# US 4,069,300 A · Process for producing .alpha.-type calcium sulfate hemihydrate

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 4,069,300 A
- Document ID: US4069300A
- Status: Granted
- Kind: A
- Application number: 05/616,312
- Filed: 1975-09-24
- Granted: 1978-01-17
- Earliest claimed: 1974-10-03
- Assignees: Taki Chemical Co., Ltd.
- Inventors: Hakuichi Akazawa; Kenichi Nishimura
- Web page: https://patentgrep.com/patent/US4069300A

## CPC

- C01F 11/46: Sulfates (dehydration of gypsum {for the production of calcium sulfate cements} C04B11/02)
- C01F: COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts of peroxyacids C01B15/00; sulfides or polysulfides of magnesium, calcium, strontium, or barium C01B17/42; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds other than ammonia or cyanogen containing nitrogen and non-metals and optionally metals C01B21/082; amides or imides of silicon C01B21/087}; metal {imides or} amides C01B21/092, {C01B21/0923}; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanic acid C01C3/14; salts of cyanamide C01C3/16; thiocyanates C01C3/20; {double sulfates of magnesium with sodium or potassium C01D5/12; with other alkali metals C01D15/00, C01D17/00})

## Abstract

A process for producing .alpha.-type hemihydrate calcium sulfate by oxidizing calcium sulfite with an oxidizing agent in a suspension containing at least one anionic, nonionic or amphoteric surface active agent.

## Claims

### Claim 1

A process for producing .alpha.-type hemihydrate of calcium sulfate by oxidizing calcium sulfite with air or oxygen at a temperature in the range of from 90.degree. C to 130.degree. C in a suspension containing surface active agents, the suspension containing seed crystals of .alpha.-type hemihydrate of calcium sulfate and having a pH in the range of from 3 to 6 and the surface active agents being at least one agent selected from the group consisting of (a) anionic surface active agents having a sulfonic acid group as the hydrophilic atomic group and having an alkyl, alkyl-aryl or alkylallyl group as the hydrophobic atomic group; (b) non-ionic surface active agents having a polyoxyethylene chain as the hydrophilic atomic group and having an alkyl or alkylphenoxy group as the hydrophobic atomic group and (c) amphoteric surface active agents of a betaine.

### Claim 2 (depends on 1)

The process of claim 1 wherein the surface active agents are at least one agent selected from the group consisting of alkylsulfonic acids and salts thereof, alkylbenzenesulfonic acids and salts thereof, .alpha.-olefinsulfonate, alkylnaphalenesulfonate, polyoxyethylene alkyl ether, alkylbetaine and polyoxyethylene alkylphenol ether.

### Claim 3 (depends on 1)

A process according to claim 1 wherein the amount of said surface active agent is 0.2 to 5% by weight on calcium sulfite.

### Claim 4 (depends on 1)

A process according to claim 1 wherein the concentration of calcium sulfite in the suspension is 5 to 30% by weight.

### Claim 5 (depends on 1)

A process according to claim 1 wherein the pH adjusting agent is sulfuric acid or sulfurous acid.