A New Coal Flash Pyrolysis Method Utilizing Effective
Radical Transfer from Solvent to Coal
Kouichi Miura,* kazuhiro Mae, Seiji Asaoka, Tomonori Yoshimura, andKenji Hashimoto
Research Laboratory of Carbonaceous Resources Conversion Technology, and Department ofChemical Engineering, Kyoto University, Kyoto, 606 Japan
Received August 16, 1990. Revised Manuscript Received January 4, 1991
A new coal flash pyrolysis method was developed for drastically increasing the total volatile matterand the liquid products under mild conditions. The original idea of this method lies in the realizationsof effective hydrogen trnsfer from the hydrogen donor solvent to the coal fragments during the flash
pyrolysis. To realize it, we found the contact at the molecular level between the solvent and the coalfunctional groups was essential in addition to the matching of the dehydrogenation rate of the solvent and theprimary decomposition rate of coal. Contact at the molecular level was achieved by swellingthe coal with solvent at 100-250℃ under a pressurized atmosphere (1Mpa). When two coals wereswollen by tetralin, tetralin penetrated into the micropores of its molecular size by enlarging the pores.
Pyrolyzing the swollen coal in a Curie-point pyrolyzer at 670, 764, and 920 ℃ in a helium stream
at atmospheric pressure resulted in production of 56% of volatile master for Taiheiyo (TC, Japanesesubbituminous coal) and surprisingly 67% for Morwel1 (MW, Australian brown coal). A maximum
liquid yield from MW reached more than 42%, which was larger by 24% than that from the raw coal.
It was clarified that this significant increase was brought about by a physical effect as well as theeffective hydrogen transfer from/via tetralin.

Introduction
Since pyrolysis of coal is the first step of all coal conversion processes, its understanding is essential for theeffective used of coal. The pyrolysis of coal consists of twoseries of reactions: the first is primary decomposition,
which consists of the formation of radical fragments andtheir stabilization, the other is the secondary gas-phasereaction of the gaseous components produced by the
primary decomposition. The product yield during thepyrolysis depends strongly on coal type and operatinghydrogen from other sources to coal for increasing the tar
yield.
Several methods have been proposed to supply hydrogento coal during the pyrolysis. Hydropyrolysis is a representative one of such methods. This generally requires
severe reactiori conditions: high hydrogen pressure, hightemperature, and long residence time. Even if the told
volatile matter was increased by this method, the increaseof liquid yield could not be expected as Wanzl indicated.1
Flash pyrolsis in methane,2.3 toluene,4 or methanol5
atmosphere was proposed. These methods intended tosupply hydrogen or methyl radicals produced by the de-composition of the gases, but these methods did not succeed in increasing the total volatile matter by an appreciable amount.
Next, an attempt was made to pretreat coal before thepyrolysis by gases such as hydrogen, carbon dioxide, Steam,and so on.6 A similar attempt involved the adsorption oforganic substances on coal before pyrolysis.7 These attempts intended to supply some radicals from the gases
or organic substances to coal during the pyrolysis. Thesemethods, however, could attain only a slight increase of
the total volatile matter.
More recently, Graft et al.8.9 have proposed the pretreatment of coal by subcritical steam before pyrolysis.
They reported drastic increases of both the total volatile
matter and the tar yield by pyrolyzing a bituminous coal
(Illinois No. 6) at 900 ℃ under 50 atm of steam. Graftet al. concluded that this significant effect was brought
about through the modification of coal by the subcriticalstew, probably by the breakage of some ether links in thecoal. However. Kahn et al.10 could not observe such significant increase When they traced this method. This mar
present some uncertainty about Graffs method.
Another approach is a catalytic mash pyrolysis of coal.
The consensus obtained from many studies11-17 seems tohe that the catalyst is effective only for the secondary
gas-phase reaction. Therefore, the increase of total volatile
matter may not be expected by the catalytic flash pyrolysis.
