Production process for producing water-absorbent polymer particles and belt dryer

Patent metadata

Field	Value
Publication number	US-10647787-B2
Application number	US-201615571868-A
Country	US
Kind code	B2
Filing date	Apr 15, 2016
Priority date	May 8, 2015
Publication date	May 12, 2020
Grant date	May 12, 2020

Abstract

A production process for production of water absorbing polymer particles, including drying an aqueous polymer gel in a belt drier with a conveyor belt having a drier setup in the interior, in which drying air in the interior of the drier setup is conducted in countercurrent counter to the conveying direction and the interior of the drier setup is kept substantially at a reduced pressure relative to the ambient pressure outside the drier setup, and the interior has and/or forms a pressure zone, and is especially divided into a number of pressure zones.

First claim

The invention claimed is:

1. A production process for production of water absorbing polymer particles, where the production process has the following process steps:
polymerizing (S 1 ) an aqueous monomer solution or suspension for production of an aqueous polymer gel (S 2 ),
drying (S 3 ) the aqueous polymer gel in a belt drier with a conveyor belt ( 400 ), by accommodating the aqueous polymer gel on the conveyor belt ( 400 ) and conveying the polymer gel on the conveyor belt ( 400 ) in a conveying direction (C) of the conveyor belt ( 400 ),
crushing and/or grinding (S 4 ) the dried polymer gel to give water-absorbing polymer particles, where, for drying (S 3 ):
the belt drier has a drier setup ( 101 ) in the interior ( 101 i ) of which the conveyor belt ( 400 ) is guided, wherein
drying air in the interior ( 101 i ) of the drier setup ( 101 ) is conducted in countercurrent (C′) counter to the conveying direction (C) and the interior of the drier setup ( 101 ) is kept at a reduced pressure (p_U) relative to the ambient pressure (p_A) outside the drier setup ( 101 ), and the interior ( 101 i ) has a pressure zone (DZ), wherein, in line with conveying direction (C):
a first internal pressure is formed as inlet pressure at a polymer gel inlet ( 100 A) in at least one of the pressure zone (DZ) with a first pressure differential (ΔpA) from an ambient pressure (p_A), and
a second internal pressure is formed as outlet pressure at a polymer gel outlet ( 100 B) in the at least one pressure zone (DZ) with a second pressure differential (ΔpB) from an ambient pressure (p_A), where
the second pressure differential (ΔpB) is smaller than the first pressure differential wherein
the pressure zone (DZ) in the interior ( 101 i ) of the drier setup ( 101 ) or a pressure zone subregion (DZT 1 , DZT 2 ) of the pressure zone (DZ) is bounded by means of a transverse wall (QWa, QWe, QWi) oriented at right angles to the conveying direction of the conveyor belt.

2. The production process according to claim 1 , wherein
a pressure profile (DP) is formed, having at least one pressure gradient range (GRAD) at or between the polymer gel inlet ( 100 A) and the polymer gel outlet ( 100 B) of the pressure zone (DZ), and the pressure gradient region (GRAD) has a pressure stage (DS 1 , DS 2 , DS 3 ), pressure ramp or pressure variation at a transverse wall (QWa, QWe, QWi).

3. The production process according to claim 1 , wherein
the interior ( 101 i ) of the drier setup ( 101 ) is divided into a number of one or more pressure zones (DZ) and/or pressure zone subregions (DZT 1 , DZT 2 ), and/or
at least one pressure zone (DZ) extends over at least one or more than one, last drier zones (TZ, 310 ),
and/or the number of one or more pressure zones (DZ) and/or pressure zone subregions (DZT 1 , DZT 2 ) is formed within an end zone (EZ) upstream of a discharge module ( 300 ).

4. The production process according to claim 1 , wherein the interior of the drier setup ( 101 ) is kept at a reduced pressure (p_U) within a region of up to −20 mbar, relative to the ambient pressure (p_A) outside the drier setup ( 101 ), and the ambient pressure (p_A) is an atmospheric pressure outside the drier setup ( 101 ).

5. The production process according to claim 1 , wherein the first and second pressure differentials from ambient pressure are based on an internal pressure above the conveyor belt ( 400 ), where the internal pressure above the conveyor belt ( 400 ) is a reduced pressure in the range of up to −10 mbar, and/or an internal pressure beneath the conveyor belt ( 400 ) has been lowered by a value between 0.5 mbar and 5 mbar compared to the internal pressure above the conveyor belt ( 400 ), with aqueous polymer gel lying on the conveyor belt ( 400 ).

