Method and apparatus for displacing liquor from a slurry of particulate solid material

A method of displacing liquor from a particulate solid material comprising:

• forming the particulate solid material into a layer on a movable filter medium;
• transporting the layer by means of the filter medium through a washing zone in which the layer is contacted alone the path of movement thereof with a wash medium while maintaining in a region over the layer a gaseous atmosphere, the wash medium serving to displace liquor from the layer and passing, together with the liquor and gas from said atmosphere, through the filter medium;
• recovering the gas and treating it to eliminate or at least reduce contamination thereof by the liquor;
• and
• reintroducing the treated gas into said atmosphere at a location such that the gas passing through the layer at a location downstream of, or within a downstream section of, the washing zone is less contaminated with liquor than that passing through the layer at a location upstream of, or within an upstream section of, the washing zone.

A process for the filtration and washing of terephthalic acid obtained from a reaction vessel as a slurry with an aliphatic carboxylic acid employed as solvent in the reaction, said process comprising:

• (a) contacting the terephthalic acid, initially in the form of said slurry, with a filtration surface acting as a support so as to form the terephthalic acid as a layer on said surface and transporting the terephthalic acid on said filtration surface through a number of zones;
• (b) initially subjecting the slurry to filtration while traversing a first zone to remove said solvent through the filtration surface and thereby produce a first drained wet deposit;
• (c) thereafter washing the first wet deposit while traversing a second zone and effecting filtration through said filtration surface to separate from the terephthalic acid any solvent remaining in the first deposit and the wash liquor used for washing;
• (d) establishing in said second zone and/or at least one further zone downstream of the second zone a gaseous atmosphere by means of a gas which passes through the filter medium;
• and supplying said gas in such a way that a concentration gradient is produced in the gas atmosphere such that solvent contamination in the gas passing from said atmosphere through the filter medium decreases in the direction of travel of the filter medium.

A process for the filtration and washing of terephthalic acid obtained from a reaction vessel as a slurry with an aliphatic carboxylic acid employed as solvent in the reaction, said process comprising:

• (a) contacting the terephthalic acid, initially in the form of said slurry, with a filtration surface acting as a support so as to form the terephthalic acid as a layer on said surface and transporting the terephthalic acid on said filtration surface through first and second zones;
• (b) initially subjecting the slurry to filtration while traversing said first zone to remove said solvent through the filtration surface and thereby produce a first drained wet deposit;
• (c) thereafter subjecting the first wet deposit to a series of washing stages while traversing said second zone and effecting filtration through said filtration surface to separate from the terephthalic acid any solvent remaining in the first deposit and the wash liquor used for washing, said washing stages with the exception of the final washing stage being effected using wash liquor obtained from a succeeding stage in countercurrent fashion so that said deposit is contacted with wash liquor of increasing purity as it progresses through said second zone;
• (d) pressurising said first and second zones by means of a gas which passes through the filter medium together with the solvent and the wash liquor;
• and
• (e) supplying said pressurising gas in such a way that, on the slurry side of the filter surface, the gas present in at least the final stage of said second zone is less contaminated with said solvent than the gas present in said first zone.

A system for processing a slurry comprising particulate solid material and a liquor, said system comprising:

• means for filtering the particulate solid material to form a layer thereof on a movable filter medium;
• a washing zone;
• means for driving the filter medium so as to transport the layer through the washing zone;
• means for applying wash medium to the layer during traverse of the washing zone, the wash medium serving to displace liquor from the layer and passing through the filter medium;
• and
• means for establishing in said washing zone and/or a zone downstream thereof a gaseous atmosphere from which gas passes through the layer and the filter medium, said atmosphere-establishing means being arranged to produce a concentration gradient such that the extent to which the gas passing through said layer and the filter medium is contaminated with said liquor decreases in the direction of travel of the filter medium.

A process for the filtration and washing of terephthalic acid obtained from a reaction vessel as a slurry with an aliphatic carboxylic acid employed as solvent in the reaction, said process comprising:

• (a) contacting the terephthalic acid, initially in the form of said slurry, with a filtration surface acting as a support so as to form the terephthalic acid as a layer on said surface and transporting the terephthalic acid on said filtration surface through a number of zones;
• (b) initially subjecting the slurry to filtration while traversing a first zone to remove said solvent through the filtration surface and thereby produce a first drained wet deposit;
• (c) thereafter washing the first wet deposit while traversing a second zone and effecting filtration through said filtration surface to separate from the terephthalic acid any solvent remaining in the first deposit and the wash liquor used for washing;
• (d) establishing in said second zone and/or at least one further zone downstream of the second zone a gaseous atmosphere by means of a gas which passes through the filter medium;
• and supplying said gas in such a way that a concentration gradient is produced in the gas atmosphere such that solvent contamination in the gas passing from said atmosphere through the filter medium decreases in the direction of travel of the filter medium;
• (e) separating the gas from solvent vapours entrained in the gas flow;
• and
• (f) re-introducing the gas into the gaseous atmosphere at different locations along the path of travel of the filter surface, the gas supplied to the more downstream location or locations being subjected to a higher degree of separation from said solvent.

A process for the filtration and washing of terephthalic acid obtained from a reaction vessel as a slurry with an aliphatic carboxylic acid employed as solvent in the reaction, said process comprising:

• (a) contacting the terephthalic acid, initially in the form of said slurry, with a filtration surface acting as a support so as to form the terephthalic acid as a layer on said surface and transporting the terephthalic acid on said filtration surface through first and second zones;
• (b) initially subjecting the slurry to filtration while traversing said first zone to remove said solvent through the filtration surface and thereby produce a first drained wet deposit;
• (c) thereafter subjecting the first wet deposit to a series of washing stages while traversing said second zone and effecting filtration through said filtration surface to separate from the terephthalic acid any solvent remaining in the first deposit and the wash liquor used for washing, said washing stages with the exception of the final washing stage being effected using wash liquor from a succeeding stage in countercurrent fashion so that said deposit is contacted with wash liquor of increasing purity as it progresses through said second zone;
• (d) pressurising said first and second zones by means of a gas which passes through the filter medium together with the solvent and the wash liquor;
• and
• (e) supplying said pressurising gas in such a way that, on the slurry side of the filter surface, the gas present in at least the final stage of said second zone is less contaminated with said solvent than the gas present in said first zone;
• (f) separating the gas from solvent vapours entrained in the gas flow;
• and
• (g) re-introducing the gas into the gaseous atmosphere at different locations along the path of travel of the filter surface, the gas supplied to the more downstream location or locations being subjected to a higher degree of separation from said solvent.

A system for processing a slurry comprising a particulate solid material and a liquor, said system comprising:

• means for filtering the particulate solid material to form a layer thereof on a movable filter medium;
• a washing zone;
• means for driving the filter medium so as to transport the layer through the washing zone;
• means for applying wash medium to the layer during traverse of the washing zone, the wash medium serving to displace liquor from the layer and passing through the filter medium;
• and
• means for establishing in said washing zone and/or a zone downstream thereof a gaseous atmosphere from which gas passes through the layer and the filter medium, said atmosphere-establishing means being arranged to produce a concentration gradient such that the extent to which the gas passing through said layer and the filter medium is contaminated with said liquor decreases in the direction of travel of the filter medium;
• means for recovering the gas after passage through said layer and treating it to eliminate or at least reduce contamination thereof by the liquor, wherein the recovered gas produces at least two gas streams, at least one of which is less contaminated with solvent than the other or others, and is reintroduced into said atmosphere at a location downstream of the other gas stream or streams to produce said concentration gradient.