To summarize, only Graff et ai succeeded in the drastic
increase of both the total volatile matter and the liquidyield, although they employed fairly severe experimental
conditions. Their idea lies in the modification of coal
before the pyrolysis. On the other hand, other methods
intend to supply some radicals from hydrogen or organic
substances to coal during the pyrolysis. The failure ofthese methods seems to suggest the difficulty in controlling
the primary decomposition of coal. To supply the radicals
to coal effectively and to increase the total volatile matter,the formation rate of the radicals must match that of theradical fragments from coal at first. Furthermore, bothradicals must be in close enough spatially to react witheach other, because the reaction rates among the radicals
are much faster than the transport rate of the radicals. So,
it is necessary to find some means to fulfill the above
requirements for increasing the total volatile matter during
the pyrolysis.
In this paper we present a new efficient method forincreasing both the total volatile matter and the tar yield
during the pyrolysis under a mild condition. our idea isto supply the hydrogen radical from the hydrogen donor
solvent to the coal fragments within the coal particles. To
accomplish intimate contact between the solvent and thecoal, the coal was pretreated by the solvent at 100-250℃
under 1 MPa of nitrogen. Through this treatment. the coalparticles were swollen and the solvent was retained intimately within the micropores of coal. The coal swollen by
the solvent was pyrolyzed in a flash mode in an inert gas
atmosphere. Drastic increse of the total volatile matterand the tar yield was attained. We will show this drastic

increase is brought about by a physical effect and theeffective hydrogen transfer from/via tetralin.
Experimental Section
Sample Preparation. A Japaneses coal Taiheiyo (TC), andan Australian brown coal, Morwell (MW), were used as raw coals.
Their Properties are given in Table I. The coal, whose particle
size was ca. 1 mm, was predried at 110 ℃ for 24 h. Then thecoal was ground into fine particles of less than 74 μm and was
dried in vacuo again at 110℃ for 1h before use.
Coal samples retaining tetralin within the particles were prepared as follows: the coal particles were mixed with tetralin in theratio of 10 to 6 by weight in a stainless tube reactor, then they
were heated to a temperature between 25 and 350 ℃ under the
1 MPa of nitrogen by immersing the reactor into a temperature-regulated sand bath. By this treatment coal particles wereswollen when the temperature was between 100 and 250 ℃. andtetralin was retained in the coal matrix
To estimate properly the effect of tetralin during the flash
pyrolysis, two other samples were prepared by the following
pprocedure :the tetralin treated coal was degassed at 70℃ in vacuo
for 1 h to completely remove the retained tetralin (vacuum-driedcoal, VDC). When the swelling was irreversible, swollen but
tetralin free coal was obtained. This sample was pyrolyzed to
examine the physical effect of swelling on the pyrolysis. To doso, however, tetralin must be removed completely from the tetralin-treated coal (TTC) and chemical characteristics of the coalshould not be changed signification by the vacuum drying. Thiswas examined for a TC which was swollen at 250℃. Table Ⅱ
gives the amount of tetralin removed in the tetralin-treated coaland the amount of tetralin removed by the vacuum drying Bothamounts coincide within experimental error, confirming that
tetralin was almost completely removed from the tetralin treatedcoal by the vacuum drying. Significant difference was not foundbetween the ultimate analysis of the raw coal and that of thevacuum dried coal as shown in Table 1 So, we assumed that thevacuum-dried coal prepared from TC was different from the raw
coal mainly in physical properties. Several partially degassed
samples were also prepared to adjust the amount of tetralin
retained. These samples were utilized to examine the effect of
the amount of tetralin retained on the pyrolysis.
Another sample was prepared to estimate the contribution ofpyrolysis of tetralin on the product yields from the tetralin treatedcoal. A char produced under a high-temperature pyrolysis of
Taiheiyo coal, which was confirmed not to be pyrolyzed further,
was also treated by tetralin in the same manner as was employed
to prepare the tetralin-treated coal. The amount of tetralin in
the char was adjusted to be nearly equal to that of the tetralintreated coal. This sample was pyrolyzed to obtain the yield ofeach component from tetralin.