6. The production process according to claim 1 , wherein the first and second pressure differentials from ambient pressure are based on an internal pressure above the conveyor belt ( 400 ), where
the first pressure differential from atmospheric pressure at a polymer gel inlet ( 100 A) of the pressure zone (DZ) is between −10 mbar and −1 mbar, and/or
the second pressure differential from atmospheric pressure at a polymer gel outlet ( 100 B) of the pressure zone (DZ) is between −3 mbar and 0 mbar.

7. The production process according to claim 1 , wherein
a pressure profile (DP) of a pressure variation in the pressure zone (DZ) and/or pressure zone subregion (DZT 1 , DZT 2 ) is adjustable independently of an ambient pressure, and/or
the pressure profile (DP) with respect to a pressure zone (DZ) and/or pressure zone subregion (DZT 1 , DZT 2 ) forms through an input setting of an intake valve or intake throttle ( 710 ) at a polymer gel inlet ( 100 A) to a pressure zone (DZ) and/or pressure zone subregion (DZT 1 , DZT 2 ) and through an output setting of an output valve or output throttle ( 720 ) at the polymer gel outlet ( 100 B) of a pressure zone (DZ) and/or pressure zone subregion (DZT 1 , DZT 2 ).

8. The production process according to claim 1 , wherein, for drying (S 3 ):
an air withdrawal conduit ( 340 ) connected to the drier setup ( 101 ) to remove air and an air recycling conduit ( 350 ) connected to the drier setup ( 101 ) to supply air are formed, said air recycling conduit ( 350 ) being connected to said air withdrawal conduit ( 340 ), where
recycled air (RL) is withdrawn from the drier setup ( 101 ), optionally from an end zone (EZ), and fed back via the air recycling conduit ( 350 ) to the drier setup ( 101 ), where an air withdrawal conduit ( 340 ) and/or air recycling conduit ( 350 ) is connected for flow purposes to a pressure zone (DZ), and/or
waste air from the drier setup ( 101 ) is removed at least partly in a waste air conduit ( 360 ), where the waste air conduit ( 360 ) proceeds from a further air-guiding orifice to the pressure zone, and/or
the belt drier takes the form of an air circulation belt drier operated with circulating air (UL) and which, to guide the circulating air, takes the form of a drier setup ( 101 ) comprising the conveyor belt ( 400 ), in which the drying air is circulated in a drying zone (TZ) as the circulating air (UL).

9. The production process according to claim 1 , wherein, in the pressure zone (DZ), the pressure profile:
is formed by a throttle-controllable volume flow rate of feed air, optionally at the polymer gel inlet ( 100 A) of the pressure zone (DZ) and/or pressure zone subregion (DZT 1 , DZT 2 ), and/or
is formed by a throttle-controllable volume flow rate of waste air optionally at the polymer gel outlet ( 100 B) of the pressure zone (DZ) and/or pressure zone subregion (DZT 1 , DZT 2 ), and/or
the adjustment of the volume flow rates in the pressure zone (DZ), forms the pressure profile (DP).

10. The production process according to claim 1 , wherein the pressure zone (DZ) is divided into a number of pressure zones.

11. A belt drier for drying an aqueous polymer gel in a production process according to claim 1 , where
the belt drier has a drier setup ( 101 ) in the interior ( 101 i ) of which the conveyor belt ( 400 ) is guided,
wherein
drying air in the interior ( 101 i ) of the drier setup ( 101 ) can be conducted in countercurrent (C′) counter to the conveying direction (C) and the interior of the drier setup ( 101 ) can be kept at a reduced pressure (p_U) relative to the ambient pressure (p_A) outside the drier setup ( 101 ), and the interior ( 101 i ) has and/or forms a pressure zone (DZ), wherein, in line with conveying direction (C):
a first internal pressure is formed as inlet pressure at a polymer gel inlet ( 100 A) in at least one of the pressure zones (DZ) with a first pressure differential (ΔpA) fro

Assignees

• Basf Se

Inventors

• Grünewald Gerald
• Funk Rüdiger
• Weismantel Matthias

Classifications

• B01J20/3021

  Milling, crushing or grinding · CPC title

• F26B5/041

  for drying flowable materials, e.g. suspensions, bulk goods, in a continuous operation, e.g. with locks or other air tight arrangements for charging/discharging · CPC title

• C08J3/12

  Powdering or granulating · CPC title

• F26B17/04

  the belts being all horizontal or slightly inclined (F26B17/08 takes precedence) · CPC title

• B01J20/261

  obtained by reactions only involving carbon to carbon unsaturated bonds (macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds per se C08F) · CPC title