         35

Fat              0.1

Fibre            0.5

Ash             1.0

Total carbohydrate    25.2

Source: Walsh, (2003)

Furthermore, most yam tend to be rich in thiamin, ribo lailin, nialin etc (Egbe et. al, 1984)

2.6   Diseases of Yam

Yam are being affected by the following diseases:

  • Anthracnose (scorch) (colletotrichum gloeosporioides: – It is a small, dark brown spot or black lesions on leaves which may be surrounded by a chlorotic halo; leaf necrosis; die back of stem; withered leaves and scorched appearance. It can be by using plant yam varieties that are resistant to anthracnose such as TDA 291.
  • Dry rot disease (caused by yam namatode) (scutellonema):- the infected tubers show dry rot of I to 2cm initially this dry for is of cream and light yellow lesan appear just below the outer skin without any external symptom. It can be managed by using disease free tuber/setts for planting
  • Yam mosaic disease:- the common symptom are infected leaves show yellow and green patterns (called mosaics) between the veins (called vein banding). It can be managed by the use of healthy and disease free tubers or setts for planting and also collecting of crop debris and destroying them.

2.7   Uses/Importance of Yam

  • Tuber is the main part of the yam plant which has high carbohydrate content (low in fat and protein) and provides a good source of energy.
  • Unpeeled yam has vitamin C
  • It is medicinal because it is use as a heart stimulant (attributed to its chemical composition, consist of alkaloids of saponin and sapogenin);
  • It is used in the industry in production of starch.
  • It is used in rituals and festivals

2.8   Alkanols

Most common aliphatic alkanols contains only bond hydroxyl group in each molecule they are referred to as monohydric alkanols form a homologous series with the general formula CnH2n+1.OH. Since the group CnH2n+1 is the alkyl group and can be represented generally by R the general formula of the monohydric alkanols can also be written as R0H. The name of each homologue is divided by dropping the end e of the corresponding alkene and replacing it with all the IUPAC and common name of first few members of the alkanol series is shown in table 2. 

Table 2: the IUPAC and common names of the first few members of the monohydric alkanol series (Ababio, 1990,)

Molecule Formula Structural Formula   LUPAC Name Common Name
CH4O                   CH3 OH               Methanol     Methyl alcohol

C2H6O                 CH3CH2 OH        Ethanol          Ethyl alcohol

C3H8O                 CH3 (CH2)2 OH       Propan-1-ol           n-propyl alcohol

C3H8O                  CH3CHOHCH3         pron-2-0      lso-propyl alcohol

C4H10O                 CH3 (CH2)3OH         Butan-1-ol      n-butyl alcohol

2.9   Types of Alcohols

According to Ogbuka (2005) alcohols are classified according to the members of hydroxyl groups present per molecule, namely; monohydric alcohol e.g CH3CH2OH, dihydric alcohol e.g OH-CH2-CH2-OH e.g 1,2 – ethane diol or ethylene, polyhydric alcohol e.g OH-CH2-CHOH CH2OH e.g glycerol or propane-1,2,3, triol.

  1. Monohydric Alkanols

According to stroke, (1972), the monohydric alcohols occur in nature in combination with carboxylic acid as esters-these compounds are responsible for much of the taste and smell of flowers and fruit. These characteristics odour make the valuables ingredients for perfume.

The monohydric alkanols form homologous series with the general formula CnH2n+2O, which is written more satisfactory as CnH2n+1 OH, since their functional group is the hydroxyl group. For example, CH2OH (methanol), CH3CH2OH (ethanol). The monohydric alcohols are subdivided into primary secondary and tertiary forms. The three classes of alcohol show different chemical properties when oxidized. A primary Alkanol has only one alkyl group attached to the carbon atom that carries the hydroxyl group, a secondary alkanol has two while a tertiary alkanol has three. The examples are shown below;

H                            H                               CH3

 

CH3        C      OH   CH3    C       CH3    CH3       C     OH

H                         OH                             CH3

Primary alcohol             Secondary alcohol        Tertiary alcohol

2.10 Description of Ethanol

Ethanol also commonly called alcohol, ethyl alcohol, and drinking alcohol, is the principal type of alcohol found in alcoholic beverages, produced by the fermentation of sugar by yeasts. The molecule is a simple one being an ethyl group linked to a hydroxyl group. Its structural formula CH3 CH2OH is offer abbreviated as C2H5OH / C2H6O Ethanol is a volatile, flammable, colourless liquid with a slight chemical odor.

It is used as antiseptic, a solvent, a fuel and due to its low freezing point, the active fluid in many alcohol thermometers.

2.11 Properties of Ethanol

2.11.1 Physical Properties of Ethanol

  • Ethanol is a colourless, volatile liquid and possessed of a characteristic smell (Holderness and Lambert, 1976).
  • It is readily soluble in water in all preparation (due to the presence of the hydroxyl group)
  • It has a boiling point of 78oC
  • It has no action on litmus paper.

2.11.2     Chemical Properties of Ethanol

Combustion:- Alcohol burns readily in oxygen to produce carbon dioxide and water C2H5OH+3O3            2(O2+3H2O, other reaction of alcohols are characterized by functional group (-OH) Which may involve either cleavage of ROH.

Both may produce a mixture of substitution and elimination products that depends essentially on the nature of the alkyl group to which the hydroxyl group is bonded (Ogbuka, 2005) these reaction are

Oxidation

Ethanol is readily oxidized to ethanol by worrying with potassium heptaoxodichromate (vi) solution, which has been acidified with dilute

2.12 Preparation of Ethanol

  • By the hydrolysis of alkyl halide with agueous alkali or silver oxide suspended in water

RX+ NaOH                           ROH + Nax

RV + NgOH                 ROH +Agx

e.g C2H5Br + NaOH     wash            C2H5OH + NaBr

  • Hydrolysis of ester with alkali this is simply saponification of ester

R’COOR2 + KOH                           R’COOR + R2OH

CH3COOC2H5 + NaOH   boil     CH3 COONa + C2H5OH

  • By fermentation process.

Ethanol can be obtained by fermentation process. Fermentation is the decomposition of complex organic compound into simple compounds through the agency of enzymes.

Enzymes are organic catalysts secreted by living cells. The starting material is always starch (C6H10O5)n, which is obtained from sources depending on the particular country. Common sources of starch are corn of various sorts, wheat, barley, potatoes molasses e.t.c (Ogbuka, 2005).

2.13 Uses of Alkanols (Ethanols)

  • Ethanol is an important solvent used to dissolved resins varishes, lacques, soaps perfumes, dyes, drug, and flowing extracts.
  • It is a raw material used in the manufacturing of many inracing core and in rocket.
  • Preservation of specimen food etc
  • Ethanol is present in many alcoholic beverages such as bee, wines and spirits (e.g whisky gin brandy, ram etc).
  • Sterilization process for example for example cleaning the skin before injection.