The swelling ratios of the tetralin-treated coal and the vacuum-dried coal were measured by a volumetric method.18 The
volume of micropores less than 1 nm in diameter was obtained
for the raw coal and the vacuum-dried coal by analyzing theadsorption isotherm of CO2 measured at 0℃. The temperature-programmed desorption (TPD) of tetralin from the tetralin-treated coal was also performed useing a themobalance (Shimazu Co. Ltd., TGA 50).
FIash Pyrolysis. Samples prepared above were pyrolyzed witha Curie-point pyrolyzer (Japan Analytical Ind., JHP-2S) in thehelium flow of atmospheric pressure. Figure1 shows the schematic
diagram of the experimental apparatus. About 2 mg of Sample
wrapped up tightly by a ferromagnetic foil win Placed in a small
quarts reactor (4.0 mm i.d.) and heated to a temperature between
670 and 920℃ at the rate of 3000 ℃/s by an induction heating
coil to be pyrolyzed rapidly. Since this heating scheme heats up
only the foil wd the coal particles, volatile products were immediately cooled down by the helium gas flowing at a high now
rate. The gas-phase secondary reactions were largely suppressed,
which enables the examination of the primary decomposition ofcoal solely as mentioned in earlier works.1.19,20 Tar Produced wastrapped completely by the quartz wool placed just below the foil.
Gaseous products were all led to a gas chromatograph equippedwith a Porapak Q column to analyze inorganic gases (H2, CO, CO2,
and H2O) and hydrocarbon gases (CH4, C2H4, C2H6, C3H6, C3H8,
C4H8, C4H10, C6, and C6 gaseous compounds, benzene, toluene,
and xylene). The yields of char and tar were measured from theweight changes of the foil and the reactor. The sine experiment
win performed several times to check the reproducibility of theresults.
Calculation of the Product Yield of the Tetralin-TreatedCoal. Since tetralin is also pyrolyzed during the flash pyrolysisof the tetra1in-treated coal, its estimation is necessary to represent
properly the product yield deriving solely from the coal. However,
it is impossible in a strict sense, because we are expecting interactions between tetralin and the coal. Then we used thefollowing equation to calculate the yield of each component, Yi,
deriving from the coal as a first approximation
Yi. = {(yield from the tetralin-treated coal) (yield from tetralin)/(1 - w) (1)where w is the weight fraction of tetralin in the tetralin-treatedcoal. This equation is suitable to judge if there is an interaction
between the coal and the solvent. The yield calculated by thisequation coincides with that of raw coal if there are no interactions
between tetrlin and the coal.
Results and Discussion
Change of Physical and Chemical Properties during the Swelling of Coal. The Swelling characteristics
of several coals by various solvents Were examined in detailin a separate paper.21 In this paper the swelling characteristics that would be intimately related to the pyrolysis
are discussed. The upper graph of Figure 2 shows thechange of the swelling ratio against the swelling temperature. TC (open circles) began to swell with tetralin at 70℃, and the swelling ratio reached up to 1.34 at above 170℃. MW (open triangles) began to swell at lower temperatures and reached a maximum swelling at around 100
oC. The swelling ratio of MW at lW oC was nearly equal
to that of TC swouen above 170 oC.
The swelling ratio of the VDC is also Shown by theclosed symbols in Figure 2. The TC swollen at below lW℃ shrank reversibly to its original state by vacuum drying,
but the coal swollen at above 100 ℃ did not shrink completely, and the swelling at 250 ℃ was interestingly almost
irreversible. On the other hand, the MW swollen returnedto the original volume apparently at all the swelling temperatures. This is probably because MW consists ofsmaller and more flexible structures.
By utilizing the vacuum-dried coal prepared from TC,
we can examine the physical change brought about by theswelling. The lower graph of Figure 2 shows the volumeof micropores less than 1 nm in pore radius for the VDC.
