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PSE Chem

VIEWS: 4 PAGES: 4

  • pg 1
									PSE 476                                   Homework #6                                           Due 2/9/07


1) Please draw the reaction products (and intermediates) for the "stopping" reaction of
   this molecule. (4 points) Show the mechanism (i.e. the series of intermediates) by
   which that group is peeled from the polymer. Hint: Draw that one group in a
   straight chain form rather than a ring form. Then show the reaction steps.
                                                   OH                                          OH
           OH

                                                            O                                       OH O
                O        HO               O                          HO               O
  O
                     O                        HO                 O                        HO               OH
      HO
                                   OH O                     OH                 OH O
                OH

                              OH                                          OH




2) Please show the reaction pathway (all the steps with arrows) for the conversion of
   galactose to an isosaccharininc acid (4 points)



3) Imagine that you would like to produce isosaccharinic acids from wood
   hemicelluloses for use as concrete set retarding agents. Would it be best to produce
   these from hardwoods or softwoods? Please explain why you chose your answer. (2
   points)


4) Please explain why glycosidic cleavage of cellulose is more of a problem than the
   peeling reaction. (1 point)

5) What type of compound is the precursor for hexenuronic acids? (1 point)

6) Anthraquinone is a useful additive in alkaline pulping because: (1 point)
    a) It reduces the peeling of carbohydrates
    b) It reduces glycosidic cleavage of carbohydrates
    c) It acts as a nucleophile and cleaves lignin ether linkages
    d) a&b
    e) b&c
    f) a&c
    g) All of the above
7) Which form of AQ reacts with lignin? (1 point)
    a) Anthraquinone
    b) Anthrahydroquinone
8) In a kraft cook, which chemical can be replaced by AQ? (1 point)
    a) NaOH
    b) NaHS
    c) Na2CO3
9) Which carbohydrate is most stabilized through the addition of AQ? (1 point)
    a) Cellulose
    b) Xylans
    c) Glucomannans
10) AQ oxidizes the end groups of carbohydrates to: (1 point)



                                                        1
PSE 476                              Homework #6                               Due 2/9/07

    a) Isosaccharinic acids
    b) Metasaccharinic acids
    c) Aldonic acids
    d) Uronic acids
11) AQ is added to pulping reactions at approximately what level? (1 point)
    a) 1%
    b) 0.1%
    c) 0.001%
    d) 10%
12) AQ works better with which of the following? (1 point)
    a) Hardwoods
    b) Softwoods
13) True or False: Pulp yield is partially increased by the addition of anthraquinone
    because delignification rate is increased so there is less time for peeling reactions to
    degrade the carbohydrates. (1 point)
    a) True
    b) False
14) How does the addition of polysulfides improve pulping? (1 point)
    a) It reduces the peeling of carbohydrates
    b) It reduces glycosidic cleavage of carbohydrates
    c) It acts as a nucleophile and cleaves lignin ether linkages
    d) a&b
    e) b&c
    f) a&c
    g) All of the above
15) How are polysulfides formed? (1 point)
    a) Addition of elemental sulfur to white liquor
    b) Oxidation of white liquor
    c) Both of the above
16) What is the problem with using polysulfides? (1 point)
    a) Polysulfide degradation above 130 C
    b) Addition of sulfur to white liquor to forms polysulfides increases odor problem.
    c) Oxidation reactions to form polysulfides can lead to excessive formation of
        thiosulfate.
    d) All of the above
    e) None of the above
17) Approximately how much gain in yield can be obtained using polysulfides? (1
    point)
    a) 0.1%
    b) 1%
    c) 5%
    d) 10%
18) True or False: The positive affects on pulp yield of polysulfide and anthraquinone
    are additive. (Meaning that the yield gains obtained by using either additive
    separately are also obtained if they are added together). (1 point)
    a) True
    b) False



                                              2
PSE 476                               Homework #6                               Due 2/9/07

19) True or False: Changes in the amount of peeling may be measured by determining
    the EA of the liquor throughout a kraft cook. (1 point)
    a) True
    b) False
20) The goal of kraft pulping is to: (1 point)
    a) Dissolve extractives
    b) Saponify esters
    c) Make the lignin alkali soluble through fragmentation reactions.


21) Which type of alpha-O-4 group is cleaved with HO-? (1 point)
    a) Etherified phenolic groups
    b) Free phenolic hydroxyl


22) Which type of beta-O-4 group is cleaved by OH-? (1 point)
    a) Free phenolic hydroxyl
    b) Etherified alpha hydroxyl
    c) Stilbene structures

23) Which of these reactions is very fast? (1 point)
    a) Cleavage of alpha-O-4 by OH-
    b) 5-5 Carbon-Carbon linkage
    c) Stilbene structures

24) There are many linkages in lignin that are not cleaved in kraft pulping but affect the
    reaction anyway. Why is this? (1 point)
    a) Reactions of these linkages will consume OH- and HS-.
    b) Reactions of some of these sites can lead to condensation reactions increasing the
        size of the lignin molecules.
    c) Although not cleaving the lignin molecule, reactions of some of the groups will
        result in the formation of new phenolic hydroxyl groups which can speed up the
        pulping.
    d) a&b
    e) a&c
    f) All of the above.

25) Which is true about the affect of effective alkali on the loss of lignin? (1 point)
    a) Increase EA and lignin removal declines
    b) EA does not affect lignin removal
    c) Increase in EA only increases the rate of lignin removal in the bulk phase.


26) At what temperature does the loss of cellulose start? (1 point)
    a) Room Temperature
    b) 160-170 ºC
    c) 120-130°C




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PSE 476                              Homework #6                            Due 2/9/07


27) The loss of xylan through peeling reactions is less than glucomannans because: (1
    point)




28) Why is sulfidity important during the bulk delignification phase of a kraft cook? (1
    point)




29) Which of the following is easier to kraft pulp? (1 point)
    a) Softwood
    b) Hardwood




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