final exam revision‘s answer
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Dr Yu’s partSection B:2.First generation and second generation of biofuel productionThe main distinction between first and second generation fuels is feedstock used. First generation biofuel use food-crops; seeds, grains or sugars (often edible) as feedstock directly, while second generation biofuel using non-edible residues of food crop production, which mainly are lignocellulosic biomass, such as waste wheat-straw.The common method of first-generation biofuel production is ethanol made by fermenting sugar extracted from starch contained in starch-laden crops. In the production of second generation of biofuel, enzymatic hydrolysis of cellulose is carried out by yeast that has been genetic engineered to be able to convert cellulose to ethanol.Nowadays, scientists are encouraged to focus on second-generation biofuel, which is more environmental-friendly and sustainable. But first generation biofuel causes social ethical argument and food insufficient problem.Hence, in general, first generation biofuel companies cannot get subsidize from government but second generation biofuel companies have able to gain.First-generation fuels are already being produced in significant commercial quantities in a number of countries. Second-generation fuels are not yet being produced commercially in any country.3. Describe the method in the determination of pesticide residues in vegetables andfruits.In this experiment, enzyme assays are involved. Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition. For pesticide residue, enzyme inhibition is used.(a)Reaction:Normally, when substrate was added into the enzyme solution, substrate will react withenzyme rapidly and compose a red-color substance. Thus, after adding substrate,solution color turns red.(b)Inhabitation:However, pesticide contains a specific chemical which act as an inhibition role. Whensubstrate and inhibition present in a same solution at the same time, enzyme could preferto bind to inhibition instead of substrate. Nevertheless, the reaction between inhibitionand enzyme can not form any colorful substance. From this point, solution color doesnot turn.To sum up,→→ If the solution color turns red, the solution does not contain pesticide.→→ If the solution color does not turn red or just a few red, the solution contains pesticide.The quantity of pesticide is inverse proportional with level of red color turned.From this point, measurement of pesticide residue involved the use of spectrograph. The less red color, the more pesticide level in the sample is.Equation: Inhibition rate =(△A0－△A t) ÷△A0×100%where △A0 is the change of absorbance in control in 3 minutes△A t is the change of absorbance in sample in 3 minutesIf Inhibition Rate, IR for short, is higher than 50%, it stands for the presence of pesticides residues, presented as Fail.If IR is lower than 40%, it stands for the absence of pesticides residues, presented as Pass.If IR is between 40% and 50%, the experiment must be repeated once again.Section C:A = - log10 T or A = log10 (1/T)A = 2 - log10 %TThese equations reveal that transmittance and absorbance are inversely related. That is, the more a particular wavelength of light is absorbed by a substance, the less it is transmitted. Moreover, the inverse relationship between A and T is not linear, it is logarithmic. Therefore, if 50% of the photons of monochromatic light are transmitted by a sample (T is 0.5), it follows that 50% of the photons areabsorbed, but A is not 0.5, A is 0.3. If 10% of the photons of monochromatic light are transmitted by a sample (T is 0.1), it follows that 90% of the photons are absorbed, but A is not 0.9, A = 1.0. When A is 2.0, 99% of the photons of monochromatic light are absorbed, and when A is 3.0, 99.9% of the photons of monochromatic light are absorbed.A spectrophotometer is capable of displaying both transmittance and absorbance. Usually you will be required to record one of these. It is then easy to calculate the other if it is needed later.A sample calculation is shown below.Cytosine has a molar extinction coefficient of 6*103 at 270 nm at pH 7. Calculate the absorbance and percent transmission of 1*10-4 M cytosine solution in a 1-mm cell.Solution: For1*10-4M, the absorbance A is given as,A = log(I0/I) = e * b * c = 6*103 * 0.1 * 1*10-4 = 0.06in percent transmission, I/I0 * 100,A% = 10-0.06 * 100 = 101.94 (%) = 87.10 %Car&Ruan’s part (2*2’ + 2*10’)Experiment 1: Activated carbonClassifications (Maybe long question )Activated carbons are complex products which are difficult to classify on the basis of their behaviour, surface characteristics and preparation methods. However, some broad classification is made for general purpose based on their physical characteristics.Type Made from Size ApplicationActivated carbon powders or finegranules less than 1.0 mmbetween.15and .25 mmSpill cleanup,Groundwater remediation, Drinking waterfiltration,Air purification,Volatile organic compounds capture frompainting, dry cleaning, gasoline dispensingoperations, and other processesPowdered activated carbon (PAC) crushed or groundcarbon particlesretained on a50-mesh sieve(0.177 mm)Added directly to process unit, gravityfiltersGranulated activated carbon (GAC) 0.297 mmsmaller externalsurfacewater treatmentPelleted activated carbon (EAC) Consists of extrudedand cylindricalshaped activatedcarbon0.8 to 5 mm gas phase applications (low pressuredrop, high mechanical strength, lowdust content)Impregnated carbon Contain inorganicimpregnantair pollution control (H2S adsorption)Polymers coated carbon coated with abiocompatiblepolymerHemoperfusion.Other special forms Clothes and fiberReview questions4.1 What properties attribute to the adsorption ability of activated carbon?Because activated carbon has high surface area, so, activated carbon is active. Sufficient activation for useful applications may come solely from the high surface area, though often further chemical treatment is used to enhance the adsorbing properties of the material. Activated carbon also has high degree of microporosity, just one gram of activated carbon has a surface area of approximately 500 m², as determined typically by nitrogen gas