The micropore volume of the vacuum-dried coal preparedfrom the TC swollen at 250 ℃ is about 1.5 times larger
than that of the raw coal. This indicates that tetralin
penetrated into these micropores by enlarging the pores
during the swelling. Since the dimensions of these micropores are comparable to those of tetralin molecule,tetralin is expected to interact both physically and chemically with the functional groups in the coal such as -OH,
-COOH, etc.
The strength of interaction between the coal and tetralinin the tetralin-treated coal can be examined by the TPDof tetralin from the tetralin-treated coal. Figure 3 shows
the TPD curves for Several samples. The TPD curve of
the TC treated at 25 ℃ just corresponds to that of theevaporation of tetralin, but the other curves Show thatabout 0.I kg/kg of tetralin is retained strongly by the coal.
This figure suggests that a part of tetralin in the tetralin-treated coal of MW is also retained in the microporesof the dimension of tetra1in molecule. Thus it can bevisudized that the micropores in the tetralin-treated andswollen coal are filled by tetralin and that tetralin and thefunctional groups of coal are in close contact. This situation is completely different from the tetralin-treated but
nonswollen coal such as the one prepared at 25℃.
Fhsh Pyrolysis of Tetralin. Figure 4 shows the
product yield obtained by pyrolyzing the char retaining
tetralin. The char yield from tetralin was less than 10%
at all temperatures. The yields of other components are
all less than 1 wt % as shown in the above graph, but thetemperature dependency is different among the components. Both the hydrocarbon gas (HCG) yield and theyield of the sum of benzene, toluene, and xylene (BTX)
increased monotonously, whereas the H2 yield had amaximum around 750℃. This shows that reaction rates
among the hydrogen radical and other small radicals suchas methyl radical are accelerated above 750℃. The
amount of hydrogen used for these reactions is fairly large
if it is represented in molar basis. To summarize the above
results, there is a possibility that the reactions between
the hydrogen radical deriving from tetralin and the radical
fragments of coal will occur if they are close enough spatial1y.
Effect of Pretreatment Temperature on Tar Yield.
To find an optimum swelling temperature, the tetralintreated coals prepared at several temperatures were pyrolyzed at 764 ℃. Figure 5 shows the total volatile matter
wd the tar yields against the swelling temperature. Boththe total volatile matter and the tar yield of the tetralintreated coal were the same as those of the raw coal at the
8Welling temperature of 25℃, but they reached about 1.5
timc8 larger than those of the raw coal at 100-250℃. This
result shows that tetralin is effective in increasing the total

volatile matter and the tar yield only when the coal isswollen and tetralin is retained in the micropores as Figure
2 shows. The amount of total volatile matter and the tar
yield were very small at the swelling temperature of 350℃. This is because the coal partly decomposed and reacted with tetralin during the treatment at this temperature. For MW, both the total volatile matter and the tar
yields of the tetralin-treated coal were much larger thanthose of the raw coal at the swelling temperatures of100-250℃, although the results are not shown. However,it was found that MW started to decompose at around 170℃. From above results, the swelling temperature was
decided to be 250 ℃ for TC and 100 ℃ for MW.
Effect of the Amount of Tetralin in the Coal. The
effect of the amount of tetralin retained in the coal on the
total volatile matter and the tar yield was examined at thepyrolysis temperature of 764 ℃. Samples of different
tetralin content were prepared by changing the vacuumdrying time of the tetralin-treated coal prepared from TC
at 250 ℃. Since these samples are different only in thetetralin content judging from the swelling ratio of thevacuum-dried coal (VDC) shown in Figure 2, they aresuitable to examine the effect of the amount of tetralin.
Figure 6 shows the total volatile matter and the tar yield
during the mash pyrolysis against the amount of tetralinretained in the coal. The Sample of zero tetralin content
was completely dried (VDC). Since the vacuum-dried coalis still swollen by 30% , this sample has much larger porevolume than the raw coal as shown in Figure 2. The total
volatile matter and the tar yield of the vacuum-dried coal
were About 3-4 wt % larger than those of the raw coal.
