Efficient methods and compositions for recovery of products from organic acid pretreatment of plant materials

A method of recovering lignin from a lignin suspension produced from a concentrated extraction liquor with a dry matter content of about 50 to about 65% derived from organic acids pretreatment of plant material, the method comprising the steps of:

• a) separating lignin from the lignin suspension, wherein the lignin is separated by centrifugation with a centrifuge thereby forming a separated lignin and a first centrifugate, and
• b) cleaning the separated lignin in the centrifuge by multiple applications of wash solution onto the separated lignin during centrifugation, to form at least a second and third centrifugate, wherein the multiple applications of wash solution comprise a sequential application starting with a first application of a wash solution comprising a first organic acids content washing water, and a second application of a wash solution comprising a second organic acids content washing water, wherein the organic acids content in the first organic acids content washing water is greater than the organic acids content in the second organic acids content washing water, and
• c) recovering the first centrifugate and the second centrifugate for use in hemicellulosic juice concentration, and
• d) recycling the third centrifugate for producing the lignin suspension in step a) by mixing the third centrifugate with the concentrated extraction liquor, and
• e) discharging the separated lignin from step b) from the centrifuge.