The Temperature of KOH and Ligin should be room Temperatur around 298,15 K, Water has a fraction with room temperature and a fraction around 353,15 K, but perhaps its ok to consider all components at standard temperature.
You can retrieve specific heat data for KOH aq. solutions (≤ 9.09 mol %; 19 ºC) from Table 2-212, at: R.H. Perry, D.W. Green, J.O. Maloney (Eds.), "Perry's Chemical Engineers’ Handbook", 7th ed., McGraw-Hill, 1997; or earlier eds.
Thank you very much for your answer. Would you account for the lignin dry mass proportion by summing up the cps by their relative weight fraction?
The lignin dissolved in KOH aq. sol. is likely present as the potassium salt of lignosulfonic acid; let us denote it as LigOK, while we may denote lignin as LigOH. We can expect the concentration of dissolved KOH to change, accordingly: LigOH (s) + KOH (aq) → LigOK (aq) + H2O (l), what may be seen as a dehydroxylation reaction which enthalpy may be somewhat significant compared with solvation contributions. In the absence of thermochemical data for that reaction, it may be judged preferable to estimate the enthalpy or heat capacity contribution from LigOK (aq) to the solution by means of considering a lignin precipitation reaction, since the corresponding precipitation enthalpy is likely to be much smaller, possibly neglectable compared with other contributions. Lignin precipitation could possibly be achieved by adding mineral acid or CO2. For the last case: LigOK (aq) + CO2 (aq) + H2O (l) → LigOH ↓(s) + KHCO3 (aq). Neglecting precipitation enthalpy: ΔHf[LigOK (aq)] ≈ ΔHf[LigOH (s)] + ΔHf[KHCO3 (aq)] - ΔHf[H2O (l)] - ΔHf[CO2 (aq)].
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