This means that the pore enlargement by swelling contributed to the increase of the tar yield. This is simply
a physical effect. Both the total volatile matter and thetar yield increased gradually with the increase of tetralin
content. These increases are judged to be brought about
by a chemical effect of tetralin. The total volatile matterand the tar yield of the coal treated at 25℃, which are
shown for comparison, are almost sine as those of the raw
coal, althought the tetralin content of the coal is the largest.
This indicates again that the swelling is essential for increasing the coal conversion.
Since swelling is realized by enlarging micropores as fully
discussed in a separate paper21 and as briefly mentioned
earlier in this paper, tetralin is penetrating into the micropores of the dimension of tetralin. molecule in the tetralin-treated coal. This penetration will cause some interactions between tetralin and some functional groups ofthe coal. Therefore, tetralin is probably retained by theStronger attractive force in the swollen coal than in the
nonswollen coal. Thus, tetralin in the swollen coal is expected to have stronger interactions with the coal fragments during the pyrolysis, which will contribute to increase the total volatile matter. On the other hand, tetralinin the nonswollen coal did not penetrate into micropores.
Therefore, little increase of the total volatile matter is
erpected.
Effect of the Pyrolysis Temperature on the Product Yield. Figure 7 shows each yield of the TTC, the
VDC, and the raw coal against the pyrolysis temperature
for TC. The char yield of the tetralin-treated coal is lower
than that of the raw coal at all the temperatures by 4-10
wt %. The char yield of the vacuum-dried coal is also 4
wt % lower than that of the raw coal.
The tar yield of the tetralin-treated coal increased with
the increase' of temperature and reached a maximum valueof 32 wt % daf at the pyrolysis temperature of 764℃,
which was 1.5 times larger than that of the raw coal. Thenit decreased and was almost equal to that of the raw coalat 920℃. This temperature dependency is similar to thatof the H2 yield from the pyrolysis of tetralin (see Figure4). On the other hand, the tar yield of the vacuum-driedcoal was larger than that of the raw coal by 4 wt % irrespective of pyrolysis temperature.
The inorganic gas (IOG) yield of the tetralin-treated coal
was slightly smaller than that of the raw coal or the vacuum-dried coal. This difference was due to the differenceof H2O yield. The hydrocarbon gas (HCG) yield and thetotal yields of benzene, toluene, and xylene (BTX) were
nearly equal at the temperatures lower than 764℃. These
yields of the tetralin-treated coal at 920℃, however, werelarger than those of the other two samples. The H2 yieldof the tetralin-treated coal was smaller than that of theraw coal at temperatures lower than 800 OC, but exceededthat of the raw coal at 920℃. The H2 yield of the vacuum-dried coal was almost same as that of the raw coal at
all the temperatures.
Figure 8 shows the yield of each product of the tetra1in-treated coal and the raw coal for MW. The propertiesof the vacuum-dried coal prepared from MW were almost
the same as those of the raw coal, and the product distribution during the pyrolysis of the vacuum-dried coal was
also almost the same as that of the raw coal. Therefore,
the results of the vacuum-dried coal are not involved in
Figure 8. The char yield of the tetralin-treated coal wasmuch smaller then that of the raw coal at an temperatures.
The tar yield of the tetralin-treated coal increased with
the increase of temperature and surprisingly reached 42
wt % daf at 920℃, which is 2.3 times larger than that of
the raw coal. This yield is almost comparable to that of
the liquid yield attained in the coal liquefaction.22 on theother hand, the HCG yield of the tetralin treated coal was
equal to that of the raw coal up to 764℃, but was lower
at 920℃. The inorganic gas and the H2 yields of thetetralin-treated coal were much lower than than of the raw

coal at all the temperatures. The large difference of the
inorganic gas yield between the raw coal and the tetralin-treated coal again came from the difference of the H20
yield.
