Page 72 - Materials Chemistry, Second Edition

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TABLE 2.18 Cleaner Production 53
Possible Chemical Substitutes

Substitute for sodium sulfide $/ton
• Glucose (75%) 280
• Dextrose 700
• Dextrine 260
• Hydrol (glucose water) 0

Substitute for acidified dichromate $/ton
• Hydrogen peroxide 480
• Sodium perborate 560
• Ammonium persulphate 1,400
• Sodium bromate 1,400
• Potassium iodate 1,400

CP techniques implemented
An evaluation was undertaken to assess the viability, costs, and quality of using
various potential substitutes for sodium sulfide and acidified dichromates.
A summary of possible substitutes and costs is shown in Table 2.18.
Laboratory trials were initially used to determine the optimum combina-
tion of reducing sugars and alkali. Pilot trials were then carried out to refine
the preferred substitute:

• Substitution of sodium sulfide: Dextrine and hydrol shown in Table
2.18 were rejected as they gave a poor depth of shade. Glucose and
dextrose both gave good depths of shade when used with sodium
hydroxide. Glucose was therefore preferred as a substitute to sodium
sulfide because of its lower cost.
• Substitution of dichromate: In El-Nasr Spinning and Weaving, sodium
bromate and potassium iodate, shown in Table 2.18, were rejected as
these chemicals are corrosive, unsafe to handle and expensive. Hydro-
gen peroxide was also rejected, as it is not suitable for use with woven
fabrics. Sodium perborate and ammonium persulphate were both
acceptable; however, sodium perborate was preferred due to its lower
cost. In Dakahleya Spinning and Weaving and AmirTex, hydrogen
peroxide was preferred as it is particularly suitable for processing
knitted fabrics.

A summary of fabric quality, before and after, at Dakahleya Spinning and
Weaving is shown in Table 2.19. During the trials it was noted that when
glucose is added in stages the depth of shade was significantly improved.