5-7 OCTOBER

ISFR

2011

147

TOLEDO (SPAIN)RECOVERY OF TANTALUM FROM CAPACITOR WITH SOLVOTHERMALTREATMENTM. Sasaki1, S. Ishikawa2, K. Nasu2, A. T. Quitain2, and M. Goto3
1 Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
2 Department of Applied Chemistry and Biochemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
3 Bioelectrics Research Center, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japane-mail:msasaki@kumamoto-u.ac.jp

Abstract
Liquefaction of resin in the tantalum capacitors were challenged in sub-critical fluids with a batch-type stainless steel(SUS316) reactor for perfect recovery of high purity tantalum and also efficient conversion to valuable chemicals When 1Methyl-2-pyrrolidone (NMP) was used as a solvent for the capacitor treatment, we found that resin was able to besolubilized and separated from the capacitor at 300 oC for 6 h in the presence of K3PO4 catalyst. In contrast, in the caseof benzyl alcohol (BZA) solvent, the solubilization rate of resin was lower than that in case of NMP at 300 oC for 4 hrs
with catalyst. We also found that resin solubilization of resin without any catalyst became faster than that in the presenceof catalyst.

Keywords: Subcritical fluid, benzyl alcohol, Capacitor, Tantalum, Solvothermal.

1. Introduction

2. Materials and Methods

Tantalum capacitor is a small-sized and has large
capacity, and is indispensable for electronic equipment.
The demand increases year by year. In addition, there
are quite large number of non-standard products (scrap)
generated during the capacitor manufacturing process
and used tantalum capacitors. If both the efficientconversion of resin to valuable chemicals and perfect
recovery of tantalum can be realized, the technique canbe utilized as a novel and effective usage method of
precious petroleum resources. So far, a new techniquewith oxidative degradation of tantalum capacitors at hightemperatures has been proposed. However, there wasroom for improvement in the points that reactions have to
be carried out at high temperatures like 1,200 oC and that
this technique required leaching processing thistechnique.
In this study, we aimed to develop a novel technique forcomplete recovery of tantalum from capacitors in hightemperature and high-pressure solvents (1-Methyl-2pyrrolidone (NMP) and benzyl alcohol (BZA)). Also, weinvestigated possibility that polymer resin in thecapacitors was able to be depolymerized or liquefied tovaluable chemicals. Especially, in case of BZA use, we
challenged to explore optimum conditions wheretantalum was successfully able to recover from thecapacitors by this technique. If sub-critical BZA is foundto be applicable to chemical recycling, the present
chemical recycling processes using NMP solvents will bealternate to more environmentally benign ones.

Tantalum capacitors were used as starting materials.
NMP, which is commonly used as a solvent, and BZA
were used as reactive solvents in this study. In case ofcatalytic reaction experiments, K3PO4 catalyst (WakoPure Chemicals, Osaka) was also used.
Reactions of tantalum capacitors were carried out with abatch-type stainless steel (SUS316) reactor whose innervolume was 8.8 mL. About 3 g of tantalum capacitors, 3mL of NMP (or BZA), and K3PO4 catalyst (finalconcentration: 0.33 mol/L) were loaded into the reactor.
After sealed, the reactor was put into an electric furnace(see Fig. 2) which had already preheated at desired
reaction temperatures (275 – 300 oC) and reactions oftantalum capacitor were initiated. After 1 – 6 h, it wasquenched rapidly by iced water bath to terminate furtherreaction.

interiores libro.indd 147

Fig. 1 A batch-type reactor used in this study.

26/9/11 13:13:15

148

6th International Symposium on Feedstock Recycling of Polymeric Materials

BZA solvent, the X value was 7.2 wt% at 300 oC for 4 hrsin the presence of K3PO4 catalyst, which was lower thanthat in case of NMP solvent.
1009080

XR / wt%

70Fig. 2 Electric furnace for solvothermal treatment oftantalum capacitor.
Products were filtrated and liquid and solid portions wereobtained. The solid portion was fractionated by groundingby hand about 10 times and by using a wire sieve (16mesh) with repeated water washings to remove polymer
resin-based portion from solid one. After drying, the solidportion was weighed and then calculated liquefaction rate(X) and resin removal rate (XR) by the following
equations;
X (wt%) = (1 – W/W0) x 100
XR (wt%) = X/X0 x 100

(1)
(2)

where W0 is the dry weight of capacitors (g), W is the dryweight of solid residues (g), and X0 is initial content of
resin in the tantalum capacitor which has been
determined in the preliminary experiment (in this case, X0= 43 wt%).
The solid residue obtained was also analysed by XRF,
XPS and so on to understand the elemental composition.

60504030
20
100NMPNMP w/Cat.

BZA

BZA w/Cat.

Fig. 3 Comparison of the XR values in sub-critical NMPand BZA at 300 oC for 4 hrs.
This result clearly indicates that the operating condition
should be optimized in the case of BZA solvent. Also, we
found from the result that the liquefaction rate and resin
removal rate in the absence of K3PO4 catalyst became
higher than those in the presence of the catalyst.
Although the reaction mechanism for resin
depolymerization in sub-critical BZA is now unclear, butwill be provided at the conference.

Acknowledgement
This work was performed by the support of Kumamoto
University Global COE (Centers of Excellence) program“Global Initiative Center for Pulsed Power Engineering”.

3. Results and Discussion
At first, in order to understand optimum treatment time forcomplete capacitor fractionation between tantalum andpolymer resins, liquefaction experiments were conducted
at various treatment times at a constant temperature of300 oC in the presence of K3PO4 catalyst. Table 1
summarizes a time course of liquefaction rate (X) andresin removal rate (XR) of tantalum capacitor. The X
value increased with treatment time and reached 41 wt%
for 4 hrs, especially for more than 6 hrs the resin wasperfectly separated from capacitors. From this result, wefound that NMP at the subcritical state (300 oC) was able
to solubilize resin in the capacitor and to recovertantalum at identical condition.
Table 1. Time course of liquefaction rate (X) and resin
removal rate (XR) of tantalum capacitor in sub-critical
NMP at 300 oC with K3PO4 catalyst.
Time / hX / wt%
XR / wt%

21536

44195

643100843100

Next, BZA solvent was employed to the treatment oftantalum capacitor. Fig. 3 shows the result. In case ofinteriores libro.indd 148

26/9/11 13:13:15