Mechanism of the Increase of Total Volatile Matter
And Liquid Yield. Figures 7 and 8 clearly show that the
proposed method is effective for increasing both the total
volatile matter and the tar held with pyrolysis under sucha mild corlditior1. We will examine the mechanism of thepyrolysis of the tetralin-treated coal based on the above
results.
The physical effect can be examined solely by comparing
the product distribution between the vacuum-dried coaland the raw coal for TC. The total volatile matter of thevacuum-dried coal increased by 3-4% at all temperaturesin comparison with that of the raw coal as shown in Figure
7. This increase was due to the increase of the tar yield.
It was supposed that the increase of micropore volume
caused by the tetralin pretreatment facilitated the escapeof the tar vapor, which would be captured by the charradical in the nonswollen coal, from the coal particles. Thisis further substantiated by pyrolyzing several vacuumdried coal samples of different micropore volumes. The
vacuum-dried coal samples were prepared by changing thedegree of swelling. The total volatile matter and the tar
yield are plotted against the micropore volume of thevacuum-dried coal in Figure 9. Good correlations indicate
the validity of the above reasoning. It is possible to increase the total volatile matter by several percents by
utilizing only the physical effect: pore enlargement causedby the swelling.
Next, we will discuss he chemical effect of tetralin on
the pyrolysis of coal. Since the effect of tetralin seems to
be different between TC and MW, we will examine theeffect for each coal.
For TC, we can discuss solely the chemical effect oftetralin by comparing the product distribution between
the tetralin-treated coal and the vacuum-dried coal.
Tetralin contributed to increase both the total volatile
matter and the tar yield at the temperatures less than 800℃. At 920℃ the effect was only to rearrange the productdistribution of the total volatile matter. We presume thatthe increase of both the total volatile matter and the tar
yield was brought about by not only the effective hydrogentransfer from tetralin to the coal but by the effective
utilization of small radicals such as OH and H from thecod for stabilizing the coal fragments. The latter. Transfer

was expected because the yields of H20 and H2 of thetetralin-treated coal were significantly smaller than thoseof the vacuum-dried coal. At 920℃ tetralin contributed
only to decompose the primary pyrolysis products further.
This is probably because the decomposition rate of tetralin
did not match the primary decomposition rate of TC at
this temperature.
For MW, we cannot distinguish the physical effect arid
the chemical effect. So, we will discuss the chemical effectby assuming that the physical effect is similar to that forthe pyrolysis of the tetralin-treated coal of TC. Then we
regard the significant decrease of the H2O yield and theH2 yield of the tetralin-treated coal in comparison withthose of the raw coal as the chemical effect caused bytetralin. Since the large increase of the tar yield of thetetra1in.treated coal is compensated by the decrease of thechar yield, the H20 yield, and the H2 yield, and partly by
the hydrocarbon gas yield as shown in Figure 8, the significant amount of small radicals (H', 'OH, 'CH3, etc.)
deriving from the coal was judged to be utilized to stabilize
the coal fragments as tar. This must be realized in virtueof the presence of tetra1in, although we cannot clarify themechanism now.
To summarize the discussion, we can say that two conditions are essential for the proposed method to be valid.
The first one is the Contact of molecular level between
tetralin and the functional groups of coal, and the otherone is the matching of the decomposition reactions of thecoal and tetralin. The second condition is probably fulfilled by choosing a proper combination of coal and solvent,but the first condition is difficult to realize. Therefore,
the success of the proposed method lies in the realizationof the contact at molecular level between the Solvent andthe coal through the swelling by the solvent prior to thepyrolysis. Tetralin in the micropores of the swelling coal
will have strong interactions with the functional groupsof coal including the noncovalent linkages such as phenolicacid hydrogen bonds. When this swelling coal is pyrolyzed
in a flash mode, strong interactions will arise between.
tetralin and the functional groups. Our image of the pyroiysis is the reaction of tetralin and the functional groups
in a confined microspace. The reaction conditions areprobably comparable to those under a high pressure oftetralin. So, this is, so to speak, the flash liquefaction ofcoal in the micropores. We must also stress the derivative
effect of swelling on the pyrolysis. The swelling facilitates
the escape of the coal fragments from the coal particles
by enlarging the micropores of coal.