adsorption.4.2 What are the two major production processes for making activated carbon? Briefly describe them.Activated carbon can be produced by carbonaceous source materials like nut shells, coconut husk and so on. It can be produced by two processes; physical reactivation and chemical activation.Physical reactivation is defined as the source is developed into activated carbons using high temperature or hot gases. This is generally done by one or a combination of the two processes; Carbonization and Activation/Oxidation. Carbonization means material with carbon content is pyrolyzed at temperatures in the range 600–900 °C, in absence of oxygen (usually in inert atmosphere with gases like nitrogen). Activation/Oxidation means raw material or carbonized material is exposed to oxidizing atmospheres (oxygen or steam) at temperatures above 250 °C, usually in the temperature range of 600–1200 °C.Chemical activation is prior to carbonization. The raw material is impregnated with certain chemicals. The chemical is typically an acid, strong base, or a salt. Then, the raw material is carbonized at temperatures (450-900 °C) lower than physical reactivation. Chemical activation is preferred over physical activation owing to the lower temperatures and shorter time needed for activating material.4.3 In terms of physical characteristics, what are the five classes of activated carbon?Powdered activated carbon, Granular activated carbon, Extruded activated carbon, Pelleted activated carbon, Impregnated carbon, Polymer coated carbon and others.4.4 What environmental applications could activated carbon be used for?Activated carbon can be used in gas, water purification, metal extraction, sewage treatment and so on. In environmental applications, activated carbon has applications in removing pollutant from air, water and in industrial processes such as; spill cleanup, groundwater remediation, drinking water filtration, air purification and absorbing volatile organic compounds.Experiment 3: Total nitrogenMacro-Kjeldahl MethodPrinciple: In the presence of sulfuric acid (H2SO4), potassium sulfate (K2SO4), and cupric sulfate (CuSO4) catalyst, amino nitrogen of many organic materials is converted to ammonium. Free ammonia also is converted to ammonium. The produced ammonium is then converted to ammonia after the addition of base. And then the ammonia is distilled from an alkaline medium and absorbed in boric acid. Finally, the ammonia may be determined colorimetrically, by ammonia-selective electrode, or by titration with a standard mineral acid.Ammonia:- conversion to gaseous fromNH4+ + OH- NH3 + H2O, pH = 9.5- distillation and absorptionNH3 + H3BO3NH4+ + H2BO3-- titrationH2BO3- + H+H3BO3Organic nitrogen - Acid digestionOrganic nitrogen + H2SO4 (NH4)2SO4 + CO2 + H2ODigestion reagent (K2SO4 & CuSO4) added to raise digestion temperature to 370o CProcedure:a.Standard ammonium chloride preparation.b. Sample preparation.c. Digestion. Add a few glass beads, mixing, boil, white fumes are observed. Digested 30 min, color become transparent and pale green.d. Distillation. Cooling, dilute to 100 ml, mix. Add 25 mL sodium hydroxide-thiosulfate reagent to form an alkaline layer at flask bottom. Connect flask to a steamed-out distillation apparatus and swirl flask to insure complete mixing. Distill and collect 200 mL distillate. Use 25 mL indicating boric acid as absorbent solution when ammonia is to be determined by titration.e. Final ammonia measurement. Titrate ammonia in distillate with standard 0.02N H2SO4 titrant until indicator turns a pale lavender.Calculation:The total nitrogen in the sample can be calculated from the following equation,mg N/L = (A–B) / L samplewhere A = amount of N of the sample calculated by the standard curve, mg; B = amount of N of the blank calculated by the standard curve, mg.Sunshine’s part. (2*2’+1*15’)Experiment 2:The Van Dorn SamplerMulti-function water quality meterPH meterTurbidity meter-principle:comparison of the intensity of light scattered by the sample under defined conditions with the intensity of light scattered by a standard reference suspension under the same conditionsDesiccator: cool the evaporating dish and Gooch crucible.Gravimetric method to measure TS, TDS, TSS.(make up the volume to a settled volume)Procedure of measuring the TDS, TSS:Preparation of Gooch crucible with glass-fiber filter and evaporating dish: heat clean crucible and dish to 103 to 105℃for 1 h. Store and cool dish in desiccator until needed. Weigh immediately before use.Pipette 50 ml well-mixed sample (pipette from the approximate midpoint) onto a glass-fiber filter with applied vacuum.Wash with three 10-mL volumes of deionized water.Transfer total filtrate (with washings) to a weighed evaporating dish and evaporate to dryness on a stream bath and then transfer the dishes to the drying oven, dry evaporated sample for at least 1 h in an oven at 103 to 105℃.---(For TDS)Transfer crucible and filter combination to the drying oven, dry evaporated sample for at least 1 h in an oven at 103 to 105℃.---(For TSS)Cool in desiccator to balance temperature, and weigh.Repeat cycle of drying, cooling, desiccating, and weighing until a constant weight is obtained.Procedure of measuring TS:Preparation of evaporating dish: heat clean dish to 103 to 105℃for 1 h. Store and cool dish in desiccator until needed. Weigh immediately before use.Pipette 50 ml well-mixed sample(pipette from the approximate midpoint) to a preweighed dish. Evaporate to dryness on a stream bath and then transfer the dishes to the drying oven, dry evaporated sample for at least 1 h in an oven at 103 to 105℃ .Cool dish in desiccator to balance temperature, and weigh.Repeat cycle of drying, cooling, desiccating, and weighing until a constant weight is obtained.Experiment 4: P, Ca. P.Ca.Dr Lee ’s part Melamine in milkunk unk unk std unk std std unk V V A A V C C -=+where C unk is the concentration of melamine in the unknown sample C std is the concentration of melamine in the melamine stock solution V std is the volume of melamine stock solution V unk is the volume of the unknown sample A unk is the peak area of melamine in the unknown sample A unk+std is the peak area of the melamine in the spiked unknown sample。
