LIANT POUR CARBONE ET PROCEDE DE FABRICATION

BINDER FOR CARBON AND PROCESS FOR PRODUCING SAME

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A binder for carbon with reduced calcination is
obtained by addition of approximately 0.1% by weight of B203 to
the binder precursor from a coal tar distillation residue. The
efficiency of the Inhibitor thus is approximately trebled as com-
pared with the addition to the finished binder.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A binder for carbon based on coal tar with additions of
boron oxide as oxidation inhibitor, in which the binder
maximally contains 0.3% by weight of boron oxide and is
obtained by adding the boron oxide to a precursor of the
binder and by subsequently further processing the precursor
to the carbon binder, the precursor of the binder being
selected from topped-off coal tar or its distillation
residues having a lower softening point than the binder.
2. A binder as in claim 1, wherein the precursor is a
distillation residue of coal tar.
3. A binder as in claim 2, in which the precursor is a
normal coal tar pitch.
4. A binder as in claim 1, 2 or 3, which contains 0.03 to
0.3% by weight of boron oxide.
5. A binder as in claim 1, 2 or 3, which contains
approximately 0.1% by weight of boron oxide.
6. A process for producing the binder as in claim 1,
wherein the boron oxide is mixed with the precursor in liquid
form and the mixture is further processed to the carbon
binder by at least one of vacuum distillation and carrier gas
distillation in one or several stages, wherein the maximal
bottom temperature in the last distillation stage is above
200°C.
7. A process as in claim 6, wherein the maximal bottom
temperature is the last distillation stage is in the range of
350 to 380°C.

Description

The present Inven~lon relates to a blnder based on coal
tar, whlch has Improved propertles and Is Intended for carbon
materlal. The present Inventlon also relates to a process for
produclng sald blnder.
Carbon materlals for the productlon of carbon mouldlngs
such as anodes, electrodes and ilnlngs conslst oF a mlxture of
solId carbon such as anthraclte, pltch coke, petrol coke and car-
bon black, and a carbon-petroleum-orlglnatlng bltumlnous blnder.
The materlals preferably contaln petrol co~e and coai tar pltch.
They are used prlmarlly for the productlon o~ precalclned or
self-calclnlng (Soderberg) anodes for the alumlnlum electrolysls.
~ecause of the slde-reactlons (oxldatlon) and the anode decompo-
: sltlon (sandlng) the consumptlon of anode materlals Is hlgher
than Is requlred solely for the reductlon of the alumlnlum oxlde.
It Is known that speclflc Impurltles In both the cokeand the blnder, such as sodlum, calclum and vanadlum compounds,
accelerate the oxldatlon and that the addltlons of boron and
phosphorus compounds show Inhlbltlng effects (Llght Metals, 1982,
~ Page 713).
: ;:
:`
US-PS ~,188,279 Proposes the productlon of carbon
mouldlngs from carbon materlals wlth 15 to 35% by welght of
blnder and 0.1 to 3% by welght of boron compounds or 0.5 to 5% by
welght of phosphorus compounds as oxldatlon Inhl b Itor, the
Inhlbltor belng added to the homogenlzed mlxture or It Is admlxed
wlth the blnder component prlor to the addltlon of the carbon
materlal.
It Is also posslble to add all the three components
i
slmultaneously and to homogenlze them, as descrlbed In the
Example. The calclnatlon Is reduced by 15% by an addltlon of 8%
by welght of borlc acld, relatlve to the coal-tar pltch blnder.
It has now been ~ound that the addltlon of borlc acld

In the speclfled amounts causes the formatlon of VB and TB, whlch
crystalllze out In the alumlnlum melt and, In the further pro-
cesslng of the alumlnlum to form folls, they cause the formatlon
of holes In the folls.
Phosphorus compounds, such as P205, also are less sult-
able Inhlbltors slnce they reduce the current yleld In the elec-
trolytlc process.
Therefore, the present Inventlon reduces the amount of
Inhlbltors In the blnder and In the carbon whlle slmultaneously
Improvlng thelr efflclency.
Accordlng to the present Inventlon, a blnder Is used
whlch contalns maxlmally 0.3% by welght of boron oxlde and Is
obtalned by addlng the boron oxlde to the blnder precursor and by
subsequently further processlng the precursor to a carbon blnder.
Topped-off coal tar or dlstlllatlon residues of thls
tar havlng a lower softenlng polnt than the blnder are used as
blnder precursor. On addlng the boron oxlde (B203) the precursor
Is processed to the deslred blnder by vacuum dlstlllatlon or/and
carrler gas dlstlllatlon In one or several stages.
~ 25 A coal tar pltch Is preferably used as precursor so
; ~ that the processIng can be carrled out In one stage, for example,
in an agltator retort or In a thln-fllm evaporator, under con-
trolled condltlons.
In order to avold reduclng the reslstance of the blnder
~;~ to aglng, the dlstl~latlon should be carrled out at bottom tem--
peratures of lower than 380C. Thls applles partlcularly to the
productlon of blnders for Soderberg materlals. In the last dls-
tlllatlon stage the maxlmal bottom temperature should not be
below 350C slnce otherwlse an op~lmal homogenlzatlon wlll not be
attalned.
- 2 -
:

5~
The boron oxlde content in the blnder Is In the range
of 0.03 to 0 3% by welght, preferably at approxlmately 0.1% by
welght. In thls range the addltlon of B~03 has no negatlve
effect on the wettlng propertles of the blnder or on the coklng
properties of pltch-coke mlxtures.
The present Inventlon wlll be further Illustrated by
way of Example 1 and the Comparlson Examples 2 and 3 hereafter.
Example 1
1000 parts by welght of a normal coal tar pltch, char-
acterlzed by the analytlcal values llsted In Table 1, are melted
down under an Inert gas, heated to 180C and then mlxed wlth 1
part by welght of B203 for 2 hours whlle stlrrlng. The mlxture
Is then disillled In an agltator retort under a pressure of 100
mbars up to a bottom temperatwre of 360C. A blnder havlng the
; analytlcal data llsted In Table 2 Is thus obtalned wlth a yleld
~; Of 9~%.
~ 22 parts by welght of thls blnder are mlxed wlth 78
;~ parts by welght of petroleum coi~e of defIned granulometry and
then moulded to mouldlngs. The mouldlngs, calclned at 960C, are
oxldlzed at 960C In a C02 current In order to measure the C02
z5 reactlvlty.
:~
The C02 reactlvlty Is a crlterlon of the anode consump-
tlon In the alumlnlum electrolysls. The entlre calclnatlon Is
composed of the dlrect calclnatlon and the dust formed, the lat-
ter belng a ~unctlon of the granulometry of the petroleum col<e.
Furthermore, the denslty, the specl~lc electrlcal resistance and
the bendlng strength of the test speclmens were determlned. The
results have been llsted In Table 3.
- 3 -

Example 2 corresponds to Example 1, but the boron oxlde
Is added to the blnder (cooled to 200C) only after the dlstilla-
tlon. Thls does not affect the yleld oF blnder. The propertles
of the blnder have been llsted In Table 2 and the results of mea-
surements on the test specImens In Table 3.
Table 3 ~Com~arlson)
Example 3 corresponds to Example 2 but wlthout the
addltlon of B203. The analytlcal values of the blnder have been
llsted In Table 2 and the results of measurements on t~e test
speclmens In Table 3.
Tab ! e 1
Anal~tical Data of the 81nder Precursor
20 softenlng polnt (Kraemer-Sarnow) 68C
Insoluble In toluene (Tl)26.3% by welght
Insoluble In qulnolIne (Ql)6.2% by welght
coklng resldue (Alcan) 51.4% by welght
ash formers 0. 23% by welght
_ ~I
.

~35~
Table 2
Analytlcal Data of the B Inder
_
~ _ 3
softenlng polnt
tK.-S.) (C) 95 94 95
TI (% by welght)30.~ 30.0 30.4
QI (% by wei~h~) 7.0 7.1 7.0
coklng resldue (Alcan)
~ ~ 6~hj~__________gg,~____
Tab!e 3
Values Measured on the Test SpecImen
- -. .
~_~ ~_ _~
C2 r~actlvlty:
dlrect calclnatlon
(mg/sq.cm h) 16.1 17.8 18.7
20 dust formed
(mgtsq.cm h) 4.5 6.7 6.4
; total calclnatlon
(mg/sq.cm h) 19.6 23.5 26.1
denslty (kg/dm3)1.48 1.47 1.47
- speclflc electrlca~ resl-
slstance ( ~ m) 68 67 67
bendlng strength ~
(1Q5 N/sq.m) 261 251 243
As the Tables 2 and 3 show the addltlon of the boron
oxlde before or a~ter the dlstlllatlon ca~ser nelther a change of
; the analytlcal data of the blnder nor a chan~e of the electrlcal
or mechanlcal propertles of the test speclmens produced there-
from, wlthln the llmlts of accuracy of measurement.
~'
_

~ 5~
Thus, for an addltlon of B203 after the dlstlllatlon
the entlre calclnatlon decreases by approxImately 7% by welght
and In the addltlon before the dlstlllatlon accordlng to the pre-
sent Inventlon It decreases by approxlmately 22% by welght. Both
the dlrect calclnatlon and the formatlon of dust show slmllar
results.
It has thus been shown that by the addltlon of boron
oxlde to the blnder precursor, accordlng to the present Inven-
tlon, rather than to the fInlshed blnder or to the carbon mate-
rlal, Its Inhlbltlng effect can be Increased by a multlple. It
Is thus posslble to reduce substantlally the consumptlon of
anodes wlth small amounts of Inhlbltor that are tolerable for the
alumlnlum Industry.
: 16
~: ~ 25
: . `
: ~ :
~:~ 3~
.
~`~ - 6 -
\
,
,