Validity of the Proposed Method from a Practical
Viewpoint. Up to now we have shown the effectivenessof the proposed method based on the yield calculated by
eq 1. Equation 1 is suitable to judge if there is an interaction between the coal and the solvent, wd the difference
between the yield calculated by eq 1 and that, of the raw
coal is due to the interaction. Then the fact that the yieldof total volatile matter calculated by eq 1 was much larger
than that of the raw coal for both TC and MW clearly
indicates the effectiveness of the proposed method forincreasing the total volatile matter.
From a practical viewpoint, however, the following
criticism may arise: discussion based on eq 1 is not fair,because tetralin is also pyrolyzed and a part of it is converted to char. So, even if the amount of total volatile
matter calculated by eq 1 is larger than that of the raw
coal, the effectiveness of the proposed method could not
be proven. This could only be established when theamount of total volatile matter obtained by the method
is larger than the sum of the amount of tetralin used andthe amount of the total volatile matter obtained from theraw coal. To answer this criticism, the following examination was performed.
In Table Ⅲ the amounts of char, tar, and gaseous
products obtained by pyrolyzing the raw coal and thetetralin-treated coal, and also the vacuum-dried coal forTC, under the specified conditions are shown for both TC
and MW. The values are all represented on the basis ofunit weight of the raw coal to facilitate the direct comparison of each other. The values in the column identified
by calcd were obtained by simply adding the amount of
tetralin in the tetralin-treated coal to the amount of tar
obtained from the pyrolysis of the raw coal. Then thecomparison of the amount of each product between the
TTC and the cacd columns allows us to judge if the
proposed method is practically effective.
For TC, the amount of tar deriving from the tetralintreated coal is a little larger than the calculated one, but
the char yield is almost the same. This indicates that the
proposed method is not so effective for TC in a practicalsense. For this coal, the increase of the total volatile matterbrought about by the interaction with tetralin was canceledby the char prduced through the pyrolysis of tetralin. For
MW, on the other hand, the amount of tar from the tet-ralin-treated coal i8 larger than the calculated one by
0.l615 kg/kg of coal, indicating that the proposed method
is effective even in practical applications.
The pyrolysis of the tetralin-treated coal was not effective in increasing the total volatile matter for TC in thepractical sense, but there is an option for this coal. As
discussed earlier, the tar yield and the total volatile matterof the vacuum-dried coal were 3-4% larger than those of
the raw coal at all temperatures. A typical result is foundin Table Ill. Since it is possible to recover all the tetralinused for the swelling through the vacuum drying, theabove-mentioned values are the net increase of the tar yieldand the total volatile matter. So, the pyrolysis of thevacuum-dried coal definitely increases both the tar yieldand the total volatile matter in practical processes also.
In the discussion of this section the tetralin recovered
was not distinguished from the tar produced. This is partly
because we could not analyze the tar composition, butmainly because tetralin is just a model solvent used for theswelling to show the validity of the proposed method. In
practical applications, less expensive solvents such as thepartly hydrogenated coal tar23 could be used. In that casethere will be no need to distinguish the solvent used forthe swelling from the tar produced during the pyrolysis.
Summarizing the above discussion, it can be safely
stated that the proposed method is effective for increasing
the total volatile matter during the flash pyrolysis of coal.
Acknowledgment. This work was financially supported by the Ministry of Education, Culture and Scienceof Japan through the Grant-in-Aid on Priority-Area Research (Grant No. 62603014, 63603014 and 01603012).
Registry No. Tetralin, l19-64-2.