Dry single-stage method of sodium tripolyphosphate production – technological and economic assessment

Zygmunt Kowalski,Danuta Pawłowska-Kozińska,Katarzyna Gorazda,Regina Kijkowska,Marcin Banach,Anna K. Nowak,Zbigniew Wzorek

doi:10.2478/pjct-2014-0007

Abstract

Abstract The study presents a technology of sodium tripolyphosphate (STPP) production with the use of a dry, single-stage method. The reacting substrates (concentrated wet-process phosphoric acid - WPPA and solid Na2CO3 ) are mixed with a recycled final product (STPP) in a mixer, then a „quasi-dry” mixture is calcined in a rotary kiln. Thanks to that, some stages of a classic method of STPP production are eliminated: one of the two-stage neutralization of the phosphoric acid with sodium carbonate at temperature ~80°C, filtration of the neutralised solution and its evaporation, as well as the stage of drying a solution of mono- and di-sodium orthophosphate in a spray dryer. According to the presented technical and economical analysis, the costs of STPP production using a single-stage dry method can be 10% lower compared to the classic method.

Highlights

Sodium tripolyphosphate (STPP) is used as a builder of washing powders and other cleaning agents
At the third stage the mixture of pyrophosphates from the second stage is calcined in a rotary kiln, which results in further condensation to sodium tripolyphosphate
This study presents the technology of sodium tripolyphosphate production using the single-stage dry method as well as its economical analysis[8]

Summary

INTRODUCTION

Single-stage dry method (Fig. 1) consists in mixing of reacting substances - concentrated WPPA and powde-. If we use the recycled STPP in Form II in the mixture of orthophosphates we will obtain (both in a rotary kiln (430oC) and in a stationary chamber furnace (400oC)) Form II of STPP as a product. The difference between the currently described method and the quoted one is the use of concentrated WPPA that reduces the consumption of energy used for the evaporation of water from the system, as well as the use of a lower amount of the recycled STPP. 1 – neutralization mixer-reactor, 2, 5, 7 – screw conveyor, 3 – rotary kiln, 4 – hammer mill, 6 – bag filter, 8 – fan, 9 – chimney.

RESULTS AND DISCUSSION

CONCLUSIONS

LITERATURE CITED